# High or Low QMS, Which Is Better For Infinite Baffle?



## SmoothSQ (Sep 28, 2010)

I'm trying to decide between two pairs of 12" subs to use in an infinite baffle application. The main difference that sticks out to me between the two subs is the Qms spec. The Fi Car Audio sub has a Qms of 4.00 and the Infinity DVQ has a Qms of 10.52 .
Most IB subs that I see have a high Qms -- is that necessary?
Would a high or low Qms be advantageous for my application?

Here are the sub's specs:

*Fi IB312

Fs: 23.6hz
Re: 2.8 ohms
Qms: 4.00
Qes: .64
Qts: .55
Mms: 214g
Sd: 480cm^2
Vas: 83.4L
Spl: 83.4dB
Bl: 11.8
Xmax: 30mm
Rms: 550w @ 20hz*

*Infinity Perfect12d VQ

Fs: 22.01hz
Re: 1.66 ohms
Qms: 10.52
Qes: .64
Qts: .60
Mms: 189.8g
Sd: 491cm^2
Vas: 94.28L
Spl: 84dB
Bl: 8.28
Xmax: 16.75mm
Rms: 400w*

Please tell me which you think would be best to use for IB.
They both would probably do fine IB, but would the difference in Qms make a noticeable or significant difference?
Please help me out here. Thanx


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## FLAstrongman (Sep 22, 2010)

A high Qts is what you want to look for when choosing an IB sub. Ideally over .8 is what you want.


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## SmoothSQ (Sep 28, 2010)

FLAstrongman said:


> A high Qts is what you want to look for when choosing an IB sub. Ideally over .8 is what you want.


Neither one of them have a Qts that high though. What about the Qms?
Which sub do you think would perform best IB?


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## [email protected] (Jun 12, 2008)

I dont run IB but I think its a combination of FS and QTS. I would run the FI sub as it has way more excursion.


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## IBcivic (Jan 6, 2009)

you may want to look at acoustic elegance IB12's , also


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## FLAstrongman (Sep 22, 2010)

I would also go with the Fi. You'll notice it has a much higher Qts then any other sub in Fi's line up.


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## Knobby Digital (Aug 17, 2008)

Qms itself doesn't matter, just total Q (Qts).

.4-.6 or so would be ideal for a trunk IB.


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## SmoothSQ (Sep 28, 2010)

amitaF said:


> you may want to look at acoustic elegance IB12's , also


I looked there first. All I saw was a 15" version. I don't have enough clearance for that.


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## SmoothSQ (Sep 28, 2010)

duplicate post


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## IBcivic (Jan 6, 2009)

AE makes IB10-12-15...read their forum

i personally have 3 x IB12's behind my rear seat


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## SmoothSQ (Sep 28, 2010)

Well, if the Qms spec doesn't really carry any weight, I guess the best choice would be the Fi sub, because of the displacement advantage.

I'm curious though...Why do so many IB subs have a high Qms?
That's really the reason why I was unsure about the Fi sub, because it's Qms spec wasn't like any of the other subs, and I thought that would cause a noticeable performance difference.


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## Knobby Digital (Aug 17, 2008)

SmoothSQ said:


> Well, if the Qms spec doesn't really carry any weight, I guess the best choice would be the Fi sub, because of the displacement advantage.
> 
> I'm curious though...Why do so many IB subs have a high Qms?
> That's really the reason why I was unsure about the Fi sub, because it's Qms spec wasn't like any of the other subs, and I thought that would cause a noticeable performance difference.


Stiff suspension for cone control.


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## Cruzer (Jul 16, 2010)

sorry, how do u model IB in winisd? i wanted to see the AE vs the FI


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## IBcivic (Jan 6, 2009)

multiply the driver's v.a.s by 10


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## SmoothSQ (Sep 28, 2010)

Knobby Digital said:


> Stiff suspension for cone control.


So high Qms = more cone control?
Wouldn't that be a good thing IB since there won't be any air spring like there would be in a sealed box?

Sorry about all the questions. I'm just trying to understand completely before I make my purchase.


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## Knobby Digital (Aug 17, 2008)

SmoothSQ said:


> So high Qms = more cone control?
> Wouldn't that be a good thing IB since there won't be any air spring like there would be in a sealed box?
> 
> Sorry about all the questions. I'm just trying to understand completely before I make my purchase.


Sure, but it has to be balanced with the motor strength/force, which is how you get total Q.

You could have 2 woofers, one with a _weak_ motor and a complaint suspension and another with the opposite and both may have the same Qts.


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## SmoothSQ (Sep 28, 2010)

amitaF said:


> AE makes IB10-12-15...read their forumt


I was talking about their store. All they have listed in-stock is the 15" model.
I was going to try an Av15-X, but for the last few months, they kept pushing the in-stock date back by another month, and I got tired of waiting.

I don't even see an estimated date for an IB12.


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## SSexpo03 (Jul 30, 2010)

Use the Fi or AE and sell me the Infinity!


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## IBcivic (Jan 6, 2009)

SmoothSQ said:


> I was talking about their store. All they have listed in-stock is the 15" model.
> I was going to try an Av15-X, but for the last few months, they kept pushing the in-stock date back by another month, and I got tired of waiting.
> 
> I don't even see an estimated date for an IB12.


they are probably are still made to order.


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## SmoothSQ (Sep 28, 2010)

Thanks guys. I'll weigh everything out and make a decision.
I really do appreciate the speedy responses.


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## sqshoestring (Jun 19, 2007)

Look at the Fs and Qts. The Fs will tell you how low roughly it likes to play, 20Hz is ideal but you will not get that with a smaller sub. Qts tells you how 'happy' the sub is to play down to Fs. So if it has a high qts of .7 it will play a lot at 20-40Hz roughly and give you a flat response in a car. If it had a low qts of say .3 then it would roll off down there and you would get less bottom, would have to EQ up maybe under 40Hz to get it flat. With no EQ it would sound strong from maybe 40Hz on up. Its because it is damped, while the high qts is not damped and plays a lot more close to Fs. On the other hand the damped driver does not care much about a box and the un-damped driver does. That is why an IB driver will lose its bass in a small box and a low qts driver will not so much. It helps to get winISD and model each type to see what they do. Not always true, but as a general rule low qts is a tiny box sub and high is IB sub...in the middle is versatile and vented subs. Qts .5 tends to be middle ground.

Model IB in the volume of your trunk plus a little for leaks/flexing. Usually over Vas it will work ok, 10x Vas is for home setups. With a model you can vary the volume and see where the rolloff stops changing often around Vas size, then going larger nets you little change. If you get a ton of cone area in a small trunk however you can start to lose bass because the 'box' is too small, and a slightly lower qts like .4-.5 might actually work better than .7. With a 15", you can often use say a .5 qts because a 15 is so large and so low an Fs it makes a lot of low bass naturally, so high qts is not as important with large (15 and more) drivers. Low Fs still is, it tends to be where the driver stops you would have to lay power on and EQ to push beyond it.

Those two drivers are pretty similar in Fs and Qts, and tuned pretty nicely for a car IB. The one with more xmax will likely have more maximum output, can reach lower with more output because getting low burns xmax very fast. If you want loud with IB you start running a SS filter to cut the bottom off, or run more cone area/xmax. You will find some home theater stuff that has the lowest Fs and highest qts, but you really don't need it in a car. The AE IB15 is pretty flat in most cars and is a good reference for the ideal specs for IB use. If you use some other driver, note that it will only handle about half its box rated power when used IB or it will xmax on low bass. If you prefer more of an SPL sound, strong around 50Hz, then you might like a mild qts around .4-.5 better than .7. You might like a Fs higher than 20. Sometimes that is why people like 10s better than 12s or 15s. Me I like 20Hz a lot or close as I can get to it. But a good IB sub will be somewhat flat so you can EQ it the way you like easily. Of course your cabin gain is going to change the response.

I ran quad infinity 1252w 12s, they are Fs 24 and Qts .46. They did jsut what you would figure, they got low but tended to be stronger 40Hz and above. I had to kill 50Hz on the EQ and use two 50Hz LP filters to get them flat, and boost 20 and 30Hz a little. Then they had lots of bottom they would really move the air on only 420rms, and were rated at 150rms each for IB double that in a box. I imagine two of them would not shake the car like quads, good idea to go with more xmax if you want it to pump hard. Now I'm running pyle 15s with Fs20 and Qts .7, they are not as capable as better subs but a pair of them is doing well so far for what I need. Lower xmax subs can work well, until you need more xmax lol. A pair of expensive IB 15s can start to break parts of your car.


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## SmoothSQ (Sep 28, 2010)

sqshoestring said:


> Look at the Fs and Qts. The Fs will tell you how low roughly it likes to play, 20Hz is ideal but you will not get that with a smaller sub. Qts tells you how 'happy' the sub is to play down to Fs. So if it has a high qts of .7 it will play a lot at 20-40Hz roughly and give you a flat response in a car. If it had a low qts of say .3 then it would roll off down there and you would get less bottom, would have to EQ up maybe under 40Hz to get it flat. With no EQ it would sound strong from maybe 40Hz on up. Its because it is damped, while the high qts is not damped and plays a lot more close to Fs. On the other hand the damped driver does not care much about a box and the un-damped driver does. That is why an IB driver will lose its bass in a small box and a low qts driver will not so much. It helps to get winISD and model each type to see what they do. Not always true, but as a general rule low qts is a tiny box sub and high is IB sub...in the middle is versatile and vented subs. Qts .5 tends to be middle ground.
> 
> Model IB in the volume of your trunk plus a little for leaks/flexing. Usually over Vas it will work ok, 10x Vas is for home setups. With a model you can vary the volume and see where the rolloff stops changing often around Vas size, then going larger nets you little change. If you get a ton of cone area in a small trunk however you can start to lose bass because the 'box' is too small, and a slightly lower qts like .4-.5 might actually work better than .7. With a 15", you can often use say a .5 qts because a 15 is so large and so low an Fs it makes a lot of low bass naturally, so high qts is not as important with large (15 and more) drivers. Low Fs still is, it tends to be where the driver stops you would have to lay power on and EQ to push beyond it.
> 
> ...


That was very informative. Thanx a lot man.


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## SmoothSQ (Sep 28, 2010)

amitaF said:


> you may want to look at acoustic elegance IB12's , also


I'm really interested in their IB12A. Even though the specs don't look even remotely similar to any IB sub specs that I've seen before, I'd like to have that super-low inductance.

The problem is, AE's customer support has been quite disappointing.
I've called many times inquiring about possible modifications to subs and technical questions, and I've only once been able to speak with John. When I can't speak with John, which is 99% of the time, the lady answering the phone tells me to email him. According to her, that is the best way to reach him -- but he doesn't reply.
I was going to place an order for a pair of his IB12A subs tomorrow, but I don't know now. I'll just wait until he replies. If he doesn't reply, I'll just pass on buying his subs. It really makes me wonder what I'd have to go through if I made a purchase and then later needed some warranty work on my subs.
I'd really like to give his products a shot, in spite of the poor customer (potential customer)support, but it's up to him.


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## hottcakes (Jul 14, 2010)

that was a most informative post. confirmed quite a bit on what i was thinking about the whole IB setup.


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## Knobby Digital (Aug 17, 2008)

sqshoestring said:


> If you prefer more of an SPL sound, strong around 50Hz, then you might like a mild qts around .4-.5 better than .7. You might like a Fs higher than 20. Sometimes that is why people like 10s better than 12s or 15s. Me I like 20Hz a lot or close as I can get to it. But a good IB sub will be somewhat flat so you can EQ it the way you like easily. Of course your cabin gain is going to change the response.


I don't quite follow. Maybe something's lost in translation. 

.7 may have the lowest f3, but the low-low comes from a lower Q alignment. That's why IB is so efficient on the bottom. Because we're not raising the Q by putting the driver in an enclosurre. BCAE has a nice li'l section with a graph and all that.

*




Qtc is the total Q of the speaker in an enclosurre including all system resistances. A Qtc of .707 is the most common and generally produces the flattest frequency response with approximately a 6dB/octave rolloff. Higher values of Qtc will give a peak in the output with a sharper rolloff. A lower Qtc will start to roll off earlier and will roll off at a slower rate. If you don't know what Qtc you need, start with a Qtc of .707.

Violet = Qtc: 0.9; Green = Qtc: 0.8; Red = Qtc: 0.7; Yellow = Qtc: 0.6; Cyan = Qtc: 0.5;










Click to expand...

*


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## sqshoestring (Jun 19, 2007)

What the high qts affects all depends on the Fs. If you have a Fs of 50 then above 50 will be boosted and under will lose, that is why good IB subs have Fs of 20 then everything above 20 is boosted by a high qts and you don't really go under Fs. If you don't want 30Hz, then get a sub with Fs around that and high qts will only boost above 30. Sure low qts has a slower roll off, and less output until you get really low, but even there they are inefficient so they have to handle a lot of power to make them work down there. You can run lower qts that has a roll off and it will naturally give you a weaker bottom, that will give you a more SPL type sound with no EQ.

Higher qts essentially acts like putting the sub in a box, without the box. Low Q subs are made to have a smaller box to push their lower Q up to normal levels. Since some can handle so much power and have big xmax you can force them to play under Fs which subs tend to not like and people rarely tried to do back in the day of small amps, weak EQ power, and high Q subs.

Qts is boost above Fs, it is tuning, you can force a sub to play anything until it hits xmax no matter the tuning if you Eq it and lay power to it....but it will be harder to tune unless you have a good EQ and it will require a larger amp. So you can tune them by buying the sub with better response IB, or if the sub is HD enough you can force it to play what you want and screw the tuning (then you look at xmax and power handling more).

Really the only time you want a low Q sub for IB, is when you want to play it below Fs....because you are using a sub that is too small to handle that frequency. It can work with huge xmax and more power and EQ. Meanwhile someone else tosses an AE15 IB in the back and it sounds great on low power without much EQ.

*
It is best to model them I only look at Fs/qts to decide if I will bother modeling them for a particular use.*


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## hottcakes (Jul 14, 2010)

any of that relevant to mounting mids in doors? adequately sealed of course. not trying to thread-jack, a short, simple and sweet answer'll do.


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## RMF419 (Feb 13, 2008)

Thanks sqshoe that was very informational, I am looking to go IB also. Trying to figure what subs to use. I only have room for 2 10's, unless I move my amp rack.


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## RMF419 (Feb 13, 2008)

What do you think of these specs for an IB setup. Is the xmax killing it.
Power handling: 150 watts RMS/300 watts max 
VCdia: 1-1/2" 
Le: 1.24 mH 
Impedance: 4 ohms 
Re: 2.65 ohms 
Frequency response: 27-1,000 Hz 
Fs: 27 Hz 
SPL: 86.5 dB 1W/1m 
Vas: 3.15 cu. ft. 
Qms: 9.83 *Qes: 0.65 
Qts: 0.61 
Xmax: 6.0 mm 
Dimensions: Overall diameter 10", Cutout diameter 9", Depth 4-1/2"


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## SmoothSQ (Sep 28, 2010)

sqshoestring said:


> What the high qts affects all depends on the Fs. If you have a Fs of 50 then above 50 will be boosted and under will lose, that is why good IB subs have Fs of 20 then everything above 20 is boosted by a high qts and you don't really go under Fs. If you don't want 30Hz, then get a sub with Fs around that and high qts will only boost above 30. Sure low qts has a slower roll off, and less output until you get really low, but even there they are inefficient so they have to handle a lot of power to make them work down there. You can run lower qts that has a roll off and it will naturally give you a weaker bottom, that will give you a more SPL type sound with no EQ.
> 
> Higher qts essentially acts like putting the sub in a box, without the box. Low Q subs are made to have a smaller box to push their lower Q up to normal levels. Since some can handle so much power and have big xmax you can force them to play under Fs which subs tend to not like and people rarely tried to do back in the day of small amps, weak EQ power, and high Q subs.
> 
> ...


In my experience, subs with a Q in the mid-30s had more output at and above 55hz -- and subs with a Q in the high-40s and up had more output below 55hz. Maybe that has something to do with why many lower Q subs have a higher efficiency rating than high Q subs.

Since the output increased as frequency increased, and in-car, there is usually more boost as the frequency decreases, the lower-Q subs have always sounded a lot closer to being flat without EQ, than the higher-Q subs have.
In my car, higher-Q subs have always sounded bottom-heavy.

Btw, when I modeled two of the Acoustic Elegance IB12A subs, along with a pair of each of the higher-Q subs that I mentioned in my first post, WinISD showed the AE IB12A (.35 qts) completely owning the other subs throughout the entire bass frequency range. That 5 decibel efficiency advantage really makes a difference.
That super low inductance would be nice for IB too.


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