# Low F3 or just EQ?



## UCF52 (Nov 20, 2007)

I've been playing around in WinISD and modeling up many drivers and it seems the trick to get a mighty low F3 (25-35hz)is generally large and low-tuned. Whereas sealed enclosures seem to yield a higher F3 (40-50hz). 

[keep in mind this is my general consensus] 

So, a low F3 will cost you a lot of space. What are the disadvantages of going with a sealed enclosure (accepting a higher F3) and just EQing (along with any cabin gain) your low end? My guess is enclosure efficiency - but is it more desirable to have the enclosure do the work or your processing?


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## UCF52 (Nov 20, 2007)

Surprised no one touched this yet. Back up ^^


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## 60ndown (Feb 8, 2007)

if you have good power, you dont need a big box

http://www.diymobileaudio.com/forum/showthread.php?t=38784&highlight=cabin+gain


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## ChrisB (Jul 3, 2008)

UCF52 said:


> I've been playing around in WinISD and modeling up many drivers and it seems the trick to get a mighty low F3 (25-35hz)is generally large and low-tuned. Whereas sealed enclosures seem to yield a higher F3 (40-50hz).
> 
> [keep in mind this is my general consensus]
> 
> So, a low F3 will cost you a lot of space. What are the disadvantages of going with a sealed enclosure (accepting a higher F3) and just EQing (along with any cabin gain) your low end? My guess is enclosure efficiency - but is it more desirable to have the enclosure do the work or your processing?


I have a little bit of first hand experience with a pair of JL Audio 10w3v2s that have an F3 of 43.8 Hz in JL's recommended sealed enclosure. They handle 300 watts RMS each, and I gave the pair 1,200 watts RMS while EQing them in an attempt to get some better low end response out of them. Those poor 10" subwoofers hit their physical limitations trying to reproduce low frequencies with EQing and more power 

The bottom line is I replaced them because there is no way I am building a 7 cubic foot ported box to get the low frequency extension out of them that WinISD says I need.

ETA: I didn't like the JL Audio subs because listening to Drum and Bass without getting any bass sucks big time!


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## Knobby Digital (Aug 17, 2008)

UCF52 said:


> but is it more desirable to have the enclosure do the work or your processing?


Depends on the equipment you're using and how much space you're willing to give up.

If the subwoofer system (sub, box, amp, and its installation) reaches its limit, then it's done. No amount of EQ can make a subwoofer system reproduce frequencies at a level that it can't.


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## UCF52 (Nov 20, 2007)

60ndown said:


> if you have good power, you dont need a big box
> 
> http://www.diymobileaudio.com/forum/showthread.php?t=38784&highlight=cabin+gain


Damn, I've read through that a few times - I think reading it again for the 3rd time it's starting to make sense. :blush:



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.





BEAVER said:


> 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?


After reading through the thread last time this is what I planned to do (I have the space), but if I can go sealed and get the same results, why go ported and give up the space?



BEAVER said:


> 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.


I think this is what I was trying to get at. In an effort to save space can one forgo a vented enclosure - go sealed - accept a higher F3 - rely on cabin gain to pick up the lower end (effectively lowering your F3) - and then use an EQ to get it where you want it from there.

Basically, what is wrong with doing that ^^? My guess is efficiency...? Is it better to let the box to most of the work or the EQ?

I think I just need to re-read Andy's posts and maybe it will click.


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## Knobby Digital (Aug 17, 2008)

UCF52 said:


> rely on cabin gain to pick up the lower end (effectively lowering your F3)


Unless you've plotted the q of your car, I don't think it's wise to just rely on the cabin gain.


Your ear and how you hear things also comes into play.

Regardless what an RTA says, how many cars have you been in where 20hz has the same impact as 40?


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## UCF52 (Nov 20, 2007)

icehole said:


> Unless you've plotted the q of your car, I don't think it's wise to just rely on the cabin gain.


Well, cabin gain + EQ. 

I'm going to go with what I originally planned, a large and low-tuned enclosure because I have the space, but I am just curious for the sake of learning.


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## BoomHz (Apr 20, 2007)

Andy hit it on the head with a sledge hammer. I've been gettin better overall response through projects using this method.


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## 14642 (May 19, 2008)

That's the main trade-off. Space vs. efficiency at low frequencies. Remember, that 3dB of boost requires twice the power. 12dB of boost requires 16 times the power. And...every halving of frequency requires 4 times the excursion to maintain the same output level. If you have plenty of Xmax and an unlimited supply of power, then you can go as small as you want. If you don't, however, and you go for small sealed, you'll pay the price in distortion. The amp will clip hard and the coil will leave the gap. When the coil leaves the gap, that adds 3rd order harmonic distortion and that's the kind that sounds bad--like mechanical noise.


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## UCF52 (Nov 20, 2007)

Andy Wehmeyer said:


> That's the main trade-off. Space vs. efficiency at low frequencies.


That's what I wanted to hear. I'm going to re-read that thread again, but I pretty sure I fully understand what I was unsure about. Thanks Andy - you do an awesome job making technical stuff understandable for us less fortunate  Thanks for all of your insight!


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## 14642 (May 19, 2008)

My pleasure. Glad I can help.


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## Eric Stevens (Dec 29, 2007)

UCF52 said:


> I've been playing around in WinISD and modeling up many drivers and it seems the trick to get a mighty low F3 (25-35hz)is generally large and low-tuned. Whereas sealed enclosures seem to yield a higher F3 (40-50hz).
> 
> [keep in mind this is my general consensus]
> 
> So, a low F3 will cost you a lot of space. What are the disadvantages of going with a sealed enclosure (accepting a higher F3) and just EQing (along with any cabin gain) your low end? My guess is enclosure efficiency - but is it more desirable to have the enclosure do the work or your processing?


Remember that WinISD cannot model transfer function/ cabin gain. And transfer function is a dynamic process that changes with both static and dynamic displacement.

I have a system that according to LEAP in a 1/2 space environment is -3dB at 78Hz, when put into the car a 1991 mercury Sable it is +12 dB at 20Hz compared to 80Hz with a very smooth frequency response even at high resolution measurements.

So using a program such as WinISD is just a tool, for proper utilization it requires that you understand the environment you are designing the system for.

Eric
Image Dynamics


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## UCF52 (Nov 20, 2007)

Eric Stevens said:


> Remember that WinISD cannot model transfer function/ cabin gain. And transfer function is a dynamic process that changes with both static and dynamic displacement.
> 
> I have a system that according to LEAP in a 1/2 space environment is -3dB at 78Hz, when put into the car a 1991 mercury Sable it is +12 dB at 20Hz compared to 80Hz with a very smooth frequency response even at high resolution measurements.
> 
> ...


Thanks for chiming in Eric! (Though I only understood about 1/3 of that :blush: :blush

I think what you're saying is cabin gain can drastically change what may be a perfect model in an ideal environment (a room with no reflective surfaces - not a car's cabin). So to your last point, how does one account for the environment they are using? I'm guessing EQ?

Is there still a better way to approach this than building an enclosure that models well in a perfect environment (large, low-tuned, efficient), utilize processing from there (EQ) to tame uncontrollable boosts in your specific environment (cabin gain)?



> And transfer function is a dynamic process that changes with both static and dynamic displacement.


Does this mean cabin gain can change relative to the subs output? Maybe if you could expand on this or if you have any links...?


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## Eric Stevens (Dec 29, 2007)

UCF52 said:


> Thanks for chiming in Eric! (Though I only understood about 1/3 of that :blush: :blush
> 
> I think what you're saying is cabin gain can drastically change what may be a perfect model in an ideal environment (a room with no reflective surfaces - not a car's cabin). So to your last point, how does one account for the environment they are using? I'm guessing EQ?
> 
> ...


Car is anything but a good environment for sound reproduction. But for sub-bass the car is actually much better than a large environment, much easier to get very low bass at high level than in large room.

Transfer function is the effect the environment has on the frequency response and energy the system reproduces. Because the cars interior is low in volume it creates a dramatic increase in low frequency energy with more increase as the frequency gets lower. The amount of increase is proportional to volume of the cars interior versus the subwoofer displacement. So static displacement would be cone area and the transfer function of a single 8" subwoofer is very different from the transfer function of a pair of 15" subwoofers.To further clarify,with more cone area you get more of an increase in low frequency output/energy for the same amount of system power. 

I prefer a low Q large displacement system which will yield smooth frequency response good output and low distortion. Basically in a sedan or coupe I like a pair of 15" subwoofers what I have termed trunk baffle. Great SQ output and great use of available space.

Andy W. prefers to do a large ported system and then EQ out the resulting peak in the frequency response. Many years ago I had a large ported system in my car with a very low F3, I have not tried this in recent years because when I tried my preferred method in previous paragraph it sounded so good and worked so well I have never tried the ported method again.

Eric
Image Dynamics


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## UCF52 (Nov 20, 2007)

Eric Stevens said:


> Car is anything but a good environment for sound reproduction. But for sub-bass the car is actually much better than a large environment, much easier to get very low bass at high level than in large room.


Is this why downfiring or firing a home sub into the corner of the room is so common?



Eric Stevens said:


> Transfer function is the effect the environment has on the frequency response and energy the system reproduces. Because the cars interior is low in volume it creates a dramatic increase in low frequency energy with more increase as the frequency gets lower. The amount of increase is proportional to volume of the cars interior versus the subwoofer displacement. So static displacement would be cone area and the transfer function of a single 8" subwoofer is very different from the transfer function of a pair of 15" subwoofers.To further clarify,with more cone area you get more of an increase in low frequency output/energy for the same amount of system power.
> 
> I prefer a low Q large displacement system which will yield smooth frequency response good output and low distortion. Basically in a sedan or coupe I like a pair of 15" subwoofers what I have termed trunk baffle. Great SQ output and great use of available space.
> 
> ...


Wow, that made perfect sense and really explained a lot, thank you so much for taking the time to spoon feed a noob! 

IB is not really an option in my case (or would require extensive work), so I think I will do the large ported system and work the EQ. Again, I really appreciate the explanation.


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## npdang (Jul 29, 2005)

Several other things to look out for... 

1. You're working off a manufacturer spec sheet. If you're thinking about a vented system, you will most likely need to measure the actual small signal parameters themselves as drivers tend to have rather large manufacturing variances and the sensitivity in a vented setup is very sensitive to changes in small signal parameters.

2. Large signal analysis. Modelling with WinISD only takes into account small signal parameters. Once you begin putting larger amounts of power into the driver what you modeled using a 1/4 watt test signal becomes largely irrelevant.

3. WinISD doesn't take into account the room's effect on the frequency response. The only solution here is to actually measure the driver+enclosure in the car. EQ of some kind, or placement may help to solve the bumps and dips in the response. I prefer to find a solution that requires the least amount of EQ, that best fits the target response I'm shooting for. At this point it's really a matter of knowing your car and how your personal tastes translate into what you can measure.


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## UCF52 (Nov 20, 2007)

npdang said:


> Several other things to look out for...
> 
> 1. You're working off a manufacturer spec sheet. If you're thinking about a vented system, you will most likely need to measure the actual small signal parameters themselves as drivers tend to have rather large manufacturing variances and the sensitivity in a vented setup is very sensitive to changes in small signal parameters.


I remember reading another post by you that mentioned the same thing. I will pick up one of those thingys at parts express.

Question: If I am using more than one driver in the same enclosure, what do I do if I get different number readings from each driver? Would it be recommended to try and find a single driver solution to less complicate things? 



npdang said:


> 2. Large signal analysis. Modelling with WinISD only takes into account small signal parameters. Once you begin putting larger amounts of power into the driver what you modeled using a 1/4 watt test signal becomes largely irrelevant.


Hmm, is there any way to account for this? Or is there is a general, common change that occurs that can be applied?



npdang said:


> 3. WinISD doesn't take into account the room's effect on the frequency response. The only solution here is to actually measure the driver+enclosure in the car. EQ of some kind, or placement may help to solve the bumps and dips in the response. I prefer to find a solution that requires the least amount of EQ, that best fits the target response I'm shooting for. At this point it's really a matter of knowing your car and how your personal tastes translate into what you can measure.


Well, I don't have an RTA tool, so measuring the driver+enclosure in the car really isn't an option. Am I just getting ready to face a lot of trial and error with box building?

And I'm really not too familiar with my car's environment. I'm sure that there are some generalities that can be made for all mid-size SUV as far as transfer function and driver/enclosure placement is concerned, right?


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## FG79 (Jun 30, 2008)

I hope people searching for LOW BASS in a car (which on the forums is quite frequent) are not mistaking 30-40 hertz response for 50-80 hertz response.

There's really not a ton of music from my experience that consistently requires high SPL levels in the low frequency range (say sub 40-45 hz). Even a lot of the heavy rap and electronic music rarely dip super low. What I thought was 35, turned out to be 50. 

I'm not saying a system should not be capable of having good response all the way down the range, it's just that too often great midbass response is sacrificed to get ultra low end that's not really that necessary. 

Cars do a great job of getting nice SPL in the lower octaves due to the cabin gain. The focus should be on getting more SPL in the 60-150 hertz region. 

If only a 6.5" or 8" midbass driver could be put in a properly tuned vented enclosure up front, people would truly be smiling from ear to ear. 

Anyways, to get back on topic....you can get nice smooth response with either sealed or vented, low Q or higher Q. All depends on driver and enclosure...no hard and fast rules. 

Your ear is the final tuning judge.


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## mvw2 (Oct 2, 2005)

UCF52 said:


> And I'm really not too familiar with my car's environment.


_This_ is the biggest issue. In order to choose a good sub + enclosure setup, you really do need to at least have a basic understanding of the cabin gain in your car. This sort of requires that you need to at least try a sub or two in your car, in a variety of enclosures, and figuring out how they operate inside and outside the car(test run in home for example). Get a feel for what gain effects you have and what frequency response works well in the car.

In the end, you always have the option to simply EQ as needed in the end. Build a box appropriate for the sub, then EQ to your liking. Ideally, you'd want an exact fitting sub + enclosure, but that's tough to do. There will almost always been some level of EQing done at the end.


Points specific towards your Low F3 sub versus EQing would yield two cases. Basically, a low F3 sub is generally a large box sub. One benefit of this design is efficiency. The EQing approach means you're running a smaller box sub with an overly high F3 (for the specific car). The benefit is the smaller box size that generally comes with this design. The downside is lower efficiency as you will have to more forcefully produce the lower frequencies.


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## Knobby Digital (Aug 17, 2008)

FG79 said:


> Even a lot of the heavy rap... rarely dip super low.




Depends on what type of rap you're listening to...


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## UCF52 (Nov 20, 2007)

FG79 said:


> I hope people searching for LOW BASS in a car (which on the forums is quite frequent) are not mistaking 30-40 hertz response for 50-80 hertz response.
> 
> There's really not a ton of music from my experience that consistently requires high SPL levels in the low frequency range (say sub 40-45 hz). Even a lot of the heavy rap and electronic music rarely dip super low. What I thought was 35, turned out to be 50.
> 
> ...


I see what you're saying and I'm not looking to jack up a certain region of the FR, I'm just looking for a flat response for as much of the sub frequency spectrum that I can - and what the best methods to accomplish this are.



mvw2 said:


> _This_ is the biggest issue. In order to choose a good sub + enclosure setup, you really do need to at least have a basic understanding of the cabin gain in your car. This sort of requires that you need to at least try a sub or two in your car, in a variety of enclosures, and figuring out how they operate inside and outside the car(test run in home for example). Get a feel for what gain effects you have and what frequency response works well in the car.


This is what I feared, but it makes sense. I'm sure as I get some more time under my belt with a sub system in I will start to notice my in car responses and what affects it may have.



mvw2 said:


> In the end, you always have the option to simply EQ as needed in the end. Build a box appropriate for the sub, then EQ to your liking. Ideally, you'd want an exact fitting sub + enclosure, but that's tough to do. There will almost always been some level of EQing done at the end.


This is what I will rely on. My searching has led me to believe that my vehicle's cabin gain is (or at least should be) lightly boosting the lower end of the FR spectrum. 




mvw2 said:


> Points specific towards your Low F3 sub versus EQing would yield two cases. Basically, a low F3 sub is generally a large box sub. One benefit of this design is efficiency. The EQing approach means you're running a smaller box sub with an overly high F3 (for the specific car). The benefit is the smaller box size that generally comes with this design. The downside is lower efficiency as you will have to more forcefully produce the lower frequencies.


Since I have the room I will build the box as efficient as I can. What worries me is npdangs points. If all this modeling is done with information that may not represent anything close to real world application, then why even use it. 

I'm not competing, I'm just an average joe who likes a half way decent stereo. If all this extra complication is for such minute changes then it just isn't worth the hassle.

If I build an enclosure that yields me a nice plot in WinISD, and EQ what the car changes, could I really be in for some trouble or is satisfaction likely to occur p) ?


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## FG79 (Jun 30, 2008)

icehole said:


> Depends on what type of rap you're listening to...


Are you referring to that Miami Bass type sound?


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## Knobby Digital (Aug 17, 2008)

FG79 said:


> Are you referring to that Miami Bass type sound?


Hells no. That's club music, so they keep the bass in a range that sounds good on PA speakers.

Despite what a lot of people think there's a lot of subleties in all types of hip-hop. You just have to pay attention, but that requires an interest in the music.


Sorry, back on topic.


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## mvw2 (Oct 2, 2005)

The sub has its own frequency response

Add enclosure which modifies low end frequency response and influences relative Q of the system.

Place in car which adds resonances at various frequencies which can boost or cut various frequency points.

Sub frequency response + enclosure effect + car cabin effect = flat response

...or as close as you can get.

Sub + enclosure + cabin gain + EQ = flat

This is what you will end up with.

If you notice, you can influence the end frequency response with any of these 4 areas. You can address frequency resonse via sub choice, enclosure design choice, placement within the car, and finally with EQing. From this, you should gain the understanding that you have a bit of freedom in choice. You can create the desired end result in more then one way. It just depends on which way(s) you want to go about doing that. Each part will provide only a certain amount of control, and each will have their own benefits and drawbacks.


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## UCF52 (Nov 20, 2007)

mvw2 said:


> The sub has its own frequency response
> 
> Add enclosure which modifies low end frequency response and influences relative Q of the system.
> 
> ...


Man, you make things really easy to understand, thanks!

Sub/enclosure knowledge before this thread *
Sub/enclosure knowledge after this thread ****

Thanks to all those who have provided insight - you guys have been more than helpful!


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## mvw2 (Oct 2, 2005)

It's the gist, but it lacks all the finer details. Yet in the end, you still need a sub that provides the sound characteristics you like and configure it in a way that has the correct end frequency response. Now this may mean making a choice between sub A and sub B or running sub A in a sealed box or a ported box. The EQing will depend on how far you are off to begin with, and it will rely on the HU you run and if it has extensive enough EQing to have good influence over the bass region. For example, if one runs a very mildly featured HU, they would rely heavily on gettting the sub + enclosure + cabin gain right because the EQ part of the equation would be very limited. If you are looking for a very, very specific sound, you may only have choices of sub A or sub B but not subs C through Z. In this case, you are required to work around the sub more so. If you must only build/run sealed enclosures, you are limited in that area and require a sub choice and subsequent EQing to get the job done. Cabin gain is more so static. You can get some variation through install location, but it's sort of always there and somewhat specific to the car. It's also something you can't _choose_. You're sort of stuck with whatever you've got, and you have to work around that fact.


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## 14642 (May 19, 2008)

1. Displacement is cone area x excursion.
2. No matter what drivers you use, the same bass requires the same displacement. One 8" woofer will have to have much higher excursion to make the same bass as a 15" woofer. 
3. Transfer function (more appropriately called cabin gain) is dependent on "dynamic displacement", but the change in displacement caused by the movement of the cone is miniscule compared to the volume of air in the car. The cabin gain of the car is not different enough between an 8" woofer and a 15" woofer to worry about.
4. The difference in performance between small signal and large signal can be significant and it's mostly a change in Qes caused by a rise in DCR caused by heating in the voice coil. That change can be a big problem for midrange drivers, but for subwoofers in boxes tuned to low frequencies, a 10% change in Fb caused by the change in Q might be 3or 4 Hz. No big deal. The change in Qb isn't a big deal either, because of point #5 below.
5. The EQ fixes all of this because the EQ will be adjusted while the system is playing at "large signal". It also allows you to compensate for the car's cabin gain, so there's no need to sample a bunch of woofers and make a bunch of measurements before you choose a woofer and a box.


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## norcalsfinest (Aug 30, 2008)

Andy Wehmeyer said:


> 1. Displacement is cone area x excursion.
> 2. No matter what drivers you use, the same bass requires the same displacement. One 8" woofer will have to have much higher excursion to make the same bass as a 15" woofer.
> 3. Transfer function (more appropriately called cabin gain) is dependent on "dynamic displacement", but the change in displacement caused by the movement of the cone is miniscule compared to the volume of air in the car. The cabin gain of the car is not different enough between an 8" woofer and a 15" woofer to worry about.
> 4. The difference in performance between small signal and large signal can be significant and it's mostly a change in Qes caused by a rise in DCR caused by heating in the voice coil. Fs also rises. That change can be a big problem for midrange drivers, but for subwoofers in boxes tuned to low frequencies, a 10% change in Fb caused by the change in Fs is 3 or 4 Hz. No big deal. The change in Q isn't a big deal either, because of point #5 below.
> 5. The EQ fixes all of this because the EQ will be adjusted while the system is playing at "large signal". It also allows you to compensate for the car's cabin gain, so there's no need to sample a bunch of woofers and make a bunch of measurements before you choose a woofer and a box.


And andy drives the nail home.

In my experience, i've always had the best results with vented enclosures tuned low.

If i can get a sub/enclosure combo to measure flat in an anechoic environment with tools such as WinISD Pro, that is a good enough starting point for me. Then, I'll toss the combo in the car and EQ down the low end to get the response i need.

My old setup was a vented eD 13Av.2 in 2.5 @ 30Hz. Physically, this was about the largest box i could fit. Modeled in WinISD Pro, I had about a 4dB peak at 35-36Hz. This was clearly audible in car. The graph just really confirmed what i was hearing. Using the PEQ of my 9887, i would normally set an EQ with a Q of 1 centered at 31.5Hz with a gain of -7dB. This would tame the low end hump for SQ listening. When I wanted to get loud at tailgates or what have you, I'd set the EQ back to flat. It wasn't hard to do with a large 12" driver, ~28mm of usable excursion, and 1200+ watts RMS.

Use WinISD Pro as a starting point. The old WinISD beta sucks. Once you get an enclosure that measures flat, throw it in the car. Play different test tones and listen for intensity differences between the frequencies. Tone down the ones that are noticeably louder. EQ up the ones that seem to be lacking. 

How you orient the driver in relation to the port, and how the box is oriented in the car can all change this as well.

For example, in my car, in a sealed enclosure, I'd have output and phase problems with the box on the driver side of the car rear firing. So, i'd move it to the passenger side.

In a vented enclosure, firing the driver/port upward toward the roof killed the response, and a definite loss in output occured. to remedy this, i fired the woofer and port toward the rear, loading off of the hatch/tail gate.


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## 14642 (May 19, 2008)

If you search for the thread "given that cabin gain..." you'll see a bunch of transfer function plots. In another test, we placed the box all over the car and discovered that the placement of the box didn't affect frequencies below 40 or 50 Hz, but did affect the midbass, where there is a possibility of cancellation. 60 Hz is affected by firing the box up or moving it to the center of the car. These frequencies are affected by the size of the car, but not by much. The difference betwen an MGBGT and a Suburban are worth noting, but the difference between a Jetta and a Passat aren't.

The placement of the port isn't critical. Remember, the box is tuned low, and Fb is the frequency where the port is responsible for all the output. The Q of the port's response is pretty high, and the wavelengths are very long at the Fb of the box. Moving the port a few inches or to a different surface won't matter.

Also, there's really no need to check the frequency response of the box after it's built, so long as you build it according to the model. I've never used WinISD, but if it doesn't include the Le of the driver in the model, it isn't worth much for car audio subwoofers, which usually have multilayer coils. The inductance is a low pass filter, and combined with the high pass filter inherent in the woofer, it can create a very different curve, although this is more problematic for sealed enclosures.

If you want to measure the anechoic response of your speaker and you don't have $100,000 for an anechoic chamber, make the measurement outside at least 30 feet or so from any wall or other large obstruction. Place the box on the ground, place the mic on the ground 2 meters away, point the woofer at the mic and make your measurement. 

*Finally, we should all get one thing straight, an anechoic room is optimum for measuring the response of a speaker, but it's not an optimum environment for listening. In fact, listening in an anechoic chamber is horrifying. It sucks. Fortunately, there's no way to remove all the reflections in any room in which you'd actually listen and certainly not in a car, so the point is moot. *

*Is there anyone here who claims that an anechoic room is optimum or claims that eliminating reflections is important ever listened in an anechoic room? *


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## norcalsfinest (Aug 30, 2008)

Andy Wehmeyer said:


> I've never used WinISD, but if it doesn't include the Le of the driver in the model, it isn't worth much for car audio subwoofers, which usually have multilayer coils. The inductance is a low pass filter, and combined with the high pass filter inherent in the woofer, it can create a very different curve, although this is more problematic for sealed enclosures.



WinISD pro DOES include Le, as well as many other uncommon but important specs. It also allows you to account for the environment (temperature, air pressure, etc) as well.

anechoic is only useful for showing the unaltered response of a box/driver combination IDEALLY. In car, the response is obviously different, and that's where the EQ comes in.

As far as port placement, i meant moreso in relation to the car, not in relation to the woofer.

Loading the port off of a hatch or trunk yields a higher output USUALLY than not. Just like in the home environment when people utilize downfiring/floor loading or corner loading.


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## invecs (Jul 30, 2005)

Andy,

I'm sold on your idea of going ported with all the pro's related to it...been reading alot about the ported design since then. I've read that distortion greatly increases below the tuning frequency...if for example the sub was tuned to 25Hz, then one plays the Planet Krypton track in the IASCA cd which has an 18Hz note...will I risk damaging the sub or make the sub sound distorted?


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## UCF52 (Nov 20, 2007)

I'm using WinISD Beta and it does include Le. Here is the plot I am working with. It is a pair of JBL GTO 10's.










Transfer Functions (thanks Andy)









Enclosure - subs facing rear of vehicle, port a few inches away from the rear quarter panel. 









So, cabin gain is likely to affect 50hz and below, enclosure (driver/port) placemnt is likely to have some affect on 60hz and above. The only thing that concerns is my EQ - it's graphic -these are the bands I have control of 20—31.5—50—80—125—200. 



Andy Wehmeyer said:


> Building a vented box with a flat response and the lowest F3 possible and using 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.


I think I am going to take your advice here. I don't have a whole lot of power, but I have plenty of space. Go with the most efficient enclosure in an ideal environment and EQ out cabin gain.


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## Eric Stevens (Dec 29, 2007)

Andy Wehmeyer said:


> 3. Transfer function (more appropriately called cabin gain) is dependent on "dynamic displacement", but the change in displacement caused by the movement of the cone is miniscule compared to the volume of air in the car. The cabin gain of the car is not different enough between an 8" woofer and a 15" woofer to worry about.
> .


Andy, 

I agree on the dynamic displacement but not with the static displacement.

Have you measured the difference between an 8" and 15" or even in pairs? 

While I have never directly measured the difference the results of other independent measurements and implementation of subwoofers in systems suggest that there is a significant difference especially below 50 Hz. Going from an SD of 220 cm2 to 800 cm2 is significant as far as the driver goes even though small relative to the volume of an vehicle interior. My belief is once you enter a constant pressure domain the SD of the system has a much more dramatic effect.

I agree the difference is nothing to worry about, and most people shouldnt worry about it.

For those that are struggling to understand what is happening and how to do it better will need to understand the differences.

Eric
Image Dynamics


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## UCF52 (Nov 20, 2007)

Eric Stevens said:


> Andy,
> 
> I agree on the dynamic displacement but not with the static displacement.
> 
> ...


So, what you are saying is cabin gain is affected by the drivers SD, just not enough to warrant any concern for the average person...?


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## 14642 (May 19, 2008)

Sd isn't displacement, it's cone area. Vd is maximum displacement and it's Sd x Xmax. the maximum displacement of a smal cone can be just as much as a large one, provided it moves further. It's analogous to bore and stroke for an engine. Transfer function is a measure of what the car does, and that measurement is independent of the woofer. THe frequency response of the woofer in the car is the combination. If an 8" woofer and a 15" woofer have the same response in the same enclosure, the end result will be the same. If they don't, then the difference between the in-car measurements will be simply the difference in their anechoic responses.


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## UCF52 (Nov 20, 2007)

Okay, so cabin gain remains constant regardless of your sub system. It's when your driver+enclosure (with it's out of car FR) interact with the effective cabin environment (affecting your driver+enclosure FR), then you get your uncorrected (flat EQ) FR. At this point you can make corrections via an EQ. That make any sense?


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## Eric Stevens (Dec 29, 2007)

Andy Wehmeyer said:


> Sd isn't displacement, it's cone area. Vd is maximum displacement and it's Sd x Xmax. the maximum displacement of a smal cone can be just as much as a large one, provided it moves further. It's analogous to bore and stroke for an engine. Transfer function is a measure of what the car does, and that measurement is independent of the woofer. THe frequency response of the woofer in the car is the combination. If an 8" woofer and a 15" woofer have the same response in the same enclosure, the end result will be the same. If they don't, then the difference between the in-car measurements will be simply the difference in their anechoic responses.



Yes Sd doesnt equal Vd. But is the part of Vd that will have the most significant effect. And yes the transfer function is separate of the subwoofer in use. We are working in an application that is power limited so efficiency is a significant factor and consideration. So to think that an 8" can give us the same displacement as a 15" with the average drivers used this is unrealistic, especially if we are trying to make a somewhat low distortion system. Technically you are correct but in application it is more argumentative than it is reality.

I am trying to present this in a way that is easily understood and will be applied correctly without a deeper understanding of the fundamentals of the application.


Eric
Image Dynamics


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## norcalsfinest (Aug 30, 2008)

Eric Stevens said:


> Yes Sd doesnt equal Vd. But is the part of Vd that will have the most significant effect. And yes the transfer function is separate of the subwoofer in use. We are working in an application that is power limited so efficiency is a significant factor and consideration. So to think that an 8" can give us the same displacement as a 15" with the average drivers used this is unrealistic, especially if we are trying to make a somewhat low distortion system. Technically you are correct but in application it is more argumentative than it is reality.
> 
> I am trying to present this in a way that is easily understood and will be applied correctly without a deeper understanding of the fundamentals of the application.
> 
> ...


A large low excursion driver will almost always have lower linear distortion than a driver with high excursion and lower Sd. That's simple physics.

If a 15 has 15mm xmax and a 12 needs around 24mm of excursion to match the same output, the 12 is obviously going to distort more than the 15 unless the motor design of the 15 is just horrible or the motor of the 12 is superb. Non-linear distortions will rise rapidly as the coil starts to leave the gap and Bl is drastically lowered. Le induced distortion will also rise in the 12, as well as a slew of other problems.

I can't agree more with Eric in this regard.


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## 14642 (May 19, 2008)

But that isn't the issue here. I'm not disputing that the larger Sd results in less excursion than the smaller woofer for any given displacement, I'm also not disputing that the reduction in excursion provides a potential reduction in distortion. In fact, that's one of the main reasons to use the vented box--to reduce excursion. The additional benefit is the additional output provided by the port. That additional output allows us to reduce the power required of the amplifier using a big fat cut with the EQ. It just so happens that the frequency that will need to be cut once the enclosure is in the car will be above the tuned frequency of the box, pretty close to the frequency where the woofer's excursion is at its maximum. Since we've removed a bunch of ampifier power with the EQ, we've also reduced the potential for amplifier clipping and increased the headroom available for peaks. The only area where the vented box is likely to have more distortion than the big woofer in a sealed box (or IB) is far below Fb. If the box is tuned near 30Hz, the excursion maximum below Fb won't be a problem with most music content.

All of this depends on a port that's large enough not to make a bunch of noise. 

I am disputing that the cabin gain is related to the displacement of the woofer, except to say that there's no cabin gain if there's no sound.


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## sqshoestring (Jun 19, 2007)

I've also run into ease of tuning issues. If you tune a sub to run what you want, say play to 30Hz with relatively small drop off so large ported for example, it will play the 30Hz without big power. But they also tend to be easier to tune because the response does not drop off like a brick like a small box will. So even if you feed a small box way more power and EQ it, often I (maybe not you, and without expensive RTA/etc) find it harder to get the right sound. It is always easy to get rid of bass, but to gain it is harder. I'm not saying the right sub in a small box can't work great, just that your setup better be sorted and employ particular products. A lot of common subs don't get low in smallish enclosures even though their manufacturers like to say they do, it is even obvious with many if you model them.

Far as modeling, I like to do it the way I did my current car. I put any sub/box in the trunk and see what it does, what I have to EQ or can EQ/tune to get it to work plus what it sounds like with no EQ. I model that sub and see what I have. Then I say it needs more X Hz or less Y Hz, and go about building something that fits the car more to my liking. I use the model to compare, that way cabin gain or whatever has little effect on it. It works, if I change to a model with more 30Hz I get it.

I like to run IB subs, get the lows and no box. They still get the roll off like sealed but it is a shallow slope so not that bad to tune at least with larger subs. Still this car I could not get low with <2cf boxes and single 12s I tested with subs I had around. Could not get say 35Hz and less it just went away. Now have four 12s IB and still have to force the lows but they can get 20Hz louder than I need. But I think like someone posted above a pair of 15 might be ideal, I'm sure with four 12s I am running out of 'box' because putting something in my trunk tunes them higher....maybe I could get lower with 15s, and that would mean less power/EQ needed. Of course I only have 400rms now and the subs hardly move at normal listening volumes, say 1/4 of xmax roughly gets quite loud for listening.

I guess to simplify if your subs are tuned closer to what you will play them at, and have a smoother response, it usually makes them easier to tune and blend into your system. I don't even bother to figure out the car, I like to try something and find out...then change to what it needs to make me happy.

Far as 20Hz music, I been driving around for months now playing all kinds of music and I'd guess that minimum 75% of it I hear a change when I run the 20Hz EQ up and down on my Pioneer 880's EQ. To me <30Hz gives a presence in the sound like you might get live or in a theater. Anything less is lacking to me and I listen to various music from 80s rock to today's popular to dance music, plus some other stuff. Been pulling out all kinds of stuff just to test this premise that most music does not have ~20Hz and I'm not hearing much truth to that. A lot of music may not have much material there, but what is there offers impact and ambiance. On the other hand I don't crank it up really loud that often, and when I do I'm not too worried about quality. So running a lot of cone area is ideal with subs; low excursion makes for good SQ and I don't worry about buying expensive subs. Long as I have some room or can do IB, I think Andy is spot on as usual. But, I have to say that getting <30Hz in a car is usually hard for me to do. Most cars I've had just don't get it down there without overbuilding like these quad 12s....but maybe went little too far with this one.


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## Oliver (Jun 25, 2007)

Andy Wehmeyer said:


> Sd isn't displacement, it's cone area. Vd is maximum displacement and it's Sd x Xmax. the maximum displacement of a smal cone can be just as much as a large one, provided it moves further. It's analogous to bore and stroke for an engine. Transfer function is a measure of what the car does, and that measurement is independent of the woofer. THe frequency response of the woofer in the car is the combination. If an 8" woofer and a 15" woofer have the same response in the same enclosure, the end result will be the same. If they don't, then the difference between the in-car measurements will be simply the difference in their anechoic responses.


This works for me !

I run an 8W7 in a Honda Civic with a modded Linear power [ DPS 500 ], power produced at higher ohmage.


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## Eric Stevens (Dec 29, 2007)

Andy Wehmeyer said:


> But that isn't the issue here. I'm not disputing that the larger Sd results in less excursion than the smaller woofer for any given displacement, I'm also not disputing that the reduction in excursion provides a potential reduction in distortion. In fact, that's one of the main reasons to use the vented box--to reduce excursion. The additional benefit is the additional output provided by the port. That additional output allows us to reduce the power required of the amplifier using a big fat cut with the EQ. It just so happens that the frequency that will need to be cut once the enclosure is in the car will be above the tuned frequency of the box, pretty close to the frequency where the woofer's excursion is at its maximum. Since we've removed a bunch of ampifier power with the EQ, we've also reduced the potential for amplifier clipping and increased the headroom available for peaks. The only area where the vented box is likely to have more distortion than the big woofer in a sealed box (or IB) is far below Fb. If the box is tuned near 30Hz, the excursion maximum below Fb won't be a problem with most music content.


Well understood just from experience your comments without being quantified will be taken at simplest face value with no regard or understanding of the forces at work. 

Your idea of the ported enclosure and EQ for flat is really peaking my interest. It sounds like it should work very well. Looks like I will have some fun playing with ported enclosures. For those that want to boom and have good SQ its as simple as going to a flat EQ and getting back the 6dB of ripple in car at 45 Hz when feeling the urge to disturb the peace.

Eric
Image Dynamics


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## mvw2 (Oct 2, 2005)

norcalsfinest said:


> A large low excursion driver will almost always have lower linear distortion than a driver with high excursion and lower Sd. That's simple physics.
> 
> If a 15 has 15mm xmax and a 12 needs around 24mm of excursion to match the same output, the 12 is obviously going to distort more than the 15 unless the motor design of the 15 is just horrible or the motor of the 12 is superb. Non-linear distortions will rise rapidly as the coil starts to leave the gap and Bl is drastically lowered. Le induced distortion will also rise in the 12, as well as a slew of other problems.
> 
> I can't agree more with Eric in this regard.


I'm curious how many people come to this realization in their car audio hobby. I wish I could say 100%...eventually. I can very easily suggest to someone to run a 12" (minimum), 15" or 18" woofer. In recent times, I really try to shy away folks from thinking about all these small 8" and 10" configurations...unless they're running an array or something.



Eric Stevens said:


> Well understood just from experience your comments without being quantified will be taken at simplest face value with no regard or understanding of the forces at work.
> 
> Your idea of the ported enclosure and EQ for flat is really peaking my interest. It sounds like it should work very well. Looks like I will have some fun playing with ported enclosures. For those that want to boom and have good SQ its as simple as going to a flat EQ and getting back the 6dB of ripple in car at 45 Hz when feeling the urge to disturb the peace.
> 
> ...


This is what I've been doing with all my recent subs. Ported flat and then EQ as needed. Part of the problem for me personally is that I have crap for low end cabin gain in my car. I've come to know the best configuration is a sealed box sub with a F3 of 30Hz. This is pretty much flat in my car. Otherwise, I go ported with most subs simply to maintain a low end output without forcing the need of EQ to get it, although I may need to EQ down a little on the bottom end. I find it simpler with ported and that ported is less limited by design, i.e. less excursion use. This is, or at least should be for most, an intriguing idea to me. Low end output and no heavy excursion needs, win, win short the group delay. For me, I can't see myself ever running a sealed box setup anymore unless I'm willing to run a generally larger box, larger coned woofer with a low F3. Whenever I'm compelled to run a 15" or 18" in a 3 cu.ft.-5 cu.ft. I may have a sealed box sub back in my car.


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## FG79 (Jun 30, 2008)

Eric, how does that ID Charger you guys built sound? IIRC, it had 6 8" woofers on the parcel shelf using the trunk as the enclosure.

To me, that might be the best of both worlds. Using small woofers for the midbass punch and allowing them a humongous enclosure to play the deep notes. When you have six 8" woofers together, that's plenty of cone area to get you nice SPL. Bonus if you have them all very close together.

Another thing about running smaller woofers IB versus larger woofers (on a parcel shelf at least), is that the smaller woofers will take up less space on the baffle than larger ones, thereby separating the front/back waves better. This is often an overlooked free benefit when building enclosures. The bigger the baffle, the better.

Not an issue though when building the baffle behind the rear seats.


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## FG79 (Jun 30, 2008)

Eric Stevens said:


> Well understood just from experience your comments without being quantified will be taken at simplest face value with no regard or understanding of the forces at work.
> 
> Your idea of the ported enclosure and EQ for flat is really peaking my interest. It sounds like it should work very well. Looks like I will have some fun playing with ported enclosures. For those that want to boom and have good SQ its as simple as going to a flat EQ and getting back the 6dB of ripple in car at 45 Hz when feeling the urge to disturb the peace.
> 
> ...


It's a tough thing to do right, but if done right, a great vented enclosure can be worth all the effort in the world. 

The only question remains....is ported worth it if you could jam 2 extra woofers in a sealed enclosure of similar volume? 

I love the challenge and novelty factor of it, but it might not be for everyone.


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## FG79 (Jun 30, 2008)

norcalsfinest said:


> A large low excursion driver will almost always have lower linear distortion than a driver with high excursion and lower Sd. That's simple physics.
> 
> If a 15 has 15mm xmax and a 12 needs around 24mm of excursion to match the same output, the 12 is obviously going to distort more than the 15 unless the motor design of the 15 is just horrible or the motor of the 12 is superb. Non-linear distortions will rise rapidly as the coil starts to leave the gap and Bl is drastically lowered. Le induced distortion will also rise in the 12, as well as a slew of other problems.
> 
> I can't agree more with Eric in this regard.


Yeah, if you want to match the SPL output of 15s with an 8 or a 10, just get more of them. Increasing xmax is not going to get you what you want despite what JL's website tells you.

I'd love to get my hands on some of the few low excursion 15s built....the IDW15, the JL 15W2/W4, and also those USD 15s. A shame they discontinued them...anyone know how to get them?


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## mvw2 (Oct 2, 2005)

FG79 said:


> It's a tough thing to do right, but if done right, a great vented enclosure can be worth all the effort in the world.
> 
> The only question remains....is ported worth it if you could jam 2 extra woofers in a sealed enclosure of similar volume?
> 
> I love the challenge and novelty factor of it, but it might not be for everyone.


You're assuming you will actually end up with a smaller volume. Sure sealed is smaller, but now you're running two woofers instead or perhaps one larger woofer that may actually be of a larger volume then a different, small box geared, and ported setup. For example, what sub are you going to use that will fit in 2 cu.ft. sealed and get a F3 of 30Hz and will do plus 120dB without over excursion? I know I can do this ported pretty easy. Sealed, it becomes dependent on the sub used and if you are building an overly high Q sub + box design, sacrificing some dampening control.

In my mind, high F3, small box sealed designs are great if you have plenty of cabin gain to work with or are happy EQing and have a good amount of excursion. Ported is very versatile, and a lot of packages fit within 2-3 cu.ft. and allow F3s and response shapes (wink ) to your liking. If I don't mind +4 cu.ft. enclosures, I wouldn't mind stepping back to sealed but a large 15" or 18" woofer with a decent amount of excursion, or multiple woofers to get the needed cone area.

One thing people don't realize about ported is that because you both have box size and tune frequency, you have the ability to manipulate the response shape of the woofer, letting you better fit the cabin gain of the car if you know what to shoot for.


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## npdang (Jul 29, 2005)

What I hate about vented enclosures is if you mess up somewhere and your frp is much higher than anticipated, the unloading and 4th order rolloff makes it difficult if not impossible to get the low end sensitivity you want.


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## UCF52 (Nov 20, 2007)

npdang said:


> What I hate about vented enclosures is if you mess up somewhere and your frp is much higher than anticipated, the unloading and 4th order rolloff makes it difficult if not impossible to get the low end sensitivity you want.


So, what is your suggestion... don't screw up the enclosure design or go another route? I know there are many variables that would need to be considered, but I'm just speaking generalities.


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## mvw2 (Oct 2, 2005)

Sealed is easy. Sealed is forgiving. Ported gives you an extended low frequency response without the excursion need. However, the response _shape_ is different, and one of the two setups will fit better in a car. Generally, this is sealed and the gentle roll off counters pretty well the cabin gain response. However, we're back to cabin gain as the main driver in subwoofer and enclosure choice.

For ported enclosures, test the driver being used (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-803), and then be decently exact with the box design. If you don't want to invest, then build a test box that you can change volume and using an adjustable port length. You can manipulate the test box until you end up with a package that works best in-car. Then build the real box. Port is really mainly sensitive to port tune frequency. Box size isn't tremendously influential other then the fact that a change in volume equals a change in port length to get the same end tune frequency.


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## UCF52 (Nov 20, 2007)

mvw2 said:


> Sealed is easy. Sealed is forgiving. Ported gives you an extended low frequency response without the excursion need. However, the response _shape_ is different, and one of the two setups will fit better in a car. Generally, this is sealed and the gentle roll off counters pretty well the cabin gain response. However, we're back to cabin gain as the main driver in subwoofer and enclosure choice.
> 
> For ported enclosures, test the driver being used (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-803), and then be decently exact with the box design. If you don't want to invest, then build a test box that you can change volume and using an adjustable port length. You can manipulate the test box until you end up with a package that works best in-car. Then build the real box. Port is really mainly sensitive to port tune frequency. Box size isn't tremendously influential other then the fact that a change in volume equals a change in port length to get the same end tune frequency.


Good advice, thanks.



mvw2 said:


> Box size isn't tremendously influential other then the fact that a change in volume equals a change in port length to get the same end tune frequency.


I've noticed this when playing in WinISD.

So, would a logical route to consider be trying a sealed enclosure and if cabin gain + EQ and output are giving you what you want then stick with it. Basically, start simple and if it satisfies then why bother...? The only thing that kind of floats in the back of my head is efficiency. To me it just seems the best thing to do is to build the most efficient enclosure you can alleviating stress on your equipment and working through any added difficulties that may arise.


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## npdang (Jul 29, 2005)

UCF52 said:


> So, what is your suggestion... don't screw up the enclosure design or go another route? I know there are many variables that would need to be considered, but I'm just speaking generalities.


Overcompensate on the low end... or use a PR


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## UCF52 (Nov 20, 2007)

npdang said:


> Overcompensate on the low end


Could you elaborate, I'm not sure what you mean :blush: ? Are you saying use a upward skewed curve on the FR plot? Sorry for the ****ty learning curve :blush: 



npdang said:


> ... or use a PR


Dude, I'm just starting to get this, don't be throwing curve balls at me.


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## mvw2 (Oct 2, 2005)

A passive radiator does the same thing as a port does, but it's easier to work with in terms of tuning the frequency. You simply add or remove mass to adjust the resonance frequency of the passive radiator. It's a little more expensive then simply using a port, but it also means you don't have the port volume either which can save a good deal of space. The price generally puts off most folks as well as the PR not really being all that stable in a moving car. It's essentially a speaker without the motor, but then you add a bunch of weight to it.


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## UCF52 (Nov 20, 2007)

mvw2 said:


> A passive radiator does the same thing as a port does, but it's easier to work with in terms of tuning the frequency. You simply add or remove mass to adjust the resonance frequency of the passive radiator. It's a little more expensive then simply using a port, but it also means you don't have the port volume either which can save a good deal of space. The price generally puts off most folks as well as the PR not really being all that stable in a moving car. It's essentially a speaker without the motor, but then you add a bunch of weight to it.


Hmm, I do have two blown JL W6.v1 sitting here.


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## Foglght (Aug 2, 2007)

Lots of learning here. Interesting, but some of it seems to be overkill for what this guy wants to do. 

Personally, I've modeled and built 4 different sub enclosures for my cars using winisd. I didn't expect them to turn out perfect, but they ALL followed the tuning pretty closely when I considered cabin gain. 

One of the things I didn't see mentioned was the delay with a ported box. When tuning low, I've found that ported boxes can have some nasty delay where you feel the hit, then hear the boom. Very prevalent at lower frequencies. Check the phase delay on the Winisd tab. I don't know if that has anything to do with it, but it seemed to go with what I was hearing.

What I also found was that what you lose in low end with a sealed box, you gain with the cabin, especially in a hatch/wagon.


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## UCF52 (Nov 20, 2007)

Foglght said:


> Lots of learning here. Interesting, but some of it seems to be overkill for what this guy wants to do.


You're probably right; it doesn't take much to please me. I'll likely build a vented enclosure and a sealed enclosure and see which one I can get to sound best. I really like learning about it though, and I never meant for this thread to be just about my situation, more or less strike up a debate and see if I could apply it to my situation. 



Foglght said:


> One of the things I didn't see mentioned was the delay with a ported box. When tuning low, I've found that ported boxes can have some nasty delay where you feel the hit, then hear the boom. Very prevalent at lower frequencies. Check the phase delay on the Winisd tab. I don't know if that has anything to do with it, but it seemed to go with what I was hearing.
> 
> What I also found was that what you lose in low end with a sealed box, you gain with the cabin, especially in a hatch/wagon.


Interesting, lets see if we can get some more thoughts on this.


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## Foglght (Aug 2, 2007)

UCF52 said:


> You're probably right; it doesn't take much to please me. I'll likely build a vented enclosure and a sealed enclosure and see which one I can get to sound best. I really like learning about it though, and I never meant for this thread to be just about my situation, more or less strike up a debate and see if I could apply it to my situation.


I'm no expert by any means, but with everything that I have seen lots of these guys post about, there are SOOOO many factors that could go into making a speaker box. You have to find the most limiting component of your system and go from there. If you don't have a lot of EQ adjustability, don't screw around with a peaky ported box. A natural roll-off with a nice sealed enclosure will probbaly work much better.

With a ported box, the -3db point (Winisd) will be just about the point in ANY car where the response drops off. Yeah, it might be off by a couple of hz, but that doesn't matter all that much unless you are building a comp system. Plus, those types of small things can be tuned out. 

All of these guys have great information though.


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## UCF52 (Nov 20, 2007)

Well, I don't have a parametric EQ, so fine tuning the lower region (or any region for that matter) of the FR spectrum is not going to be really easy. This is probably my biggest limiting factor. I'm pretty flexible with enclosure size and driver selection. 

So, to apply this to my situation, should it be a concern of mine that using a vented enclosure, effectively lowering my F3 (raising low end response), and risk that cabin gain will boost my low end beyond the control of my EQ...?


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## sqshoestring (Jun 19, 2007)

npdang said:


> Overcompensate on the low end... or use a PR


I never have enough low end, sealed is the worst. Then again I don't tend to throw 1Kw of power at them either when I can do other things. Seems to me the closer your flat sub response to ideal, the better off you will be. I try to make the box large as I can, with IB subs I try to use double the drivers. I don't even like a lot of efficient IB drivers they are tuned too high, though inefficient is not usually the ticket either (for IB, like it is for small box). I'll guess and say the above quote means error on the 'too much bottom' side not just right or lacking. I've been doing subs for 20yr and never recall having too much bottom in a sub setup. Sure they can get loud at 50Hz but most can't at 30....and that peak trashes your SQ. In the end it all depends on what you want of course.

If you can get your hands on an alpine g190, they work nice for the sub. There must be other parametrics out there, the HU with them seem to be pricey yet.


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## UCF52 (Nov 20, 2007)

sqshoestring said:


> I never have enough low end, sealed is the worst. Then again I don't tend to throw 1Kw of power at them either when I can do other things. Seems to me the closer your flat sub response to ideal, the better off you will be. I try to make the box large as I can, with IB subs I try to use double the drivers. I don't even like a lot of efficient IB drivers they are tuned too high, though inefficient is not usually the ticket either (for IB, like it is for small box). I'll guess and say the above quote means error on the 'too much bottom' side not just right or lacking. I've been doing subs for 20yr and never recall having too much bottom in a sub setup. Sure they can get loud at 50Hz but most can't at 30....and that peak trashes your SQ. In the end it all depends on what you want of course.
> 
> If you can get your hands on an alpine g190, they work nice for the sub. There must be other parametrics out there, the HU with them seem to be pricey yet.


I have pretty minimal power on tap (relative to others) and I tend to listen to my stuff pretty loud, so efficient for me is a must. I am also going to stick with the processing I have in my deck. I'll go large vented, rely on cabin gain and EQ to flatten everything out and hope for the best.


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## sqshoestring (Jun 19, 2007)

UCF52 said:


> I have pretty minimal power on tap (relative to others) and I tend to listen to my stuff pretty loud, so efficient for me is a must. I am also going to stick with the processing I have in my deck. I'll go large vented, rely on cabin gain and EQ to flatten everything out and hope for the best.


That is what I would do. I think I posted before I don't really try to tune the subs before they are in the car, sure I will guesstimate but that is all. Lot of people like to try to calculate exactly what they need and I find it not possible and/or a waste of time. I can toss a spare box/sub in and get an idea of what I need, that gives me a baseline in winisd to start from since I'm not measuring cabin gain or any other complex effect the car has on the sub's sound. I'd recommend that for anyone starting out, experimenting and tuning will teach you a lot. I have a 10 and 12 in sealed boxes I paid <$40 total each shipped off epay for example, just to toss around. One mtx and one sony. The 12 box I can port or seal, have other 12s I've had in it. Used stuff is great way to test then sell it for same price when your done, if you shop a little.

Oh I like running less power, its more fun and less hassle. Or maybe I just get a kick out of more from less. Sometimes you just need it though. My quad IB 12s only have 400rms, so 100 each. I can clip the amp and not hit xmax, but by then I can't hear the highs and the roof/etc is shaking a lot crossed at 40-50Hz. It is EQed so 20 and 50Hz sound about the same volume with tones.

Many years back 2x75 was a pretty big amp, though at today's ratings that would be well over 100x2 I imagine. Somewhat efficient subs and ported can get pretty loud on it.


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## UCF52 (Nov 20, 2007)

Cool, thanks for the reassurance. And as you said, I'll probably learn a lot by just experimenting and become more familiar with my in-cabin acoustics. Maybe I'll post my thoughts here once I get up and running.


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## Oliver (Jun 25, 2007)

Tune low and use subsonic [24 dB slope] at several HZ below tuned frequency 

look for green number under "mach" in WINISD [ chuffing issues with red number ].


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## UCF52 (Nov 20, 2007)

a$$hole said:


> Tune low and use subsonic [24 dB slope] at several HZ below tuned frequency
> 
> look for green number under "mach" in WINISD [ chuffing issues with red number ].


I'm glad you brought that up. I cannot for the life of me seem to figure out how to get that "vent mach" into the green. Any tips? I'd like to use aero port(s).


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## 14642 (May 19, 2008)

Aero ports are OK. Anything with a big flare will help with port noise. 

I don't recommend home-brew passive radiators. If they're properly designed, they're great. However, just changing the mass isn't the proper way to do it. Compliance and mass are the tools to tune a radiator and changing compliance isn't easy. Ports are free.


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## UCF52 (Nov 20, 2007)

Andy Wehmeyer said:


> Aero ports are OK. Anything with a big flare will help with port noise.
> 
> I don't recommend home-brew passive radiators. If they're properly designed, they're great. However, just changing the mass isn't the proper way to do it. Compliance and mass are the tools to tune a radiator and changing compliance isn't easy. Ports are free.


Yeah, I was just kidding about the "home brew" PR's. I was planning on using the aero ports that can be had over at PE. 

Any tip on getting the vent mach into the green?


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## 14642 (May 19, 2008)

Use the largest diameter possible or use two ports. Nothing smaller than a 4" diameter port.


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## UCF52 (Nov 20, 2007)

Andy Wehmeyer said:


> Use the largest diameter possible or use two ports. Nothing smaller than a 4" diameter port.


Just to be clear, of the three (port area, volume, length) port area is the most significant, correct? Also, isn't total Sd of the drivers significant in how much port surface area there should be?

I've been playing with different sizes and it seems I can fit two 3" aeros or one 5" aero. Two 4" aeros are pushing it ~ leaves me 8" from the end of the port and the wall of the enclosure.


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## 14642 (May 19, 2008)

Port area and length are the important parameters. The larger the area, the longer the port will be for the same tuning frequency. One 5" is better than two 3" ports, but two 4" ports would be better. The mouth of the port ought to be at least one port diameter away from a wall that's parallel to the port's mouth. Sd is often used as a rule of thumb, but the reality is MUCH more complicated. Has to do with the velocity of the air, friction against the inside of the port and the shape of the entrance and exit.


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## UCF52 (Nov 20, 2007)

Andy Wehmeyer said:


> Port area and length are the important parameters. The larger the area, the longer the port will be for the same tuning frequency. One 5" is better than two 3" ports, but two 4" ports would be better. The mouth of the port ought to be at least one port diameter away from a wall that's parallel to the port's mouth. Sd is often used as a rule of thumb, but the reality is MUCH more complicated. Has to do with the velocity of the air, friction against the inside of the port and the shape of the entrance and exit.


In that case it looks like I can fit the two 4" ports. Do the ports need to be arranged in any particular way? For example, can each ports mouth originate on two different baffles and terminate at two different locations (assuming a safe distance from enclosure walls)?


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## 14642 (May 19, 2008)

Yes.


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## UCF52 (Nov 20, 2007)

> Do the ports need to be arranged in any particular way?





> For example, can each ports mouth originate on two different baffles and terminate at two different locations (assuming a safe distance from enclosure walls)?





Andy Wehmeyer said:


> Yes.


To which one...


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## 14642 (May 19, 2008)

Doh...sorry. The ports can be anywhere. Remember, you're tuning to a really low frequency where the wavelengths are really long. A few inches isn't going to make any difference.


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## UCF52 (Nov 20, 2007)

Andy Wehmeyer said:


> Doh...sorry. The ports can be anywhere. Remember, you're tuning to a really low frequency where the wavelengths are really long. A few inches isn't going to make any difference.


Cool, thanks man, for all of the help and insight. I'm sure others will find your thoughts to be very helpful as well.


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## sqshoestring (Jun 19, 2007)

You could also do an external port as another option, though some say there are issues with not having a baffle on the port end or they build one. I've had it work, box can be that much smaller.


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## UCF52 (Nov 20, 2007)

sqshoestring said:


> You could also do an external port as another option, though some say there are issues with not having a baffle on the port end or they build one. I've had it work, box can be that much smaller.


Yeah, I've been playing around with different options/layouts. Thanks.


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## sqshoestring (Jun 19, 2007)

I want to make a tube sub, because they are so much lighter, but not gotten to that yet since I can have IB subs in this car. I saw a cool one that had ports out one end and ran along the bottom to a baffle that covered the other driver end. That way driver and ports were on the one end in a baffle, and the tubes were like legs so it could not roll over/etc.


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## npdang (Jul 29, 2005)

When you're boosting at 20hz with a parametric eq, chances are you're also boosting up to 40hz or even 60hz depending on the Q of your filter.

You're also discounting non-linear distortion from the sub. Almost all subs playing at 20hz have significant levels of higher order distortion products even out past 100hz.

So in other words, not really a good test of whether or not you can hear 20hz or what type of music have strong 20hz content. If you want to know, it's better to run your music through a spectrum analyzer with the EQ flat.


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## sqshoestring (Jun 19, 2007)

npdang said:


> When you're boosting at 20hz with a parametric eq, chances are you're also boosting up to 40hz or even 60hz depending on the Q of your filter.
> 
> You're also discounting non-linear distortion from the sub. Almost all subs playing at 20hz have significant levels of higher order distortion products even out past 100hz.
> 
> So in other words, not really a good test of whether or not you can hear 20hz or what type of music have strong 20hz content. If you want to know, it's better to run your music through a spectrum analyzer with the EQ flat.


I was doing that with a Pioneer 880 HU. It normally is around +3db at 20Hz, 31 is level, 50 is -3db. 80 is +3db due to weak midbass and the rest is mostly 0db. I have HU LP at 50Hz and amp LP at 45, using both. I don't hear much distortion playing tones, but sure it might have some. By ear I can't hear subs play tones above 60Hz, 50 and 20 are about the same volume and 30-35 are only slightly stronger. Seems to have a slight slope down from 35 to 60, all by ear though. I used to have a parametric on it that worked well, but it also had capability to LP at 30 or 35, which is where I ran it. This HU is not low enough at 50, even running the amp on top of it at just under 50 (low as it goes) is just enough to quell the natural tendency of IB to blast ~50Hz and up. Subs are infinity 1252s that seem to model pretty low when IB, and are even recommended for IB use.


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## npdang (Jul 29, 2005)

sqshoestring said:


> I was doing that with a Pioneer 880 HU. It normally is around +3db at 20Hz, 31 is level, 50 is -3db. 80 is +3db due to weak midbass and the rest is mostly 0db. I have HU LP at 50Hz and amp LP at 45, using both. I don't hear much distortion playing tones, but sure it might have some. By ear I can't hear subs play tones above 60Hz, 50 and 20 are about the same volume and 30-35 are only slightly stronger. Seems to have a slight slope down from 35 to 60, all by ear though. I used to have a parametric on it that worked well, but it also had capability to LP at 30 or 35, which is where I ran it. This HU is not low enough at 50, even running the amp on top of it at just under 50 (low as it goes) is just enough to quell the natural tendency of IB to blast ~50Hz and up. Subs are infinity 1252s that seem to model pretty low when IB, and are even recommended for IB use.


It's probably safe to say that a significant amount of what you're hearing is distortion (>20%) but perhaps you are not recognizing it as such. It's usually not obvious "breakup" that most people would consider to be "distortion" until you reach closer to 100%.

Distortion, if you're not trained and setup to listen to it can be very subtle, especially in the lowest audible octave.


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