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polyfill in the compression chamber (Read 3947 times)
bnew63
Ex Member



polyfill in the compression chamber
10/16/05 at 03:35:49
 
Just finished WO #4 with 12" eminence woofers.I've put small amounts of polyfill in some of my previous WO's.I've stuffed this one pretty heavy with fill.
Correct me if I'm wrong,the fill tricks the woofer into thinking it has a bigger compression chamber.
So if it sounds a bit muddy will removing some fill correct this. ???
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gexter
Ex Member



Re: polyfill in the compression chamber
Reply #1 - 10/16/05 at 05:12:43
 
funny thats what I hear too, from others I mean.
the word packed if you mean loosely packed. fluffy, light and full kinda like the fiber version of dreamwhip.


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bnew63
Ex Member



Re: polyfill in the compression chamber
Reply #2 - 10/16/05 at 06:14:03
 
Gex you are a dilligent one,alway there.
Yes loosley packed would have been a better description.The other WO's I've made I just stapled a 2" layer around the chamber and had good results.I thought I'd try a little more fill to see the affect.
Again correct me if I'm wrong,a larger compression chamber will allow a speaker to go deeper but can lossen up the bass.Inversly a smaller chamber,less low end but tighter bass.
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« Last Edit: 10/16/05 at 06:15:37 by bnew63 »  
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gexter
Ex Member



Re: polyfill in the compression chamber
Reply #3 - 10/16/05 at 14:05:16
 
I don't know the science but if the chamber is already too small or correct for the sub I don't think adding more fiberfill will make it muddy, but play and find out.
a chamber that is too large will.
Hanging out on this forum has left me in a position where I have to start learning the science and more book research .


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« Last Edit: 10/17/05 at 05:59:01 by gexter »  
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J_Rock
Ex Member



Re: polyfill in the compression chamber
Reply #4 - 10/17/05 at 04:21:45
 
In the compression chamber? we are talking about the chamber with the throat exit in it right?  if so the fiberfill should help absorb some of the distortion in the higher frequencies a sub produces, and it should lower your response, meaning better low end.

In the sealed chamber it will trick the sub into thinking it is in a larger chamber that it actually is, which is beneficial when the chamber is between 75 and 100% its needed size.(depends on how much fiberfill goes in.)  If the sealed chamber was correctly sized or a bit large and the fiberfill was added, it could muddy your bass by creating a larger chamber.

If it is in the actuall compression chamber, well that would trick the sub into thinking it had a larger compression area which could result in worse response, in the form of slower and lower bass.  

I think...
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jj420
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Re: polyfill in the compression chamber
Reply #5 - 10/20/05 at 16:57:07
 
if youre talking about the sealed chamber then Jrock has it, but you need between 2 and 3 pounds per cubic foot in order to make a differnce, thats a lot of fiberfill and its packed pretty tightly at 3lbs per cube.  The approximate gain from this amount is about 30% in apparent volume.

lining the sealed volume has no effect in a subwoofer as the waves are just too long to benefit., the compression chamber and horn walls would benefit from lining though, and not in any small sense either, by lining the parts of the horn that have the highest pressure you can eliminate a great deal of harmonics and harshness.

unless you have found a driver that is well suited to the volume of the sealed chamber in the WO then stuffing is a good idea for the sealed side, as a larger volume increases efficiency and low end response.  As far as muddying the bass, there may be a slight increase in group delay, but as long as the apparent volume is enough to control the cone you shouldnt have any negative consequences.
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BigAir
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Re: polyfill in the compression chamber
Reply #6 - 10/22/05 at 19:16:09
 
Wouldn't lining the compression chamber with fiberfill slow down the air flow and make the compression chamber seem longer than it really is?  That should lower the tuning just like it would in a transmission line enclosure.   That's something I've been meaning to experiment with.
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jj420
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Re: polyfill in the compression chamber
Reply #7 - 10/24/05 at 01:01:17
 
you would have to line the whole thing rather extensively, and it would be hard to get good uniformity, lining the high pressure areas though, with a good layr can lower the tuning of those sections specifically and eliminate distortion causing turbulence.
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gexter
Ex Member



Re: polyfill in the compression chamber
Reply #8 - 10/24/05 at 01:27:45
 
packed tight eh?
I will have to verify that and maybe change my answer.
so no it's not my final answer.
I use packing specifically for what jj calls harmonics and harshness.
I use it stapled and glued to the walls depending on the enclosure.
I have not seen a big differance in packing in a sealed enclosure to "trick" into thinking its bigger. But evidently I was misinformed on how it was to be used.


good point Big Air on the TL's I guess it really depends on where you are using it and how. the TL is loosely packed is it not. and fiberfill would not be used as a lining. a flat matt of whatever would be used. Differant use and results.

turbulence can slow air flow down and have a positive effect on desired sound can it not? what happens when you blow air through  a batch of fibre fill? a uniform vortex?

Just tossing stuff around to get some answers

Gex
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jj420
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Re: polyfill in the compression chamber
Reply #9 - 10/27/05 at 15:09:53
 
"lining" (attaching a layer uniformly to the walls) slows down airspeeds, this makes a nicer sound

"Stuffing" (filling a cavity with light fiberfill) dissipates pressure more efficiently than just air, and you need between 2 and 3lbs per cubic foot to make a difference.  above 3lbs per cube though, diminishing returns, theres not too much more to be had.

lining deals with resonances, standing waves, airspeed etc

stuffing deals with only one thing, dissipation of the backwave.  the purpose of a box is to contain the backwave off the cone, in order to do that, you need a certain volume of air to dampen it.  air with thousands of tiny light fibers to move mixed in dampens energy a lot faster and more efficiently, creating the illusion of a bigger box.

so, stuff your chambers, and line your throats (i know, i know, that sounds bad, get your mind out of the gutter)
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BigAir
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Re: polyfill in the compression chamber
Reply #10 - 10/28/05 at 13:52:06
 
[quote author=jj420  link=1129433749/0#9 date=1130422193]"lining" (attaching a layer uniformly to the walls) slows down airspeeds, this makes a nicer sound

"Stuffing" (filling a cavity with light fiberfill) dissipates pressure more efficiently than just air, and you need between 2 and 3lbs per cubic foot to make a difference.  above 3lbs per cube though, diminishing returns, theres not too much more to be had.

lining deals with resonances, standing waves, airspeed etc

stuffing deals with only one thing, dissipation of the backwave.  the purpose of a box is to contain the backwave off the cone, in order to do that, you need a certain volume of air to dampen it.  air with thousands of tiny light fibers to move mixed in dampens energy a lot faster and more efficiently, creating the illusion of a bigger box.

so, stuff your chambers, and line your throats (i know, i know, that sounds bad, get your mind out of the gutter) [/quote]

That's not always the case.  Stuffing will change the tuning of any enclosure whether it's sealed, vented, a horn or transmission line. Transmission lines enclosures are very sensitive to any kind of stuffing.  It's because of the air speed that you spoke of.  If you have an enclosure that is perfectly tuned, you will throw it off by adding stuffing and make it sound worse.  I'm pretty sure that if you add stuffing to the compression chamber and/or the throat of a WO, you will lower the tuning substantially.  Not that there's anything wrong with that.  It's just going to sound different and probably lose a little output.  Depends on your drivers and environment.  
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bnew63
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Re: polyfill in the compression chamber
Reply #11 - 10/28/05 at 22:39:56
 
Who knew there was so many things to consider over a little stuffing.I have changed the amount of polyfill several times in my most recent WO.Stuffing it quite full in the compression camber does dampen the volume a bit.It's hard to tell the difference between just lining the chamber and none at all.
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BigAir
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Re: polyfill in the compression chamber
Reply #12 - 10/29/05 at 16:26:06
 
Depending on the kind of sound you're after and your drivers, I would think that you would get the best results by stuffing the sealed chamber.  The reason is that  by stuffing the sealed chamber you should be able to make it slightly smaller and maximize the compression chamber.  A larger compression chamber and throat area should increase output.  There's a lot more to consider though, room/vehicle size and treatments, drivers, etc... I use Bass Box Pro to model my enclosures.  It takes amount of stuffing into account.  That way you should be able to model it almost perfectly for your drivers.  Have fun. Cheesy
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lunarlab
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Re: polyfill in the compression chamber
Reply #13 - 11/03/05 at 06:05:21
 
I have a nice loose fill for my Wo's of very torn apart polystuff.  A loose torn fill about 3/4 of the way up the sealed side with one inch poly stapled around the sides.  I played around with the amount for a whole evening untill I found the right amount.  It is a compromise of volume and damping....the rule of thumb is about a 25 % increase in box volume for a full poly stuffed box.  The sealed side is about .7 cubic feet so a half stuff will give me about a 12 % increase in apparent box volume. I have been reading some old school sound engineering books and have been studying up on the speed of sound.  If you have many faceted surfaces for sound to reflect off it takes a longer path.  Each time sound is reflected it is slowed down.  This effect to the woofer gives a longer path for the sound to follow and inversly makes the woofer see a larger cavity. This works to a point, where the sound is blocked by the volume of your polystuff if it is too tightly packed and actually removes box volume.... Remember...a nice loose to medium stuff is more ideal for accoustically tricking your woofer into seeing more box volume....
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