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I'm stuffed!

Is this the model that you're talking about:
http://www.humanspeakers.com/e/epi200.htm

It is well known that placing damping behind a driver lowers the effective Qts, and the EPI and Genesis speakers were based on a fairly high Qts woofer better optimized for sealed box designs. I rebuilt a pair of Genesis 2's, a similar design with a passive radiator, and they were filled with yellow fiberglass. I wanted to experiment with 2-3" of wall lining, stuffing behind the woofer but no stuffing behind the PR, this makes the most sense IMO when a high Q woofer is used.

What we usually do not want is to lower the passive radiator Q which is what happens when you place damping material directly behind the radiator.

The guideline for just lining the walls is very old, and midbass cavity resonances will certainly be better controlled with more damping material - too much and you'll significantly reduce the low bass output at Fb.
 
My polk SDA-1's utilize a 12"" PR and employ fiberfill within the upper part of the cabinet with none in the area where the passive radiator does its work..... the most interesting fiberfill/passive radiator combo,I've seen, was the Kef 204 with the "rectangular' PR and a rather precisely defined channel running vertically in the center of the speaker, the channel created with Kef's own version of filler, rather firm relative to other materials.
 
Pete B said:
Is this the model that you're talking about:
http://www.humanspeakers.com/e/epi200.htm

It is well known that placing damping behind a driver lowers the effective Qts, and the EPI and Genesis speakers were based on a fairly high Qts woofer better optimized for sealed box designs. I rebuilt a pair of Genesis 2's, a similar design with a passive radiator, and they were filled with yellow fiberglass. I wanted to experiment with 2-3" of wall lining, stuffing behind the woofer but no stuffing behind the PR, this makes the most sense IMO when a high Q woofer is used.

What we usually do not want is to lower the passive radiator Q which is what happens when you place damping material directly behind the radiator.

The guideline for just lining the walls is very old, and midbass cavity resonances will certainly be better controlled with more damping material - too much and you'll significantly reduce the low bass output at Fb.
Click to expand...

Exactly right, on all points.

The Qts of the EPI/Genesis woofer is indeed moderately high- I've measured different models, and the variations have been between about .4 and .52 or so. IIRC, the lower-Q models were the ones with the shorter voice coil windings (about 5/8" winding pack length, as opposed to just over 3/4" length for the longer-pack drivers).

The admonition I gave about leaving a "tunnel" of open space between the woofer and passive radiator, is exactly along the lines of what Pete says about not wanting to lower the resonant Q of the passive radiator (or port, for that matter) itself. The energy transferred to the radiator is where low bass support comes from... damping that away just throws away low-bass output.

Ken's statement about the complexity of stuffing/damping material behavior is definitely correct, IME. And the sometimes puzzling aspect about it, is that different aspects seem to dominate depending on HOW DENSELY the stuffing is packed. Just ask the transmission line guys! You can go from a slight reduction in midrange frequency "talk" with wall lining only (absorption), to an increase in effective volume (moderate "fill" over most of the area) due to thermodynamic effects, to a change in the velocity of sound (moderately tight stuffing- as in T-lines)... or anything in-between, as well as other effects...

Regards,
Gordon.
 
My EPI 100's have all had Fiberglass Stuffing.
Genesis 1+ = Fiberglass.
My EPI 200c's have carpet padding.

They must have had a reason.:scratch2:
 
BrocLuno said:
Still curious - which kind of carpet padding? How thick, how applied?
Click to expand...

Foam type... about 3/4" to 1" thick.

A couple of them that I opened (presumably for the first time), had the padding in an interesting pattern... it was two pieces, bent into a U-shape each along the vertical axis, that if you looked downward through a cutaway profile of the cabinets, would have formed a "W" pattern, with the center point of the W being right behind the woofer and passive radiator. IOW, there was a "peak" formed by the inner edges of the two foam padding sheets, that met right behind the woofers, the centers of the foam sheets were against the back wall of the cabinet, and the outer edges were along the side walls of the cabinet...

Indeed, a strange setup... but should have done a pretty good job of breaking up many acoustic modes inside the cabinet.

BTW: When adding stuffing to these- I'd put it inside the "valleys" formed by the foam sheets, and loosely fill up the valleys...maybe adding more to the upper part of the cabinet (away from the woofer and PR) than near the woofer/PR...

Regards,
Gordon.
 
spkrdtr said:
(BTW, KK, nice strat. wish I hadn't sold mine 40 yrs ago).
Click to expand...


Thanks! I figure that, despite missing out on the financial appreciation of all the "vintage" gear I have sold cheap, it is necessary to make room for new old stuff....

What kind of Strat did you have?

-k
 
ken kantor said:
Thanks! I figure that, despite missing out on the financial appreciation of all the "vintage" gear I have sold cheap, it is necessary to make room for new old stuff....

What kind of Strat did you have?

-k
Click to expand...

Sunburst with mahogany fretboard. I modded it with a switch to allow complete control over all 3 pickups. Sold it to buy a Gibson ES 175 after jazz took over my soul.
 
I have a old Sunburst/mahogany US Bullet, if you know that guitar. It's a short-scale with a unique neck profile, but not a "student" guitar. I just love it... it's one of my very favs of all my guitars, partly due to my small very small hands, but partly due to its fit, finish, feel and tone.

I generally didn't use it if I played a party, as the above picture. That's my other fav guitar. It's a Strat Plus, and the only guitar I have ever heavily modified with parts. When I used to play out more, it was my go-to guitar.

OK, I know we are off topic, and I know I am a dismally bad guitarist. So how about if we bring this message home with a discussion of open vs. sealed guitars, and how they sound when stuffed with cigarette butts....

-k
 
ken kantor said:
....

OK, I know we are off topic, and I know I am a dismally bad guitarist. So how about if we bring this message home with a discussion of open vs. sealed guitars, and how they sound when stuffed with cigarette butts....

-k
Click to expand...

LOL! :guitar: :music:
 
"Some idiot sold me this '64 sunburst Strat for $300 in '72!"

Guess who the idiot was?

[And the Tele, too.... :pity: ]
 
GordonW said:
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.
Click to expand...

I looks like someone took your idea of blending stuffing fibers and commercialized it.
See what MCM Elect. is selling:
http://www.mcmelectronics.com/product/LS00916
 
Understanding that this is an old thread, here is some new info:
I have a pair of EPI 200C's (as repeatedly discussed in this thread).
BEFORE reading this excellent info, I was told by a fellow EPI lover to use a couple of bags of Acousta Stuf Polyfil. I was careful not to obscure the openings on the radiators. I thought they sounded quite nice (don't stop here). They originally had the Foam multi colored and pretty thick (at least an inch, probably thicker) carpet pad. When I recapped (single 10uF Clarity Cap SA)these recently, I pulled out ALL of the ASP and re-inserted the original pads in the W shape the Gordon described. I did just one and listened to compare. Lo and Behold! The EPI engineers knew something. The danged carpet padded speaker did EVERYTHING better from the mid bass down. It wasn't close. Some additional damping in places might be good, but I don't thinkl I left enough "tunnel" between the woofer and the passive when using the Acousta Stuf. Anyway, the speakers sound terrific. The Clarity Cap did wonderful things for openess. I love these speakers again!
 
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