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Discussion Starter #1
TLDR: Can a high Q sub stage be EQ'd down to restore good transient response?

Ok... It is my understanding that a high Q Sub stage will suffer in it's transient response. If i'm mistaken, I'm confident someone with let me know! :) Assuming this is true, can the High Q be EQ'd down and transients restored?

Why I am asking: I am planning out my IB sub build and am looking at either using 2x FI IB3v2 12 OR 2x the 15" in the trunk of a 07 Mustang GT Convertible (yes, there is air pass-through with top up or down AND I am open to hearing about other subs if they are better than the FI IB3). I will be using a Focal FPD 900.1, which I already own.

In WinIsd, when I use a "box size" of 14 cu ft, based on the cu ft stated in the manual, the 2x 12's model an almost perfect 707 alignment. When I model the IB3 15's it is more like .90 QTC. Of course, I would love to have the extra output of the 15's but I don't want my sub stage to suck and miss out on one of the benefits of going IB, amazing transient response.

Can a high Q sub stage be EQ'd down to restore good transient response?
 

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A Qtc of .9 isn't so grossly high that it can't be tamed. However, what's more important is the acoustics of the vehicle and what it will contribute to the response. What you don't want is a response that is off from the target to the point that you're taxing the EQ just to correct response shortcomings.

Man & Machine... Power Extreme!
 

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Discussion Starter #3
Thanks man! I guess I will go with the increased cone area. Even though hip hop is my favorite music, I’m not a basshead but who doesn’t like showing off every once in a while?!? LOL! More cone area!

Regarding the interior... Since I have a soft top (or no top), I’m not gonna get the same amount of bump from transfer function


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QTC=.9 is rather fun and enjoyable to listen to IB

So I’m not sure what your understanding of transient response is.

Modeling a 14cuft enclosure in winisd will model a 14cu ft enclosure. I would try modeling a 1000 cu ft enclosure and ignore the vas T/S parameter as means of a box size as that’s just metric that tells you how compliant the mechanics are compared to the stiffness of an air volume. All it’s saying is “this is how stiff the compliance is equal to”. It dosent mean if the box is bigger than this it won’t remove compliance.

It’s funny I just today ordered DATSv3 and this same thing is what one thing I’ll be measureing when I do IB builds.

I would try modeling it in a 1000cu ft enclosure and go down from there. You won’t be able to determine the actual Q without being able to measure the air resistance against the diaphragm with the trunk shut. (If it’s a atmospheric IB than use 1000cuft) you can use rew and measure the driver in open air in a baffle using your amp and source and than put in car and measure and compare the responce and get an idea what the system Q is that way but it’s not precise.

You won’t go lower than QTS, period. But the trunk will raise the Q a tiny bit. If you have a back seat in the way of the IB partition that can further raise the Q from the front side of the cone.

Transient responce is better with a high Q system, and low frequency extension comes with a low Q system. High Q has a peak if higher than your .707 and the higher the system Q the bigger the peak and the steeper the rolloff. Low Q obviously will have an extended responce and create a smooth knee that is depressed down (damped). Low Q will loose transient responce as the compliance is damped acoustically in IB.

That is all motor force and compliance jibberish that beyond that gets too complex for me.

I would estimate a raised Q by closing the trunk with a 15” sub with modest xmax ability. I’m going out on a limb to say maybe a .1 rise is Q ish for the average truck install. Until I have recieved DATS I won’t be able to measure such so that is a guess from experience and my gut feeling.

If your sub QTS is above .6 it should be transient. Just try to keep the system Q below about 1.2 with a fs in the high 20s low 30s would be my recommendation.
And try to make less restrictive between the car IB side than the trunk IB side for a better transfer function.

Hope that helps some
 

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Some say to calculate using a box as large as possible. I always calculate using actual or estimated trunk size and adjust Ql (leakage loss) and it has been more accurate to me in prediction along with measuring the vehicle (so many don't do this). With the other train of thought you could load as many subs you wanted and Q would never rise. You could stuff the trunk with as much junk and the response would not be affected. Ummm yeah. so much for that theory.

On the other hand, the difference in Q between .7-.9 is so little for most subs, but again.... the real culprit to look out for is what the vehicle does to the response. Have EQ? Just get close enough and don't worry about it. Such things mattered much more back when EQ & DSP weren't easily attained by the average consumer.

Man & Machine... Power Extreme!
 

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Some say to calculate using a box as large as possible. I always calculate using actual or estimated trunk size and adjust Ql (leakage loss) and it has been more accurate to me in prediction along with measuring the vehicle (so many don't do this). With the other train of thought you could load as many subs you wanted and Q would never rise. You could stuff the trunk with as much junk and the response would not be affected. Ummm yeah. so much for that theory.

On the other hand, the difference in Q between .7-.9 is so little for most subs, but again.... the real culprit to look out for is what the vehicle does to the response. Have EQ? Just get close enough and don't worry about it. Such things mattered much more back when EQ & DSP weren't easily attained by the average consumer.

Man & Machine... Power Extreme!
I like that, lol. Completely agree, it’s like , if you can feel wind coming out the trunk seal than the trunk does “something “.

It will be nice to actually measure it. I’m going to have to start watching erin tube and get brushed up on my advanced measuring technique. :)
 

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(These are generalizations)
Think of Qts more like the shape of the roll off of the subwoofer and FS as the region of roll off. Higher Q tends to extend deeper and have a sharper roll off whereas lower Q tends to start rolling off sooner but at a shallower rate. VAS is also important. A lower vas tends to need less airspace for a flatter response and a higher vas tends to need more airspace. When you put a speaker into an airspace too small, you increase the Qtc and you notice a hump in response before rolloff. When you put a speaker into an airspace larger than needed, you lower the Qtc and it rolls off a little sooner and extends a little deeper.
When you have an enclosure of optimal size for a speaker (let's say a 0.7 Qtc alignment), as you increase the enclosure size you reduce the amount of "pressure" inside the enclosure and vice versa. This can also increase (for smaller enclosures) or decrease (larger enclosures) the power handling of the driver. There are other considerations of course like heat, power compression, etc.

All that said, for infinite baffle drivers we typically like to see: Enough cone area, lower FS, higher Qts (Though not critical) and plenty of xmax. This means our driver will extend deep and have enough cone area and xmax to play the lowest frequencies with enough output. You will also get cabin gain which will reinforce the output of the low end- another reason why Qts is not critical (and EQ helps to compensate for some early roll off).

Also, please keep in mind that all vehicles have interior vents, typically located in the trunk/wheel well area on both sides which are for providing a means of pressure release when doors close in the cabin. So when you are thinking about the volume of the trunk as an enclosure, it is not sealed and unless you have some serious cone area, you can probably just model it like an unlimited airspace.
 

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The Q of the sub(s) and Q of the system are two different things. High Q sub is usually good for IB, and it boosts at the Fs of the sub in the car, the high Q (like .7) means higher peak output at Fs. If you are above Vas a ways you will get close to spec, if you have a small trunk you start to push Fs up higher. This means high Q sub at 20hz is great and gets low, but high Q at 40hz will boom a lot. Or if you have a tiny trunk that high Q at 20 hz is not going to be at 20hz anymore. You can EQ this I'd recommend a PEQ for best results. If you build it with a sub tuned better you wont have to tune it with EQ as much. When you look at subs generally the larger the sub the lower the Fs but of course the Vas is larger or Q is smaller. A smaller Q say .4-5 range can work better in a small trunk (or more cone area and/or less space build) just like they work better in a small box, but most cars you don't have to go there. That is when a simple model can show you what you are going to get. If you really want the extra bump of 15s I would go with them unless the model is terrible looking. You can EQ 3db, more than that gets harder. You still need the cone area or xmax to move the air you need for the output you want. So if you want a ton of output you use large high xmax subs as many as you can fit and more power, and just EQ them. Its not the most ideal but same thing as using a small box high power sub. I used to figure loosely double the sub IB to beat a ported box, more cone area or xmax is where its at with IB and large subs have lower Fs they are naturally tuned lower. I built a quad 12s IB with Fz 40 and it sounded terrible to me. Finally got a PEQ on it and I could make it sound any way I liked, it was great. However it was so heavy I could feel it driving. I swapped to pair of 15s and tuning was way better higher .7 Q and fs 20 with those. Hardly EQ them at all and much lighter setup in car. Output is slightly less but its basically more than I needed anyway and hits the 20hz range no problem, I even turned the SS filter off as I only had 500rms on them.
 

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(These are generalizations)
Think of Qts more like the shape of the roll off of the subwoofer and FS as the region of roll off. Higher Q tends to extend deeper and have a sharper roll off whereas lower Q tends to start rolling off sooner but at a shallower rate. VAS is also important. A lower vas tends to need less airspace for a flatter response and a higher vas tends to need more airspace. When you put a speaker into an airspace too small, you increase the Qtc and you notice a hump in response before rolloff. When you put a speaker into an airspace larger than needed, you lower the Qtc and it rolls off a little sooner and extends a little deeper.
When you have an enclosure of optimal size for a speaker (let's say a 0.7 Qtc alignment), as you increase the enclosure size you reduce the amount of "pressure" inside the enclosure and vice versa. This can also increase (for smaller enclosures) or decrease (larger enclosures) the power handling of the driver. There are other considerations of course like heat, power compression, etc.

All that said, for infinite baffle drivers we typically like to see: Enough cone area, lower FS, higher Qts (Though not critical) and plenty of xmax. This means our driver will extend deep and have enough cone area and xmax to play the lowest frequencies with enough output. You will also get cabin gain which will reinforce the output of the low end- another reason why Qts is not critical (and EQ helps to compensate for some early roll off).

Also, please keep in mind that all vehicles have interior vents, typically located in the trunk/wheel well area on both sides which are for providing a means of pressure release when doors close in the cabin. So when you are thinking about the volume of the trunk as an enclosure, it is not sealed and unless you have some serious cone area, you can probably just model it like an unlimited airspace.
I think winisd max is 1000cuft
That’s why I said 1000 (maybe it’s just my version of winisd idk)
I think we’re in complete agreement otherwise.
 
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