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Small sealed box= MORE cone control

31K views 57 replies 20 participants last post by  jackal28 
#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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#4 ·
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 **** 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 **** ton of power into a small encl without it distorting. On the other hand you need a **** ton of power because it's a small encl. ;)
 
#5 ·
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:.
 
#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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#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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#10 ·
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.
 
#14 ·
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.
 
#12 ·
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.
 
#13 · (Edited)
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:)
 
#15 ·
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.
 
#19 · (Edited)
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.
 
#21 ·
Erin, the purpose of this thread was to discuss the blanket statement that's always thrown around that a smaller box equals more cone control. Usually used when talking about IB, some people act as if the cone will just flop around uncontrollably if the box is taken away. I know Qts matters and Qtc is ultimately what matters but regardless of Qts, wouldn't you say that putting any sub into a smaller enclosure causes it to have less but not necessarily too little "cone control"?
 
#22 ·
Thank you for the explanation Erin. There's so many factors to consider, and lots more reading to do :)

Also on a sidenote, going along with Spyke, what box building software do you recommend Erin? I notice you are using BassBox Pro on what you uploaded. And I guess from looking around PWK uses his own custom software to take into account cabin response and location correct? Just wondering what would be an all around good program to get a close approximation of performance in a car. I just fiddle with WinISD.

Oh and I posted in one of your threads, I was wondering if you could point me to a pic of the finished product of the kicks you showed in Bing's installer review subforum. Sorry for being off topic...
 
#25 · (Edited)
So, for arguments sake (and hopefully this is enough information), lets compare a couple of scenarios (assume all have the same x-max and power available)....

1) a subwoofer, say 15" that has a QTC of .3 in infinite baffle and when tested in car, it has a final QTS of .35....what characteristics about how this setup should sound like should one expect?

2) the same subwoofer now put in an enclosure that models to a final QTS (in car for arguments sake) of .707. Is the cone experiencing more control from the enclosure? How does this sound as compared to the IB install?

3) Same as #1, except the sub has a QTC of .65 and a final QTS of .707 infinite baffle. Will this sub sound the same as the sub in scenario #2?

Furthermore is air spring represented in the QTS? If not, how would that further impact the sound?
 
#26 ·
So, for arguments sake (and hopefully this is enough information), lets compare a couple of scenarios (assume all have the same x-max and power available)....

1) a subwoofer, say 15" that has a QTC of .3 in infinite baffle and when tested in car, it has a final QTS of .35....what characteristics about how this setup should sound like should one expect?

2) the same subwoofer now put in an enclosure that models to a final QTS (in car for arguments sake) of .707. Is the cone experiencing more control from the enclosure? How does this sound as compared to the IB install?

3) Same as #1, except the sub has a QTC of .65 and a final QTS of .707 infinite baffle. Will this sub sound the same as the sub in scenario #2?
Thanks, Jerry, those are the kind of questions I was trying to ask.
 
#27 ·
I always thought the whole idea of using a qts .7 sub IB was because you ended up with a proper Q= .7. That was before everyone had unlimited EQ power, in fact hardly anyone had much EQ power so it sounded like crap if you did not tune the sub correctly. Yes some cars were different/etc, but it got you close. Today you can use about anything, subs are much better so even with bad tuning you can EQ out your odds of getting a sub that does something strange is pretty slim. That said I still like to error on install tuning, its way easier to tune and rarely does something I don't like....bigger drivers look cooler and are more efficient, etc. It often makes the install harder though.

The only cone control I know of, is with a cheap sub a smaller box will control it enough to allow it to handle more power. This will result in more spl in higher frequency if it does not blow up from thermal load. It will keep the cone from xmax as soon at low frequency you are not going to be hearing much of....lol. I don't know what this has to do with SQ so I never paid that much attention to it excepting some cheaper mids/woofers I installed AP to 'control' them more lol. If you don't have a real capable xover it can help you out, since I used AP more or less as a high pass.

Cone control, funny. Not much different than 1,000 watts which tells you nothing about sound quality or how loud it can get. I like IB because the cone does move, and makes me bass. No cone moving means no bass, excepting at port tuning of course if you have a vented enclosure. By far the cone moves where the amp tells it to, above anything else.
 
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#28 ·
That's just it, I was saying that a box does not control the cone, other than to reduce efficiency. My theory is that the box reduces the damping which I might be correctly or incorrectly associating with control.
 
#29 ·
Dang, I was going to say that my experience with small, sealed box, 10" subwoofers were that they made great midbass drivers. I was going to go with the pre-fab Audio Integrations subwoofer enclosure for the WRX, but, I have yet to be wowed and amazed with the output from a single sealed 10" subwoofer.

I believe I would like 3 IB 10s better than a single sealed 10... Now to find 3 decent IB 10s. I need to remeasure because I may be able to do 3 12s IB without manifolding them.

EDIT: I almost forgot... If you want cone control, build a servo drive!
 
#30 ·
Bigger sealed enclosure (lower Qtc) sound cleaner imo, they lose power handling but in a SQ oriented system that may not matter. Group delay is a derivation of frequency response, so if you EQ a bigger/smaller enclosure to produce the same FR I bet noone can tell the difference between them. Small enclosures should have higher non linear distortion. Qtc between 0,6-0,9 often work pretty good in a car. Go for a lower Qtc if you got the space and EQ down the extended lower response to decrease cone movement and you should have pretty clean sounding subbass. Combine low Le with low Qtc and transistant response should theoreticly be as good as possible. Then again, it's so hard to control the enviroment in a car so the small differences might not be noticable. Modes and resonances are the two most important factors for crappy response. A good parametric EQ can make lot of systems sound pretty damn good.

Ported might even be a better solution if you can EQ the peak created. I can't tell the difference between sealed/ported when FR is EQed to same curve.
 
#35 ·
Control can be good and it can be bad. In this case the air spring effect is actually a resistance or limiting form of control. To me this is a negative form of control. I have always looked at this topic as you need more power to control the cone in a smaller box. I say it this way because you are fighting this air spring that is constantly applying an opposite force on the cone and suspension. With an opposing force you have a chance of causing the weakest part of the speaker to give a little. This can lead to non linear movement of the cone. Since the music signal is always changing direction fast the air spring is also changing in the opposite direction. With little power the spring might actually win. With more power you can more effectively push/pull thru this resistance (the air spring) and have better ability to prevent non linear movement i.e. more cone control.
 
#45 ·
Thanks again, Andy, for clearing this up. You have a way of making this stuff so easy to understand.

I've been looking into this more lately because I have a set of 10" midbasses in the doors with a Qts of .6 and a 3.5" midrange in the kicks with a Qts of .2, both running IB (well almost IB on the midbass). No complaints with the sound, just trying to understand it better.
 
#53 ·
The further you are away from Fs with the crossover on the lowend of a passband, the less you have to worry about the Q of the driver in the enclosure. At 2x Fs it really doesn't matter. The closer to resonance, the more it matters...especially IB where Qts= system Q.

All of this deals with the anechoic shape of the lowend response.
 
#47 ·
The problem and what makes it so difficult for so many to understand is that the MOTOR controls the cone movement and the suspension OPPOSES the motor. A spring is NOT a damper. A spring is the OPPOSITE of a damper. A super ball is the opposite of an avocado.

Let's use another example. Does a spring mattress or a tempurpedic mattress offer more control?
 
#50 ·
It's so simple when you put it that way. Before this thread, I had a theory and it kind of made sense to me but now it seems so simple. A spring and damper are actually opposites. A spring stores energy and will reverberate unless you have a shock to oppose the spring, to absorb the "overshoot" of the spring. So is this overshoot why we sometimes see a peak when modeling subs in too small of a box in WinISD? Would that be considered distortion since it's not a part of the original signal?

Going a little off topic, it seems like the MS8 has an easier time "dealing" with lower Qtc subs. Would you say this is correct some of the time?

Sorry Andy but I have so many questions to ask when you're online.:D
 
#54 ·
When you think about it, this also explains why adding "stuffing" to small enclosures with a high Q improves the perception of transient response. The fill material attenuates the ringing produced by the system, thus leading to the false assumption that the smaller box is "quicker" regardless of the compliance of the suspension.
 
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