Difference in sound depending on stuffing - AVS Forum
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post #1 of 13 Old 04-23-2012, 07:14 AM - Thread Starter
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I have this whole project going with sealed subwoofers and multiple placements yadda, yadda, yadda.

I used polyfill for the first time, one pound per cu. ft. Has anyone ever noticed a difference in sound, either measurable or not with different materials....

My main subs use yellow, itchy, hazard to breath OC ( the fluffy unfaced wall cavity insulation ).

Why do i ask this.... Well my 12" subs seem to have a sound which is kinda of a signature, that my 15's do not have. I'm positive there little in the way of measuring that would help unless it is a ringing of some sort........

Many have said that the 240watts are running out pretty quick and could be a source of the signature... Who knows...

KG
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post #2 of 13 Old 04-23-2012, 01:02 PM
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Originally Posted by kgveteran View Post

I have this whole project going with sealed subwoofers and multiple placements yadda, yadda, yadda.

I used polyfill for the first time, one pound per cu. ft. Has anyone ever noticed a difference in sound, either measurable or not with different materials....

Adding fill based on anything other than measured results is a crap shoot at best. Different materials have different indexes of resistivity, and unless you measure the cab with various levels of fill, whatever it may be, you have no idea what's actually going on.
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Why do i ask this.... Well my 12" subs seem to have a sound which is kinda of a signature, that my 15's do not have.

There's at least a half dozen reasons why that would be the case, not counting the damping.

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post #3 of 13 Old 04-23-2012, 01:14 PM - Thread Starter
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Originally Posted by Bill Fitzmaurice View Post

There's at least a half dozen reasons why that would be the case, not counting the damping.

( in my shifty 1950's actor voice ) Go on .........

I think its the hipass/lopass filtering. It just has a very recognizable sound.
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post #4 of 13 Old 04-25-2012, 12:56 PM
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Originally Posted by Bill Fitzmaurice View Post

Adding fill based on anything other than measured results is a crap shoot at best. Different materials have different indexes of resistivity, and unless you measure the cab with various levels of fill, whatever it may be, you have no idea what's actually going on.
There's at least a half dozen reasons why that would be the case, not counting the damping.

Okay, so how do you measure the results of the damping. Are you just speaking of the basic FR measurements?
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post #5 of 13 Old 04-25-2012, 02:11 PM
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Okay, so how do you measure the results of the damping. Are you just speaking of the basic FR measurements?

Measure the Q and FR. If the Q is too high and the FR shows a response bump above the intended F3 you need more damping. If the Q is too low and FR shows a sensitivity loss above the intended F3 it's over damped.

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post #6 of 13 Old 04-25-2012, 03:02 PM
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http://www.data-bass.com/data?page=content&id=79

I found this to be interesting.
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post #7 of 13 Old 04-25-2012, 04:50 PM
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Originally Posted by Thatsnasty View Post

http://www.data-bass.com/data?page=content&id=79

I found this to be interesting.

Interesting, but incomplete. The effects of stuffing sealed cabs are seen in the FRD, impedance and Q. Q is the cause, FR and impedance are the results. If you don't measure Q you see what happens but not why. More important, Q tells you instantly if a better result can be had by adding more stuffing. If Q reads 0.7 or so you know that it's as good as you can get, and there's no reason to try to make it better.

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post #8 of 13 Old 04-25-2012, 07:37 PM
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Originally Posted by Bill Fitzmaurice View Post

If you don't measure Q

Sorry for the quasi-hijack (and my ignorance): do you know of a nice write-up of different measurement techniques, from easy to precise? Is it possible to estimate Q with modelling software?
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post #9 of 13 Old 04-26-2012, 06:33 AM
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Originally Posted by ReneV View Post

Sorry for the quasi-hijack (and my ignorance): do you know of a nice write-up of different measurement techniques, from easy to precise? Is it possible to estimate Q with modelling software?

Most box programs, like WinISD Alpha Pro, do show the Q of a modeled sealed alignment. What most don't show is how much Q can be lowered with stuffing. Lowering Q by a factor of 0.2 with stuffing is an average figure, so if you want a net Q of 0.7 you can start with a design with a Q of 0.9, for instance, and add stuffing to get it to the target 0.7. You can only confirm the result by measuring the Q with WT3 or the like. Also be aware that while you can lower the Q with stuffing the result will not duplicate that of a larger box, though it will be reasonably close.

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post #10 of 13 Old 04-26-2012, 08:07 AM
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Originally Posted by Bill Fitzmaurice View Post

Most box programs, like WinISD Alpha Pro, do show the Q of a modeled sealed alignment. What most don't show is how much Q can be lowered with stuffing. Lowering Q by a factor of 0.2 with stuffing is an average figure, so if you want a net Q of 0.7 you can start with a design with a Q of 0.9, for instance, and add stuffing to get it to the target 0.7. You can only confirm the result by measuring the Q with WT3 or the like. Also be aware that while you can lower the Q with stuffing the result will not duplicate that of a larger box, though it will be reasonably close.

Does this apply to ported subs, too?

Edit: does Q have a searchable name?
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post #11 of 13 Old 04-26-2012, 09:32 AM
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Originally Posted by ReneV View Post

Does this apply to ported subs, too?

No, as you tailor response of a vented box with the vent tuning.

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post #12 of 13 Old 04-26-2012, 03:14 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Most box programs, like WinISD Alpha Pro, do show the Q of a modeled sealed alignment. What most don't show is how much Q can be lowered with stuffing. Lowering Q by a factor of 0.2 with stuffing is an average figure, so if you want a net Q of 0.7 you can start with a design with a Q of 0.9, for instance, and add stuffing to get it to the target 0.7. You can only confirm the result by measuring the Q with WT3 or the like. Also be aware that while you can lower the Q with stuffing the result will not duplicate that of a larger box, though it will be reasonably close.


Here's the driver link, amyone interested in modeling my driver

http://www.parts-express.com/pe/show...number=295-464

If you do, thanx ahead of time. Best guess for cu ft is 2.0
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post #13 of 13 Old 04-26-2012, 05:40 PM
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No, as you tailor response of a vented box with the vent tuning.

Thanks!
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