# given that 'cabin gain' is a reality, do we need a low fs?



## 60ndown

or will a driver/box combo that rolls off about 45-37 actually sound better in a vehicle?

just thinking out-loud?

again.

why would we want a driver/box combo that plays well into the low 20s if cabin gain is there anyway?


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## 60ndown

what sub/box combo are you using and how is it eq'd?

in what vehicle?


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## chad

Yes you don't need to go nearly as low with the enclosure as you do anechoic.

BUT it is vehicle dependent, big ass van, not much gain, especially up higher, tiny ass hatchback, watch out!


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## Neil

Well you've noticed something it takes people years to notice: low frequency performance in a vehicle can easily become quite excessive if not approached correctly. In fact, I can tell you that I have read a large number of reviews where people have talked about how the driver has little upper frequency extension. The reality was that there was no limiting factor (like inductance), but that the use of the driver in a medium-to-large ported enclosure tuned below 40 Hz with a lot of throw and a lot of power has a tendency (when paired with the cabin gain typical in most vehicles) to make the bottom end much too strong. Likewise, this is also frequently misinterpreted as a "slow" or "sloppy" driver.

Just another example of how 99% of us have ears that simply can't be trusted.


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## capnxtreme

If anyone can help contribute how we go about calculating our vehicle's transfer function, that would be awesome. Cause really, that's all we have to do to prove or disprove OP's idea. I am newb but I suspect it's the right idea.


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## Et Cetera

I have actually found subs with higher fs to integrate easier and sound more natural. Another thing, subsonic filter is your friend.


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## Neil

Et Cetera said:


> I have actually found subs with higher fs to integrate easier and sound more natural. Another thing, *subsonic filter is your friend*.


Slower than the speed of sound? 

An infrasonic filter may help. High or low Fs isn't really critical (I'd still prefer a much lower Fs)...you just have to use the right enclosure with the right amount of power for an even response that blends well with your entire system.


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## Scott Buwalda

capnxtreme said:


> If anyone can help contribute how we go about calculating our vehicle's transfer function, that would be awesome. Cause really, that's all we have to do to prove or disprove OP's idea. I am newb but I suspect it's the right idea.


In a _purely_ theoretical sense, "transfer function" will begin to occur at the vehicle's Fs, and will increase at an order of 12 dB/octave. Remember, pure theory here. So if the Shroeder Frequency of your car is 52 Hz, at 26 Hz it will be at a theoretical +12 dB. This is true until the extent of linear pistonic ability of the driver is reached as well.

Scott


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## 14642

Shroeder has never played the piano anywhere near my car and Snoopy has never driven it. 

Here are some measured transfer functions.


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## sundownz

Thats some huge gain down low - thanks for the graph


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## 60ndown

Andy Wehmeyer said:


> Shroeder has never played the piano anywhere near my car and Snoopy has never driven it.
> 
> Here are some measured transfer functions.


looks to me then like i need a subwoofer with an fs of 76 for a nice flat response 

nice graph, thanks.


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## npdang

Thank you Andy, this definitely deserves to be placed somewhere for easy reference.

I usually find the limiting factor for a sub's upper end extension is 1) rear seats/trunk mounting and like Devildriver mentioned, excessive low end gain swamping out the upper end (funny to consider 60hz+ "upper end" response).

In my experience, I find the flattest response in my car (honda accord) comes with a system frc of ~65hz with a Qtc of ~.85. There might still be some low end gain in the lowest octaves on a mic, but to my ears it's completely in balance with the frontstage.


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## 14642

I find that the best-sounding, lowest-distortion and most efficient use of woofer dollars, enclosure dollars and amplifier power can be had by:

Building a vented box with a flat response and the lowest F3 possible and usiing an EQ to eliminate the peak in the car. That minimizes the amount of power the amplifier has to make, minimizes the driver's excursion, leaves lots of juice available for transient peaks, and minimizes driver and amplifier distortion. 

Requires a larger box and a parametric EQ, though.


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## cvjoint

I like to make use of the lower end gain. I typically use large midbass drivers with 12db HP @63hz to match flat. What few people realize imo is that even if the midbass drivers go flat down to 63hz they might roll off excessively beyond that. A typical 24db xover for sub and 6.5 inch midbass is not going to sum up flat even if the sub does it's job up high.


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## sundownz

Would explain why a customer put one of my 15" Nightshade SPL drivers in a sealed box and actually liked it quite a bit - the F3 is right at 60 Hz in a bit under 1 ft^3 sealed for the 15" version. I believe he had it in about three times that for a nearly critically damped Qtc.

It was doing 140 - 142 dB on music as well. I bet they wouldn't sound half bad for SQ in a sealed box with a bit longer coil to increase linear x-max - right now overhang is 16mm.

Makes me want to try it out myself and take a listen now that I'm thinking about how much gain the transfer function gives


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## 14642

When you set up an electronic crossover, which is a combination of a high pass and a low pass, the crossover points that you select indicate a -3dB point (depending ont he alignment, but we'll assume Butterworth for this exercise). When the gain in the passband of two filters with the same frequency is the same, then that frequency is the crossover frequency. If you adjust the gain of either HP channel or LP channel, it's no longer the crossover frequency.

Check out the graph below. The LP and HP that are at the same level have a crossover point of 73Hz and 4th order slopes. If I boost the gain of the LP channel, the real crossover point (the point where the lines cross) changes. 









Just because you have the dial set to 63Hz, that doesn't mean that's your crossover frequency. I use 10" woofers and 6" midbass drivers and 4th order slopes and it blends just fine.


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## 60ndown

sundownz said:


> - the F3 is right at 60 Hz in a bit under 1 ft^3 sealed for the 15" version. I believe he had it in about three times that for a nearly critically damped Qtc.


help me understand this please,

in a larger box i see less air pressure/resistance and therefore less control over the cone, why is a bigger box 'critically damped'? 

id have thought a small box would critically 'control' the cone ?

and a big box just slop about?


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## 60ndown

Andy Wehmeyer said:


> When you set up an electronic crossover, which is a combination of a high pass and a low pass, the crossover points that you select indicate a -3dB point (depending ont he alignment, but we'll assume Butterworth for this exercise). When the gain in the passband of two filters with the same frequency is the same, then that frequency is the crossover frequency. If you adjust the gain of either HP channel or LP channel, it's no longer the crossover frequency.
> 
> Check out the graph below. The LP and HP that are at the same level have a crossover point of 73Hz and 4th order slopes. If I boost the gain of the LP channel, the real crossover point (the point where the lines cross) changes.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Just because you have the dial set to 63Hz, that doesn't mean that's your crossover frequency. I use 10" woofers and 6" midbass drivers and 4th order slopes and it blends just fine.


i like jou


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## sundownz

60ndown said:


> help me understand this please,
> 
> in a larger box i see less air pressure/resistance and therefore less control over the cone, why is a bigger box 'critically damped'?
> 
> id have thought a small box would critically 'control' the cone ?
> 
> and a big box just slop about?


It's actually a bit opposite:

http://www.geocities.com/kreskovs/Sealed.html

The 0.707 alignment does have a lower F3 than the 0.500 alignment, though, which is why it is quite often preferred.


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## cvjoint

Gotcha. You could use more output on the sub side of things to change the real crossover point. This method can even alleviate some of the mismatching effects of a weak midbass extension but you've created an animal that is what...20db above full range FR.

I love midbass as much as I love sub bass and therefore I match them accordingly. Here's my highway setting with 20-200hz matched and leveled 8db above average:










City settings and auditioning levels are only 2-3db above average making for a fairly flat FR. Sub and midbass are then boosted together. We're not all bass heads!


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## 14642

60ndown said:


> help me understand this please,
> 
> in a larger box i see less air pressure/resistance and therefore less control over the cone, why is a bigger box 'critically damped'?
> 
> id have thought a small box would critically 'control' the cone ?
> 
> and a big box just slop about?


 
Consider the following Thiele and Small parameters:

Cms = The compliance of the suspension--how easily it's moved
Vas = Cms expressed as a volume of air that has the same compliance

These two are a measure of the suspension's restoring force--how much the suspension pushes back when the motor moves the cone. 

Q is a measure of the amount of overshoot allowed at resonance. High Q means that the speaker keeps moving after the signal goes away. Low Q means that the speaker stops moving more quickly when the signal goes away. 

Qms is the amount of overshoot that the suspension allows
Qes is the amount that the motor allows
Qts is the total and the formula for Qts is the product of Qms and Qes over the sum of Qms and Qes--like resistors in parallel.

Now...if you look at the parameters for 99% of the speakers that are available you'll see that the Qms is always MUCH higher than the Qes. That means that the suspension allows MUCH more overshoot than the motor. Thinking a little further, you'll discover that what that really means is that the MOTOR controls the motion of the cone and the suspension contributes very little control. Both the motor and the suspension work to overcome the inertia of the moving MASS. The motor does a better job than the suspension. essentially, the suspension screws things up. The suspension is there mostly to keep the coil from leaving the gap and should be designed to apply very little force until that is about to happen.

Resonance is the point where the motor and suspension make the hand-off. Above resonance, the motor provides nearly all the control and below resonance, the suspension does more work. Above resonance we say a speaker is mass controlled and below we say it's stiffness controlled. Above resonance the motor overcomes the inertia of the moving MASS and below resonance the motor overcomes the COMPLIANCE of the suspension.

Here's an example: a super-ball is a high Q device and one of those squeezable things in the check out line of Bed Bath and Beyond is a low Q device. When you drop the super ball, it bounces back nearly to the same height as from where it was dropped. That squeezy thing falls with a thud and doesn't bounce at all.

The super ball bounces back because the rubber has a VERY HIGH restoring force--very low compliance or very low VAS. The squeezy thing has a very high compliance--very high VAS. It ABSORBES the force of the impact. 

Now, back to the boxes. A woofer by itself with no box is controlled mostly by the motor but the restoring force of the suspension causes it to bounce around a bit at resonance after it should have come to a stop. When we put the woofer in a box, we ADD restoring force because the cone compresses (and rarefies) the air in the box when it moves, causing it to bounce around even more--it's a stiffer super ball. The Q is increased (and so is the frequency of resonance). If the box is bigger, there's less force applied to the cone when the air is compressed and more if the box is smaller. The box RAISES the Q. A small box raises the Q more than a large one. For a small sealed box, you need a woofer with a very low Q. A woofer with a higher Q will need a larger box. The box provides the additional overshoot necessary to achieve the desired Q.

Here's how sealed box design works. The box raises the Qms of the speaker and we choose a box volume that raises it enough to produce the desired response. Qtc is a measure of how much overshoot the whole system of box and woofer allow at resonance. A Qtc of .707 provides the best combination of flat response and low frequency extension. However, there is some overshoot involved. A Qtc of .5 is critically damped or "transient perfect". There's less overshoot.

Before you freak out and decide that you should always build a box with a Qtc of .5 for best accuracy, we have to think a little further:


Choosing .7 is like saying, "well, I know it can't be flat, so I'll choose to make it as flat as possible to the lowest frequency possible and i'll deal with the group delay (inaccuracy) below the cutoff frequency." Choosing a lower Q is like saying, "Well, it can't be flat and I don't care about low frequency extension, so I'll minimize the SLOPE of the rolloff for less group delay. I'll make it more inaccurate at some frequencies and less inaccurate at the lowest frequencies." 

Why would we want overshoot? Because if the woofer contnues moving, it makes bass. We want the woofer to continue moving a little bit at resonance, to boost the bass at the bottom of the response for better low-frequency extension and flatter response. Choosing a lower Qtc is essentially managing the compromise a little differently.


The reason we care more about flat response and low frequency extension more than minimizing overshoot is because flat frequency response from the system IS transient accuracy, by the Fourier Transform. Choosing a Qtc of .7 is like saying "I want perfection down to the lowest frequency possible". Choosing .5 is like saying, "I'd prefer to have the transient accuracy be less screwed up at the very lowest frequencies and in order to get that I'll let it be a little scewed over a wider range of frequencies"

The easiest and best rule is to choose flat response and wide bandwidth if it's accuracy that you're after.


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## 60ndown

Andy Wehmeyer said:


> Consider the following Thiele and Small parameters:
> 
> Cms = The compliance of the suspension--how easily it's moved
> Vas = Cms expressed as a volume of air that has the same compliance
> 
> These two are a measure of the suspension's restoring force--how much the suspension pushes back when the motor moves the cone.
> 
> Q is a measure of the amount of overshoot allowed at resonance. High Q means that the speaker keeps moving after the signal goes away. Low Q means that the speaker stops moving more quickly when the signal goes away.
> 
> Qms is the amount of overshoot that the suspension allows
> Qes is the amount that the motor allows
> Qts is the total and the formula for Qts is the product of Qms and Qes over the sum of Qms and Qes--like resistors in parallel.
> 
> Now...if you look at the parameters for 99% of the speakers that are available you'll see that the Qms is always MUCH higher than the Qes. That means that the suspension allows MUCH more overshoot than the motor. Thinking a little further, you'll discover that what that really means is that the MOTOR controls the motion of the cone and the suspension contributes very little control. Both the motor and the suspension work to overcome the inertia of the moving MASS. The motor does a better job than the suspension. essentially, the suspension screws things up. The suspension is there mostly to keep the coil from leaving the gap and should be designed to apply very little force until that is about to happen.
> 
> Resonance is the point where the motor and suspension make the hand-off. Above resonance, the motor provides nearly all the control and below resonance, the suspension does more work. Above resonance we say a speaker is mass controlled and below we say it's stiffness controlled. Above resonance the motor overcomes the inertia of the moving MASS and below resonance the motor overcomes the COMPLIANCE of the suspension.
> 
> Here's an example: a super-ball is a high Q device and one of those squeezable things in the check out line of Bed Bath and Beyond is a low Q device. When you drop the super ball, it bounces back nearly to the same height as from where it was dropped. That squeezy thing falls with a thud and doesn't bounce at all.
> 
> The super ball bounces back because the rubber has a VERY HIGH restoring force--very low compliance or very low VAS. The squeezy thing has a very high compliance--very high VAS. It ABSORBES the force of the impact.
> 
> Now, back to the boxes. A woofer by itself with no box is controlled mostly by the motor but the restoring force of the suspension causes it to bounce around a bit at resonance after it should have come to a stop. When we put the woofer in a box, we ADD restoring force because the cone compresses (and rarefies) the air in the box when it moves, causing it to bounce around even more--it's a stiffer super ball. The Q is increased (and so is the frequency of resonance). If the box is bigger, there's less force applied to the cone when the air is compressed and more if the box is smaller. The box RAISES the Q. A small box raises the Q more than a large one. For a small sealed box, you need a woofer with a very low Q. A woofer with a higher Q will need a larger box. The box provides the additional overshoot necessary to achieve the desired Q.
> 
> Here's how sealed box design works. The box raises the Qms of the speaker and we choose a box volume that raises it enough to produce the desired response. Qtc is a measure of how much overshoot the whole system of box and woofer allow at resonance. A Qtc of .707 provides the best combination of flat response and low frequency extension. However, there is some overshoot involved. A Qtc of .5 is critically damped or "transient perfect". There's less overshoot.
> 
> Before you freak out and decide that you should always build a box with a Qtc of .5 for best accuracy, we have to think a little further:
> 
> 
> Choosing .7 is like saying, "well, I know it can't be flat, so I'll choose to make it as flat as possible to the lowest frequency possible and i'll deal with the group delay (inaccuracy) below the cutoff frequency." Choosing a lower Q is like saying, "Well, it can't be flat and I don't care about low frequency extension, so I'll minimize the SLOPE of the rolloff for less group delay. I'll make it more inaccurate at some frequencies and less inaccurate at the lowest frequencies."
> 
> Why would we want overshoot? Because if the woofer contnues moving, it makes bass. We want the woofer to continue moving a little bit at resonance, to boost the bass at the bottom of the response for better low-frequency extension and flatter response. Choosing a lower Qtc is essentially managing the compromise a little differently.
> 
> 
> The reason we care more about flat response and low frequency extension more than minimizing overshoot is because flat frequency response from the system IS transient accuracy, by the Fourier Transform. Choosing a Qtc of .7 is like saying "I want perfection down to the lowest frequency possible". Choosing .5 is like saying, "I'd prefer to have the transient accuracy be less screwed up at the very lowest frequencies and in order to get that I'll let it be a little scewed over a wider range of frequencies"
> 
> The easiest and best rule is to choose flat response and wide bandwidth if it's accuracy that you're after.


thanks, A LOT.


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## ZoNtO

You know, its threads like these and the people that post in them that make me love this website! The wealth of information here is just incredible and always makes me want to improve my system even more!

Thanks all for these posts! When I'm not on my phone I'll probably print this thread out!


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## Scott Buwalda

To stimulate even more conversation...getting away *slightly* from sealed box design, but still in the same grocery store department...

Andy, you mention the phenomenon of "overshoot." We can add "undershoot" to the list as well. This is called electromotive force (EMF). Of importance to this discussion is "back EMF." Back-EMF is produced every time the amplifier sends a signal that causes the cone to move. There is an importance here to amplifier damping factor, and of even greater importance to the use of passive crossovers. Andy, care to continue on in your excellent discussion?

Scott


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## Dangerranger

Andy Wehmeyer said:


> I find that the best-sounding, lowest-distortion and most efficient use of woofer dollars, enclosure dollars and amplifier power can be had by:
> 
> Building a vented box with a flat response and the lowest F3 possible and usiing an EQ to eliminate the peak in the car. That minimizes the amount of power the amplifier has to make, minimizes the driver's excursion, leaves lots of juice available for transient peaks, and minimizes driver and amplifier distortion.
> 
> Requires a larger box and a parametric EQ, though.


^x2

My preferred method as well when space allows. I don't know why people feel so guilty about EQ'ing down the boost in response created by a vented enclosure, it has so many other benefits that are overlooked. I tend to tune low enough that the group delay doesn't get too high, hopefully it is able to be pushed outside of the intended frequency range. If this is accomplished I feel the benefits of drastically lowered distortion levels at ANY volume level as well as the headroom opened up FAR outweigh the drawbacks in group delay and phase. In fact doing this in many cars, and tuning the response, I've never had anybody get in the car and say the system didn't sound better than an equivalent sealed system.


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## BlackSapphire

Andy Wehmeyer said:


> Consider the following Thiele and Small parameters:
> 
> <snip>


Andy, that is one of the very best posts I've read on here to date. Thank you x1000.

I'm questioning my QTC of .8 now but that's another story.


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## 60ndown

BlackSapphire said:


> I'm questioning my QTC of .8 now but that's another story.


throw some scrap wood in there = .5.6.7.waddeva u want


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## Salami

ZoNtO said:


> You know, its threads like these and the people that post in them that make me love this website! The wealth of information here is just incredible and always makes me want to improve my system even more!
> 
> Thanks all for these posts!



100% agree!!!!! Thanks. 

Subscribed to thread.


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## Thumper26

wow, great thread! Andy, way to make things easy to understand! Keep it up!


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## 14642

60ndown said:


> throw some scrap wood in there = .5.6.7.waddeva u want


Reducing the volume by adding wood will raise the Q. .8 is close enough to .7 that it doesn't matter.


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## 60ndown

Andy Wehmeyer said:


> Reducing the volume by adding wood will raise the Q. .8 is close enough to .7 that it doesn't matter.


doh!

im off to read your post again


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## cvjoint

Andy Wehmeyer said:


> Before you freak out and decide that you should always build a box with a Qtc of .5 for best accuracy, we have to think a little further:
> 
> 
> Choosing .7 is like saying, "well, I know it can't be flat, so I'll choose to make it as flat as possible to the lowest frequency possible and i'll deal with the group delay (inaccuracy) below the cutoff frequency." Choosing a lower Q is like saying, "Well, it can't be flat and I don't care about low frequency extension, so I'll minimize the SLOPE of the rolloff for less group delay. I'll make it more inaccurate at some frequencies and less inaccurate at the lowest frequencies."


I'm a little lost trying to make sense of these. Can we perhaps think in Infinite Baffle domain to make things easier for us non EE majors? 

It seems to me that a low Q with a flat frequency response is ideal. Is that achievable or is a low Q intrinsically weak on the low side? When you talk about low Q being inaccurate at "some frequencies," what exactly are these frequencies? If it's like 100hz and we cross at 80hz that we have a clear winner. 

Going back to the .7 Q, would ideal situation be a cutoff frequency at 20hz or bellow? I'd think you would have correct accuracy above 20hz.


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## 14642

> I'm a little lost trying to make sense of these. Can we perhaps think in Infinite Baffle domain to make things easier for us non EE majors?
> 
> It seems to me that a low Q with a flat frequency response is ideal. Is that achievable or is a low Q intrinsically weak on the low side? When you talk about low Q being inaccurate at "some frequencies," what exactly are these frequencies? If it's like 100hz and we cross at 80hz that we have a clear winner.
> 
> Going back to the .7 Q, would ideal situation be a cutoff frequency at 20hz or bellow? I'd think you would have correct accuracy above 20hz.


Yes, flat frequency response and low Q with a cutoff frequency at or below 20Hz would be ideal, but it isn't practical nor is it necessary. 

If you look back over this whole thread, the answer may become clear. 

1. Flat frequency response *is* accurate time response.
2. The cabin gain, (transfer function) of the car makes a sealed box with a -3dB point that corresponds to the +3dB point on the transfer function curve have flat response at low frequencies.
3. You'll never fix all the frequency response problems without an EQ. This should be obvious in the transfer function graph I posted.
4. Since you have to have an EQ for good sound, build a vented box for much better efficiency and remove the peak with the EQ for lower distortion and better dynamics (since there will be plenty of power left over after you cut 45Hz or so by about 12dB).
5. If you can't afford to lose additional space to a vented box, you can make up for it with a woofer with high Xmax and lots of power.


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## 14642

Scott Buwalda said:


> To stimulate even more conversation...getting away *slightly* from sealed box design, but still in the same grocery store department...
> 
> Andy, you mention the phenomenon of "overshoot." We can add "undershoot" to the list as well. This is called electromotive force (EMF). Of importance to this discussion is "back EMF." Back-EMF is produced every time the amplifier sends a signal that causes the cone to move. There is an importance here to amplifier damping factor, and of even greater importance to the use of passive crossovers. Andy, care to continue on in your excellent discussion?
> 
> Scott


Back EMF isn't mysterious. It's expressed in simple form in the impedance curve of the speaker. 










The offset of the curve above 0 ohms is the DC resistance of the voice coil. The DCR (or Revc) is chosen to determine how much current will flow through the coil at a given voltage. A designer would choose 2 ohms , 4 ohms 8 ohms or some other value to determine what kind of amplifier ought to be used with the speaker, basically.

Res is "motional impedance" or Back EMF. As Scott wrote, when the speaker moves, it makes a voltage--just like the alternator in your car. A coil of wire moves inside a magnetig field and a voltage is produced. THe speaker does that most efficiently at resonance, and that's why there's a huge peak in the impedance (abbreviated "Z") curve. That peak is back EMF and it's a voltage that causes current to flow opposite the current from the amplifier. That's why it can be expressed simply as impedance. There's no need to try to eliminate it or to think that you're somehow being robbed of amplifier power. That peak IS the Q of the driver. Back in the Richard Clark days, aperiodic membranes were popular and the reason was because he said that eliminating the peak would provide better power transfer from the amplifier to the speaker. It's a really inefficient way to improve the system because reducing the Q means reducing the bass.










Since the membrane reduced the bass by reducing the Q ("aperiodic" means "without resonance" and with no resonance there's no Q), they included a little box that went in the signal line to the amplifier that was a high-pass filter with a Q that put the bass back in. That filter and its Q required lots of power, so big amps were required to get lots of bass with low distortion. It's kinda like dragging around a trailer filled with gasoline. The added weight means poorer fuel economy and the aditional gas is required to be able to go the same distance.

The best use of an aperiodic membrane is to get rid of cone distortion from the woofer by mounting it between the cone and the listener. The impedance peak isn't a big problem and money spent trying to eliminate it is money better spent on french fries.

OK, back to Scott's point and on to damping factor--possibly the most misunderstood spec ever invented. 

Below is a simple model of a speaker from an electrical POV.









You'll see some of the same abbreviations here that are on the Z curve above. Ces is capacitance (an elctrical analogue for the suspension's compliance) that causes the slope on the right side of the peak and Les is inductance (the electrical analogue of the mass of the moving assembly) that causes the slope on the left side of the peak. The top of the peak is purely resistance or Res and it's thepoint where the inductive reactance and the capacitive reactance are equal (where the interaction of the mass and the compliance keep the cone moving--like the pendulum in a grandfather clock). The impedance peak at resonance is the primary back EMF generator.

Now, if we think about how a speaker works, it'll be clear which of these components causes motion. When a current passes through a wire, a magnetic field is generated. In a speaker that wire is wound into a coil--an inductor--which helps us control the magnetic field.










The magnetic field that's generated pushes and pulls against the static magnetic field created by the magnet and the top and bottom plates of the speaker and causes the cone to move:










When we pass an alternating current through the coil, the speaker moves back and forth:










OK, so what's the component of the speaker that turns the current from the amp into motion? The voice coil's inductance. The Revc controls the amount of current flow and the inductance moves the cone. Inductors also store energy in the form of current. when the music signal goes away, the current that's stored in the inductor flows back toward the amplifier and when the current flows, it causes the speaker to move. We call that "overshoot", "ringing", etc. When the current finally stops flowing, the speaker stops moving.

Damping Factor says that if the output impedance of the amplifier is really low, then more current will flow through the amplifier's output impedance and the energy will be dissipated faster, minimizing the ringing for "better control of the speaker". The damping factor formula is:

Speaker's nominal impedance/amplifier's output impedance = damping factor. 


I've added an amplifier and its output impedance to the speaker model diagram. 










Now...Damping Factor says that the amplifier's output impedance will cause current to flow from the inductor faster if the output impedance is lower. Let's say that this is a 4 ohm speaker and the DCR is 3.2 ohms. Let's say this is a great amplifier with a damping factor of 1000 at 4 ohms. The output impedance of the amplifier would be .004 ohms. 

Since the amplifier's output impedance is in series with the speaker's Revc, we ADD the amplifier's output impedance to Revc to find out how much current will flow...Hmmm...now we have 3.204 ohms. Not much difference...since the Revc is so much higher than the amplifier's output impedance, it's Revc that determines how much current flows from the inductor. In this case, the Revc has about 800 times as much influence on speaker control as the amplifier's output impedance. 

Amps don't control how quickly the speaker comes to a stop when the signal goes away and damping factor is NOT a useful measure of how much control an amp has over the motion of the speaker when the signal goes away.

Output impedance and any series resistance (if it's high enough) can have an effect on the sound of a speaker. I'll explain that tomorrow morning.

Now, I have to go mow the lawn.


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## Oliver

Thank You, Andy !! 

Of note: The best use of an aperiodic membrane is to get rid of cone distortion from the woofer by mounting it between the cone and the listener.


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## Et Cetera

Excellent thread! sticky please!


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## 60ndown

Andy it is truly a gift to find someone who actually makes simple clear and concrete statements about why and how audio works.

thank you.


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## jlm1519

Et Cetera said:


> Excellent thread! sticky please!


X 2!


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## cvjoint

Andy Wehmeyer said:


> Yes, flat frequency response and low Q with a cutoff frequency at or below 20Hz would be ideal, but it isn't practical nor is it necessary.
> 
> If you look back over this whole thread, the answer may become clear.
> 
> 1. Flat frequency response *is* accurate time response.
> 2. The cabin gain, (transfer function) of the car makes a sealed box with a -3dB point that corresponds to the +3dB point on the transfer function curve have flat response at low frequencies.
> 3. You'll never fix all the frequency response problems without an EQ. This should be obvious in the transfer function graph I posted.
> 4. Since you have to have an EQ for good sound, build a vented box for much better efficiency and remove the peak with the EQ for lower distortion and better dynamics (since there will be plenty of power left over after you cut 45Hz or so by about 12dB).
> 5. If you can't afford to lose additional space to a vented box, you can make up for it with a woofer with high Xmax and lots of power.


I see many reasons why #4 will hardly ever be satisfied. More often than not we build boxes that are smaller than prescribed to save space and because frankly most just come out that way: we forget about bracing and we go back in there, we forget about driver displacement etc. In the case a box is built to spec, there is still the issue with EQing that is taken to lightly. I've never had the possibility to EQ more than 10db in any band, our car audio processors are limited to that effect. 

#1 is what really intrigues me, and that is why I'm quoting you bellow: 



Andy Wehmeyer said:


> The reason we care more about flat response and low frequency extension more than minimizing overshoot is because flat frequency response from the system IS transient accuracy, by the Fourier Transform.


So...it doesn't matter how you achieve flat response because flat is accurate? Low Q flat response = high Q flat response?



Andy Wehmeyer said:


> Now...Damping Factor says that the amplifier's output impedance will cause current to flow from the inductor faster if the output impedance is lower. Let's say that this is a 4 ohm speaker and the DCR is 3.2 ohms. Let's say this is a great amplifier with a damping factor of 1000 at 4 ohms. The output impedance of the amplifier would be .004 ohms.
> 
> Since the amplifier's output impedance is in series with the speaker's Revc, we ADD the amplifier's output impedance to Revc to find out how much current will flow...Hmmm...now we have 3.204 ohms. Not much difference...since the Revc is so much higher than the amplifier's output impedance, it's Revc that determines how much current flows from the inductor. In this case, the Revc has about 800 times as much influence on speaker control as the amplifier's output impedance.
> 
> Amps don't control how quickly the speaker comes to a stop when the signal goes away and damping factor is NOT a useful measure of how much control an amp has over the motion of the speaker when the signal goes away.
> 
> Output impedance and any series resistance (if it's high enough) can have an effect on the sound of a speaker. I'll explain that tomorrow morning.
> 
> Now, I have to go mow the lawn.


As the "DIYMA Damping Factor" I have to say I've never been explained better in any thread so far. Your reasoning goes on to make my life useless and I shall soon have to change my designation on the board. Thanks...

What should my function be..."DIYMA's Highest Revc"? I'm going to guess 8 ohms loads ftw!


----------



## 60ndown

just for those of us (me) that are still struggling to understand this,

1.'ideal' box size = .707 = perfect transients and flat from 20-80hz

2.larger than 'ideal' = .5 "critically damped" better low end gets sloppy higher up?

3.smaller box = .9 'under damped' , less low end, thighter in the higher freqs?

can you put it in these ^ terms so i can 'get it' PLEASE.


----------



## Scott Buwalda

Andy: nice post. Now tell the crowd what happens to back-EMF, damping factor, and resonance when a passive crossover is added into the mix.

Scott


----------



## envisionelec

Andy Wehmeyer said:


> The easiest and best rule is to choose flat response and wide bandwidth if it's accuracy that you're after.


_That_ was a very good explanation in terms that most people can understand. Thank you.


----------



## 14642

60ndown said:


> just for those of us (me) that are still struggling to understand this,
> 
> 1.'ideal' box size = .707 = perfect transients and flat from 20-80hz
> 
> 2.larger than 'ideal' = .5 "critically damped" better low end gets sloppy higher up?
> 
> 3.smaller box = .9 'under damped' , less low end, thighter in the higher freqs?
> 
> can you put it in these ^ terms so i can 'get it' PLEASE.


Al of this really applies mostly to resonance and regions near resonance. A couple of octaves above resonance, the box doesn't have much to do with how the woofer sounds (unless it's leaky, flexes a lot or buzzes).

1. .707 = flat response and lowest -3dB point
2. .5 = higher -3dB point and more gradual roll-off below F3
3. .9 = peak in the response above the -3dB point, steeper roll-off below that.


----------



## 14642

Scott Buwalda said:


> Andy: nice post. Now tell the crowd what happens to back-EMF, damping factor, and resonance when a passive crossover is added into the mix.
> 
> Scott


Scott, 
I'm not sure what you're getting at, except to further complicate this. 

Anyway, I think we now understand that damping factor, which is a quality associated with an amplifier, isn't an indicator of anything. I'm going to stop using that term now.

The output impedance of the amplifier, if it's great enough, can have an effect on the sound of the system, and that amplifier quality is often called "outut regulation" and is included in the CEA 2006 standard. Here's how that works:

As we know from yesterday, the amplifier's output impedance is in series with the speaker. By Kirschoff's laws, the voltage in a series circuit divides proportionate to the resistance. Let's say our amplifier has an output impedance of 1 ohm and we're using a 4 ohm speaker. If the amplifier makes 20 volts (100 watts at 4 ohms by P = E^2/R), then 1/5 of the voltage is dropped across the output impedance and 4/5 of the voltage is dropped across the speaker. 1/5 of the voltage is 4 and 4/5 of the voltage is 16. Now, we can figure out how much power is dissipated by the amplifier's output Z by 4^2/1. Which is 16 watts. 16^2/4 = 64. So, our amplifier that made 100 watts at 4 ohms makes 80 watts at 5 ohms and only 64 of those watts make it to the speaker. OK, an amp with an ouptut impedance of 1 ohm would make a better door stop than an amplifier, but it makes a good example and the math is easy.

In that example, we used the nominal impedance of the speaker (as if it was a simple resistor). A speaker isn't a resistor, so if we wanted to figure out how the frequency response of the speaker would be affected by the output impedance we would use the measured impedance at a bunch of frequencies, do the math and plot the curve. Since the voltage from the amp divides proportionate to the series resistances, it's easy to see that the output impedance has a greater effect at frequencies where the speakaer's impedance is lowest and a smaller effect at frequencies where the speaker's impedance is greatest. If the amplifier's output impedance is really high, if you put a resistor in series with the speaker, or if you use 1000 feet of 30 gauge cable, resonance will be nearly unaffected, but the frequencies above that will be more affected.

Lovers of Tube amplifiers claim that the 2nd order distortion makes them sound warmer, but I don't think that's what causes that effect. Our brains find very low levels of constant distortion objectionable--zero crossing distortion at 1% is nasty. Distortion on transient peaks has to be about 20% before we say it's as nasty as 1% constant distortion and it's nearly inaudible at 10%. If it was second order distortion that made tubes sound good, there would have to be whole lot of distortion.

However, many old tube amps had VERY high output impedance. that output impedance attenuates the midrange and leaves the bass unaffected. If you're driving a full range home speaker, the midrange would be attenuated a little, but the bandwidth of the attenuation would be large--we can hear .5dB of attenuation if the bandwidth is more than an octave wide--but the bass would be unaffected. There's the "warmth" that tube lovers love.

Passive crossovers don't screw things up, they're just tools that we use to modify the impedance of the loudspeaker at some frequencies to cause less power to be applied to the speaker at those frequencies. The simplest explanation of how they work is that they raise the impedance at frequencies we want to get rid of so the amplifier makes less power at those frequencies. A capacitor on a midrange or a tweeter raises the impedance at low frequencies so less power makes it to the speaker. 

There are many different ways to design passive networks, but two are prevalent. The cheesy way is to calculate the value of the components using the nominal impedance of the speaker (as if it was a resistor) and then apply the crossover to the speaker (like the way we use active crossovers). Passive crossovers depend on the load impedance to determine the frequency, Q and slope of the filter, and applying a filter designed to provide particular values to a resistive load won't have the same response when applied to a speaker with an impedance CURVE. People who design these kinds of crossovers often use a Zobel network to flatten the impedance that the crossover "sees", so the response applied to the speaker is what they originally designed. 

The other way to design the crossover (now made pretty easy since we can use computers to model the response) is to use the actual speaker's impedance as the terminal load in the calculations and to choose the component values according to the impedance curve of the speaker. that's the best and most economical way, but without modeling software, it's very difficult.

To Scott's point, all passive components have their own DC resistance, which we often refer to as parasitic. That resistance only screws things up if we don't consider it in the design of the network.


----------



## BEAVER

Great thread. Let me see if I can sum up Andy's take on enclosures, correct me if I misunderstood something...

Build a large, low tuned ported box that achieves a flat response *outside of the car*... then cut the bloated frequencies caused by cabin gain with the EQ. Is this it, in a nutshell?


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## 14642

That's it. One can never have enough EQ.


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## BEAVER

Thanks Andy. Your an asset to the community. I'm sure I speak for many when I say, it's nice to have you here.


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## 14642

Thanks!


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## 60ndown

Andy Wehmeyer said:


> Al of this really applies mostly to resonance and regions near resonance. A couple of octaves above resonance, the box doesn't have much to do with how the woofer sounds (unless it's leaky, flexes a lot or buzzes).
> 
> 1. .707 = flat response and lowest -3dB point
> 2. .5 = higher -3dB point and more gradual roll-off below F3
> 3. .9 = peak in the response above the -3dB point, steeper roll-off below that.


1.recc box size

2.smaller than recc under damped

3.larger thsn rec over damped

am i close? just trying to match the terminology with the box


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## BEAVER

I think you have 2 and 3 reversed.


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## 60ndown

BEAVER said:


> I think you have 2 and 3 reversed.


exactly, i bet there are a few of us that are not certain yet.


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## BEAVER

Let me rephrase it then... You have 2 and 3 reversed. 

To verify this simply go to WinISD and plot the same drivers in small and large enclosure. The shape of the graphs will show you what he's saying.


----------



## 60ndown

BEAVER said:


> Let me rephrase it then... You have 2 and 3 reversed.
> 
> To verify this simply go to WinISD and plot the same drivers in small and large enclosure. The shape of the graphs will show you what he's saying.


ive never played with winisd, 

but thanks for the clarification.


----------



## BEAVER

no problem. you should check out winisd sometime. it's pretty neat.


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## cvjoint

Andy Wehmeyer said:


> As we know from yesterday, the amplifier's output impedance is in series with the speaker. By Kirschoff's laws, the voltage in a series circuit divides proportionate to the resistance. Let's say our amplifier has an output impedance of 1 ohm and we're using a 4 ohm speaker. If the amplifier makes 20 volts (100 watts at 4 ohms by P = E^2/R), then 1/5 of the voltage is dropped across the output impedance and 4/5 of the voltage is dropped across the speaker. 1/5 of the voltage is 4 and 4/5 of the voltage is 16. Now, we can figure out how much power is dissipated by the amplifier's output Z by 4^2/1. Which is 16 watts. 16^2/4 = 64. So, our amplifier that made 100 watts at 4 ohms makes 80 watts at 5 ohms and only 64 of those watts make it to the speaker. OK, an amp with an ouptut impedance of 1 ohm would make a better door stop than an amplifier, but it makes a good example and the math is easy.


My amplifier's output impedance is listed to be smaller than .02ohms. Tell me if my math is correct: 4^2/.02=800watts??? How can I use this?


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## Oliver

Damping> http://en.wikipedia.org/wiki/Damping

quote:

In playing stringed instruments such as guitar or violin, damping is the quieting or abrupt silencing of the strings after they have been sounded, by pressing with the edge of the palm, or other parts of the hand such as the fingers on one or more strings near the bridge of the instrument.

end quote:


----------



## Oliver

Quote:

Critical damping
When ζ = 1, (defined above) is real, the system is said to be critically damped. A critically damped system converges to zero faster than any other without oscillating. An example of critical damping is the door-closer seen on many hinged doors in public buildings. Most guns are also critically damped so that they return to their original position, after the recoil due to firing, in the least possible time.

end quote:


----------



## 14642

cvjoint said:


> My amplifier's output impedance is listed to be smaller than .02ohms. Tell me if my math is correct: 4^2/.02=800watts??? How can I use this?


 
The math is correct. What are you trying to figure out? The point of the whole post is that there's no need to do that math or to even be concerned about the output impedance of the amplifier unless the output impedance is within a few ohms of the speaker's nominal impedance. You'd have to search far and wide to find an amp with an output impedance that high--and it would be apointless search.

Hook up the speaker and enjoy it. Worry about the frequency response in the car and not the output impedance of the amp.


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## cvjoint

Andy Wehmeyer said:


> The math is correct. What are you trying to figure out? The point of the whole post is that there's no need to do that math or to even be concerned about the output impedance of the amplifier unless the output impedance is within a few ohms of the speaker's nominal impedance. You'd have to search far and wide to find an amp with an output impedance that high--and it would be apointless search.
> 
> Hook up the speaker and enjoy it. Worry about the frequency response in the car and not the output impedance of the amp.


I was just surprised to see such a large number, I thought it would converge to 0watts. But I'm over my head in this :blush:

How about running higher impedance speakers? Are there any obvious benefits aside from the amplifier cooling better? I've seen folks repeatedly trying to run a passive set down to 2 ohms. My amps run hot enough at 4 ohms, there is a lot of midrange content necessitating constant draw.


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## guisar

If you want to compute your vehicles transfer function, using RTA or equivalent sweep from 20 to around 300 (wavelength of 4') out in your yard or a large, quiet area. Now, run the same waveform while the system is inside your car. The difference is the gain of your car in that frequency range.


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## SSSnake

> That's it. One can never have enough EQ.


AMEN! The problem is knowing what to do with them!


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## sundownz

Good posts Andy


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## caraudiofan21

Andy, great to have someone like you to be on this forum. Your thread is very helpful.

With regards to the Damping Factor discussion, you mentioned that the inductance from the speaker will dissipate quicker with a lower nominal speaker + amp output impedence after the music signal ends. Does that also mean that the speaker will come to a stop quicker with a 2 ohm nominal speaker as compared with a 4/8 ohm speaker? How would that affect the frequency response with a 2ohm speaker vs. 4/8 ohm speaker, all else being the same (incl sensitivity, etc.)?


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## Electrodynamic

Great posts Andy!


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## 14642

caraudiofan21 said:


> Andy, great to have someone like you to be on this forum. Your thread is very helpful.
> 
> With regards to the Damping Factor discussion, you mentioned that the inductance from the speaker will dissipate quicker with a lower nominal speaker + amp output impedence after the music signal ends. Does that also mean that the speaker will come to a stop quicker with a 2 ohm nominal speaker as compared with a 4/8 ohm speaker? How would that affect the frequency response with a 2ohm speaker vs. 4/8 ohm speaker, all else being the same (incl sensitivity, etc.)?


 
Let's back up a little:

1. Speaker Q is a measure of damping and the value of Q is inversely proportionate to damping--higher Q means LESS damping. 

2. The inductor stores energy and the energy is dissipated through whatever is in the circuit with the coil's inductance--the amplifier's output impedance, the speaker's DC resistance, the resistance of the speaker wire, the DC resistance of any passive crossover, etc.

3. The speed at which the energy stored in the coil stops causing the cone to move depends on the amount of energy stored and the resistance. This is referred to as "time constant" of the circuit made up of the resistance and the inductance.

If everything else was the same including the coil's inductance, then the speaker would come to rest more quickly if it had a 2-ohm DCR rather than a 4-ohm DCR. 

However...everything else can't be the same because reducing the impedance means a shorter wire in the voice coil or a larger gauge--that's how you reduce the impedance. The shorter or thicker wire would result in fewer turns around the voice coil former. Fewer turns means less inductance. Less inductance means less stored energy. Less stored energy means less time to dissipate. Less time to dissipate the energy would mean better damping. Better damping would mean lower Q. Lower Q would mean less output near resonance. Less output around resonance would mean less bass. Getting the bass back would mean a smaller box. A smaller box would require more excursion. More excursion would require a longer voice coil. A longer voice coil would mean a longer wire. A longer wire would mean higher DCR and more inductance...and so on and so forth.

Engineers often use special milled wire designed to manage this compromise (that's what edge-wound wire is).

Everything is interrelated and if it's damping you're concerned about, then you need to pay attention to Q--that's what Q indicates. The amplifier doesn't help enough to matter. The effect of reduced Q on frequency response is a higher -3dB frequency and a more gradual roll off.


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## iyamwutiam

guisar said:


> If you want to compute your vehicles transfer function, using RTA or equivalent sweep from 20 to around 300 (wavelength of 4') out in your yard or a large, quiet area. Now, run the same waveform while the system is inside your car. The difference is the gain of your car in that frequency range.


Great idea.

Andy:
Seems like perfect timing. I wanted to ask a few questions:
1. I have measured ambient noise (engine on) in park at around 60db but it was a radio shack meter. What is the 'average' ambient noise level for a car when traveling and at rest?
2. When you are driving - which (tire noise/wind noise/road noise) whatever it is - is low frequency in nature. Has anyone measured the spectrum of frequencies that are heard during driving (say on an asphalt highway- like wind noise)? I know that Alpine has an 'adaptive' EQ - but it seems to me - thats a lot of noise. Does this contribute to the sense of not having enuf bass when driving as compared to being parked?

3. How much does deadening effect the curve you displayed in terms of cabin gain. Would you see no change in gain or at what freq? - for example your diagram shows gain the most dramatic in the bigger cars- Yukon 1996 versus Jetta-or mini-cooper'-- isn't this this counter-intuitive?

Thanks


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## cvjoint

I've measurer road noise to be 70db at 80mph on a decent freeway in my Accord. I generally feel that road noise comes in mostly in the midbass region and I boost accordingly on the go.


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## 60ndown

Andy Wehmeyer said:


> Let's back up a little:
> 
> 1. Speaker Q is a measure of damping and the value of Q is inversely proportionate to damping--higher Q means LESS damping.
> 
> 2. The inductor stores energy and the energy is dissipated through whatever is in the circuit with the coil's inductance--the amplifier's output impedance, the speaker's DC resistance, the resistance of the speaker wire, the DC resistance of any passive crossover, etc.
> 
> 3. The speed at which the energy stored in the coil stops causing the cone to move depends on the amount of energy stored and the resistance. This is referred to as "time constant" of the circuit made up of the resistance and the inductance.
> 
> If everything else was the same including the coil's inductance, then the speaker would come to rest more quickly if it had a 2-ohm DCR rather than a 4-ohm DCR.
> 
> However...everything else can't be the same because reducing the impedance means a shorter wire in the voice coil or a larger gauge--that's how you reduce the impedance. The shorter or thicker wire would result in fewer turns around the voice coil former. Fewer turns means less inductance. Less inductance means less stored energy. Less stored energy means less time to dissipate. Less time to dissipate the energy would mean better damping. Better damping would mean lower Q. Lower Q would mean less output near resonance. Less output around resonance would mean less bass. Getting the bass back would mean a smaller box. A smaller box would require more excursion. More excursion would require a longer voice coil. A longer voice coil would mean a longer wire. A longer wire would mean higher DCR and more inductance...and so on and so forth.
> 
> Engineers often use special milled wire designed to manage this compromise (that's what edge-wound wire is).
> 
> Everything is interrelated and if it's damping you're concerned about, then you need to pay attention to Q--that's what Q indicates. The amplifier doesn't help enough to matter. The effect of reduced Q on frequency response is a higher -3dB frequency and a more gradual roll off.


i think i love you andy


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## 60ndown

cvjoint said:


> I've measurer road noise to be 70db at 80mph on a decent freeway in my Accord. I generally feel that road noise comes in mostly in the midbass region and I boost accordingly on the go.


id say road noise is mostly below 140hz.


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## 14642

Yeah, road noise is a pain in the ass. When I used to live in El Paso, I used to drive to Austin on weekends to see my girlfirend (now ex-wife, but that's another long story better suited for a counselor or comedian than this forum). Anyway, the interstate between El PAso and Van Horn was paved with little pebbles and the shape of the noise was VERY different than the the noise driving on better roads. I used to have a separate EQ for those 90 miles. That road caused a lot of noise even at 500Hz, which was surprising. Mostly, it's negligable above 200Hz, but the car has a lot to do with it. 

If you have an iPod, get the stereo microphone recorder from Griffin. It's cheap. Record the noise. Then download audacity at http://audacity.sourceforge.net/. You can open the file in that program and see a frequency analysis. Or, play it in windows media or some other program and and measure it with some RTA software. 

Or, if you guys want to make the recordings and email them to me, I'll do the analysis of the data and post the graphs here. Send me any file format you want but be sure it's less than 10MB!

[email protected]


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## 60ndown

Andy Wehmeyer said:


> Yeah, road noise is a pain in the ass. When I used to live in El Paso, I used to drive to Austin on weekends to see my girlfirend (now ex-wife, but that's another long story better suited for a counselor or comedian than this forum). Anyway, the interstate between El PAso and Van Horn was paved with little pebbles and the shape of the noise was VERY different than the the noise driving on better roads. I used to have a separate EQ for those 90 miles. That road caused a lot of noise even at 500Hz, which was surprising. Mostly, it's negligable above 200Hz, but the car has a lot to do with it.
> 
> If you have an iPod, get the stereo microphone recorder from Griffin. It's cheap. Record the noise. Then download audacity at http://audacity.sourceforge.net/. You can open the file in that program and see a frequency analysis. Or, play it in windows media or some other program and and measure it with some RTA software.
> 
> Or, if you guys want to make the recordings and email them to me, I'll do the analysis of the data and post the graphs here. Send me any file format you want but be sure it's less than 10MB!
> 
> [email protected]


does that mean a person could eq 85% or the road noise out? 

if they were doing the same journey regularly? kinda like 'noise cancelling' ?

very cool idea for commuters (with 30 band eqs) ida thought.


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## GlasSman

60ndown said:


> does that mean a person could eq 85% or the road noise out?
> 
> if they were doing the same journey regularly? kinda like 'noise cancelling' ?
> 
> very cool idea for commuters (with 30 band eqs) ida thought.


And very doable if your processor TONS of EQ and multple presets.


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## 14642

60ndown said:


> does that mean a person could eq 85% or the road noise out?
> 
> if they were doing the same journey regularly? kinda like 'noise cancelling' ?
> 
> very cool idea for commuters (with 30 band eqs) ida thought.


 
It doesn't mean you can get rid of the noise--you can boost the output at the same frequencies as the noise so you'll still be able to hear them. Getting rid of the noise requires active noise cancellation.


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## capnxtreme

Andy, thanks for contributing!! Really awesome. I'm gonna have to try that Griffin iPod recorder.


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## GlasSman

Some of this thread needs to be stickied...or parts of it put into a sticky thread on Subwoofer fundamentals.


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## Steak

Great thread, just spent the better half of my afternoon reading and understanding it 

now is there any chance that the more knowledgeable folks can give me a hand with this? http://www.diymobileaudio.com/forum/showthread.php?p=477877&posted=1#post477877

not trying to hijack this great thread, just very confused and Im pretty sure my iissue relates directly to the contents of this thread. Thanks.


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## aztec1

There's so much good information in this thread. Thanks!

It makes me wonder how much does placement of the sub change cabin gain? What about the direction of the vent in relation to the cone?


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## Patrick Bateman

Andy Wehmeyer said:


> I find that the best-sounding, lowest-distortion and most efficient use of woofer dollars, enclosure dollars and amplifier power can be had by:
> 
> Building a vented box with a flat response and the lowest F3 possible and usiing an EQ to eliminate the peak in the car. That minimizes the amount of power the amplifier has to make, minimizes the driver's excursion, leaves lots of juice available for transient peaks, and minimizes driver and amplifier distortion.
> 
> Requires a larger box and a parametric EQ, though.


I totally agree. I think it's funny that when a lot of people aren't satisfied with how their subs "hit" they start fiddling with the EQ on their amp. Next thing you know they've dialed in +6db of EQ at 45hz... Which makes things WORSE.

The problem is TOO MUCH low end, not too little.

Often dialing in a CUT at 45hz will massively raise power handling by reducing excursion, allowing you to get back a lot of that visceral impact of the sub that you were missing.


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## 60ndown

Patrick Bateman said:


> I totally agree. I think it's funny that when a lot of people aren't satisfied with how their subs "hit" they start fiddling with the EQ on their amp. Next thing you know they've dialed in +6db of EQ at 45hz... Which makes things WORSE.
> 
> The problem is TOO MUCH low end, not too little.
> 
> Often dialing in a CUT at 45hz will massively raise power handling by reducing excursion, allowing you to get back a lot of that visceral impact of the sub that you were missing.


unless your looking for visceral impact at 30 hz.


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## BEAVER

I'm sorry to bring this back, but I was reviewing the graph Andy posted earlier and have a quick (dumb?) question...

How could you have *negative* cabin gain? The chart reads from -15 to +35. What am I missing here?


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## 60ndown

^ im guessing the chart only deals with 80 hz and down , before that 81-20,000 its below concern?



Andy Wehmeyer said:


> Here are some measured transfer functions.


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## 60ndown

oh i see the greenish line at 68 hz - 15, im guessing thats some kinda cancellation due to resonance of the vehicle/phase issue?

maybe thats a ported box tuned low and rolls off steep at 60?


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## 60ndown

hmm? lots of them see to be -ve?


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## 60ndown

im guessing the subs are crossed at 55hz + or - for testing?


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## BEAVER

60ndown said:


> im guessing the subs are crossed at 55hz + or - for testing?


Doh. You're probably on the right tack here...


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## 14642

No, sub was mounted in a small sealed box in the rear right corner of the car and the mic was in the listening position (driver's seat). The in car measurement was divided by the anechoic measurement of the same sub made at precisely the same drive level. Measurement bandwidth was 10 Hz to whatever the top of the graph shows. The measurements I posted are the frequency response of the car with the speaker in its location independent of the speaker's response. The placement of the sub makes little difference below 40-50 Hz, but it does affect everything above 50. Dips and peaks in the frequency response above 50Hz are the result of cancelation and reinforcement. The first mode (first big peak or more often dip above 50Hz) is pretty easy to predict by measuring the size of the car.I also have an analysis of door/window/trunk open and closed that supports my often scoffed-at suggestion the opening the door, window or trunk simply tunes the listening space. Apparently that explanation isn't sufficiently mysterious enough for most folks who would like it to be more complicated or would like some poorly documented or prroly reasoned explanation about delay and phase to prevail. One of these days I'll post the, but I can't do it now from my blackberry.


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## 14642

Oh, to answer the question more specifically (hopefully with better spelling), the anechoic measurement was made at 1 meter. The inverse square law dictates a reduction in measured output of -6dB for every doubling of distance...speaker in the rear right corner of the car accounts for the overall reduction in level and is different in different cars. Obviously, the speaker is closer in an MG than in a suburban.


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## BEAVER

Seeing how much gain is really there, I'm surprised you're such a big proponent of vented enclosures. It seems that there is plenty of gain in just about every vehicle for a flat response with a sealed allignment... But I understand you have you're reasons, as outlined previously.


----------



## twista17

great thread going on here, i couldn't stop myself reading this at work. our company sells subwoofers in the Philippines and this is just a great eye opener.

andy, this is so timely, i am in a rebuild stage and have been debating on the following scenarios for my (SQ) competition system:

1) big sealed box - for more output
2) vented box tuned at 38hz - can EQ the peak frequency with my processor
3) convertible box from sealed to vented - is this even possible?

currently running a RE Audio SX12 in a vented box and i EQd the peak frequency and am loving how the subwoofer is full and tight even though my initial thoughts were it won't go well with my Morels up front. its been almost three weeks and i think i have dialled the sub in to go really well with my front stage that i somehow forget i am using a vented box.

my only issue is that i am not so satisfied with the 18hz tone in the IASCA disc track 9. in a vented box it feels that it barely shakes your car compared to when in a sealed box. well come to think about it, my JL10W7's performance it this track didn't satisfy me. maybe i'm asking too much 

anyway, thanks again for andy for such a great post!


----------



## Oliver

Tune your enclosure lower than 18 Hz 

I've seen ported and sealed box made for the same sub


----------



## Oliver

Andy Wehmeyer said:


> I also have an analysis of door/window/trunk open and closed that supports my often scoffed-at suggestion the opening the door, window or trunk simply tunes the listening space. Apparently that explanation isn't sufficiently mysterious enough for most folks who would like it to be more complicated or would like some poorly documented or prroly reasoned explanation about delay and phase to prevail. One of these days I'll post


Scoff, scoff 

Next thing, you'll be saying that a pump increases pressure in a sealed space


----------



## lust4sound

Andy Wehmeyer said:


> Yes, flat frequency response and low Q with a cutoff frequency at or below 20Hz would be ideal, but it isn't practical nor is it necessary.
> 
> If you look back over this whole thread, the answer may become clear.
> 
> 1. Flat frequency response *is* accurate time response.
> 2. The cabin gain, (transfer function) of the car makes a sealed box with a -3dB point that corresponds to the +3dB point on the transfer function curve have flat response at low frequencies.
> 3. You'll never fix all the frequency response problems without an EQ. This should be obvious in the transfer function graph I posted.
> 4. Since you have to have an EQ for good sound, build a vented box for much better efficiency and remove the peak with the EQ for lower distortion and better dynamics (since there will be plenty of power left over after you cut 45Hz or so by about 12dB).
> 5. If you can't afford to lose additional space to a vented box, you can make up for it with a woofer with high Xmax and lots of power.


This is the info I've been looking for. It's off to studying now!! It's going to take me a while to completely understand it all, but I'll get there or die trying*!! (*how to use this info to make the right choices for my desired goal)

I've been rambling on with questions regarding this very info on a different thread. 60Ndown referred me here. THANKS BUDDY!

Thanks Andy for all the info. Could you possibly take the time to guide me if I sent a PM with my intended goal? Info in layman terms on how to get where I want to go? In order to save you from being bombarded with help inquiries, perhaps you can PM me with a simple Yes or No? 

Or, I could pop the question here, all could benefit from your response? 

If "NO" on both counts, I wouldn't take offense, I realize you're probably a very busy dude...

I'll find a way to make use of all the valuable info you've already provided, just have to read it over a bunch of times till it finally sinks in....

This site is awesome, so glad I found it, already learned so much from it. Learned almost enough to finally get what I want out of my system!! Since I started here, I've already made great strides toward improving my sound, all thanks to people like Andy, and Mark AKA "Here-I-Come" as well as too many others to name!


----------



## 60ndown

lust4sound said:


> This is the info I've been looking for. It's off to studying now!! It's going to take me a while to completely understand it all, but I'll get there or die trying*!! (*how to use this info to make the right choices for my desired goal)
> 
> I've been rambling on with questions regarding this very info on a different thread. 60Ndown referred me here. THANKS BUDDY!
> 
> Thanks Andy for all the info. Could you possibly take the time to guide me if I sent a PM with my intended goal? Info in layman terms on how to get where I want to go? In order to save you from being bombarded with help inquiries, perhaps you can PM me with a simple Yes or No?
> 
> Or, I could pop the question here, all could benefit from your response?
> 
> If "NO" on both counts, I wouldn't take offense, I realize you're probably a very busy dude...
> 
> I'll find a way to make use of all the valuable info you've already provided, just have to read it over a bunch of times till it finally sinks in....
> 
> This site is awesome, so glad I found it, already learned so much from it. Learned almost enough to finally get what I want out of my system!! Since I started here, I've already made great strides toward improving my sound, all thanks to people like Andy, and Mark AKA "Here-I-Come" as well as too many others to name!


what do you want?

sq,spl, or.....sql?


----------



## 14642

PLease ask the question here.


----------



## 14642

twista17 said:


> great thread going on here, i couldn't stop myself reading this at work. our company sells subwoofers in the Philippines and this is just a great eye opener.
> 
> andy, this is so timely, i am in a rebuild stage and have been debating on the following scenarios for my (SQ) competition system:
> 
> 1) big sealed box - for more output
> 2) vented box tuned at 38hz - can EQ the peak frequency with my processor
> 3) convertible box from sealed to vented - is this even possible?
> 
> currently running a RE Audio SX12 in a vented box and i EQd the peak frequency and am loving how the subwoofer is full and tight even though my initial thoughts were it won't go well with my Morels up front. its been almost three weeks and i think i have dialled the sub in to go really well with my front stage that i somehow forget i am using a vented box.
> 
> my only issue is that i am not so satisfied with the 18hz tone in the IASCA disc track 9. in a vented box it feels that it barely shakes your car compared to when in a sealed box. well come to think about it, my JL10W7's performance it this track didn't satisfy me. maybe i'm asking too much
> 
> anyway, thanks again for andy for such a great post!


It's unfortnate that the IASCA judges think that 18Hz tone should shake the car. I seem to remember looking at that on a spectogram and discovering that it's something like 20dB below the rest of the music. When I've competed, I've added a very narrow band of EQ--Q of 25, F of 18 and boost of about 20dB so the judges could get their jollies without the EQ affecting any other track. If the box is tuned to 38Hz, the response is probably pretty far down at 18. Try tuning the box lower. IF you have a parametric EQ, use it for that track or for IASCA judging in general.


----------



## tspence73

Andy Wehmeyer said:


> Shroeder has never played the piano anywhere near my car and Snoopy has never driven it.
> 
> Here are some measured transfer functions.


I've been wanting to add a pair of midbasses to my system and was thinking of the range between 70Hz-250Hz for this very reason. My comps simply aren't able to keep up with the subs and a BIG gap from 60Hz to 90Hz is very noticeable to me. The frequencies from 30Hz to 50Hz are just gigantic (like 115db SPL) and then a REALLY sharp drop right at 60Hz to 90Hz (102db). There is no way my component speakers can keep up with that without giving extra noises. 

So, I thought by keeping the subs lowpass at around 90Hz and running a midbass with a sharp sub-sonic filter at 70Hz and a lowpass of 250Hz that I could get that 60Hz-90Hz range boosted by up and then use my sub amp's 45 Hz EQ and my headunit's 60Hz EQ to try and get the rest of the humps and dips moved closer.

This also accomplishes giving me a bit more excitement up front, which I wanted anyway. Do I have a good idea by adding a pair of midbasses you think?


----------



## 14642

Get an RTA and figure out why there's a huge dip betwen 60 and 90 Hz. If I had to guess, I'd guess there's a phase problem between the sub and the other speakers due to crossovers or speaker placement. Try crossing the sub at 90 and the front speakers at 90. Disconnect the rear speakers. If you have a big dip, change the polarity of the sub. 

What are the crossover slopes? 

Adding a dedicated pair of midbass drivers can help if you require really high listenin levels, but at lower levels, even a 4" or 5" can be made to integrate well with a sub provided you have the necessary tools. The most important of those is a parametric EQ of some sort that will allow separate adjustment for left and right.


----------



## Brian Steele

Andy Wehmeyer said:


> Oh, to answer the question more specifically (hopefully with better spelling), the anechoic measurement was made at 1 meter.


A close-miked measurement should work as well, particularly as of more concern here is the shape of the transfer function, rather than the absolute gain. 

I like the idea of using a vented box and EQ, btw. Even better, if you know the actual transfer function of your vehicle, and you have access to a modeling program that allows you to include the effects of cabin gain, you can design a vented box that takes the cabin gain into consideration to produce a flat response, and probably eliminate the EQ entirely (or at least minimize the requirement to use it). I did just that a few years ago with my "subwoofer with cabin gain compensation" project - see http://www.diysubwoofers.org/projects/car/sub3/. I scrapped that box shortly afterwards though - not because it didn't work well (it did - it sounded excellent), but because there was no more space in the trunk of my vehicle to hold my beer cooler for those weekend trips to the beach .

A few more things:

1. Designing for a flat bass response curve in-car might not be the best approach. First there's that pesky noise floor to consider, and secondly there's always the question of personal preference. I like a slowly-rising bass response below about 100 Hz or so.

2. Any speaker response modeling for car audio subwoofers should take into consideration the response at the target power levels too. That flat frequency response at 1W might look great on paper, but if the design results in a system that has the sub running out of excursion at low power levels within the passband, it will sound like ass when you turn up the volume .


----------



## tspence73

Andy Wehmeyer said:


> Get an RTA and figure out why there's a huge dip betwen 60 and 90 Hz.


I've already used an SPL meter with test tones to find why certain bass sounds were really low compared to how they normally sound on the home system. I found a REALLY steep drop. At 50Hz, (0db) the SPL meter was at 115db. 60Hz (0db) was 102db. In just that small distance there is a huge drop akin to a low-pass filter at 30db/octave.

I was convinced my previous sub amp was broken or the built-in crossover was stuck or malfunctioning. But after switching out the sub-amp with a new one it was clear that this was an acoustic problem. When looking at that response graph it's pretty clear what people have been saying about 'cabin gain'. That is exactly what seems to be happening to me. 



> If I had to guess, I'd guess there's a phase problem between the sub and the other speakers due to crossovers or speaker placement.


There is a phase knob on my sub amp. Should I try playing with that and re-test at 60Hz?



> Try crossing the sub at 90 and the front speakers at 90. Disconnect the rear speakers. If you have a big dip, change the polarity of the sub.


I'm assuming that with a phase adjustment this shouldn't be necessary? And, the rear speakers are toast, so they are not being used now.



> What are the crossover slopes?


I'm using 120Hz right now due to the amp on the comps being set at 160-watts RMS. After trying out a lower crossover setting with my new amp I'm just not happy with what sounds like slight motor noises from the speaker. On the previous amp I got the same noises at a 60Hz setting. With this more powerful amp the problem occurs at even 90Hz.



> Adding a dedicated pair of midbass drivers can help if you require really high listenin levels,


I want very loud levels for the sake of clean peaks and dynamics. Also for those rare times where I want to play some aggressive rock and alternative.



> but at lower levels, even a 4" or 5" can be made to integrate well with a sub provided you have the necessary tools. The most important of those is a parametric EQ of some sort that will allow separate adjustment for left and right.


At the levels I've been trying to set my equipment, the 6010cs comps just aren't able to keep up or play frequencies under 100Hz clean. When I can actually hear the motor of the driver and not clean bass, I can't stand it. But I don't want to give up the mids and highs that I like from them. I'm pretty sure the dedicated midbass is the way to go unless I want to run with a 120Hz highpass. Well, the 120Hz highpass just doesn't sound, 'right' to me. Something is missing. When I adjust the crossovers so the comps are at 80Hz and up, I really like it but I can't get the volume up loud enough to make me happy.


----------



## 14642

Fix the dip before you add more speakers. Try the phase control.


----------



## Brian Steele

Andy Wehmeyer said:


> Fix the dip before you add more speakers. Try the phase control.


Andy, FWIW, I've seen similar dips in the frequency response in my last two vehicles (see the 20Hz - 200Hz TF for my Hyundai Tucson attached). Your cabin gain graph also features similar dips for some vehicles.


----------



## tspence73

Andy Wehmeyer said:


> Fix the dip before you add more speakers. Try the phase control.


I can with a 120Hz crossover along with an EQ/shelf at 55Hz and below. My amp has a 'narrow Q' +/-18db filter @ 45Hz that I can use to help some of the problem, but if it truly is a 'narrow Q', then Frequencies at 25Hz-30Hz will still be very high.

Also, I would like to try and have as much headroom as possible on the system, so that when I do 'crank it' or ask the system to give some strong output, it can without strain. 'Without strain' is VERY important to me. It's what I think separates average/everyday setups from exceptional systems. I want my music listening to be an 'experience', not just backround filler on a boring drive.


----------



## lust4sound

Found this link. It's not about cabin gain, but it makes for some very informative reading.

It discusses the Linkwitz transform circuit and its affects on subs in small sealed enclosures. 

EG: How to flatten response and get 20HZ extension from a tiny sealed enclosure. 

It also discusses many other things EG: What to look for in terms of driver parameters to yield optimal output per watt, etc etc 

http://sound.westhost.com/project71.htm

I'm a noob, just starting to understand the "in depths" of serious audio. Let me know if I'm even in the ballpark with this one will ya's?


----------



## exmaxima1

lust4sound said:


> Found this link. It's not about cabin gain, but it makes for some very informative reading.
> 
> It discusses the Linkwitz transform circuit and its affects on subs in small sealed enclosures.
> 
> http://sound.westhost.com/project71.htm


I used that circuit for my home subwoofer and it works very well. I put a huge woofer in a tiny sealed box to push the Fc to about 70 hz, which is ABOVE my crossover point. That circuit, connected to a 1000 watt power amp, provides EQ at 12 dB/oct to complement the rolloff of the subwoofer.

The advantage of this admittedly inefficient configuration is the total lack of resonances in the usable bandwidth---ala the BagEnd ELF system.

Sounds totally effortless and natural.

Matthew


----------



## exmaxima1

60ndown said:


> ^ im guessing the chart only deals with 80 hz and down , before that 81-20,000 its below concern?


In the Jan/Feb 1996 issue of Car Stereo Review, Tom Nousaine wrote a great article revealing cabin gain. Since then, some companies such as Alumapro, have used that same generic transfer function with good commercial results. The article is long out of print, but the basic curve is:

0 db @ 70 Hz
+1 @ 60
+5 @ 50
+10 @ 40
+15 @ 32
+19 @ 25
+22 @ 20 
+27 @ 16 

If you plug that curve into your speaker program to sum with your speaker's predicted response, you can readily see that it doesn't take a huge speaker system to realize a deep flat response in a car.

Good Luck!

Matthew


----------



## lust4sound

exmaxima1 said:


> I used that circuit for my home subwoofer and it works very well. I put a huge woofer in a tiny sealed box to push the Fc to about 70 hz, which is ABOVE my crossover point. That circuit, connected to a 1000 watt power amp, provides EQ at 12 dB/oct to complement the rolloff of the subwoofer.
> 
> The advantage of this admittedly inefficient configuration is the total lack of resonances in the usable bandwidth---ala the BagEnd ELF system.
> 
> Sounds totally effortless and natural.
> 
> Matthew


So it's robs you of power, but makes up for it by benefiting in the lower register in an application where space may be of an issue?

Is it used, seldom used or never used in car audio applications?


----------



## ChrisB

I had a servo feedback unit designed to work with an Orion 250 SX, but I don't have my 250 SX back yet  It is supposed to flatten the response from 20 to 100 Hz no matter which size sub I go with. The only thing is I need to select subwoofers with a certain T/S parameters.


----------



## exmaxima1

lust4sound said:


> So it's robs you of power, but makes up for it by benefiting in the lower register in an application where space may be of an issue?
> 
> Is it used, seldom used or never used in car audio applications?


It is indeed power hungry, yet it uses small enclosures. Like I noted earlier, BagEnd made a commercial system for PA use, and I've seen bass players use it on stage. 

Never seen it in a car, though it would be far less efficient in that application. The cabin gain would compensate for much of the power needed, so the bulk of the EQ would be over a limited range. Certainly worth considering if space is a problem (like under seats), but highest quality bass is desired.

Matthew


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## 14642

Why make this so freakin' complicated? Build a box, put it in the car, and EQ it flat. IF there are cancellation problems c. 70Hz, you won't be able to fix that with an EQ. You'll have to move the sub or cross the sub over below that. Then, cross your midbass in to match and keep EQing.

It's the sound in the car that matters, not the output of the sub. The reason for the vented box simple efficiency. You can remove the peak with the EQ and then your amp doesn't work so hard.


----------



## slvrtsunami

Well said Andy. Sometimes (myself included) we tend to look at the tree's and the whole forest!


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## lust4sound

Andy Wehmeyer said:


> Why make this so freakin' complicated? Build a box, put it in the car, and EQ it flat. IF there are cancellation problems c. 70Hz, you won't be able to fix that with an EQ. You'll have to move the sub or cross the sub over below that. Then, cross your midbass in to match and keep EQing.
> 
> It's the sound in the car that matters, not the output of the sub. The reason for the vented box simple efficiency. You can remove the peak with the EQ and then your amp doesn't work so hard.


Andy, I'm of the belief that vented is the way to go. The only reason I included that link is because I am just starting to comprehend what is being discussed here. When I read that link, I wondered if it was closely related to some of the topics being discussed here, if it is, that means that I am actually beginning to comprehend this discussion. 

For vented, is Subsonic the answer for keeping the sub from unloading at frequencies it shouldn't have to deal with? EG: damaging frequencies belwo the parameter of the sub/ tuning frequency of the box?

I understand that a driver performs within it's own set of parameters. I also understand that every application has it's own special requirements with regard to driver parameters, enclosure volume, vehicle it's installed in(cabin gain) subsonic filtering, tuning, amplification (damping) etc.

Now my only problem is knowing first hand "what is required for where" is "most ideal" for "which application" and so on.

It's simple for you guys yes, you have an in depth understanding of driver parameters and how enclosures/cabin gain/filtration/EQing all in carefully considered combination can affect the outcome of a given setup. 

I could understand it in it's entirety as well, as long as it is outlined in layman terms.

Question.
I want to install 2-JL 12W7's in my work truck. I have 2 MMATS D3000.05 to power them, 1 amp per sub. The amps are designed to deliver 2500 RMS into .05 ohm load. Given the 3 ohm load per sub, would have to check with MMATS to see what the amps will do at that impedance. Hopefully, it will be sufficient enough to afford extra headroom for my sub application. 

The vehicle is a Jeep Cherokee Laredo. I want to be able to keep the space I have available in back to haul my gear around, at the same time, I want killer sub bass response FLAT and LOUD from 80HZ down to 26HZ, all in a tiny footprint. I would like to be able to trip the meters at over 140 maybe 150 on music, but thats not my goal in it's entirety. I want the whole system to be a good SQL performer. . Front stage matched at normal to moderate volume levels, not during full out sub SPL.

For front stage 
IDQ8's up front for midbass. 
May use DLS Nobelium Ultimates 4" and tweet for mids and highs. 
I have 2 MMATS SQamps, 
1) SQ4150 
1) SQ4160. 

Wanted to use 1 bridged (SQ4150) for midbass, thats 300 per side @ 4 ohms, the other MMats as a 4 channel @160 watts x 4 to power mids and tweets. 

The HU is a Kenwood DDX7015. 
XO is a PPIFRX456. 

Outside of this, I have nothing.

I've helped myself as much as I could with all the reading and questions posted in here, this is as far as I go. In layman terms, could you outline a strategy for me? EG: Processing, sub enclosure type, subsonic, EQ etc etc. 

You'd be like Jesus himself if you could hook up this info in layman terms!!

I'm new to SQ, but I'm learning fast, have this site to thank. Especially people like Ambolech, Here-I-come, 60N and Andy Boy.. There are others, too numerous to name, thanks to all..

Have at it fellas, where should I go from here? (Hell isn't the answer I'm looking for, that wouldn't be nice


----------



## 14642

Since the amplifier is really designed to drive lower impedance loads than the 3 ohms you'll be providing, get rid of one of them and drive both woofers with the other. It'll make more power into the lower impedance and save you space. Headroom happens when you don't use all the power the amp can provide for average levels--there's more available for peaks. There's no need for the other amp.

Since you'll have plenty of power and space is a big concern for you, build the optimum sealed box for the subs, or go a little smaller. You'll fix the sound with an EQ that you'll by with the money you'll make selling the unnecessary amplifier. When you buy your EQ, be sure to get a parametric model and preferrably one that will allow you to adjust left and right separately.

Once you have all of the stuff in the car, you'll find that the bass extends down to the lowest octave easily and you can use the amplifier's gain control to adjust the level of the bass. Use an RTA and measure the response of the sibwoofer with nothing else playing and the crossover set to a ridiculously high value. If you have no big dips in the response in the midbass, take a break and drink a beer.

Now, shut off the sub and measure the response of the mids and highs with no high pass filter. Make a note of where they begin to roll off. Hopefully, you'll have useable response down to 80Hz or so. If you do, set the crossover to about 80 Hz. If you have time alignment, set it now.

Turn the sub back on and adjust the subwoofer level and the low pass filter (nevermind the sub's crossover frequency) until you have about 9dB more bass than mids and highs and a smooth downward slope from 60Hz to about 160Hz. You may have to reverse the phase (polarity) of the sub to get good integration between it and the rest of the system. 

Now, use your EQ to smooth out the frequency repsponse. Try not to boost in the midbass or midrange. High frequency boost is OK if necessary. Boost anywhere within the subs passband is OK, but be careful about boosting near the crossover frequency between sub and midbass.

Getting the bass to sound like it comes from the front is a matter of the amount of bass and the slope between 60 and 160Hz. You may have to fiddle with both of those areas to get good integration. 

Bass is the easiest thing to make in cars. Bass up front is not.


----------



## lust4sound

Andy, thanks for the 411. It definitely helps..


----------



## sqshoestring

Great thread, I have the issue of = and < 30Hz being hard to find in cars I've had lately. 

So I ignore cabin gain and build to get low. I figure it is (just like you said Andy) much easier to cut out bass than to make more. I can tolerate a sub that will hit 30-35Hz well, but if not then I'm not happy and I'd much rather have a strong 30Hz and 20Hz capable. I like big vented, nice and efficient, but no room for that so I run IB if I can. Still have to boost the lows a lot, makes me wonder if the cabin gain got left out of my cars or occurs higher than 30-40Hz.


----------



## lust4sound

sqshoestring said:


> Great thread, I have the issue of = and < 30Hz being hard to find in cars I've had lately.
> 
> So I ignore cabin gain and build to get low. I figure it is (just like you said Andy) much easier to cut out bass than to make more. I can tolerate a sub that will hit 30-35Hz well, but if not then I'm not happy and I'd much rather have a strong 30Hz and 20Hz capable. I like big vented, nice and efficient, but no room for that so I run IB if I can. Still have to boost the lows a lot, makes me wonder if the cabin gain got left out of my cars or occurs higher than 30-40Hz.


My first build following Winisd was with a pair of kicker Solobaric 15L7's in a 9 CF vented box tuned to 32HZ. This in a Jeep Cherokee Laredo. I hadn't even considered Cabin gain, didn't know what it was. Just tuned the box to 32HZ as per Kickers Recs, they told me that the Solos play a half octave lower so I would easily see 25HZ extension. They weren't joking..

I had the pair configured to a single .05 ohm load (dual 2's from 2004) Powered them with a MMATS D3000.05 (2500 watts rms @ .05 ohm) The subs aren't broken in yet, brand new. Had the subsonic on the PPI FRX dialed in @ 24HZ. Minimal EQing, only what is available through my Pioneer deck, which isn't much.

BOY I TELL YOU WHAT!!! When turned up only half the way, my whole neighborhood came out to see what the commotion was about, it was that loud. I didn't want to push it any further, fear of destroying speakers that haven't been broken in. Still, I shook the neighborhood and heard no audible distress from the subs at all. I didn't hear any bottoming out, any distortion, no buzzing, rattling. Just smooth, low, deep, pounding. At only half power, it was too loud for my front stage which is a 3 way active with upwards of 1000 watts rms on tap. The mids and highs were sufficient, but the 6.5's, in their sealed enclosures would not provide the midbass to match a mere 1/4 output of the subs, thats with 300 watts per side. The drivers are not up to the task, reached the limits of excursion at 1/4 power.

I had to turn the subs almost all the way down to blend with midbass and the front stage.. When I did this, I was treated to my first glimpse of what a good system is all about. With my limited EQing and tuning by ear, it was by far the best sound I've achieved to date. (this with info I picked up here, thanks fellas)

I had little time to experiment as I quickly removed everything because I don't have an alarm system. 

It was my first Solo, designed by me, built by me Vented box build, so I was anxious to hear it. Also, my first venture into a 3 way active front stage. My God, overkill is an understatement.

My question is, would serious low end EQing help to bring that beast under control and make it a usable sub section for SQ? I'm pretty sure what I was hearing was a sharp peak in some frequency region that I had no way of controlling given my limited resources.

Not bad for a noob.. I impressed myself.. Can't wait to give it another go, this time with much better drivers up front, IDQ8's for starters.. Serious processing, RTA for tuning.. 

For subs, I will start with the Solobarics, then progressively work my way through all my different subs to hear and compare the differences.

I'll keep you guys posted, that is if you care..


----------



## Oliver

We care , maybe try a sub with a little less SPL type styling .

Something known for sound quality and thump.

Image Dynamics, IDMAX, should do the trick for you !


----------



## lust4sound

a$$hole said:


> We care , maybe try a sub with a little less SPL type styling .
> 
> Something known for sound quality and thump.
> 
> Image Dynamics, IDMAX, should do the trick for you !


I've got a few different style JL's from 12W0's all the way up to 12W7's, Orion XTR Pro 15's, 12" MMats Pro 3.0's, etc etc.. 

Kicker Solos are reputed as SPL only, I've seen a few cases proving otherwise. Never in an all out SQ car, but then again, I've not recently been in an award winning SQ car, been about 12 years or so...


----------



## Mlstrass

VERY interesting thread. I stumbled upon this idea a few years ago. I'm running a large ported box tuned to 40Hz with subs that have a high fs. I do have an SPL side to me, so the design goal leaned that way. 

But with the remote gain turned way down and the bottom freqs EQ'd back it blends VERY well with my front stage and sounds quite good. My set up is often mistaken for a couple of sealed 10's which I take as a compliment since we all know that 10's play the cleanest. 

I also wonder if having subs/power with such high output capability, but barely pushing them also makes them sound a little more accurate vs having less sub/power and having to push it much harder. 

I've owned/heard what many consider to be LSQ subs, including the FI Q, RL-P, Icons, and even an old Tempest. My current set up sounds better then all of those, even though it's not supposed to, but this thread seems to shed some light on that. Maybe I don't have ears of stone after all 

I run 2 15" AQ HDC's in 8.5cubes tuned to 40Hz. I did get my set up metered last year and it peaked at 149dB @ 31Hz, so obviously it has some VERY exaggerated bottom end, but I can easily tame that with the EQ. 

I do plan to attend some local SQ meets next year and hear some true SQ set ups and let others hear mine just to get some feedback. But I won't disclose my set up until it's been heard and fairly critiqued for fear of pre-conceived notions


----------



## 60ndown

bumptitfadaneewbs.


----------



## captainobvious

exmaxima1 said:


> In the Jan/Feb 1996 issue of Car Stereo Review, Tom Nousaine wrote a great article revealing cabin gain. Since then, some companies such as Alumapro, have used that same generic transfer function with good commercial results. The article is long out of print, but the basic curve is:
> 
> 0 db @ 70 Hz
> +1 @ 60
> +5 @ 50
> +10 @ 40
> +15 @ 32
> +19 @ 25
> +22 @ 20
> +27 @ 16
> 
> If you plug that curve into your speaker program to sum with your speaker's predicted response, you can readily see that it doesn't take a huge speaker system to realize a deep flat response in a car.
> 
> Good Luck!
> 
> Matthew



Is there a way to do this in WinISD ?


----------



## OSN

captainobvious said:


> Is there a way to do this in WinISD ?


I know you can with Bass Box Pro 6- don't know about WinISD but doubt it.


----------



## 14642

Do what? I can do this with a radio shack SPL meter and a pad of paper.

An old roommate of mine in college could (and did) do it with a sheep.


----------



## captainobvious

Andy Wehmeyer said:


> Do what? I can do this with a radio shack SPL meter and a pad of paper.
> 
> An old roommate of mine in college could (and did) do it with a sheep.


Sorry, I should have been more specific. I meant is there a way in WinISD to plug in those values to have them auto adjust the curve with those average cabin gain numbers?

Thanks.

Oh and BTW- this is a hell of a write up Andy. Thanks for taking the time to do this, its very helpful !


----------



## 14642

export the win ISD plot as a text file, import it into microsoft excel and do the post processing and graphing there!


----------



## 14642

If there's no text export function, google "windig". That's a program that will allow you to grab any graph and convert it into text. You can even use it to take graphs from my plot and combine them in Excel with your own computer enclosure model.


----------



## captainobvious

Thanks !


----------



## The Baron Groog

Andy Wehmeyer said:


> Shroeder has never played the piano anywhere near my car and Snoopy has never driven it.
> 
> Here are some measured transfer functions.


Dragging up an old pic/post here Andy, do you have this graph with just the mini's transfer on it?

Can't make out which blue line it is!


----------



## Aaron'z 2.5RS/WRX

Andy Wehmeyer said:


> I find that the best-sounding, lowest-distortion and most efficient use of woofer dollars, enclosure dollars and amplifier power can be had by:
> 
> Building a vented box with a flat response and the lowest F3 possible and usiing an EQ to eliminate the peak in the car. That minimizes the amount of power the amplifier has to make, minimizes the driver's excursion, leaves lots of juice available for transient peaks, and minimizes driver and amplifier distortion.
> 
> Requires a larger box and a parametric EQ, though.


Andy, sorry to drag this back from 3yrs ago.. (first page) 

But I wanted to ask... would there ever be a possibility of running a ported hybrid IB set-up? 

Plans are 2xIDQ15 in IB currently (most is built)... Is there a possibility of porting such a large enclosure into the cabin and actually be able to do anything with it? 

I just saw the comment (yeah i'm a little slow) and the lil'lightbulb went off... 

Thanks..


----------



## sqshoestring

I posted that question a couple times with limited response. My 15s start to drop at 30Hz and, (in a model in my trunk sq ft) ported they would peak at 30....so if I cut 30 I could have a flat line down to 20Hz ported. I need more 20-25Hz, even if I could capture half the port energy from a sloppy trunk it would help. The problem is limited room for ports, looks like the baffle would need some rebuilding and time is limited; so I'd really like to know if it would work before I invest. Would also have to put in some long tubes to the vents so my HVAC would still work, figure if the tubes are tuned to single digit Hz it should work?

I do not fully agree with all that cabin gain, IMHO in many cars it falls off at 30Hz. This could be a function of human hearing as well, just saying that to get 30Hz or less has been difficult for me in practice. On the other hand it really depends on the car and install.

I have another theory I never investigated, and that is that large enclosures port differently. Meaning they act more like an AP vented than ported, but those were experiments from long ago and it could be you need more port area or something else I did wrong. Ran some 10s in large enclosures and the port seemed to make them act more like IB in practice and did not get much from the port itself. It seemed to unload them, which was good that is what I wanted. Power required is reduced and response was better with less rolloff.

The last issue is do you need to make a special port to lower noise transfer from the trunk. I had planned on a rectangular port that turned twice and likely lined with foam/etc....though I don't get that much trunk noise from the subs now. Yet one more thing is could you hit a bump in the road and the car body shudders, would the port then fire into the cabin at tuning...ah well I might just try this some day anyway then I would know.


----------



## stills

This thread should be required reading.


How many questions have been explained here...

I took the long way and just play w/ enclosures and winisd for years.


Thank you to all contributors.


----------



## sqshoestring

I still rather tune the install if I can. Even with my DSP HU I would rather not use the EQ more than I need to.


----------



## cvjoint

sqshoestring said:


> I do not fully agree with all that cabin gain, IMHO in many cars it falls off at 30Hz. This could be a function of human hearing as well, just saying that to get 30Hz or less has been difficult for me in practice. On the other hand it really depends on the car and install.


When I was experimenting with IB I was also getting a drop in FR, but from 25hz down. Npdang suggested that the MLS settings were not giving a long enough test signal. I don't think that was the case, or that we don't hear it. I did this one test for the IB setup with the trunk open. In that case the FR continued to rise all the way to 20hz! In my case the obvious problem: not enough enclosure room. I find this to be the reason most guys don't get enough output down to 20hz. 

Now those were the days of 15s and mid size cabins. I have a convertible now and run 12s. It's far far more difficult to get output down low, even in IB. 

I'm really curious if a hybrid IB/vented setup can extend the FR and look forward to your findings or any mappings of your response.

Here's why I think it might not work:
1. A ported design needs to be executed perfectly. Unlike sealed or IB a leaking vented enclosure can easily take you far from predicted response. 
2. I prefer IB to "smart" designs because group delay does not suffer. 

I personally don't care if I use EQ. to modify the FR, and at some points in my life I used linear phase filters in which case there really wasn't any drawback to using EQ.


----------



## sqshoestring

cvjoint said:


> I'm really curious if a hybrid IB/vented setup can extend the FR and look forward to your findings or any mappings of your response.
> 
> Here's why I think it might not work:
> 1. A ported design needs to be executed perfectly. Unlike sealed or IB a leaking vented enclosure can easily take you far from predicted response.
> 2. I prefer IB to "smart" designs because group delay does not suffer.
> 
> I personally don't care if I use EQ. to modify the FR, and at some points in my life I used linear phase filters in which case there really wasn't any drawback to using EQ.


I tried the trunk open and it did not seem to change, I am at about 1.5x Vas. I can get 25Hz at a fair level 30 is stronger then flat on up. This by ear with tones no EQ. I can barely hear 23Hz on a slow swing then it comes on at 24-25. I changed amps to see if that was it as some amps will cut down there. Playing a 20Hz tone the subs are moving for sure just don't seem to get the output. It has a little more bottom with a window open but not a big difference just enough to notice, and does not seem to change the rolloff. Was LP at 50 now at 80 or 100 I think, does not really matter that much where it is so I been adding to the midbass a little. If there is a peak in response it is at 30-35Hz and mild. I posted the response model on one of my threads maybe I can find it...

Oh snap, here it is the model in my trunk ported and just IB. The IB seems accurate to what I hear but it might drop faster below 25Hz. See how I could get flat to 20 if I cut 30Hz on the ported model...supposedly lol. Right on the tuning I would make the port adjustable to tune it, a peak at 28-30 should get me what the model shows I would hope. Right now I really can't boost 20Hz well with the 880 HU EQ, I do have an alpine PEQ that can do it if I put it back in, tear all my wiring back up, you know the drill. I was thinking of a bass processor as well but never ran one.









I've contemplated going with a lower than 20Hz Fs sub such as a HT IB 15 or an 18". I'm not sure an 18 would fit in this car without some special construction, so I tossed the 15s in and took the quad 12s out. Now the rear of the car no longer sits low like before with the heavy 12s. The Fi IB18 looked interesting, though AE 15s might work better than these pyles...hard to say in my SQ listening range the xmax is not that high on these pyles so they should be working fairly well. At 30Hz they will go far louder than I need, I think even if I bump up the power on highs like I plan to do sub output will not be a problem...unless I just need more at 20Hz? These subs are also way louder inside the car than out, even all windows down.


----------



## cvjoint

Darn, I forgot to do the windows down test. In my Accord it was brutally obvious that the low end is better with the windows down. It may be that our ear is not as pressurized when the windows go down and the impression is of an extended low end. Now that the Accord is gone and the MLS computer fried I really can't run that test anymore. 

In your case there is no way to tell if the rolloff is because you can't hear 20hz or because it really does roll off. You need to test it with something other than your ears. I'm at 1/3 vas in my S2000 right now, with three AE IB12s. In the Accord I was at 1/2 vas with 2 IB15. In both situation it came out to a Qtc of .7. 

Anywho here is my test of the 3 idmax 12s, 11 cubes trunk net, 2/3 vas:








Red: seats down, trunk closed
Blue: seats down, trunk open
Black: seats up, trunk open
Green: seats up, trunk closed


----------



## BigBadBakken

Way too much reading for now so I'm subscribed for later.

Dammit, this website is ruining my marriage. ;


----------



## sqshoestring

cvjoint said:


> Anywho here is my test of the 3 idmax 12s, 11 cubes trunk net, 2/3 vas:


I wish, I'm trying to buy the stuff for an RTA I have a laptop now just not gotten to it yet. Cool chart, certainly you are seeing that you are smaller than Vas? The 12s I ran had a .46 Qts and I was right at Vas for volume. If I put stuff in the trunk it started taking the bottom away (under 30-35Hz). Trunk open was not that different iirc, but I had to cut 50Hz on the EQ all the time and quite a bit to flatten them out. These .7qts 15s need hardly any EQ, and the Fs is 20 opposed to the 12's that were 24Hz...not that different.

Window down helps dB a little I think, not that much though just enough to notice. One window down .5" is enough to change it then no further change.

Yeah not sure on the hearing, what I should do is measure voltage and see if that changes. I did look at the amperage the amp was using but forget what it said now. I can hear 25 well but it is reduced from 30Hz. Sure 20Hz is more of a feel thing almost, but I was getting more with the 12s they were EQ'd harder and moved more air...even though the 15s have a much nicer response curve. That is why I question what is happening here. I need to look up those hearing curves and see how much more dB you need from 30 to 20Hz to sound the same.
Fletcher
Oh, that was just confusing lol.

Also the subs are not linear in loudness. I can turn it up to a normal not loud level and its fine, as you can't hear the low bass that well at quiet levels in the car. Now if I turn it up pretty loud but something most people can handle the sub bass is a little reduced and I can gain it up. If I turn it up loud as the highs will play with out clipping (50-75rms/ch), then I can turn the sub amp up a lot higher. The subs will go louder yet, the pita is why do I have to turn the sub gain around just to keep it balanced. Going to try a smaller sub amp and see if it gets worse, guessing I don't need 500rms but I don't really know.


----------



## The Baron Groog

I've hopefully traced the right cabin gain for the Cooper S off Andy's graph and produced the two outputs below in BBpro. orange no gain, pink(ish) with the cabin gain factored in:


----------



## sqshoestring

The Baron Groog said:


> I've hopefully traced the right cabin gain for the Cooper S off Andy's graph and produced the two outputs below in BBpro. orange no gain, pink(ish) with the cabin gain factored in:


It is a very SPL looking response, I would not like that.

Note my 15s are at 1.5 times Vas with 2 in 15cf.

Yeah I have a laptop now too and want to get the stuff for it. I was on some threads about software but didn't have ~$100 laying around then.


----------



## cvjoint

The Baron Groog said:


> I've hopefully traced the right cabin gain for the Cooper S off Andy's graph and produced the two outputs below in BBpro. orange no gain, pink(ish) with the cabin gain factored in:


Hmm that looks exactly like what your sub would look like in my old Accord. I can definitely recognize that null at 60hz and the peak at 100hz etc. I did however have 15s in IB so from 60hz down it was nice and flat. In your case you can get the same response by cutting 50hz by 4 db or so and setting the LP at 60hz. You can also boost a bit at 25hz or 31hz but that would take away system resources. 

In fact, the 10s in my doors would look just like that on the MLS if I took the 60hz HP off. 

Now some people argue they get an exaggerated low end sometimes withe sealed or IB but I don't ever remember a single FR that looked like that in the history of DIYMA. It's hard to get subs to dig deep imo.


----------



## ncv6coupe

cvjoint said:


> I can definitely recognize that null at 60hz and the peak at 100hz etc. In your case you can get the same response by cutting 50hz by 4 db or so and setting the LP at 60hz. You can also boost a bit at 25hz or 31hz Now some people argue they get an exaggerated low end sometimes with sealed or IB but I don't ever remember a single FR that looked like that in the history of DIYMA. It's hard to get subs to dig deep imo.


I observed TheBarongroog's graph to check the speaker specs. A 10" with 4mm excursion would be up in white smoke with slinky voice coilage in 20 seconds if it got in my hands plus compound that with exactly your quote above CVJOINT= that is not a SQ 10 inch speaker that you modeled Baron. If its inductance is low it would make a hell of a un-HP'ed midbass in the front floor area though I will never do small sealed sub systems unless they are used in multiples or ported *properly*

edit..... Let me tone down my rhetoric. Small sealed systems are not all that bad but things just aren't as they may seem on the bass box pro graphs. The distortion will be exponentially worse than you may think when you put dynamic music on it. That sub is in a .1 cubic box with 4mm xmax. Cabin gain ain't gonna be soo rosey when Mr. Hoffman knocks at the door so the simulation may read one thing but Dynamic music will "sing" another story


----------



## The Baron Groog

sqshoestring said:


> It is a very SPL looking response, I would not like that.
> 
> Note my 15s are at 1.5 times Vas with 2 in 15cf.
> 
> Yeah I have a laptop now too and want to get the stuff for it. I was on some threads about software but didn't have ~$100 laying around then.


*Have the 88RS so should be able to EQ most of it down, intended pass band 20-60Hz, so large null at 60Hz shouldn't pose too much of an issue*



ncv6coupe said:


> I observed TheBarongroog's graph to check the speaker specs. A 10" with 4mm excursion would be up in white smoke with slinky voice coilage in 20 seconds if it got in my hands plus compound that with exactly your quote above CVJOINT= that is not a SQ 10 inch speaker that you modeled Baron. If its inductance is low it would make a hell of a un-HP'ed midbass in the front floor area though I will never do small sealed sub systems unless they are used in multiples or ported *properly*
> 
> edit..... Let me tone down my rhetoric. Small sealed systems are not all that bad but things just aren't as they may seem on the bass box pro graphs. The distortion will be exponentially worse than you may think when you put dynamic music on it. That sub is in a .1 cubic box with 4mm xmax. Cabin gain ain't gonna be soo rosey when Mr. Hoffman knocks at the door so the simulation may read one thing but Dynamic music will "sing" another story


*I am a little worried about the excursion on the driver, 4mm seems awfully low to me too-I'm hoping the Xmax is measured the same was as Grizz claims the new PPI subs have been done (thread on here but can't remember where). I've only just bought the driver and have wanted one since my teens-the Aliante was considered one of the best SQ drivers of it's day. Most people I'm aware of run them in 20l enclousres, Yuri is running them as midbass in his "unusuall 2-way install" thread, so had considered overlapping them with my mids as willl be footwell mounted*



ncv6coupe said:


> Turbulent air in a very small sealed box will be wreaking havoc on the inside of your subwoofers cone introducing non-linearity if the cone isn't (titanium):laugh: strong. You know what that gets you. Intermodulation. Small sealed boxes distort more. :bigcry: And lets not forget power compression will come on sooner in the oven of a box................ And no I'm not kidding here.


 From "Using WinIsd to model, what do you look for if you dont know your cabin gain?"


*Why will the distortion be so high? The cone of this driver is a flat piston design of aluminium sandwich-so should be pretty tough?*


----------



## sqshoestring

Up to 60Hz that should work like you say, true. The part above 60 looks ugly lol.

I was hoping I could toss a stupid question in here; about mics for RTAs should I assume the better ones as recommended here will work well to 20Hz? Because a lot of the SPL meters are not rated to work that low.


----------



## ncv6coupe

*disclaimer* I was not talking bad about the sub in particular. I didn't even know what sub it was. No subjectivity in my comments earlier.

I'm being very careful with how I answer you Baron but here goes

AUDIOPHILES DO NOT LIKE SUBBASS!

And unfortunately I'm not one. I was a music student. Played and owned different instruments from elementary through high school. I've heard many different brands of speakers too but stay away from the opinionated comments since we all hear differently and Lots just sound like poo to me.* tonally dull, flat pitched, not the fizzle you get from the REAL thing when pushed even remotely hard* I recently found out how sensitive I am to distortion through my system(lots of combinations). My reproduction goals are 90% different from most sound quality guys though so I'm biased towards capable loudspeakers that get LOUD and stay clean. That is the problem with my assessment I gave you. Without knowing your exact goals I will admit that I shot in the dark and commented thinking about my system goals. Thing is though I've built plenty of speaker boxes too and just gave you a feeling of mines through lots of listening and analyzing time. Most whiz bang speakers sound the same at low volume. Music is deceiving and it all starts at getting a hold of some acoustic instruments and banging out on them. Until guys do that if I go more in depth on how I feel about clean powerful sub harmonic reproduction my comments would blindly be read as the dude's who talked **** about small sealed subs which was not my intention but a single one will never get the job done seriously from 20-60 for my requirements.


----------



## Cruzer

i got a question. if i built a box for my sub(s) and made it so that it drops off fast from 60hz-70hz to match the cabin gain roughly. bare with me, were not going to get perfectly flat response.

then i get a bunch of friends to get in the car and listen. would they notice how flat the response is? would i?

i have a hard time understanding the whole flat response thing because 1. ive never heard one, even close to flat 2. is it supposed to just amaze you?

i asked someone about if u had a flat response in car, and had a few people get in and listen, would they be amazed/impressed, or would it not be hugely noticeable? he said more than likely they wouldnt be impressed. he didnt say if they would notice, or not, just that they wouldnt be impressed or probably say or comment about it


----------



## BEAVER

Most people are used to a bloated bottom end and would probably be underwhelmed with a flat response. Perhaps a true audiophile would be impressed, but how many of them do you have riding shotgun?


----------



## Cruzer

im not looking to impress people. im talking from the perspective of how noticeable, and how pleasing is a flat response.

can the average person cant notice, or appreciate it?


----------



## BEAVER

Cruzer said:


> im not looking to impress people. im talking from the perspective of how noticeable, and how pleasing is a flat response.
> 
> can the average person cant notice, or appreciate it?


Like I said, the average person is used to bloated bass. I presume that a proper set-up would leave them undewhelmed and looking for more. With a good SQ set-up, tuned to a flat response a sub disappears. 

When I tuned my set-up to provide good sound quality(to me), the first friend that sat in it said, "I thought you had a sub..." When I said I did, it's just tuned to provide better sound quality, he said, "That ****s weak. Turn it up. What's the point in having it if you're not gonna use it?"

At the end of the day, the average dude just likes boom, in my opinion.


----------



## Cruzer

haha true.

the overall spl level might not be loud, but does that mean the 30hz by the sub isnt very loud compared to the overall sound of the system?


----------



## BEAVER

Flat is flat. If its flat, its equal to the rest of the system. Problem is, most are used to it being two or three times as loud...


----------



## trojan fan

Cruzer said:


> im not looking to impress people. im talking from the perspective of how noticeable, and how pleasing is a flat response.
> 
> can the average person cant notice, or appreciate it?


Trained ears can perceive the difference, depends what side of the fence they fall on, what side are you on...LOL


----------



## cvjoint

imo almost no one likes flat.

"Audiophile" user sub is probably up to +10db compared to midbass. 

Average car audio fan is probably +30db compared to midbass. 

With that being said hardly any of the two ever have a decreasing SPL with frequency for the sub. The "audiophiles" use puny subs in small boxes whereas the bass heads use high port tunes. In both cases the FR is kinda peaky.


----------



## Cruzer

BEAVER said:


> Flat is flat. If its flat, its equal to the rest of the system. Problem is, most are used to it being two or three times as loud...


not sure what most SQ setups with flat responses have as for as DB levels, but for example your friend. you could have a say 100db flat response right? low end wouldnt be bloated but if ur sub did over 100db at all frequencies and u cut it down even to 120db, can components meet the 100 db level to flatten the response, or would they not be able to reach that high most setups?

im just trying to learn about it all. wont hear a flat response till i go to a GTG. have my EQ on the way tho!


----------



## Cruzer

cvjoint said:


> imo almost no one likes flat.
> 
> "Audiophile" user sub is probably up to +10db compared to midbass.
> 
> Average car audio fan is probably +30db compared to midbass.
> 
> With that being said hardly any of the two ever have a decreasing SPL with frequency for the sub. The "audiophiles" use puny subs in small boxes whereas the bass heads use high port tunes. In both cases the FR is kinda peaky.


good info.

are most people on here are "audiophiles"? and when they say they have a flat response they are around +db on the sub level?


----------



## The Baron Groog

sqshoestring said:


> Up to 60Hz that should work like you say, true. The part above 60 looks ugly lol.


Yup, rotten! But hopefully I traced the right line and it's giving me a true indication of what is likely to happen-if I traced the wrong line the whole thing is moot anyway!



ncv6coupe said:


> *disclaimer* I was not talking bad about the sub in particular. I didn't even know what sub it was. No subjectivity in my comments earlier.
> 
> I'm being very careful with how I answer you Baron but here goes
> 
> AUDIOPHILES DO NOT LIKE SUBBASS!
> 
> And unfortunately I'm not one. I was a music student. Played and owned different instruments from elementary through high school. I've heard many different brands of speakers too but stay away from the opinionated comments since we all hear differently and Lots just sound like poo to me.* tonally dull, flat pitched, not the fizzle you get from the REAL thing when pushed even remotely hard* I recently found out how sensitive I am to distortion through my system(lots of combinations). My reproduction goals are 90% different from most sound quality guys though so I'm biased towards capable loudspeakers that get LOUD and stay clean. That is the problem with my assessment I gave you. Without knowing your exact goals I will admit that I shot in the dark and commented thinking about my system goals. Thing is though I've built plenty of speaker boxes too and just gave you a feeling of mines through lots of listening and analyzing time. Most whiz bang speakers sound the same at low volume. Music is deceiving and it all starts at getting a hold of some acoustic instruments and banging out on them. Until guys do that if I go more in depth on how I feel about clean powerful sub harmonic reproduction my comments would blindly be read as the dude's who talked **** about small sealed subs which was not my intention but a single one will never get the job done seriously from 20-60 for my requirements.


Don't worry, wasn't getting my panties in a twist, was just asking why you thought it might not work. As far as "audiophile" I wouldn't say I'm quite there yet...

Old systems were very much SPL focused, CV Stroker 18D2 giving me 3" of steering wheel travel in my old Peugeot 306 (old split tailgate Civic sized hatch) but I've grown up a bit and finally been able to put together a system I've been wanting for years: 

Dynaudio MD102 off Genesis DM and MW162 of a Genesis ST60 (haven't found another DM yet ) each and the Aliante 10Si off another DM. Of course there were other combinations I was looking at and this more than likely won't be the final incarnation-2x IDQ10D4V2 were going to go in the boot isobarically mounted until I found out I've my 1st born on her way (just 2 weeks left so need to pull my finger out and finish the install) so elected to try and get my Aliante in the front footwell. Everthing in audio is a compromise, cost, space, resp, SPL-just trying to find the right one! (not just a Dyn nuthugger, used to run a Dyn demo car and have always wanted one since)

Music wise I'm pretty eclectic, with anything from Dubstep to Classical and while I don't want to wake the dead anymore I do still want a decent bass output. I'm aiming to get the system "flatish" from the build and then EQ to taste/munson like curve (have found they sound best to me) so any comments/suggestions are more than welcome.


----------



## sqshoestring

It also depends on what you mean by flat. I like to play a slow sweep and hear the same volume all the way up, but that is the Fletcher Munson curve; what you hear. If you measure the SPL you find the bass is much higher because your ears are not as sensitive to it especially at low volumes hence the loudness filter to compensate. To me SQ is hearing every note but to someone else it is some arcane measure of dB based on some weighting you choose. The real issue is you don't know what the engineer at the recording studio was doing anyway. I'm not saying an RTA is not useful, just saying it depends on what you do with it...and that determines if it relates to what you actually hear.

For example when you talk about a flat curve (some might say smooth response), lets say you put X artist in and play it and it sounds great the bass is thumping. Then you put Y artist in with a different style of music and the bass is gone, what the heck happened? This happens a lot and it is because the sub is peaking on certain frequencies. Artist X was on those, Y was not. You play the same music in a car with some little 8" sub installed by someone who does not like bass, and neither have any bass. If you don't want to hear part of the music I guess you don't have to, but don't call yourself an audiophile.

I do like bloated bass sometimes, but only low bass. Why, because you feel it like at a concert. Its bloated because I really don't want that high a dB in the midrange in my car its too loud. The bass I can handle just fine. Of course there is a point where it sounds too far out of balance. My 15s are good at that lol, but once in a while its just fun it depends on what I am listening to. Club/dance/etc music tends to be made for that.

The last issue I have, is that I do not always see the cabin gain people say is there or its not as low (in Hz) as they say. Some cars do have it but some don't or it is a factor of the install. Add to that major source variations and I need a sub system that puts out more than I need. So if my car lacks some gain and I put in an old CD with a far lower bass level, I can dial the bass up and hear it. Sometimes you need a lot of gain at 30-35Hz with older material, then you flip on a top40 radio station and get blown out of the car. But hey its not like I can thunder sub bass anywhere else, you bet I will in my car. You also need more capacity in your subs to reach lower, it just takes more air movement to get low and that will result in more possible SPL at higher bass ranges.


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## The Baron Groog

I realise the difference between recordings and material, also that a "flat" response can sound lifeless and dull-I'm not going for an RTA flat response, using it more as a target so "too much EQing" isn't needed. I agree SQ is hearing every note/nuance, I don't want my system colouring the sound-until I tell it too

2x 15 Ib would be great-true large cone area and minimal excursion are going to produce effortless bass, but in my car it's not an option-once the next sprog arrives I'll have to look into bigger vehicles-then will be the time to look at different formats, I'm thinking and aircooled VW bus and a TL or horn design then.

Given one of the blue lines in Andy's graph is the mini the response(if i've not picked the right line) will be close to what I've picked so shouldn't see me falling too foul-I'll build the box slightly bigger then suggested by BBpro and can always add/remove ballast to get the response needed.


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## Cruzer

i guess its just weird all these people talk about SQ, flat response, EQ, distortion, etc. etc. yet the other half of people dont care. all the people that spend all the money on top EQ, great drivers, they do it to not have a close to flat response? why not just buy nice EQ hu and keep stock speakers or some cheap ones, add small tiny 8 sealed and be done. why spend $1000s if its not a big deal


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## sqshoestring

Like I said it depends on what flat response you pick. Its also subject to what you are willing to put into a car in funds, space ate up, install complexity. I ran various single 12s, dual 10s and 12s, finally a single 10 (for the room). I got by but then had the idea what the **** I'm going IB and get me some thunder something I loved back in the day. I put quad 12s in a huge baffle and it did thunder but not ideal. The 15s fit nice, light, take hardly any room, they are much closer to ideal. Certainly can supply just about any kind of bass I want, and flexibility is something I like I can EQ them for tight bass. Yeah have to dial them back when kiddos are in the car lol. Then if you are talking highs well there is nothing wrong with wanting nice drivers for that. I have too much other stuff going on to invest that heavily in my cars anymore, its just a matter of priorities. Then I don't have to worry about theft/removal/damage near as much either only my HU is worth something and I take the face the few times the car is in a questionable area. 

You can make a good system from crappy stuff, but it is a long hard hunt to sift out the stuff that will work well. I'm really surprised these cheap subs work so well, yet many times in the past I've run cheap subs IB but multiple at low xmax like this...it can work very well. When you spend more on average you get something already at a higher level of quality/performance. The sixth pair of cheap tweeters you try might work great, the first or second pair of better ones will. So you don't have to spend a lot, but it makes it easier.

I think a lot of people want a small box to conserve room, and it is difficult to get real bottom from that. So what are they going to do; say they wish they had something better? No, they say it has a clean/tight/flat/whatever response. It is some work to put in a baffle like I have, most people are not going to do it not even close. I can build a ported box way faster, even a custom shape like an angled box. Its work to do fiberglass enclosures and I'm impressed, but most do it for more room not better bottom. And some people just like that sound. But that is the great thing about this site you can swim in a sea of selection and better find what fits your needs.


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## The Baron Groog

Cruzer said:


> i guess its just weird all these people talk about SQ, flat response, EQ, distortion, etc. etc. yet the other half of people dont care. all the people that spend all the money on top EQ, great drivers, they do it to not have a close to flat response? why not just buy nice EQ hu and keep stock speakers or some cheap ones, add small tiny 8 sealed and be done. why spend $1000s if its not a big deal


?Not quite sure what you're trying to say here? 

IMO "RTA" flat is not what I'm after-without visiting a hearing specialist I don't know how "flat" my hearing sensitivity is so there is no point having a totally flat system-just to aim for it and then EQ to my taste


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## cvjoint

The Baron Groog said:


> ?Not quite sure what you're trying to say here?
> 
> IMO "RTA" flat is not what I'm after-without visiting a hearing specialist I don't know how "flat" my hearing sensitivity is so there is no point having a totally flat system-just to aim for it and then EQ to my taste


Take a step back guys. In the context of cabin gain and therefore mono subwoofers flat might not be desirable. This does not extend as much to the higher octaves where you have a Left and Right channel. That's when high quality equalizing given both by the processor and testing equipment comes into play. You want the left and right sides too look as much alike as possible. Afterwards you can still implement a desired curve but to make it look decent and an exact copy of eachother is quite a challenge by ear.


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## The Baron Groog

Just got my system live, no EQing time as of yet and only about 10mins listening with off the cuff crossover points and slopes (it was 12.30am when I got it all powered up) but have pocket RTA on my iphone and ran a little white noise just to see what my curve looked like-near flat! Slight hump between 500Hz and 2.5Khz, but should be easy to flatten. 

What I'm ultra-effing-chuffed with is the fact my stupidly small sub enclousre works and works very well It's about .125 of a CF and has an F3 of 76.84Hz, Fb of 76.32 (modeled not measured yet) The sub only just fits in it, but it handles everything I throw at it and is flat from 30Hz to 63Hz where it's LPF'd google Linwitz Transform, and with a mini forget about the need for EQing as the cabin does it for you


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## minbari

is that those 6.5" subs you were talking about in your other thread?


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## cvjoint

1.My midbass drivers in the doors go down to 20hz in the doors but I don't think that makes them a good subwoofer. When you look at the RTA plot do you know how much of it is the fundamental and how much of it is distortion? 

2.There is also the saying "what cabin gain giveth, road noise taketh away." 

3. Where is the speaker system Q more important for transient response, sub application, midrange, tweeter? What happens to transient response in a very tiny box?


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## minbari

cvjoint said:


> 1.My midbass drivers in the doors go down to 20hz in the doors but I don't think that makes them a good subwoofer. When you look at the RTA plot do you know how much of it is the fundamental and how much of it is distortion?
> 
> 2.There is also the saying "what cabin gain giveth, road noise taketh away."
> 
> 3. Where is the speaker system Q more important for transient response, sub application, midrange, tweeter? What happens to transient response in a very tiny box?


ya, but I think these were 6.5 subs. if its the ones I am thinking of, I modeled them and they looked pretty darn good. started rolling off at 75hz or so. I may be wrong, gonna have to wait till he chimes back in.


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## The Baron Groog

Phase Linear Aliante 10". The Qtc of the box is .707-but I have never found any suggestions to put it in a box this small-smallest I have seen recommended is 20l (0.706cf)

I only have a five min drive in and out of work(need to find a longer commute) and have had a quick audition of a few tracks. All sound great, as said a little EQ work is needed when i find the time, but it's now dark and raining when I get home I've thrown some pretty heavy bass at it and it's not shown any issues as yet:

Tipper - Dissolve (Out) - YouTube
Leftfield's Leftism
DJ Shadow's Endtroducing

The car has been pretty well treated for noise, though subsequent to that my manifold/cat de-welded themselves and I "invested" £160 in a straight thru de-cat rather than BMW's £850.01+VAT (20%) for their OE cat! Sounds fantastic above 3000rpm, but if I stick below that/70mph then you'd not notice it's different to stock. Yet to get it on a fast road to audition, but given the levels atm I can't see any issue.

The sub blends effortlessly with the mids, and them with the tweeters-honestly I have surprised myself with how good it sounds with no tuning-I really was expecting a lot more tuning to get it this far-but then my previous systems weren't as well thought out/installed in the 1st place, so maybe the groundwork has paid dividends.

Below should be the phase respose and group delay models:


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## jxkey

After reading this thread... I've come to realize that you guys can probably help me battle my system issues. With my windows down and full tilt, My 2 12" AudioTechnix Tropo subs start making this awful popping noise. almost like they're bottoming out. They're in a 5 cubed box with a 13 inch high, 3 inch wide and 7" deep port. They aren't busted or blown. They sound amazing until i go full tilt with the window down, especially on the highway with a window down. Hallllp!! I'd like to get this system to around at least 140 DBL. I'm guessing my box and or port are too big for the quantity of subs I'm using.


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## minbari

5cuft seems huge for a pair of 12", but until you post the specs, who knows. I would start a seperate thread for your problem and we can look at it.

post the T/S specs on the subs and how much power, amplifier, etc.


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## jxkey

Since its a part of cabin gain. I posted here. Tropo-12D4 – 2” voice coil
Re: 4.0 ohms
Fs: 32.3 Hz
VAS: 71.1 L
Le: 2.77 mH
BL: 17.2 NA
Qes: 0.68
Qms: 4.51
Qts: 0.59
Mms: 124.4 g
RMS: 200 Watts


Hifonics Titan 2x300. Subs wired to 4 ohm load per channel.


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## minbari

is that a series VIII hifonics? love those.

my first guess is that you are over powering them a bit, but modeling shows that your box is way off. tuned to 42hz and has a massive 6db hump at 55hz.

no matter what, these dont model well in a ported enclosure unless you tune them below 25hz.

5cuft sealed looks pretty good though.


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## jxkey

Is the hump good or bad? With sealed @ 5.0 it sounds pretty muffled. I'll drop down to 20 hz and see what happens with the popping.


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## minbari

IMHO, the hump is bad. that has to be just really unbalanced.

the popping is 1 of two things:
1) Your amplifier is running out of power
2) you are bottoming the subs out. (which is easier to do once the windows are open)


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## jxkey

not running out of power. it has to be the windows down causing a pressure drop. so in theory would dropping the hz tune of the box down cause the subs to stop popping? When i plug the port the popping goes away. helping with cabin gain with windows down?


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## minbari

jxkey said:


> not running out of power. it has to be the windows down causing a pressure drop. so in theory would dropping the hz tune of the box down cause the subs to stop popping? When i plug the port the popping goes away. helping with cabin gain with windows down?


how do you know its not clipping?

its not a matter of pressure. with windows up your car becomes part of the enclosure. when you open the windows you change that tuning. ussually it doesnt make enough of a difference to matter, but if you are overpowering them to begin with, they are prolly on the edge. opening the windows just gives them enough of an extra push.

when you plug the port, it becomes a sealed box, which is a MUCH better alignment for these subs.


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## chad

I agree, or change the tuning, it looks tuned pretty high meaning that it's losing it's **** (over excursion) when trying to play down low.


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## jxkey

Whats the yellow/red lines stand for in that diagram? Don't really see much other than a flat response on red then drops off. And a huge wave with the yellow.


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## Oliver

jxkey said:


> not running out of power. it has to be the windows down causing a pressure drop. so in theory would dropping the hz tune of the box down cause the subs to stop popping


 Raise tuning and lower gain 

... or buy an SD sub from Sundownz


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## Oliver

jxkey said:


> Whats the yellow/red lines stand for in that diagram? Don't really see much other than a flat response on red then drops off. And a huge wave with the yellow.


Red = sealed
Yellow = ported


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## minbari

yellow is your ported box. huge hump that I was talking about.

red is a 5cuft sealed. as you can see, the sealed is a nice flat response.


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## jxkey

With less DB output from what I see. Meh. I've went thru 3 people giving me specs for a box on these with no desirable sound. This 5 cube box has been the cleanest, loudest and most impressive so far.


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## Oliver

jxkey said:


> _RMS: 200 Watts_
> 
> 
> _Hifonics Titan 2x300._ Subs wired to 4 ohm load per channel.


Audio Technix 200W RMS 400W Max Tropo Series Subwoofers Dual 4 Ohm 12" Sub | eBay

U need some subs fo playin - 2 - 12" Sundown Zv2's ON SAZ3500, Loud TRUNK - YouTube



minbari said:


> is that a series VIII hifonics? love those.
> 
> my first guess is that you are over powering them a bit, but modeling shows that your box is way off. tuned to 42hz and has a massive 6db hump at 55hz.
> 
> no matter what, these dont model well in a ported enclosure unless you tune them below 25hz.
> 
> 5cuft sealed looks pretty good though.


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## minbari

jxkey said:


> With less DB output from what I see. Meh. I've went thru 3 people giving me specs for a box on these with no desirable sound. This 5 cube box has been the cleanest, loudest and most impressive so far.


Then keep it and deal with over driving the subs. (or keep your windows rolled up)

I cant imagine that sounds good, but to each his own.


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## jxkey

I got these on a giveaway from AudioTechnix. They're a startup company, I'm trying to do them justice but, I don't see these being capable of anything other than moderately flexing on my hatchback. I think getting anything better than slightly blurring my vision during driving from these is impossible.


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## sqshoestring

Personally I would not be thinking of blurring vision with 200rms subs, that is not that kind of power. Even 500rms on my pair of 15s IB is not near blurring levels, though I suppose a good ported box could be 'louder' in an spl way.

My .02 says toss that amp and get one with a SS filter, or get some kind of EQ/processor with a SS. Port it to hit above your filter and roll with it. That will keep them from xmax much as possible.


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## captainobvious

Or use proper EQ and gain the benefits Andy has kindly listed out in this thread over and over. Assuming you want good accurate response, flatten out that giant hump because of the small ported box with EQ, use less amplifier power because of it and have more available during transient peaks.

Or with no eq, do as Minbari said and plug the box to go sealed which gives a nice flat response. This doesn't yield the benefit of the additional output, but it avoids a giant peak with outneeding more processing.

Of course if you're only concerned with blurring your vision with high output, then you may as well keep it as is, tuned for max output at 40hz.


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## Oliver

captainobvious said:


> Of course if you're only concerned with blurring your vision with high output, *then you may as well keep it as is*, tuned for max output at 40hz.


There are people with boom-boxes that use more powerful speakers 

*I would get REAL !
*

Sell dem winners and get youse some subwoofers and an amp !!


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## reclermo

Andy Wehmeyer said:


> Yes, flat frequency response and low Q with a cutoff frequency at or below 20Hz would be ideal, but it isn't practical nor is it necessary.
> 
> If you look back over this whole thread, the answer may become clear.
> 
> 1. Flat frequency response *is* accurate time response.
> 2. The cabin gain, (transfer function) of the car makes a sealed box with a -3dB point that corresponds to the +3dB point on the transfer function curve have flat response at low frequencies.
> 3. You'll never fix all the frequency response problems without an EQ. This should be obvious in the transfer function graph I posted.
> 4. Since you have to have an EQ for good sound, build a vented box for much better efficiency and remove the peak with the EQ for lower distortion and better dynamics (since there will be plenty of power left over after you cut 45Hz or so by about 12dB).
> 5. If you can't afford to lose additional space to a vented box, you can make up for it with a woofer with high Xmax and lots of power.


I've really enjoyed reading through this entire thread, thank you to all the contributors - particularly Andy. 

When looking at QTC of an enclosure, it is understood that a value of around 0.7 will give a response curve (anechoic) that is flat to the tuning frequency and then roll off at 12 db an octave. OK. So assuming that most of us are compelled to build smaller than optimal enclosures (with QTC exceeding 0.7), what are the advantages and disadvantages of high QTC smaller sealed enclosures?

From reading through the thread, the optimum tuning frequency shifts to the right and includes a characteristic 'hump', that can (as Andy mentioned) be equalized out. 

Given all this, my guess is that excursion of the driver is also limited in this high QTC scenario?

The reason I'm asking, is I'm intending on using a pair of JBL GTO1514D subs in small sealed enclosures of around 1.25 cubic feet a piece. JBL had recommended an enclosure of 1.5 (close enough to 1.25 with a bit of fibrefill to close the gap).

When I plug the driver's figures in at 1.25, I get a very high QTC of 1.1 with JBL's recommended enclosure size of 1.50 resulting in a QTC of 1.03. To get to a QTC of 0.7, the enclosure would have to be a huge 4.50 cubic feet. 

Am I to assume that in a perfect world, it would be optimal to go 4.5, but that the slight bump and sacrifice in lower end output would be acceptable tradeoffs when downsizing to 1.5? 

Are there significant disadvantages or characteristics for running an enclosure with a QTC of 1.0 to 1.1?

Any feedback on this would be most appreciated!


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## Hanatsu

reclermo said:


> I've really enjoyed reading through this entire thread, thank you to all the contributors - particularly Andy.
> 
> When looking at QTC of an enclosure, it is understood that a value of around 0.7 will give a response curve (anechoic) that is flat to the tuning frequency and then roll off at 12 db an octave. OK. So assuming that most of us are compelled to build smaller than optimal enclosures (with QTC exceeding 0.7), what are the advantages and disadvantages of high QTC smaller sealed enclosures?
> 
> From reading through the thread, the optimum tuning frequency shifts to the right and includes a characteristic 'hump', that can (as Andy mentioned) be equalized out.
> 
> Given all this, my guess is that excursion of the driver is also limited in this high QTC scenario?
> 
> The reason I'm asking, is I'm intending on using a pair of JBL GTO1514D subs in small sealed enclosures of around 1.25 cubic feet a piece. JBL had recommended an enclosure of 1.5 (close enough to 1.25 with a bit of fibrefill to close the gap).
> 
> When I plug the driver's figures in at 1.25, I get a very high QTC of 1.1 with JBL's recommended enclosure size of 1.50 resulting in a QTC of 1.03. To get to a QTC of 0.7, the enclosure would have to be a huge 4.50 cubic feet.
> 
> Am I to assume that in a perfect world, it would be optimal to go 4.5, but that the slight bump and sacrifice in lower end output would be acceptable tradeoffs when downsizing to 1.5?
> 
> Are there significant disadvantages or characteristics for running an enclosure with a QTC of 1.0 to 1.1?
> 
> Any feedback on this would be most appreciated!


There's nothing that says you require a Qt of 0,7 to attain the "best sound". I use a sealed enclosure with a Q of 1,2 in one of my builds, it still sounds great. System resonance (Q) is measured at Fs and these two values play a vital role in determining the low-end extension of the system. In cars we have such an enormous boost due to cabin gain so we really don't need a sub with a flat anechoic response down to the lowest audible octave. 

Depending on how big your cabin is and the placement of the enclosure, it's generally enough with a -f3 around 50-60Hz. The resonance peak caused by a high Q can be EQed down with good results. The frequencies around Fs will require much less power to reproduce due to the impedance peak, so if you want an efficient design - ignore Q (unless it's way too high) and focus on getting Fsc around 45-60Hz. 

The pros and cons of using a low vs high Q system is mainly differences in efficiency. Over a certain point high Q alignments got enough distortion to degrade the performance. I don't think this is an issue unless you go beyond Qt 1,3-1,4. A 'small enclosure' for the given woofer will raise Q and bring Fs higher in frequency - this will decrease low end efficiency more or less. It will also increase physical power handling since the air spring resist speaker excursion. In other words it acts like a highpass filter. 

Run your enclosure at 1,1 - I imagine that the effect on system overall performance is minimal. If you got access to EQ you can bring up the low end (if required), it will simply be less efficient doing it that way.


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## reclermo

Hanatsu said:


> There's nothing that says you require a Qt of 0,7 to attain the "best sound". I use a sealed enclosure with a Q of 1,2 in one of my builds, it still sounds great. System resonance (Q) is measured at Fs and these two values play a vital role in determining the low-end extension of the system. In cars we have such an enormous boost due to cabin gain so we really don't need a sub with a flat anechoic response down to the lowest audible octave.
> 
> Depending on how big your cabin is and the placement of the enclosure, it's generally enough with a -f3 around 50-60Hz. The resonance peak caused by a high Q can be EQed down with good results. The frequencies around Fs will require much less power to reproduce due to the impedance peak, so if you want an efficient design - ignore Q (unless it's way too high) and focus on getting Fsc around 45-60Hz.
> 
> The pros and cons of using a low vs high Q system is mainly differences in efficiency. Over a certain point high Q alignments got enough distortion to degrade the performance. I don't think this is an issue unless you go beyond Qt 1,3-1,4. A 'small enclosure' for the given woofer will raise Q and bring Fs higher in frequency - this will decrease low end efficiency more or less. It will also increase physical power handling since the air spring resist speaker excursion. In other words it acts like a highpass filter.
> 
> Run your enclosure at 1,1 - I imagine that the effect on system overall performance is minimal. If you got access to EQ you can bring up the low end (if required), it will simply be less efficient doing it that way.


Thank you kindly for the very detailed reply, it is much appreciated. This has given me sufficient confidence to move forward with the smaller enclosure for the 15s. The tuning frequency of the sealed enclosures will be around 55hz, so they should have plenty to deliver on the low end when factoring in the transfer function.

What I was most concerned about is issues with under/over excursion at a QTC of 1.1. I will report back on how things sound in a month or so when everything has been installed. Thanks again!


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## Hanatsu

reclermo said:


> What I was most concerned about is issues with under/over excursion at a QTC of 1.1. I will report back on how things sound in a month or so when everything has been installed. Thanks again!


Output in a sealed box is cone area (Sd)*excursion (Xmax). It will require different amounts of power getting there depending on enclosure size 

Np!


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## reclermo

Hanatsu said:


> Output in a sealed box is cone area (Sd)*excursion (Xmax). It will require different amounts of power getting there depending on enclosure size
> 
> Np!


Right, and my understanding is that a high QTC enclosure (i.e. 1.10) will require LESS power (be more efficient at the tuning frequency due to the rise in response.

Thanks again!


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## Patrick Bateman

reclermo said:


> I've really enjoyed reading through this entire thread, thank you to all the contributors - particularly Andy.
> 
> When looking at QTC of an enclosure, it is understood that a value of around 0.7 will give a response curve (anechoic) that is flat to the tuning frequency and then roll off at 12 db an octave. OK. So assuming that most of us are compelled to build smaller than optimal enclosures (with QTC exceeding 0.7), what are the advantages and disadvantages of high QTC smaller sealed enclosures?
> 
> From reading through the thread, the optimum tuning frequency shifts to the right and includes a characteristic 'hump', that can (as Andy mentioned) be equalized out.
> 
> Given all this, my guess is that excursion of the driver is also limited in this high QTC scenario?
> 
> The reason I'm asking, is I'm intending on using a pair of JBL GTO1514D subs in small sealed enclosures of around 1.25 cubic feet a piece. JBL had recommended an enclosure of 1.5 (close enough to 1.25 with a bit of fibrefill to close the gap).
> 
> When I plug the driver's figures in at 1.25, I get a very high QTC of 1.1 with JBL's recommended enclosure size of 1.50 resulting in a QTC of 1.03. To get to a QTC of 0.7, the enclosure would have to be a huge 4.50 cubic feet.
> 
> Am I to assume that in a perfect world, it would be optimal to go 4.5, but that the slight bump and sacrifice in lower end output would be acceptable tradeoffs when downsizing to 1.5?
> 
> Are there significant disadvantages or characteristics for running an enclosure with a QTC of 1.0 to 1.1?
> 
> Any feedback on this would be most appreciated!


Loudspeakers move air. That's all they do.

If you're using an exotic enclosure, you may need a specific set of t/s params. For instance, when I'm building a horn, I require drivers with specific parameters, otherwise the bandwidth is all wrong.

But with a plain ol' sealed box? All the rules about qtc, qms, qes, etc, they fly out the window.

*All of this assumes that you have an equalizer and a mic, and you can modify the response to get the target you're after.*

Once you wrap your brain around that, you'll probably start leaning towards drivers that move as much air for as little money as possible. Obviously, there are limits to this; if you drive a Nissan 370Z convertible you're going to have a hard time finding a place for two eighteens.

But if you *do* have the space for a couple of fifteens or an eighteen, put them in a tiny box and EQ them flat.

If you don't have an EQ, don't do this. But in an age of $80 DSP processors, why wouldn't you?


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## Hanatsu

reclermo said:


> Right, and my understanding is that a high QTC enclosure (i.e. 1.10) will require LESS power (be more efficient at the tuning frequency due to the rise in response.
> 
> Thanks again!


It will be more efficient around Fsc, yes. It's inversely equivalent to the impedance peak.


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## thehatedguy

You are going to need a lot of power and excursion to do a Linkwitz Transform.


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## Hanatsu

thehatedguy said:


> You are going to need a lot of power and excursion to do a Linkwitz Transform.


Agreed.

Not needed in a car though. We got cabin gain, free output


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## thehatedguy

Yeah...but that's the jist of what is being said to do in post 191.


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## Chris12

First off, I’d like to admit that I haven’t read through this entire thread.

My question is, are there any downsides to cabin gain?

Im considering a new sub and have the option of facing it toward the front of the car through the ski pass or toward the rear of the car. Thus my question..


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## sqshoestring

Its generally better to face it rearward to get more distance however you should try various placement if you can because every car is different....unless you find a consensus for a particular car that X is the best setup. I had a car that just would not get cabin gain under 40hz I finally put in IB subs and it was 10X better at 30hz. Cabin gain is great its free db output for a sub, but it can hit at different frequencies, you can get a lot or none.


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