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Default Stuffing a small sealed box, is it ok?

I've been reading around and the advice for stuffing tends to be 1lb per cu/ft of air. My question relates to making the box appear larger when it's outside the manufacturers specifications.

Subwoofer: Audison APS8 D4
Recommended box: 0.3cu/ft (8.5l)
Recommended Qtc: 0.86

My box is 8.75l, a little larger than the maximum recommended size according to the manual. I read that if I stuff the box, it will make it appear larger and thus lower Qtc, which might help with transients and flatten the response curve. With stuffing, I could make the box appear 30% larger, but the Qtc will still remain around 0.8. This seems desirable, yes?

What problems might I have if I make the subwoofer box appear larger than recommended?
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Default Re: Stuffing a small sealed box, is it ok?

A sealed enclosure is also caused acoustic suspension as it leverages the closed airspace to control the cone. When the sub plays into the enclosure, the air pushes against the cone so it helps control the suspension of the sub. So you donít want to go too big or the suspensions starts to get sloppy and could damage the driver. With that said, I donít think youíre to the point where you will cause damage unless you also put a lot more power. Go ahead with your plans but pay attention to any noises coming from the driver and turn down the volume if so. If you need to take up space in an enclosure, you can glue in some blocks of wood, XPS foam, or similar. Happy testing.
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Default Re: Stuffing a small sealed box, is it ok?

Why not EQ the response you desire?

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Default Re: Stuffing a small sealed box, is it ok?

You probably want to get into a larger box physically and not just by stuffing the one you have if possible. QTC of .85 is kind of high, and you want to get down closer to the .707 mark if possible. But for now try it in the box you have lightly stuffed, don't over stuff it. And see how it sounds. If its too boomy sounding then i would suggest a larger box.

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Default Re: Stuffing a small sealed box, is it ok?

stuff it

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Default Re: Stuffing a small sealed box, is it ok?

Quote:
Originally Posted by dgage View Post
When the sub plays into the enclosure, the air pushes against the cone so it helps control the suspension of the sub. So you donít want to go too big or the suspensions starts to get sloppy and could damage the driver.
What defines "too big"? Do TS parameters tell us? i.e. Qtc < 0.5 will likely damage the driver?

Obviously there's a range of values it will work fine, but I'm trying to get at the reason why the designer would specify a maximum of 8.5l, when a box nearly double that size will only reduce the Qtc by ~0.15.

Quote:
Originally Posted by Bayboy View Post
Why not EQ the response you desire?
Good question. I simply assumed that any mechanical method in achieving the outcome would be preferred.

Quote:
Originally Posted by miniSQ View Post
You probably want to get into a larger box physically and not just by stuffing the one you have if possible. QTC of .85 is kind of high, and you want to get down closer to the .707 mark if possible. But for now try it in the box you have lightly stuffed, don't over stuff it. And see how it sounds. If its too boomy sounding then i would suggest a larger box.
So do you think the subwoofer designer is aiming at that Qtc for sonic reasons and not for preserving the driver's integrity?

The box is already too big by a small amount, just wondering if there might be any adverse affects of being "out of spec". Or if it simply lowers Qtc and there's no problems with doing so.
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Default Re: Stuffing a small sealed box, is it ok?

Should be ok as long as you go slow and use a little lube.


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Default Re: Stuffing a small sealed box, is it ok?

The designer probably settled on a compromise between acceptable output and response in a particular range which may not look "audiophile perfect" on paper, but when combined with the car works out fine for most.

It's easy to obsess over what's the perfect Q when .707 is sometimes blindly preached, but there's many examples of well liked subs above that and without fuss.

What enlarging a sealed box does is tradeoff some mid to upper response for a bit more low end extension, but it is very possible to wind up with too much of a tradeoff.... dry boring bass with extension that may not be of advantage to certain genres. .707 is considered a good tradeoff, but the difference between that and even .6-.9 isn't much to fuss about. The same can be done with EQ unless you're limited on EQ and ppwer.

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Default Re: Stuffing a small sealed box, is it ok?

And Iíd say many manufacturers suggest too small of an enclosure for marketing reasons more than anything. If one manufacturer goes optimal, ie larger, then another manufacturer might steal sales because they say their sub works in a smaller enclosure. Sealed subs respond well to DSP if the enclosure is slightly off, especially with the small percentage differences youíre looking at with your enclosure.
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Default Re: Stuffing a small sealed box, is it ok?

Excellent advice fellas, thanks for the input. Sounds like I can happily stuff the box and EQ the rest. As long as I use lube and go slow. Got it.
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Default Re: Stuffing a small sealed box, is it ok?

That Audison recomendation is one big marketing bull shit if you ask me. Also, you will not benefit of 30% in volume rise when stuffing box with fiberfill or wool...maybe up to 20% more likely less.

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Default Re: Stuffing a small sealed box, is it ok?

What is bullshit about a suggestion by the manufacturer? Suggestions aren't rules. The manual clearly states "maximum performance in a sealed enclosure STARTING from 7.5 liters". Catch the keyword... starting? It also goes onto state the "the range of applications are wide" and suggests contacting an authorized dealer/ installer...


From that what can we gather? Not bullshit, but a mere starting guide to where outside of that you should know what you're doing, if not, seek professional assistance. By knowing that the average consumer isn't going to know the tradeoffs of Q/transient response, power handling, or even when to apply it, it doesn't make them wrong or full of fluff. Heck, most don't even use or know what a box modeling program is, how to interpret the data, much less the acoustics of their own vehicle. No manufacturer can tell you what is best for your car and tastes.... thus suggestions.

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Default Re: Stuffing a small sealed box, is it ok?

I was initially questioning box size for a couple reasons: This is my first subwoofer install. Also the technical spec sheet differs slightly from the website, thus the confusion.

The tech sheet says "from 7.5l", whereas the website says "The APS 8 D is designed to deliver maximum performance in a sealed enclosure with ultra-compact volumes from 7.5 lt. to 8.5 lt.". Couple that with their reference box in the manual being pretty close to 8.5l - that's why I bothered to ask questions here.

After the great advice here and reading around the interwebs on Qtc, I now realise the significance of "deliver maximum performance" in their marketing. The suggested upper bound of 8.5l is really a max efficiency thing, no? So if you know what you are doing and have the power to spare, you can push those suggested performance limits.
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Default Re: Stuffing a small sealed box, is it ok?

Quote:
Originally Posted by bitshifted View Post
I was initially questioning box size for a couple reasons: This is my first subwoofer install. Also the technical spec sheet differs slightly from the website, thus the confusion.



The tech sheet says "from 7.5l", whereas the website says "The APS 8 D is designed to deliver maximum performance in a sealed enclosure with ultra-compact volumes from 7.5 lt. to 8.5 lt.". Couple that with their reference box in the manual being pretty close to 8.5l - that's why I bothered to ask questions here.



After the great advice here and reading around the interwebs on Qtc, I now realise the significance of "deliver maximum performance" in their marketing. The suggested upper bound of 8.5l is really a max efficiency thing, no? So if you know what you are doing and have the power to spare, you can push those suggested performance limits.
Actually, if you have less power to spare. As stated earlier, the tradeoffs in upper response for lower extension or efficiency usually means less power required to reach maximum excursion. However, without knowing how your particular vehicle boosts the low end, it becomes an experiment. Not a bad one since sealed is very forgiving in response, especially if you have a decent EQ for corrections.

If you feel you need to increase box size substantially over the suggested, just understand the tradeoffs. Stuffing the suggested box size will have a minimal although audible effect. If you want to get an estimate of said tradeoffs, model the sub in various sizes. Quite easy and fun to do.

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