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I'm stuffed!

D

dualhead

AK Subscriber
Subscriber
Man I just finished stuffing my EPI 200C's with polyfill and my system did a giant leap forward in fidelity. I got these without polyfill. They did have carpet padding lining the interior. I was pretty happy with them. However, I left the carpet padding in and stuffed them pretty tight with polyfill from Michaels. WOW!!!!!!!!!! Best speakers I have ever owned. Imaging, realism, bass tightness, all are incredible. Thanks to all for the tips on what to stuff em with. :banana: I'm set for a long while.
 
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Those passive radiator assisted speakers really needed some stuffing. Lining of cabinets is suited only for vented deisgns, which this one is not. What you did was lower the box Q (tightens the bass) and Fs (lowers the bass).

I suggest you try Owens Corning pink fiberglass in your next set. It performs a bit better in comparison tests with wool and polyester and theoretical studies. The reason is the fibers are much smaller in diameter and provide more efficient damping and compliance properties.
 
spkrdtr said:
I suggest you try Owens Corning pink fiberglass in your next set. It performs a bit better in comparison tests with wool and polyester and theoretical studies. The reason is the fibers are much smaller in diameter and provide more efficient damping and compliance properties.
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Dr. Leach at Georgia Tech seems to agree with this finding.

However- something that I discovered while in his class- a mixture of fiberglass AND polyfill does MORE than EITHER alone. It's akin to a "saturated solution" in a liquid... you can only put SO MUCH of one thing in... but sometimes you can get MORE total solute in there, if you use MORE than one. Apparently, they work slightly differently, so a combo of both damping materials can do more than just having one...

I usually wind up with about 2:1 ratio, fiberglass:polyfill... that can help some of those "problem children" speakers where the enclosure is just a bit TOO much too small for either one to handle by themselves...

Regards,
Gordon.
 
Zilch said:
See Dickason 3.59:



In fact, see that entire chapter; PR alignments are equivalent to vented in most all design aspects.

Also, again:

http://audiokarma.org/forums/showthread.php?t=189662
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Yes, PR do behave like VA's but not in all cases - even though the 'cookbook' says so. Remember cookbooks are a guide and just like in food preparation, the cook always has the option to add or take away ingredients.

I've worked on some very sophisticated high end designs with passive radiators which were stuffed to the hilt with polyester by the manufacturer. One example is the $4000 Ensemble Reference mini-monitors made by Pawel Acoustics in Switzerland.
 
spkrdtr said:
I've worked on some very sophisticated high end designs with passive radiators which were stuffed to the hilt with polyester by the manufacturer.
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Well, you GOTTA stuff to the hilt if it doesn't do much of anything.... ;)
 
spkrdtr said:
Uh, okay, if you say so!
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Let me line it out:

1) Ken Kantor just told us two things specifically relating to this:

A) Pillow stuffing polyfill doesn't do anything, and,

B) Stuffing a vented cabinet is "bad practice."​

2) From what I understand, Dualhead's EPI 200Cs are a PR design.

3) Dickason tells us that, with respect to damping, vented-box design rules apply to PR designs, as well.

4) Dualhead stuffed his speakers "pretty tight," apparently with pillow stuffing polyfill, and claims to have achieved sonic nirvana as the result.

I don't know EPI 200C from a hole in the ground, but only if they came originally overstuffed with polyfill does that make any sense, and, in any case, it would be an exception.

What I CARE about is the principles, and if we let the exceptions define those, loudspeaker design reverts to the ignorance and chaos which once characterized it.... :yes:
 
Zilch said:
Let me line it out:

1) Ken Kantor just told us two things specifically relating to this:

A) Pillow stuffing polyfill doesn't do anything, and,

B) Stuffing a vented cabinet is "bad practice."​

2) From what I understand, Dualhead's EPI 200Cs are a PR design.

3) Dickason tells us that, with respect to damping, vented-box design rules apply to PR designs, as well.

4) Dualhead stuffed his speakers "pretty tight," apparently with pillow stuffing polyfill, and claims to have achieved sonic nirvana as the result.

I don't know EPI 200C from a hole in the ground, but only if they came originally overstuffed with polyfill does that make any sense, and, in any case, it would be an exception.

What I CARE about is the principles, and if we let the exceptions define those, loudspeaker design reverts to the ignorance and chaos which once characterized it.... :yes:
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So maybe if I unstuffed them slightly they would sound even better? I would guess I unloaded one full twenty ounce bag of polyfill plus two thirds of another between the two speakers. Tight is relative, so I think what is important is they sound great! Maybe sometime I'll take the time to experiment with different amounts, but for now I'm throwing on a Klaus Schulze record and enjoying my rig!
 
dualhead said:
So maybe if I unstuffed them slightly they would sound even better?
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I'm not going there, because I don't know how they sound to you, or what sound you might like or not.

I'm saying there are means to understand the design, and how to modify it, based upon the fundamentals. A good starting point would be ascertaining what the designer had in there originally, how much of it, and why.... :yes:
 
Human Speakers not speaking.

Zilch said:
I'm not going there, because I don't know how they sound to you, or what sound you might like or not.

I'm saying there are means to understand the design, and how to modify it, based upon the fundamentals. A good starting point would be ascertaining what the designer had in there originally, how much of it, and why.... :yes:
Click to expand...

I tried to get that info from that guy, but never received a response. These are kinda rare speakers, so I'll keep trolling for specific data. I understand your point, and the need for objective starting points. Thanks for keeping us honest.:thmbsp:
 
I would be surprised to learn that carpet padding was the manufacturer's spec.

Perhaps another AKer who has a pair could take a peek inside and report their "findings" here? :dunno:
 
Zilch said:
Let me line it out:

1) Ken Kantor just told us two things specifically relating to this:

A) Pillow stuffing polyfill doesn't do anything, and,

B) Stuffing a vented cabinet is "bad practice."​

2) From what I understand, Dualhead's EPI 200Cs are a PR design.

3) Dickason tells us that, with respect to damping, vented-box design rules apply to PR designs, as well.

4) Dualhead stuffed his speakers "pretty tight," apparently with pillow stuffing polyfill, and claims to have achieved sonic nirvana as the result.

I don't know EPI 200C from a hole in the ground, but only if they came originally overstuffed with polyfill does that make any sense, and, in any case, it would be an exception.

What I CARE about is the principles, and if we let the exceptions define those, loudspeaker design reverts to the ignorance and chaos which once characterized it.... :yes:
Click to expand...

I don't understand why Ken would say that... because we specifically tested polyfill and fiberglass here in Dr. Leach's lab... and found that they DID BOTH have some effect.

Fiberglass DID have more of an effect... but polyfill did actually have SOME effect. And the combination of the two had MORE effect than EITHER alone. We saw increases in "effective" volume (as determined by tuning shifts) of around 10-15% or so with polyfill, around 15-20% or so with fiberglass, and at least one set of tests showing nearly 25% effective increase with BOTH combined. No, we never got close to the around-40% "theoretical ideal" that would have resulted from a perfect adiabatic-to-isothermal transformation in compression/expansion behavior... but we DID manage to get over half way there...

And the difference between a "vented" and PR cabinet... the VELOCITY of the air necessary for the device to work. Since a PR has MUCH more area, the velocity is MUCH lower... and the losses in LF energy in the stuffing are MUCH less than with a vent.

So, you CAN "stuff" PR designs a LOT more than ported designs... and they will still work. IME, I still find it good to leave a "passage" between the woofer and the PR (an area mostly un-filled as a small "tunnel" between them)... but I've seen PR boxes work, pretty much to-spec, even completely full.

As for the EPI 200- EVERY pair I've EVER seen has had carpet padding inside. That's not a fluke, and it's not something somebody did on a whim. THEY did it.

Regards,
Gordon.
 
I agree with Gordon's points above. My own experiments have yielded similar empirical results. Some quick thoughts:

1- There are several types of "polyfill" available. Many of these are not very useful for acoustical applications, but there are specialized types that at least approach some of the effects of fiberglass.

2- The science behind the effects of cabinet stuffing is really, really complex. There is no short answer about how a given stuffing material and quantity will interact with a given speaker design. In some cases, damping will go up, in others it will go down. Same with effective cabinet volume.

[There are thermodynamic, effects, velocity effects, tortuosity effects, path length effects, absorption/damping effects, all interwoven and impossible to isolate, either mathematically or experimentally.]

3- Look, we all want simple answers, but that is wishful thinking. Not every sealed box relies on box compliance; "acoustic suspension" is different from "infinite baffle," and the range of between the theoretical ideals is infinite. Similarly, not every vented system has a significant Helmholtz resonance. Etc Etc.

4- Chances are high that adding a lot of stuffing within the open volume of a well-designed vented or PR box will degrade the performance. Not always, but its a reasonable bet. On the other hand, if the original design has too little damping, perhaps the additional damping would be good thing.

5- Lining the walls of a cabinet is completely different from adding stuffing to the open volume, anyway. You can do one, the other, or both.

6- If someone gets good results on their own system with a given material... fantastic! It's hard to tell what is actually going on, but listener satisfaction is the final motive in the individual case. I think it is important to respect a user's experience, and also important to avoid generalizing their results to every situation.

I'd like to write much more on this, but it is getting late in this hemisphere. I will add comments as time and travel permits...

-k
 
I have owned three sets of EPIs and worked on maybe a 1/2 dozen others and never seen carpet padding in any. By the way, you did not say which type of carpet padding (Felt or Foam - there is more than one density of either kind).

I like pillow stuffing for some applications where a modest dampening is needed. But all EPIs I have owned or worked on have had fiberglass, usually yellow. And since I worked at Owens Corning for a while back in the day, the closest to to specific type was a product called Air-Core, as used in airplane insulation. You can't get that anymore as almost all aviation has moved on to other insulating materials, but PINK will do almost as well :)
 
GordonW said:
Fiberglass DID have more of an effect... but polyfill did actually have SOME effect. And the combination of the two had MORE effect than EITHER alone. We saw increases in "effective" volume (as determined by tuning shifts) of around 10-15% or so with polyfill, around 15-20% or so with fiberglass, and at least one set of tests showing nearly 25% effective increase with BOTH combined. No, we never got close to the around-40% "theoretical ideal" that would have resulted from a perfect adiabatic-to-isothermal transformation in compression/expansion behavior... but we DID manage to get over half way there....
Click to expand...
http://www.bobgolds.com/AbsorptionCoefficients.htm
 
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