Sealed Subs and QTC (1 Viewer)

[Geoff L]

Though not the most popular here any feelings on QTC when desiging sealed subs.
When looking at extension any benfit to under or over dampening the driver. Though .707 dose generaly offer flattest response but if EQ-ing the lower end, woud there be any gain to doing this?
OR,are other driver variables important such as power handeling, X-max,etc. Thats to say clean power is not in question.
Maybe a site dealing with this and other sealed information.
Thanks guys...

 

[DanWiggins]

Geoff,
I'm a fan of sealed subs! I've always preferred the sound quality of sealed units over vented units...
As far as Qtc goes, I tend towards a Qtc of 0.577-0.6. I find I like the overall bass response better than the Qtc=0.707, especially in a room. Qtc of 0.5 sounds great, too, but to my ears doesn't sound any better than the 0.577-0.6 range, and simply requires too much box.
Parameters that are important when dealing with sealed subs include a low Fs, mid-range Qts, and long Xmax. Power handling is also important, as you'll need a good amount of power to use that Xmax.
Dan Wiggins
Adire Audio
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[Geoff L]

Thanks Dan nice to here from you.
What is it you like about droping to the high .5's on Q-?
Wont you end up with a stepper roll of and a much better chance of peeking in certian freq's? Sorry for my ignorence....

 

[DanWiggins]

Geoff,
Actually, the opposite is true. The lower the Q, the shallower the roll-off. I've found that I just get better mains and room integration with low Q designs. And that they tend to sound more natural and realistic.
Dan Wiggins
Adire Audio
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[Geoff L]

Well ya learn something new every day.
Find this very interesting. Aside from the box growing this sounds like something I'd like to try. Building another sealed sub, like I need another and expermenting. Anyway the lower QTC is something I've never tried. I may like or dislike, but proof is in the pudden so will eventually give it a shot.
More natural is a word I like when it comes to music. Boxes are made to be remade.
Quick question Dan. The 250 plate amp, would it take a 3-ohm load if not driven to hard?

 

[Phil Olson]

I am currently doing a dual Tempest low Q design sonosub, (Dans 230L X 2). I just got word that the drivers are on their way so I should be done this weekend.
I'll let you know how it sounds.
Phil

 

[ChrisA]

Going on from what Dan was saying, for sealed, IMO, bigger is almost always better.... you just approach an IB design it's all a nice grey transition anyway. For best results, I'd design it to a QTc of 0.5 on paper because as voice coils warm up the Qts rises bringing Qtc up with it. So, I'd design the volume for 0.5 or even slightly lower if you really want (0.45), of course you should take the effect of fiberglass stuffing into account also... In any case, don't be shy for building too big of a box, and there is no magic number or disadvantage if it is designed to be 0.45 on paper. As Dan mentiones, the rolloff is shallower, the large the enclosure you build (lower Qtc).
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[Geoff L]

I may very well like the musical sound of the lowered QTC but at the expence of riseing f3. Almost all sealed stuff i've done is around .7 as i am a relative newbie persay to hands on sub building.
If adding boost to the lower end to compensate for the loss down low, you then eat headroom and premature X-max, right?
If this is the case as I suspect it is, wouldnt the best trade off be somewhere in-between to keep the divers speed up and better extension on the f3. Anything below 20 or so,to me anyway,is a gimmy. Though it may be produced,--- not with any real spl considering im useing 10 and 12 inch subs with prams that allow for real in house cabnits. Not volkswagon size enclosers.
I know that a drivers prams would have everything to do with it,-- but ---Im Speaking in General.

 

[ChrisA]

Don't get hung up on F3.. Just because your F3 goes up slightly higher is not important IMO. F3 is going slightly higher, but your curve, which is everything! is flattening towards ideal. (you are improving F4 though 0 Hz). You must look at the response curve, not F3. F3 is meaningless, it is the response curve that matters. Ideally, IMO, you want to achieve 0.5 at operating temperatures.
[dream]In my next project, I hope to build an Infinite baffle or multiple large sealed subs using a pole shifter/Digital EQ. The enclosure would actually be massive concrete closets in the front 2 corners of the room, with the baffle being flush to the front wall of the listening room [/dream]

If adding boost to the lower end to compensate for the loss down low, you then eat headroom and premature X-max, right?

Adding boost to any sealed box raises the system Qtc and
increases excursion, but remember subs that tens to sound the best are those that reprduce the most linear bandwidth. When you flatten the curve by inreasing the size of the box, you do just that. When you add boost to a sealed design of say Qtc 0.5, you increase the Qtc to a higher number--the formula which eludes me. You can also buy a Marchand Bass Assist unit which provides Q control, although I have no experience with that unit or how well it works.

 

[Geoff L]

Thanks Chris,
I just got back from seeing some responce curves. Yes I see now what your talking about.
Very clear that I was cornfused! Very easy to misinterpet things you read and apply them WRONG.
The more I learn the dumber one can feel. Thanks again for the lesson. Checks in the mail.
One thing for sure,Low-Q big box.