# Why QTC of .707?



## GavGT (Sep 5, 2011)

Hi guys, after a few subjective opinions on sub box building.

I'm about to build a sealed enclosure for a pair of 10" Diamond M3101.8's. They will be wired in series at the sub, and parallel at the amp/box terminal so the amp will feed 360 rms @ 4 ohms to them. Not a huge lump of power but they are only rated around 175 each anyway.

The goal is SQ with ok output, and have looked up the specs for enclosures. A .55cb each box gives me a qtc of .674. A .8cb box lowers this to .588 and would allow a decent output for lower power applications like mine. 

I'm ok with building a smaller box but worried it will sound a bit too "peaky". Why do people aim for a qtc of .707? And would it be worth me modelling a box to aim for that ignoring the manufacturers specs? I currently have just one of the subs in a .98cb box on about 500rms and it sounds great, drops quite low, but does max out quite easily.

Any help/comments appreciated as i'm finding it difficult finding a definative answer for the .707 qtc thing.

Cheers

Gav


----------



## strakele (Mar 2, 2009)

Basically, it's considered to be the best compromise between low frequency extension, transient response, box size, power handling, output, and flat response curve.

Click this link and scroll to the table that's about halfway down:
Enclosure Dilemma


----------



## 14642 (May 19, 2008)

^^ This is correct.

From your original post, it appears that you may be worried that a larger box will allow your woofer to "max out" more easily. The difference between .588 and .7 is really no big deal. Once you put the box in the car and apply a low pass filter, you won't hear the difference.


----------



## zoomer (Aug 2, 2009)

to be more technicallly correct, qtc=707 is what is considered critical dampening. This means that the cone will return to center in the least time without overshoot. 
If you make the box smaller then the air spring is bigger and the cone will resonate more. If you make the box bigger, the spring is less and the cone will take longer to return to center.


----------



## FG79 (Jun 30, 2008)

Sometimes a lower Q can be ok, because the box will sound tighter and you can crank the gains up a little more. 

I really think for good SQ in a car that can play loud, low, punch, and be smooth you need a few subs minimum, with Q .5 - .7, or larger low tuned vented enclosures.

Two is a minimum.....four is very nice. 

High Q subs just don't sound right IMHO.


----------



## pionkej (Feb 29, 2008)

zoomer said:


> to be more technicallly correct, qtc=707 is what is considered critical dampening. This means that the cone will return to center in the least time without overshoot.
> If you make the box smaller then the air spring is bigger and the cone will resonate more. If you make the box bigger, the spring is less and the cone will take longer to return to center.


And this information is all wrong...not "more technically correct." 0.500 is critically damped. See the link from Strakele for the rest.

Also, your explanation is all mixed up. 
--If you make the box smaller, than the "air spring" is bigger and will: roll-off later, peak more more before steeply rolling off, AND take longer to return to center (make it too small and you get "boomyness" and poor transient response). 
--If you make the box bigger, than the "air spring" is smaller and will: roll-off earlier, smoothly extend as it is rolling off, AND return to center more quickly (larger enclosures sound more "smooth" with good transient response--but lose power handling).

To the OP, there is nothing wrong with lower Qtc and some people actually prefer it (myself included).


----------



## GavGT (Sep 5, 2011)

Awesome, thanks for the replies!

I always understood the differences in the sound between a large or small enclosure, as i used to play around with pre-built stuff we had lying around, but now i understand the science of it a little better.

I think i'm going to go for around the .55 cubes per sub or a little over, this will leave me a little more room in the boot for amp racks, and i don't have to have them pushed right up agains the ski hatch they will be firing through.

Thank again


----------



## pionkej (Feb 29, 2008)

FG79 said:


> Sometimes a lower Q can be ok, because the box will sound tighter and *you can crank the gains up a little more*.
> 
> I really think for good SQ in a car that can play loud, low, punch, and be smooth you need a few subs minimum, with Q .5 - .7, or larger low tuned vented enclosures.
> 
> ...


I don't see how this is possible. If a box is larger, Q goes down, as Q goes down, so does power-handling (or to be more technically correct, it will exceed Xmax more easily).

That would be like saying IB subs have maximum power handling which is not the case. 

One more important note, putting a sub in too small an enclosure does not increase power handling (you cannot exceed the thermal limit or you will still cook the speaker), it simply makes it more difficult to exceed Xmax (so you basically kill transient response AND efficiency).


----------



## GavGT (Sep 5, 2011)

FG79 said:


> Sometimes a lower Q can be ok, because the box will sound tighter and you can crank the gains up a little more.
> 
> I really think for good SQ in a car that can play loud, low, punch, and be smooth you need a few subs minimum, with Q .5 - .7, or larger low tuned vented enclosures.
> 
> ...


I toyed with the idea of a pair of Phoenix Gold XS14 12's but they like 1.7 cubes each. Shame because i think they would have sounded very nice. 

Thinking about it, i might build the box to .85 cubes each or there abouts, but add something to the inside of the box to cut the volume of air down to .55 per sub. That way i have a little more flexibility if i change to subs that like a little more.

Gav


----------



## estione (Jul 24, 2009)

Gav 

Have you thought about a tri chamber box with the port firing through the ski hatch, i've had some very good reults doing it like that


----------



## GavGT (Sep 5, 2011)

estione said:


> Gav
> 
> Have you thought about a tri chamber box with the port firing through the ski hatch, i've had some very good reults doing it like that


Yeah i had thought about it, and might do again now i have decided which of the 8 subs i have i'm going to use.

I would have to look into it again in more detail, as i'm not 100% sure what results i could get, and how it can help in my application.

Gav


----------



## estione (Jul 24, 2009)

Give Erskine ( E F MAX ) on TA a shout


----------



## zoomer (Aug 2, 2009)

pionkej said:


> And this information is all wrong...not "more technically correct." 0.500 is critically damped. See the link from Strakele for the rest.
> 
> Also, your explanation is all mixed up.
> --If you make the box smaller, than the "air spring" is bigger and will: roll-off later, peak more more before steeply rolling off, AND take longer to return to center (make it too small and you get "boomyness" and poor transient response).
> ...


I will give you the .5 qts.. i should have researched it more. was just from my memory

but imagine a car.. if you put stronger springs, or weaker shocks ( just like a smaller box) the car will bounce or resonante more as you drive over bumps. 
There is more force to overcome the damping. If the spring is week, it takes longer to overcome the resistance or friction of the shocks, thus taking longer to go back to normal . May be we are saygin the same things. different words. 
Yes a smaller box will allow you to play at higher volumes because of less cone excursion. The boomyness you hear is a resonance peak caused by underdamping, in other words, to strong a spring. 

as for transient response, it is a tricky thing. again, think of a car.. give the same shocks, a car with stronger springs will be harder to push down suddenly because you have both the shocks and the spring to overcome. Weaken the spring (large speaker box) and it will be easier to push down. But all this has to work to gether. If the damping is to low it will overshoot more after the force (voice coil current) is removed. So what is good transient responce? Fast rise time? or less overshoot. it is a balance of many factors. 

take any speaker design sofware and reduce the volume, you will get peaked bass response, but more low frequency roll off.


----------



## cvjoint (Mar 10, 2006)

zoomer said:


> I will give you the .5 qts.. i should have researched it more. was just from my memory
> 
> but imagine a car.. if you put stronger springs, or weaker shocks ( just like a smaller box) the car will bounce or resonante more as you drive over bumps.
> There is more force to overcome the damping. If the spring is week, it takes longer to overcome the resistance or friction of the shocks, thus taking longer to go back to normal . May be we are saygin the same things. different words.
> ...


How do you get higher volumes with less excursion?


----------



## pionkej (Feb 29, 2008)

See my comments below.



zoomer said:


> I will give you the .5 qts.. i should have researched it more. was just from my memory
> 
> *Mine was from memory too. *
> 
> ...





cvjoint said:


> How do you get higher volumes with less excursion?


I'm assuming he means "higher volume" from "greater power handling" due to the reduced excursion from too small an enclosure.


----------



## cvjoint (Mar 10, 2006)

pionkej said:


> I'm assuming he means "higher volume" from "greater power handling" due to the reduced excursion from too small an enclosure.


Ok, well start with something very simple and intuitive. To produce sound a speaker membrane must move. To get more output (volume, spl, whatever you want to call it) the diaphragm must move farther, aka more excursion is needed. You cannot get more output out of the same speaker in any other way. 

Proof
Since Zoomer seems to be able to model speakers I recommend the following. Plot the same speaker in two different size sealed boxes. You will note the smaller one has more top end SPL and lower bottom end SPL. At this point you may think smaller sealed boxes give off more output up top from the same excursion. Next, look at the excursion plot. You should see more excursion at the top of the range in the smaller sealed box. The extra output comes from the extra excursion allowed in the small box setting!! You can equalize the two responses and check the excursion plot, they should overlap! For a given output of x db at z frequency you need y excursion. Regardless of the box you will need the same x,z,y inputs. 

So what changes?

The smaller box will have more spring force inhibiting the cone movement for low frequencies a lot, but allowing a tad bit more excursion up top. You need more power for the same amount of y excursion at low frequencies where thermal compression is bound to set in. Power dissipation is also poorer in a smaller box because there is less ambient air to cool the coil. Then you may even stuff it with pollyfill to generate even more heat...

The ideal speaker would have a Q. of .56 in IB and will be used as such. Least power compression, best transient response. You can equalize to taste the frequency response. Sealed boxes are great at saving space in a home, they are more of a necessity than a desire.


----------



## chad (Jun 30, 2005)

The Q of the sub system goes to hell in a car... Experiment. have fun, it's DIY.


----------



## cvjoint (Mar 10, 2006)

chad said:


> The Q of the sub system goes to hell in a car... Experiment. have fun, it's DIY.


Good point Chad. I was talking to Jon W. (the magic bus guy). Aside from a few cases where we seal our mids really well all IB speakers look like crap on the WT, mine and his. I suspect this is the leakage problem, sort of an AP memberane. 

I was thinking it makes more sense to find the impedance peak with the woofer tester and then simpulate your speakers under different box sizes until they align...then read off the Qtc. If yo read off the QTC directly you get bizzare results.


----------



## pionkej (Feb 29, 2008)

cvjoint said:


> Ok, well start with something very simple and intuitive. To produce sound a speaker membrane must move. To get more output (volume, spl, whatever you want to call it) the diaphragm must move farther, aka more excursion is needed. You cannot get more output out of the same speaker in any other way.
> 
> Proof
> Since Zoomer seems to be able to model speakers I recommend the following. Plot the same speaker in two different size sealed boxes. You will note the smaller one has more top end SPL and lower bottom end SPL. At this point you may think smaller sealed boxes give off more output up top from the same excursion. Next, look at the excursion plot. You should see more excursion at the top of the range in the smaller sealed box. The extra output comes from the extra excursion allowed in the small box setting!! You can equalize the two responses and check the excursion plot, they should overlap! For a given output of x db at z frequency you need y excursion. Regardless of the box you will need the same x,z,y inputs.
> ...


It seems you and I are on the same page...and so I assume you didn't read my response to the OP and just the small part where I quoted you.

You are correct.

What I'm referencing is that many people think you get better power handling by slapping a speaker in a smaller box, where in reality you have (from above):



> If the driver is normally "power limited" by excursion, than you are probably right that you can eeek out a bit more output. The problem is that you are getting a bit more output at the cost of extra amp power, extra heat, extra power compression, and poor transient response.


----------



## pionkej (Feb 29, 2008)

cvjoint said:


> Good point Chad. I was talking to Jon W. (the magic bus guy). Aside from a few cases where we seal our mids really well all IB speakers look like crap on the WT, mine and his. I suspect this is the leakage problem, sort of an AP memberane.
> 
> I was thinking it makes more sense to find the impedance peak with the woofer tester and then simpulate your speakers under different box sizes until they align...then read off the Qtc. If yo read off the QTC directly you get bizzare results.


Let me ask (we can move to your older Qtc thread if it's more appropriate), do you think that Q matters at all if you are crossing outside the FS of driver? 

I saw where you wondered if Q matters on things like midrange. I'm inclined to say it doesn't matter for any driver as long as you cross outside of where the impedance spike occurs.

I'm actually planning to try something where I put my sub in a tiny box with a super low tune. It will roll-off like a sealed box (so most would see no benefit), but will cut excursion by 1/3, move group delay super low, and will move the impedance spike UP enough that it's outside the passband.


----------



## cvjoint (Mar 10, 2006)

pionkej said:


> It seems you and I are on the same page...and so I assume you didn't read my response to the OP and just the small part where I quoted you.
> 
> You are correct.
> 
> What I'm referencing is that many people think you get better power handling by slapping a speaker in a smaller box, where in reality you have (from above):


We overlap on nearly every point, here and also in the Dyn. thread. I think our posts complement eachother when it comes to Q. 

I'm just not quite sure about the extra output argument you give every now and then. My position is that you never get more output from a sealed (well sensitivity is higher in the top range, but only by a hair and dwarfed by loss of efficiency down low). Max output is the speaker at Xmech, max excursion. The big difference is the power requirements. If you are in the power compression range at all the IB or large sealed box will have fewer losses to heat and therefore higher output than a small sealed. 


As far as the impedance peak being outside of the band i'm again on the same page. The caveat is that in practice it's really tough to move it outside the band. The peak is one, but it has to be outside of the band in its entirety, the farther the better. There is also a lot of material that goes beyond the xover point. I have been hoping for the peak to be out of the band as well with my line array since the Faitals need a lot of room to breathe. I'm somewhere at 1 QTC with the peak just bellow the crossover point, not ideal but decent. The peak also moves further up the band if you make the box smaller.

The vented box idea is ok, I thought about something similar. The thing is, the tunning is only useful if it reduces excursion reguirements. If you move it bellow 20hz enough to reduce group delay you also increase excursion requirements. There is always a tradeoff between the ill effects of tuning and the reduction in excursion. I prefer to use a lot of surface area and a lot of stroke in simple IB. That way I get great group delay, phase characteristics and low harmonic distortion. The extra box you need for a vented allignment takes the place of a second active driver. With two active drivers you get it all. I look at vented designs as a cost cutting alternative where one driver is more expensive than the more intricate box needed. Vented is also great if you have a big room and no equalizer to shape the response.


----------



## ErinH (Feb 14, 2007)

pionkej said:


> Let me ask (we can move to your older Qtc thread if it's more appropriate), do you think that Q matters at all if you are crossing outside the FS of driver?
> 
> I saw where you wondered if Q matters on things like midrange. I'm inclined to say it doesn't matter for any driver as long as you cross outside of where the impedance spike occurs.
> 
> I'm actually planning to try something where I put my sub in a tiny box with a super low tune. It will roll-off like a sealed box (so most would see no benefit), but will cut excursion by 1/3, move group delay super low, and will move the impedance spike UP enough that it's outside the passband.


Agreed on the Q being outside the passband. Problem is most sub setups put the Q in the passband. 

The last sentence sounds like a linkwitz transform.


----------



## cvjoint (Mar 10, 2006)

Here are some measurements of my Faital first in IB, where QTC = QTS, then in the pillar pod which is a bit small:



















Here is where me and Erin disagree. He would say the QTC is what WT gives me, .99. I say I'm going to eyeball the FS, I'm thinking it's 165hz. I plot my Faitals in WinISD and change box size until I get an FS of 165, that gives me a QTS of .873. If you want to take the WT results religiously you can't really get an FS of 156 and a Q of .99. Something is wrong, and I think it's because WT gets confused when speaker boxes have any leaks at all. Eyeballing the FS and simulating it to find the Q makes more sense to me.

Anywho, I high pass at 200hz with a 24db slope. The increase in group delay from .56 ideal Q to either .87 or .99 is about .5 to .75 ms. It's not bad and hopefully inaudible.


----------



## Patrick Bateman (Sep 11, 2006)

GavGT said:


> Hi guys, after a few subjective opinions on sub box building.
> 
> I'm about to build a sealed enclosure for a pair of 10" Diamond M3101.8's. They will be wired in series at the sub, and parallel at the amp/box terminal so the amp will feed 360 rms @ 4 ohms to them. Not a huge lump of power but they are only rated around 175 each anyway.
> 
> ...


Listen to what Chad said.
Qts goes to hell in a car. This is due to cabin gain. You simply can't look at QTS without factoring in cabin gain.

A speaker with absolutely perfect frequency and transient response will go to hell when you put it in a car.

Long story short - don't worry about it. If you have some time to burn, use a simulator and figure out how to come up with a response that uses cabin gain to 'flatten' the response.


----------



## pionkej (Feb 29, 2008)

cvjoint said:


> I'm just not quite sure about the extra output argument you give every now and then. My position is that you never get more output from a sealed (well sensitivity is higher in the top range, but only by a hair and dwarfed by loss of efficiency down low). Max output is the speaker at Xmech, max excursion. The big difference is the power requirements. If you are in the power compression range at all the IB or large sealed box will have fewer losses to heat and therefore higher output than a small sealed.


I actually think you and I are saying the same thing in a different manner. I think there are rarely any positives to putting a speaker in a box too small and it seems you agree. What I'm referencing when I say that is that people mistakenly think you can get more output from a sealed speaker in too small a box...and it's because Xmax is restricted. Since they have lowered Xmax, they can now put more power to a speaker and get MORE output!!!  The problem is what you have referenced, the small amount of extra output you get is really only at the box's peak and you get it at the "small" price of: super steep roll-off after the peak, thermal compression, and terrible transient response.



bikinpunk said:


> Agreed on the Q being outside the passband. Problem is most sub setups put the Q in the passband.
> 
> The last sentence sounds like a linkwitz transform.


I agree that it is rare this can work out. In my case, it's about my only good option. Since I'm running efficient midbass speakers (JBL 660GTi) and only have 500w for the sub (JL 900/5), I needed an efficient sub(s) to match. Since the build I'm referencing is going in the "family" SUV, I had a few restrictions: spare had to stay, I couldn't lose any cargo area, and I only had room for a SUPER shallow single 12 above the spare or dual tens flanking it. (and IB was out for obvious reasons). I settled on a pair of JBL 1000GTi's.

Since the FS is high and the Qts was VERY low, I could put them into a small (relative term--1.5cu/ft) enclosure and push the Impedance UP outside the passband and still keep the Q less than .7. The problem was that the low Xmax was still being exceeded...but if I port it... And that is where my plan ended up where it did. The ports will be long, but I have plenty of room in the false floor hatch area.



cvjoint said:


> Here are some measurements of my Faital first in IB, where QTC = QTS, then in the pillar pod which is a bit small:
> 
> 
> 
> ...


You may be right about the "leaky box" issues, but I believe that the difference between 0.99 and 0.87 is minor enough you shouldn't worry much anyways. I've also been looking into group delay a bit, and from what I understand, crossovers also play a part in group delay. Enough so that when I simulate all my drivers in winISD and then plot group delay, group delay goes up as frequency goes down BUT it also nearly perfectly matches from driver to driver thanks to the crossovers. The advantage to this is that while there is delay, there isn't delay differences between the speakers in the system.



Patrick Bateman said:


> Listen to what Chad said.
> Qts goes to hell in a car. This is due to cabin gain. You simply can't look at QTS without factoring in cabin gain.
> 
> A speaker with absolutely perfect frequency and transient response will go to hell when you put it in a car.
> ...


I may end up being the one who is wrong, but I don't agree with this. Cabin gain does change the speakers frequency response, but that is also only a small part of box design (the frequency response imparted by Q). The fact is that while you can boost or shape response with EQ and/or cabin gain, you can't fix the response characteristics imparted by the box itself (Qtc and where the impedance spike occurs).


----------



## zoomer (Aug 2, 2009)

Thank you cvjoint, pionkej and Patrick for showing me how little I know! Great posts!


----------



## ErinH (Feb 14, 2007)

Guys, check this out:
mh-audio.nl - Home

Probably the most straightforward way I've seen an L-T described.


----------



## cvjoint (Mar 10, 2006)

Patrick Bateman said:


> Listen to what Chad said.
> Qts goes to hell in a car. This is due to cabin gain. You simply can't look at QTS without factoring in cabin gain.
> 
> A speaker with absolutely perfect frequency and transient response will go to hell when you put it in a car.
> ...


Agree with pionkej. It seems to me that you are completely ignoring the time domain effects of a small box. 

Best said by Lycan:

_I'm not saying inductance doesn't matter. I'm just providing an analysis outline we can use to judge it's importance. For good transient behavior, the order-of-importance is :

1. Start with classic T/S analysis ... available in your favorite modeling program You'll learn the Qtc and Fc of your sub-in-enclosure, and the impact to transient response.

2. Figure out where you're going to crossover your sub. Often dictated by localization concerns, and how strong your front midbass drivers are, in a vehicle.

3. THEN compare the inductive low-pass of a candidate sub to the intended crossover, to see if the inductance is low enough to no longer be of concern._

QTC and FC are the primary parameters that describe transient response of a speaker system. I don't doubt the car interior adds to the decay of the speaker but you simply cannot offset the poor transient of a high Q box once it's in the car. The vehicle is not a choice, the box...is! Personally I prefer to reduce ringing and overshoot as much as possible


----------



## hottcakes (Jul 14, 2010)

mr. bateman is also known to have said the following:




Patrick Bateman said:


> If you don't like the QTS of your driver, just change it. I've done it both electrically and mechanically. Check out this thread:
> 
> diyAudio Forums - Tapped Horn for Dummies - Page 1



i thought everyone knew that the whole "Q" thing went to hell once the speaker and enclosure went to hell once placed inside the vehicle because of cabin gain and what-not?


----------



## pionkej (Feb 29, 2008)

hottcakes said:


> i thought everyone knew that the whole "Q" thing went to hell once the speaker and enclosure went to hell once placed inside the vehicle because of cabin gain and what-not?


I haven't spent more than 30 seconds looking at the linked thread, and won't have time to look much more till tomorrow, but everything I saw referenced raising the Q via resistors.

What do you do when you want to lower the Q (like you'd need to do with too small of a box)???


----------



## cvjoint (Mar 10, 2006)

bikinpunk said:


> Guys, check this out:
> mh-audio.nl - Home
> 
> Probably the most straightforward way I've seen an L-T described.


One thing led to another...
Active Filters

I'll be damned, the Linkwitz Transform changes the group delay. I learned something today!


----------



## ErinH (Feb 14, 2007)

Basically, our car is the linkwitz transform.


----------



## BigRed (Aug 12, 2007)

Patrick Bateman said:


> Listen to what Chad said.
> Qts goes to hell in a car. This is due to cabin gain. You simply can't look at QTS without factoring in cabin gain.
> 
> A speaker with absolutely perfect frequency and transient response will go to hell when you put it in a car.
> ...


BINGO!! been my experience anyway


----------



## FG79 (Jun 30, 2008)

pionkej said:


> I don't see how this is possible. If a box is larger, Q goes down, as Q goes down, so does power-handling (or to be more technically correct, it will exceed Xmax more easily).
> 
> That would be like saying IB subs have maximum power handling which is not the case.
> 
> One more important note, putting a sub in too small an enclosure does not increase power handling (you cannot exceed the thermal limit or you will still cook the speaker), it simply makes it more difficult to exceed Xmax (so you basically kill transient response AND efficiency).


Trust me, this power handling issue is overrated and exaggerated. 

If you want your sub to "bump" (hate that term) then put it in a small box and call it a day. It will be peaky but it will POUND, son!

However, if you are looking for a flatter response then once you drop to .7 you're at that level of smooth response. 0.5 is a bit dryer sounding than .7 but not night & day different......turning up the gains a bit can help even it out. For argument's sake if you can make a 0.5 sound about as loud as a 0.7, it's a major win since it will sound tighter and play lower to boot. 

I think my biggest issue I see with some people here is trying to get *1* subwoofer to produce an amazing response that does eveything, like trying to find a 6'8 300 lb offensive lineman that can run the 40 yard dash in 4.4 seconds....lol.

When you move to a multi-sub setup, you can then make up for SPL by using more drivers. 4 subs of any Q will kill a single solo high Q sub, in all facets of sub reproduction.


----------



## GavGT (Sep 5, 2011)

I'd like to thank everyone who has contributed to this thread so far, some excellent information, and has really helped me stop worrying about it too much, and decide on the box i'm going to build. I'm going for about .75 cubes for each 10", maybe with a little filling. This will be the best compromise for me. Not sure what cabin gain will do for me, as its an E34 BMW saloon, and both drivers will be firing out of the ski hatch.

I'm still rubbish with Winisd etc, and don't have the time to try mastering it yet, but i will certainley come back to this thread to re-read and look at links etc

Gav


----------



## The Baron Groog (Mar 15, 2010)

bikinpunk said:


> Agreed on the Q being outside the passband. Problem is most sub setups put the Q in the passband.
> 
> The last sentence sounds like a linkwitz transform.


I've done a "LT" install in my current car, seems to be working well on initial listening/tests. http://www.diymobileaudio.com/forum/diyma-sq-forum-technical-advanced/116923-cabin-gain.html Sub is the Phase Linear Aliante 10", flat piston cone, massive VC and shallow mounting depth. 

I was concerned with over excursion, "old style" low excusrion subwoofer, but seems fine on some fairly bass heavy music-Tipper, Leftfield, DJ Shadow. Few slight issues elsewhere in the install (bad ch on one amp and turn on pop through all-FFS) that need addressing before some tuning and a final conclusion, but have to say pretty chuffed with it all so far!


----------



## quality_sound (Dec 25, 2005)

FG79 said:


> Trust me, this power handling issue is overrated and exaggerated.
> 
> *If you want your sub to "bump" (hate that term) then put it in a small box and call it a day. It will be peaky but it will POUND, son!*
> 
> ...


High gain ported or bandpass would be a _far_ better option than an undersized sealed enclosure.


----------



## cvjoint (Mar 10, 2006)

FG79 said:


> *Trust me, this power handling issue is overrated and exaggerated.
> 
> If you want your sub to "bump" (hate that term) then put it in a small box and call it a day. It will be peaky but it will POUND, son!*


I think we have a classic omitted variable bias story here. It seems to me that the difference in response curves between IB and sealed is often mistaken for SPL. Out of the box (aka no EQ.) the IB will have a flatter frequency response, more lowend sensitivity down low so less power required to reach xmax. The sealed box is peakier. 

However, say someone went through the trouble of making a proper comparison and equalized both the IB and sealed box to have the same frequency response. The IB will have more output simply because it will have less power compression. 

If you think power compression is overrated checkout the Klippel results Erin posts. You'd be surprised at the low wattage levels speakers reach high temperatures. Then imagine some of us have to use them in hot areas. During the summer I can't even hold my pillar mids in my hand. The basket temperatures are easily over 130 F without playing a thing yet. 



bikinpunk said:


> Basically, our car is the linkwitz transform.


Erin can you elaborate on this? Is pre and post EQ. always group delay and Q changing? I can see now on WinISD that adding parametric EQ. changes group delay, that's news to me, but is this always true with post EQ., like cabin gain? The Q also doesn't change in WinISD when I add parametric, is that function simply not built in?

A greater question is whether everything that we come to know as time domain behavior gets captured in group delay. If so, it seems to me that the high pass filter and cabin gain are the biggest contributors by far. Cross your drivers low???


----------



## Patrick Bateman (Sep 11, 2006)

pionkej said:


> I may end up being the one who is wrong, but I don't agree with this. Cabin gain does change the speakers frequency response, but that is also only a small part of box design (the frequency response imparted by Q). The fact is that while you can boost or shape response with EQ and/or cabin gain, you can't fix the response characteristics imparted by the box itself (Qtc and where the impedance spike occurs).


Actually that's exactly what I'm saying 

You CAN fix the response characteristics imparted by the box itself!

That's why I obsess over all kinds of crap that we CAN'T change. For instance, once a sound wave diffracts over a crappy enclosure, that's it. There's no fixing it.

And once your subwoofer runs out of xmax, that's it. You hit your mechanical limits, it's game over.

And once your amplifier runs out of headroom, you guessed it, GAME OVER

That's what's so depressing about the car audio systems from the 80s, they got a lot of this right thirty years ago. Those big infinite baffle subs and high efficiency midranges had a lot going for them. And getting your path lengths right will always yield a better image than using crappy locations and trying to 'fix' it with DSP.

And those guys used lots and lots of EQ, because it fixes a lot of problems once you use it on a soundsystem with a solid foundation.


----------



## pionkej (Feb 29, 2008)

Patrick Bateman said:


> Actually that's exactly what I'm saying
> 
> You CAN fix the response characteristics imparted by the box itself!
> 
> ...


I also agree with this (and I think CV does too). I'm a huge fan of efficiency AND optimizing install. I think that is why my MS8 install has worked so well. I have drivers that match each other and did the best I could (at the time) with minimizing reflections/maximizing pathlengths, so my "tune" isn't working as hard to hit that final "MS8 curve".

I'm still learning too and I'm excited about applying/correcting what I THOUGHT I did right in my first install in the new build in my wife's SUV.

The problem is that I still haven't seen anything other than Aperiodic where you can "fix" a high-Q or impedance spike. You can "boost" the Q with EQ, but not "cut" it.

So if a low(er) Q is critical for good tansient response, and you can always raise it with EQ but can't lower it (that I've seen), shouldn't you aim to start with a low Q and "boost" if needed? Otherwise isn't it like you mentioned with headroom and excursion...GAME OVER?


----------



## cvjoint (Mar 10, 2006)

In WinISD messing around with parametric does increase or decrease the group delay.


----------



## pionkej (Feb 29, 2008)

cvjoint said:


> In WinISD messing around with parametric does increase or decrease the group delay.


True, but I haven't seen where you can "EQ" the impedance. To me that means you can use EQ to mimic a different Q, but you can't reduce the Qtc (damping and impedance) imparted by the enclosure itself.

EDIT: I have read you can do this with a servo, but I'll admit I don't how it works either.


----------



## cvjoint (Mar 10, 2006)

pionkej said:


> True, but I haven't seen where you can "EQ" the impedance. To me that means you can use EQ to mimic a different Q, but you can't reduce the Qtc (damping and impedance) imparted by the enclosure itself.
> 
> EDIT: I have read you can do this with a servo, but I'll admit I don't how it works either.


Well, you might not have to. If the effects of the impedance as picked up by FS and QTS only affect frequency response and group delay it won't matter that you can't change the impedance directly. It seems like the EQ. can adjust both frequency response and delay. EQ. can be digital, passive, or cabin gain. 

If all this is true I'm porting my Scan Illuminator 7". If I Eq. out the gain from the vented design it seems group delay suffers only a little while excursion is ridiculously low.


----------



## 14642 (May 19, 2008)

Guys,
Group delay and transient response are linked to frequency response by the Fourier Transform, but only for a minimum phase system. A single driver in an anechoic environment is a minimum phase system. Flat frequency response IS transient accuracy. The EQ imparted by the car changes what we hear, but it doesn't change the Qtc of the speaker and box. With the EQ, it's no longer minimum phase. 

Bass is so easy. Build your box and EQ it. If you build a TINY box with a Q much greater than 1, you can still EQ it for good performance but you'll have to apply HUGE amounts of cut at the peak and provide HUGE amounts of power to add bass below the peak. 

As suggested here, the LT IS the car's response, but it's not as effective as it might be at home because for cars to sound good, we don't just nee to bring the response back to flat, we need about 9dB of additional bass below 60Hz. That calls for a bunch of additional power.


----------



## vitvit (May 3, 2011)

Andy Wehmeyer said:


> The EQ imparted by the car changes what we hear, but it doesn't change the Qtc of the speaker and box. With the EQ, it's no longer minimum phase.


Andy, could you explain why?

I play with EQ in my car often. If sub region being minimum phase at the beginning (I'm not sitting in null) no change in EQ can make it non-minimum phase. Sure, 70-100Hz and above we are not in Kansas... sorry, not in minimum phase anymore - lot of nulls there.

I do my measurements using REW - it can show "phase", "min phase", "excess phase". As well as Group delay.


----------



## cvjoint (Mar 10, 2006)

I'm also quite interested in minimum phase. With my carputer I had a bunch of FIR and min phase filters that I could use. I imagine those are distortion free filters. Does the MS8 have linear phase filters?

There is some talk on the forums about minimum phase, delay, transient response etc but I can hardly understand any of it. Maybe Andy can break it down for us at my low level. 

Andy can you come to the local So.Cal. meet early in December? 

http://www.diymobileaudio.com/forum/12-volt-events-team-diyma/117560-when-next-so-california-meca-competition.html

I'd like to pick your brains a bit senor.


----------



## 14642 (May 19, 2008)

December 10? Maybe. I'll be back from Indonesia earlier that week. 

I'll see if I can explain the concept of minimum phase and non-minimum phase. Have to do a little reading so I can simplify a bit. 

In any case, bass is the easiest thing to do in a car. Bass to midbass is the hardest thing to do in a car, but the fact that room correction and speaker correction don't have to be done separately makes EQ more effective and easier to implement. The key to success is to focus on the acoustic responses of the speakers, measured in the car, and not to be sidetracked by the rest.


----------



## 14642 (May 19, 2008)

I'm going to try to make the GTG. I think it would be fun. Have to get my head unit to boot up...


----------



## pionkej (Feb 29, 2008)

Andy Wehmeyer said:


> December 10? Maybe. I'll be back from Indonesia earlier that week.
> 
> I'll see if I can explain the concept of minimum phase and non-minimum phase. Have to do a little reading so I can simplify a bit.
> 
> In any case, bass is the easiest thing to do in a car. Bass to midbass is the hardest thing to do in a car, but the fact that room correction and speaker correction don't have to be done separately makes EQ more effective and easier to implement. The key to success is to focus on the acoustic responses of the speakers, measured in the car, and not to be sidetracked by the rest.


+1. I'd love to hear more about this as well. 

I wish I lived out Cali-forn-ee way (Southpark ) to make that meet, as it would be cool to "pick the brain" of one Andy W. 

I'm glad the OP didn't mind the wandering topic here since it seems some good info has/will come of it.


----------



## GavGT (Sep 5, 2011)

Keep it coming! I'm learning something.

I have come up with a design for my box and could do with some opinions, but have started a fabrications thread in the interests of keeping this thread on course.

Thanks again guys


----------



## sqshoestring (Jun 19, 2007)

You guys make it too complex, Q is just the tuning it has. Take a sub in sealed in winISD and drag the box size up and down and you will see the Q change. It is the shape of the curve you see. High Q is a big peak at higher frequency, .7 is near flat, lower is roll off but it does have more output at the lowest frequency because the roll off is more gentle. The sub and box affect it, but still it is just the tuning not a specific FR. So if you model an 8 and a 15, who knows what Q you would want on each to come up with the FR curve you are looking for. All .707 really means is that enclosure will give the flattest response that driver can muster for as low as it can stay flat, so it might be ideal in your living room if that driver covers the frequency you need to cover.

I also recommend you toss a temp sub in your car and EQ it, then add that EQ to the model of it to get in the area you want to be....build a new sub with a curve like that. I also say I can get rid of bass much easier than make what I don't have, so tuning lower than I need is usually ideal for me. Of course that makes a high Q sub a problem for me as it might not want to go under say 40Hz then, and my favorite bass is under 40.

What some people are saying is after all this tuning stuff....some of it really does not matter because you can just EQ it the way you want anyway. You can use a sub that sounds like crap, and EQ it. If you do, then you need a sub that can handle much more power in order to boost the frequencies it does not want to make naturally (from sub and enclosure tuning). When you look at winISD and see it -3db, you will need EQ there, if it drops more you need significant power to bring it up. This is because you need in theory twice the power to make 3dB. It depends on a lot of things what you really get such as cabin gain and all that, but you can see that power does not change dB very much. That is why if you want to use a tiny box with a big roll off on the bottom, it will take way more power and EQ on the bottom to get output back to flat....unless your car has piles of cabin gain there, or you don't care about 30Hz, etc. In the end it needs to play the sound you want to hear.

Lastly, as you come up on 20-30Hz you will need a lot more cone area or xmax to keep the spl up here, just to move the air required to make the sound.


----------



## chad (Jun 30, 2005)

sqshoestring said:


> I also say I can get rid of bass much easier than make what I don't have, so tuning lower than I need is usually ideal for me.


I agree with this, but it goes against the grain of everything car audio since 1995 or so, or at least since they invented the "small box subwoofer."

So much against that I believe it's actually difficult for people to wrap their heads around the concept.


----------



## pionkej (Feb 29, 2008)

chad said:


> I agree with this, but it goes against the grain of everything car audio since 1995 or so, or at least since they invented the "small box subwoofer."
> 
> So much against that I believe it's actually difficult for people to wrap their heads around the concept.


I'd like to note at this point that I have brought up everything Qtc/Transient Response related more out of curiousity for midbass than subs. It just happened this thread moved in the direction it did and still applies to my curiousity.

I'm personally a fan of ported and tuned as low as possible for something only playing 20-80hz or so.


----------



## thehatedguy (May 4, 2007)

Sigh...I thought it was cool back then...but now I miss those old style subs.



chad said:


> since they invented the "small box subwoofer."


----------



## thehatedguy (May 4, 2007)

Agreed on having "too much" and dialing it back than not having enough.

But I am a basshead at heart and there was never too much bass for me. Especially if I could dial it back when I wanted too.


----------



## GavGT (Sep 5, 2011)

thehatedguy said:


> Sigh...I thought it was cool back then...but now I miss those old style subs.


I have a pair of PG XS124's that want at least 1.7 cubes each, wish i had the room to do them justice


----------



## minbari (Mar 3, 2011)

thehatedguy said:


> Sigh...I thought it was cool back then...but now I miss those old style subs.


before they got stolen my blues BL10s needed about 2cuft each ported. they sounded amazing though.


----------



## M-Dub (Nov 29, 2006)

sqshoestring said:


> You guys make it too complex, Q is just the tuning it has. Take a sub in sealed in winISD and drag the box size up and down and you will see the Q change. It is the shape of the curve you see. High Q is a big peak at higher frequency, .7 is near flat, lower is roll off but it does have more output at the lowest frequency because the roll off is more gentle. The sub and box affect it, but still it is just the tuning not a specific FR. So if you model an 8 and a 15, who knows what Q you would want on each to come up with the FR curve you are looking for. All .707 really means is that enclosure will give the flattest response that driver can muster for as low as it can stay flat, so it might be ideal in your living room if that driver covers the frequency you need to cover.


Thank you for that. My head was beginning to spin. I am currently building my first ported sub box, as large as I can fit, tuned as low as I can, as flat as I can.


----------



## sqshoestring (Jun 19, 2007)

thehatedguy said:


> Agreed on having "too much" and dialing it back than not having enough.
> 
> But I am a basshead at heart and there was never too much bass for me. Especially if I could dial it back when I wanted too.


I'm right here on that lol, and yes a lot of installs I can't get what I want so I do my best. In my present case I went overboard because I could fit quad 12s IB, but the tuning was nasty. Then figured out a pair of 15s was similar on the bottom end and was a lot lighter and took less room....yeah a pair of 15s really is more than I need but you have to have them to get under 30Hz with a little spl left. In reality I can boost 20Hz and get some nice SQ range, or let them hammer at 30-35 and they still sound nice and deep. I'm sure AEs are amazing given what these cheap things do. Its awesome to have too much bass in particular under 40Hz, and since I can hardly hear 80Hz+ with them cranked way up that only happens for testing purposes.


----------



## cvjoint (Mar 10, 2006)

Andy Wehmeyer said:


> December 10? Maybe. I'll be back from Indonesia earlier that week.
> 
> I'll see if I can explain the concept of minimum phase and non-minimum phase. Have to do a little reading so I can simplify a bit.
> 
> In any case, bass is the easiest thing to do in a car. Bass to midbass is the hardest thing to do in a car, but the fact that room correction and speaker correction don't have to be done separately makes EQ more effective and easier to implement. The key to success is to focus on the acoustic responses of the speakers, measured in the car, and not to be sidetracked by the rest.


We have a new thread, this time around there is a competition but that's not usually the case at JT's meets, we just sit around showcase our toys. 

http://www.diymobileaudio.com/forum/12-volt-events-team-diyma/117755-so-california-meca-casual-meet-dec-10th.html

Do you mean having separate speaker EQ. is actually worse than L and R eq. only? I was actually quite pissed at not being able to tune each driver separately in the Pioneer P99 headunit. I'm keen on understanding the mechanism, why things work. When it comes down to it I want to understand the tradeoffs and make choices myself. People say all sorts of things on the forums, if you listen to random general guidelines you never really converge on the truth around here.


----------



## chad (Jun 30, 2005)

IMHO phase (not to be confused with polarity) is ONLY dependent between/within pass-bands of a crossover.... For the most part. There is something to be said for absolute polarity but when it comes to merely pressurizing a cabin.. That's not one of those places.


----------



## cvjoint (Mar 10, 2006)

chad said:


> IMHO phase (not to be confused with polarity) is ONLY dependent between/within pass-bands of a crossover.... For the most part. There is something to be said for absolute polarity but when it comes to merely pressurizing a cabin.. That's not one of those places.


I found a super nice article that wraps up lots of the issues with quotes and all:

Phase Distortion article

When I read stuff like this I just want to go back to Seas Excel magnesium drivers and FIR filters.


----------



## BlackFx4InTn (Apr 11, 2009)

I don't plan on running anything sealed in the very near future, but this has been a very informative thread. Subscribed.


----------

