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Best place for Polyfill?

D

dualhead

AK Subscriber
Subscriber
Hey gang, I am trying to damp a pair of EPI 200C's and am looking at places to pick up alot of Polyfill. PE has some Acustuff for an arm and a leg. Where is the cheapest place to pick up decent Polyfill? I don't want to mess with fiberglass or wool.
 
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Cool.

Like the pillow stuffing stuff? Cool. Off to Michael's. Thanks buddy, I'm still lovin' my Yammie Amp!
 
Thrift stores usually have old pillows for next to nothing. Or maybe you have some old pillows. A couple of queen-size pillows now reside in my powered Advents.
 
Wait!

Do NOT use pillow stuffing. It doesn't work. The acoustical properties of pillow stuffing are completely different from materials like "Acoustistuff," and are generally not helpful to the sound.

-k



dualhead said:
Hey gang, I am trying to damp a pair of EPI 200C's and am looking at places to pick up alot of Polyfill. PE has some Acustuff for an arm and a leg. Where is the cheapest place to pick up decent Polyfill? I don't want to mess with fiberglass or wool.
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Good inexpensive polyfill can be had from Fairfield 100% premium Polyester Fiberfill made in Danbury CT. at wwwpoly-fill.com
 
Zilch said:
Are you saying polyfill in general doesn't work, or just the specific type used in pillows?

[I'm a fiberglass guy.... ;) ]
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Is there a sonic advantage to filling a cabinet with fiberglass rather than the polyfill? :scratch2:
 
Yes, fiberglass works a bit better for sonics than polyfill. People don't like using it because it is nasty stuff that makes your skin itch, etc... so you have to wear gloves, and probably should use a respirator and work outdoors, etc... but it sounds a bit better. That said, you get probably 98 percent of the sound value with polyfill, so it is a difference you won't even hear with most speakers, and it comes without all the hassle and for a cheaper cost, so these days almost everyone (except some hard-core DIY types :D) uses polyfill.
 
tubed said:
Is there a sonic advantage to filling a cabinet with fiberglass rather than the polyfill? :scratch2:
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I think you should use proper polyfill. Only use fiberglass if the original design called for it, since it will effect the bass and midrange differently.

-k
 
I don't quite grasp why many reputable speaker makers are using polyfill in some of their better speakers if polyfill is inferior to fibreglass? What about waffle foam or for that matter, why not just line the interior of the enclosure with thick felt?
 
Depends on what type of speaker you have! Acoustic Suspension speakers respond well to left-over plush carpet cutouts from the local carpet stores.

Reflex speakers on the other hand could use acoustic materials from PE or Radio shack.

Experimenting will often pay-off in many situations - I've discovered that Pink Antistatic foam for some reason will help my speakers produce very mellow profiles. I have no explanation why but attribute it to the presence of electrical static and dry air inside the cabinets.
 
sealy said:
I don't quite grasp why many reputable speaker makers are using polyfill in some of their better speakers if polyfill is inferior to fibreglass? What about waffle foam or for that matter, why not just line the interior of the enclosure with thick felt?
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Fiberglass is a pain to work with. It's much easier to use polyfill. Easier tends to equal cheaper in manufacturing. As for waffle foam or felt, it's a different objective. With something like fiberglass fill you're trying to use the adiabatic - isothermal transformation to make the woofer "think" it's in a bigger box. With foam wall lining you're damping wall resonances and basically making an acoustic filter to absorb certain frequencies.

Ken, do you have any qualitative data about different types of poly and fiberglass? I know that somebody on the old basslist did an informal study like that but I lost it years ago in a computer changeover.

Ray
 
Check out the link I posted above for quantitative data. Qualitatively, the differences are going to depend a great deal on the exact tuning of the design, what the "alpha" of the system is, etc. In general, damping will be highest with fiberglass, and lowest with pillow stuffing.

If the unfilled system has a Qtc of .6 and an Fs of 75 Hz, clearly the pillow fill is going to sound the best. If the unfilled system has a Qtc of .9 and an Fs of 45 Hz, its going to be fiberglass, hands down. But, in between, and depending on the tastes of the listener... hard to say.

This all assumes a sealed system; fiberglass is always great to line the walls of a cabinet to reduce standing waves in a ported design where stuffing the chamber itself is bad practice.

-k
 
ken kantor said:
Please read this:

http://auralization.blogspot.com/

Polyfill works differently from fiberglass or rockwool. Pillow stuffing doesn't work at all. Sorry.

-k
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O'Hanlon there essentially derives transmission line equations for the fill materials in air. I did this myself many years ago in an undergraduate transmission line study and what is important to note is that the 7" line alone without stuffing has a complex imput impedance due to transmission line standing waves and the mismatched termination. That impedance is not the impedance of the stuffing material itself but rather it used as the resistance component of the T-line. One way to measure the impedance of a material is to use it as the termination only, not fill, of a high Q transmission line and then do the acoustical analogy of VSWR measurements by probing down the test line with a mic. This is a standard procedure in electrical microwave measurements. The acoustical method was described by Olney, in the transmission line paper that went along with this patent around 1934-1936:
http://www.google.com/patents?id=uehKAAAAEBAJ&dq=2031500

The real question is how tightly coupled the line is to the cone at the upper end of the woofer range, certainly if those impedance differences are correct, and it is tightly coupled there will be differences in the system frequency response output - measured woofer only and with the same woofer obviously. I don't have a lot of faith in O'Hanlon's paper and SPL measurements would have been a good sanity check.

There are several papers covering stuffing materials from the AES, etc. that I've mentioned in the past. Here is one available online:
http://users.ece.gatech.edu/~mleach/papers/Filling.pdf

I began to do a new study in the past few years, but never completed it due to time constraints. I found, as expected that most poly fills, indeed most fluffy materials work to lower Fc there were variations from brand to brand of poly - several I would not use in my own systems, and so far fiberglass has come out superior in every way. Most are at least better than nothing.
 
Damn, I'm going to waste all night reading tech papers, and I love it........


"We propose this explanation for why fiberglass lowers the resonant frequency of a stuffed cabinet whereas polyester does not. E.g., fiberglass adds net compliance to the overall system at low frequencies."

Thanks guy's !!!!!!!!!
 
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