[zobsky]

I've been experimenting on and off with my W-U baffles (each with a pair of pyle PPA15 woofers) over the past month or so. I figured I'd try a stuffed W-U configuration (as reccomended by some such as JohnInCR)  and cut-away the U-part if less than pleased with the results.

I read about some folks on diyaudio using cellulose attic insulation material to adequately damp the rear wave, so I tried it, using a sheet of polyfill to shield the drivers from the insulation.

The Good
Well, it definately does extend bass response lower and bring up the efficiency. Enough for most (if not all) music.

The Bad.
I've still managed to overexcurse with the occasional home theater speical effect.
The insulation has a nasty tendancy to be displaced out of the (open) back. I have a mess building up behind the drivers and probably can't live with this long term. If I really wanted to, I could probably tack a piece of cloth to cover the rear of the enclosure but I'd rather deal with something more fibrous.

Question:
What other stuffing material can you suggest that doesn't cost too much and isn't hazardous or messy. Each of my two cabinets would need roughly  4 cu. ft. of stuffing. The cellulose stuffing costed about $6 for a bag, enough for both cabinets, .. but I have a strong feeling that it is going to end up in the attic.


Thanks

[zipidachimp]

try some pillow stuffing from walmart. not hazardous.

[JohninCR]

HT effects is asking a lot regardless of the OB alignment.  Use Linkwitz's DipoleSPLmax spreadsheet to compute your limits.  I don't think the stuffing for a U has the same requirements as for stuffing in a sealed box, and you definitely don't want your drivers sucking up any loose insulation type material.  Polyfill batting is all I've used, though I have made some U-type enclosures where I believe the staggered cross-bracing helps break up the lumped mass behavior of the air in the cavity.  That's all you're trying to do when stuffing a U.  JohnK's website gives good guidance about damping a U-baffle.

John

[zobsky]

HT effects is asking a lot regardless of the OB alignment.  Use Linkwitz's DipoleSPLmax spreadsheet to compute your limits.  I don't think the stuffing for a U has the same requirements as for stuffing in a sealed box, and you definitely don't want your drivers sucking up any loose insulation type material.  Polyfill batting is all I've used, though I have made some U-type enclosures where I believe the staggered cross-bracing helps break up the lumped mass behavior of the air in the cavity.  That's all you're trying to do when stuffing a U.  JohnK's website gives good guidance about damping a U-baffle.

John

Thanks, I like to find the limits of my speaker enclosures. Eventually, I don't want these handling anything lower than 30Hz or so. I'll try and pick up some more polyfill . Fiberglass would be better, but I'm not too comfortable with having that stuff exposed to a room in the long term. I read JohnK's stuffing advice but unless we're talking about different articles, I don't have the means to take the kind of measurements he talked about.

My intended cross bracing should help keep the polyfill in the enclosure.
 I'll post some pics later

[johnk...]

A simple formula for estimating open baffle or dipole woofer SPL at any frequency in the linear roll off region (below the dipole peak) based on a max excursion of Xmax is:


SPLmax = 100 dB + 60 Log(F/30) + 20 Log(VSP)

where VSP is the volume separation product:

VSP = Xmax x Sd x Ds x N / 810000

where Xmax is in mm, Sd in cm^2, Ds is the effective front to rear separation in cm, and N is the number of drivers. For 100 dB at 30 Hz VSP must equal 1.0