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Discussion Starter #1
This is one I see a lot, a small sealed box offers more cone control than a large sealed box or IB. My opinion is a small box means less cone control and drives down efficiency and this is why over damped subs (.4 Qts and lower) work best in small boxes.

I write this because I read nearly every day that small boxes increase cone control. I think people get confused that limiting excursion and controlling the cone is the same thing when it's not. And also that high Qts subs are usually referred to as having more damping and control when I believe the opposite to be true.

It seems like the old way of thinking that IB "needs" a high Qts sub is starting to go away.

I guess .707 vs .5 critically damped Qtc would be for another thread lol.

Maybe this is another topic but why would you ever limit excursion mechanically with the air spring of a small box, reducing efficiency when you can do it electronically and retain efficiency? This is assuming your install allows a large box or IB. Serious question.

Am I right, wrong, thoughts?
 

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IMO, I don't think it really matters what the qts is. I have always preferred high qts when doing ib for car doors and such(5-8" drivers). I have never done an ib sub install but i've used a set of very low qts 5.25's and those things put out incredible bass, well incredible for 5.25's. They would blur mirrors and give a bit of chest thump. The downside is that they sounded like shit for any kind of midrange. So just based on my experience with that I would say low qts ib subs should do well.

I get your point though. The size of the box doesn't dictate cone movement the amplifier and source unit do that. A small encl will prevent over excursion to a point but while doing so will prob limit eff. (oh you just said that) I think people think that way because you can dump a shit ton of power into a small encl without it distorting. On the other hand you need a shit ton of power because it's a small encl. ;)
 

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It seems like the old way of thinking that IB "needs" a high Qts sub is starting to go away.
Hey Buick-

I just wanted to add I've used a pair of 10"s with qts of .37 in IB and spent a good amount of time listening to a pair of 12"s with a qts of .47 in IB.

As far as the 10"s go, I loved the sq in IB considerably more than when they were sealed in a .6 cu ft per driver box. The low end extension was also much nicer, limited by the subsonic.

My w15 GTI has a qts of .48 based on the spec sheet and no one will argue that sub doesn't perform well in IB.

Sorry don't know enough to put any science behind what I hear. But I can say I have really good hearing :laugh:.
 

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Discussion Starter #6
Here are some links that support my argument of smaller box= less cone control and worse transients.

subwoofer

I don't know how many times I've heard it...but it doesn't matter how many times...it's still wrong.

Putting a subwoofer in a smaller box does not increase power handling, it simply reduces efficiency and thus requires a larger amplifier. When designing a subwoofer especially one using equalization like a Bi-Quad (Linkwitz Transform) one of the primary considerations is the amplifier power required to drive the cone to it's maximum linear excursion. A bigger number here is a bad thing...not a good thing. The smaller the box, the bigger this number will be so you may want to look at the curve generated by your Linkwitz Transform software and think it is telling you that you have very high power handling but that's not what it's telling you. It's telling you that you have a very high power requirement...not power handling. It's probably telling you that the thermal limitation of the voice coil will be reached long before the excursion limitation. Contrary to popular belief, that's not a good thing. When I 'm designing a subwoofer I'm hoping that curve will tell me that 10 watts will drive the woofer to it's maximum excursion. Of course this is a very unrealistic expectation but it would be a very good thing if it were possible.

"I have +/- 25 mm linear excursion and I get it at 20 Hz with 10 watts"! Not... "I've got +/- 25 mm linear excursion and it would take 25,000 watts to exceed it at 20 Hz so I've got great power handling...I never have to worry about bottoming"! That second statement is just the wrong way to look at it folks! The less power required to bottom the woofer the better!

What your subwoofer can produce at any given low frequency is determined by one thing and one thing only. It is determined by how much air volume the woofer can displace. So, if my unrealistic subwoofer idea above were possible, it would get the most out of the woofer with just a 10 watt amplifier. If on the other hand someone has told you that you can increase your subwoofers power handling by putting it in a smaller box you will likely end up with a subwoofer that can no longer reach its full potential. With the smaller box, you have introduced a second limitation on what your woofer can produce, that is, the thermal limit of the voice coil.

A stiffer restoring force from the smaller box does not, "increase cone control". This is determined by the damping of the system. Qtc is Qtc...and this is what describes the control of the cone motion. Actually, decreasing the box size will increase Qtc and thus increase the chance of ringing...it will reduce cone motion control.

So, smaller box...more power required, possibly beyond the thermal limit...not more power handling. Also, smaller box...less control of cone not more control.

So if all the above is true how do we stop a woofer from bottoming? Well, we stop driving it in such a way as to bottom it! The question is, what is the woofer capable of based on its excursion limits. Once we know this, we can determine what HP filtering can resolve the problem. It could be that this woofer just can not produce 20 Hz at 115 db like you might want it to. That might require several times the excursion limit of the driver depending on what driver you are using. So, if you don't want it to bottom you just can't try to make it do something it can't do. Putting it in a smaller box isn't going to somehow magically enable it to do the 20 Hz at 115 db. The only viable solution is to use a HP filter. Just as with all speaker building this will be based on a balance of trade offs. If you want 20 Hz you will need to settle for less than the 115 db you hoped for or optionally you can keep your 115 db and settle for something higher than 20 Hz. You can't have both unless you get more or bigger woofers. No smaller box will change this. So, the solution is to use a HP filter to limit your woofer to a frequency range it can handle at the output level you desire. That's how you prevent bottoming, you don't put it in a smaller box and thus in a position such that it can never reach it's full potential.

Keep this one thought in mind, Infinite Baffle is better than sealed box. Infinite baffle has always been better than sealed box and it will always be better than sealed box. What is a smaller box doing? Moving farther away from infinite baffle! So, acoustically, a bigger sealed box is always better than a smaller one. The limitation should be based more on space limitations because making it smaller will never be a move toward optimization. Depending on the Q of the driver a very large box might move Qtc below the desired level but this can be corrected using the Linkwitz Transform. So the, "too big" box is still better assuming you correct the Q with a bi-quad. Of course a point of diminishing return can be reached with the box volume as the restoring force of the box becomes very small relative to that of the driver. At some point the large sealed box is essentially infinite baffle so making it bigger beyond this is not necessary.
 

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Discussion Starter #7
Another: IB subwoofer FAQ page



"9) How do I choose my drivers?

Look for woofers with a Qts that is in keeping with the sonic characteristics you want. Generally a low Fs is desirable, however drivers with a higher Fs will work, they simply require slightly more EQ. (Note; contrary to popular belief driver and and do play well below their Fs)

10) Which Qts/Qtc should I chose?

For an IB, the Qtc of the system is approximately the Qts of the driver. If you like very tight bass, chose a lower Qts driver. If you like the "HT" sound, then chose a driver with a higher Qts."


Hmmm low Qts for "tight bass". BDL, would you consider this good transient response as most do? A box raises Qtc and does not help with cone control. It's starting to look like smaller box= worse transients.
 

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Very nice write up. You were just hoping for someone to disagree with you weren't you?;)
 

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Buick, Can you suggest a good/free enclosure calculator? I currently use winisd but am looking for something that takes xmax into account.
 

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Discussion Starter #10
Very nice write up. You were just hoping for someone to disagree with you weren't you?;)
Nah, not at all. I wish I could take credit but I didn't write the last couple of posts up. I just wanted to get the enclosure size vs cone control discussed, I've never seen it as a topic, just touched on in other threads.

Part of what triggered it was going IB. I expected to have this slow, sloppy bass from what I've read on the internet but it was a real surprise when it sounded so much more natural and "quick" than the same subs in a sealed box.
 

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Nah, not at all. I wish I could take credit but I didn't write the last couple of posts up. I just wanted to get the enclosure size vs cone control discussed, I've never seen it as a topic, just touched on in other threads.

Part of what triggered it was going IB. I expected to have this slow, sloppy bass from what I've read on the internet but it was a real surprise when it sounded so much more natural and "quick" than the same subs in a sealed box.
Be careful describing a sub as "quick".:) I can imagine what you mean but I can't think of a good way to describe it.(this just based on those low q 5"mids I had) The bass was very clean almost surreal. I would love to hear some ib 15's. Is that what you have? I do like higher q for mids but I think it might be beneficial to use low q subs.
 

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I dont disagree with you one bit. over damped with a really small box means the more the sub moves, the harder it has to work to move. this is exponential since the farther you compress the air the stiffer it gets. the stiffer it gets the less likely it is to faithfully reproduce the waveform.

also, if you look at cone excursion on really small boxes vs larger boxes, it tells it all.
 

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What i think i learned?
In a vehicle there is not true IB.
large enclosure. Yes
You mount them in a sealed trunk: Measure the Sq Ft of trunk
You mount them where the back seat was: Measure the Sq Ft of cabin

So what we are really looking at is very large or small enclosures.
There is supposed to be an ideal Q number when you get the sub and enclosure together.
".707 (which some consider a perfect q)."

Ready for my learning:)
 

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Nah, not at all. I wish I could take credit but I didn't write the last couple of posts up. I just wanted to get the enclosure size vs cone control discussed, I've never seen it as a topic, just touched on in other threads.

Part of what triggered it was going IB. I expected to have this slow, sloppy bass from what I've read on the internet but it was a real surprise when it sounded so much more natural and "quick" than the same subs in a sealed box.
Have you ever listened to one of those 'boom' cars, where the bass is super loud, but the notes seem to resonate forever? Instead of a nice tight bassline, you get this big boomy bass with no definition?

That's due to resonance in the enclosure. (not the box, but the woofer alignment)

So you get this super high efficiency, but the group delay is horrendous.

Something similar happens with small sealed boxes.

That's the bad news.

The good thing is that it's all relative. If you put a woofer with a qts of 0.6 in a small sealed box, you might end up with a QTc of 1.2. But if you stick with a lowish qts, you won't get those obnoxious resonant beats.

Basically there's nothing wrong with small sealed boxes, as long as the final QTC isn't too high.
 

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What i think i learned? In a vehicle there is not true IB.
large enclosure. Yes
From the way I understand Infinite Baffle, it is possible to replicate IB in a car.

For example, take a pair of 10" subs, qts of .37.
Per specs, they are designed for .6 cu ft sealed enclosure each, so 1.2 cu ft. total
If I want them in IB, model them in an enclosure 3x the recommended, which gives me a flatter graph.
Compare that graph to my trunk size, ~15.5 cu ft, the graph doesn't change from the 3x normal spec enclosure (3.6 cu ft)
Compare that graph of the trunk space to 1,000 cu ft., graph doesn't change again.

IB is an enclosure "infinitely" large so that the enclosure no longer affects the response of the drivers, with the front wave and rear wave "infinitely" separated, correct?

Then by that definition, for those subs, I've created an IB situation in my trunk, since the space doesn't affect the response, correct?


Now situation #2, take some high qtc or multiple drivers, and you will not get the same affect. Depending on the size of the trunk and the sub(s) used, it would possibly just act like a large box at that point.


You mount them in a sealed trunk: Measure the Sq Ft of trunk
You mount them where the back seat was: Measure the Sq Ft of cabin
It doesn't matter which way the subs are facing. The cabin is suppose to be sealed from the trunk so the smaller volume of the two (cabin vs trunk) will be considered the enclosure.


Please correct me if I'm wrong guys, I'd like to learn too and this is just what I've picked up along the way so far.
 

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From the way I understand Infinite Baffle, it is possible to replicate IB in a car.

For example, take a pair of 10" subs, qts of .37.
Per specs, they are designed for .6 cu ft sealed enclosure each, so 1.2 cu ft. total
If I want them in IB, model them in an enclosure 3x the recommended, which gives me a flatter graph.
Compare that graph to my trunk size, ~15.5 cu ft, the graph doesn't change from the 3x normal spec enclosure (3.6 cu ft)
Compare that graph of the trunk space to 1,000 cu ft., graph doesn't change again.

IB is an enclosure "infinitely" large so that the enclosure no longer affects the response of the drivers, with the front wave and rear wave "infinitely" separated, correct?

Then by that definition, for those subs, I've created an IB situation in my trunk, since the space doesn't affect the response, correct?


Now situation #2, take some high qtc or multiple drivers, and you will not get the same affect. Depending on the size of the trunk and the sub(s) used, it would possibly just act like a large box at that point.
The problem here, really, is terminology and definition. Infinite Baffle really means just that: infinite baffle. It's the baffle sizes' effect on the low end response. If a baffle is only 20" square and the driver is in the center, there will be no reinforcement of the sound wave below some frequency - let's say 330hz. The larger the baffle, the more reinforcement you get down to a lower frequency. So, let's just say you use a baffle size of 40" square. You get a rolloff at 160hz. *these numbers may not be correct; I can't recall 100% that 13400/x/2 gets you there or not*
So, the idea of using an infinite baffle is to decrease the baffle rolloff frequency by providing more surface area for the soundwave reinforcement.

The term has shifted to describe an infinitely large enclosure.


Now, what I've bolded...
The qts of a driver is just that. But, when you wire one or two or more together, you change the final "Q". Heck, wiring a DVC sub can change that from wiring one of the voice coils up. You'll even notice some mfg's spec a wiring configuration for a specific wiring load if the sub has DVC's rather than SVC. Just something to consider when doing your modeling. This is why box programs have that section for wiring... the section so many of us (I'm guilty as well) skip over without paying attention to. Use it.


You got the box size correct. Really, infinte, as we use it is impractical. Just get a rough idea of your trunk size and model it. At some point, making it larger and large in the simulation has no effect and is nebulous.

As far as picking a sub by its Qts, it's a place to start, but you have to factor in the other T/S parameters as well. Not all 10", Qts=0.34 subs are created equal. I wouldn't get hung up in the differences of 1/10, but if you start going beyond that and box size is important to you, it begins to become a factor.

It doesn't matter which way the subs are facing. The cabin is suppose to be sealed from the trunk so the smaller volume of the two (cabin vs trunk) will be considered the enclosure.


Please correct me if I'm wrong guys, I'd like to learn too and this is just what I've picked up along the way so far.
This isn't really true. The problem is the relationship of the placement of the driver and the listener vs the environment. That's why some will swear they've heard a difference when they move their sub to X location and people refute the idea with the (erroneous) logic of "subs have long wavelengths".

If the placement of the woofer happens to cause a boost in response due to constructive correlation then you'll get increased output at some frequency. If the reflected signal comes back out of phase at the listening position, you'll experience a null at some frequency.


Then you have the effect of room modes which, as I've found, affect frequencies as high as 600hz.
 

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I have to say, I'm a bit surprised at the responses so far. I thought more people would be opposed to the idea.
what idea? That a small box = more cone control? It just seems like a blanket statement to me. I think it has to do with the system and application as a whole rather than just one component. I use a Alpine Type-R 10" shallow sub in my wife's car. The enclosure is a measly 0.38ft^3 (net), stuffed with fill, and it performs well. It doesn't dig low, but that was a given and not an issue for me.
It models at a Qtc of about 0.68 and the real life measurements give me 0.697.
Here's a screenshot of the model:




This model shows the box unstuffed with a Qtc of 0.84. You can see the FR sims compared as well.




If I told you I was using a box that small, without mentioning the subwoofer and goals of the system, you'd think I was stupid. I'd think I was stupid... but then I'd ask some follow up questions. ;)
Things in subwoofer land have changed a lot since I've been in car audio... and that's only been about 5 years.
 

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Discussion Starter #20
Have you ever listened to one of those 'boom' cars, where the bass is super loud, but the notes seem to resonate forever? Instead of a nice tight bassline, you get this big boomy bass with no definition?

That's due to resonance in the enclosure. (not the box, but the woofer alignment)

So you get this super high efficiency, but the group delay is horrendous.

Something similar happens with small sealed boxes.

That's the bad news.

The good thing is that it's all relative. If you put a woofer with a qts of 0.6 in a small sealed box, you might end up with a QTc of 1.2. But if you stick with a lowish qts, you won't get those obnoxious resonant beats.

Basically there's nothing wrong with small sealed boxes, as long as the final QTC isn't too high.
I agree. I should have been more specific in my original post. I assumed the "small sealed box" meant a very high Qtc.
 
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