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Question regarding stuffing a ported subwoofer

post #1 of 14
Thread Starter 
Hi there,

I would like some advice on whether stuffing a subwoofer with poly fiberfill actually fools the driver in thinking it is in a larger box. I am more than happy with my subs but I have 5kg off fiberfill in the garage left over from my sealed sub I made last year.

I am currently net at about 424 litres and would be interested in knowing if it does work how much extra would you expect in artificial volume.

I was thinking as a test to fill the subs with it to see if it would work. I wanted to ask this before I went through the pains taking task off taking the drivers out and messing around.

If its not worth doing then cool, but I thought I would ask first.

cheers guys.

Graham
post #2 of 14
You can try it but chances are slim it will do much good. Stuffing a sealed cab that has a Q of 8 or higher can lower Q, to tame a response bump, but with a VB the usual result is to mess up the box tuning.
As for fooling drivers, they're smarter than that. Lowering Q doesn't have the same result as making the cab larger. Similar, but not the same, because stuffing is a passive component, and passive components can only result in a sensitivity loss. A larger box is an active component, which can give a sensitivity gain.
post #3 of 14
Thread Starter 
Bill,

Thanks for the reply. I still have the second sub to veneer yet. I my put some in and run some REW graphs to see if there is any difference.

My previous 11 cu ft dual sealed sub had a qtc off 0.9 and I stuffed that with 4kg and that made a fair bit off difference.

cheers

Graham
post #4 of 14
gperkings1973, read Tom Nousaine article on stuffing. The smaller the box, the better the stuffing works (under 100L), up to 35% gains can he had with about 1.5lbs per cubic feet. On bigger boxes, less stuffing per cubic feet should be used, but you can still get 15-20% gains.

On your big ported sub, I would use about 3-Kilos and stuff the walls. Make sure you leave the area around the port and around the sub's motor free from stuffing. Just to give you an idea, I stuffed the walls of my 200L w/PR's sub with polyfill, about 3-lbs worth. From the measurement readings I got, the 16hz tuning dropped to about 15.5hz. On the other hand, I did notice the measurements one octave above tuning (from about 16hz-32hz) dropped a little, about 1db.
post #5 of 14
I've never used stuffing in a ported box to make it appear larger, but in some instance to control internal acoustic resonances.

There was a build here a year or so ago with a long sono, driver on one face, port on the other. Adding stuffing around but not blocking the port dramatically reduced a notch from an internal length mode. For a more conventionally shaped and sized enclosure I wouldn't bother as such issues are usually above passband. I do use it in midbass enclosures for the same reason, but then the dimensions are often more applicable to to much higher HF output, relative to a dedicated <80Hz sub.
post #6 of 14
Graham I need to stuff mine. How much would I need?
post #7 of 14
Quote:
Originally Posted by spanish68 View Post

I did notice the measurements one octave above tuning (from about 16hz-32hz) dropped a little, about 1db.

That's the detail that Nousaine left out. He only measured changes in f3 relative to transfer function magnitude, not actual broadband SPL, which shows a corresponding lessening of sensitivity along with lowering of f3. Sensitivity loss of 2dB is common with Qs of 1 or higher.
That preserves the first rule of acoustical engineering, 'There's no such thing as a free lunch'. With a larger box Q and f3 is lowered without a loss of broadband sensitivity.
post #8 of 14
Quote:
Originally Posted by kryptonitewhite View Post
Graham I need to stuff mine. How much would I need?
If I were you, I would just go to carpet store and get their leftover foam they throw away and just line the inside of your cabs. Or got to WM and get 4-6 bed pads to line your cabs. That is what I did. I need 3 of them and that's $60.

Also, you might want to add a brace or 2 more.
post #9 of 14
I'm with BFM on this one...stuffing lowers Q, which isn't the same as a larger box.

I would recommend adding just enough stuffing to tame the box resonances. This is where measuring outdoors becomes very advantageous...

I've used old carpet padding in the past and it seems to work fairly well, but I prefer buying polyfill pillows since they're self-contained and still rather cheap. You can pull pillows in and out and move them around as you chase down the resonances.
post #10 of 14
Also agreed. Stuffing is best at taming internal resonances and upper range nasties in subwoofers. The loss of efficiency and sensitivity is just that a negative not a positive.
post #11 of 14
Quote:
Originally Posted by UNICRON-WMD View Post

If I were you, I would just go to carpet store and get their leftover foam they throw away and just line the inside of your cabs.

That will do nothing. Carpet is useless and placing stuffing on the walls is where it is least effective.
post #12 of 14
Quote:
Originally Posted by UNICRON-WMD View Post

If I were you, I would just go to carpet store and get their leftover foam they throw away and just line the inside of your cabs. Or got to WM and get 4-6 bed pads to line your cabs. That is what I did. I need 3 of them and that's $60.

Also, you might want to add a brace or 2 more.

ya I don't intend to stuff, just line to dampen

It was hard enough trying to move 4' boards around in there, caulk gun, and myself lol.. it's tough to do anything as it is in there.
post #13 of 14
Quote:
Originally Posted by A9X-308 View Post

That will do nothing. Carpet is useless and placing stuffing on the walls is where it is least effective.

The carpet pad/foam, not the carpet.
post #14 of 14
Quote:
Originally Posted by UNICRON-WMD View Post

The carpet pad/foam, not the carpet.

Carpet underlay is often closed cell, so all it does it take up space and not great acoustic performance anyway - check Bob Gold. Acoustic absorption works best where the air particle velocity is highest, which is the centre of the enclosure, not the walls.
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