Stuffing myself

[fixtillbroke]

Hi Mark-

I am finishing a re-surround job on my $5 yard sale Large Advents. When I opened the cabs I was surprised to find 6 pieces of open cell foam for stuffing rather than fiberglass or poly. I hesitate to reuse these foam blocks when I remount the woofers. Has anyone made a similar discovery or switch with their own Advents, or any speaker that came with this stuff? I didn't play the speakers very much when I brought them home due to the condition of the surrounds, so I won't really know if there will be a change when I repack with the poly. Maybe I should do one of each and compaire....Hmmm. Pete

[Guest]

I have 2 pair of the "New Large Advent", and 2 pair of the Advent/1. All 4 pairs have the foam blocks and are original equipment.

[Guest]

The foam blocks were used as a “healthier” replacement for the fiberglass before they started using poly-fill, but unfortunately foam does not behave acoustically like loose fiber fill [fiberglass or poly].

Lining the walls of your cabinet with up to an inch of foam can help cut down on internal standing waves and reflections, but filling the box with foam is not a good idea. Loose fiber fill behaves in such a way that it makes the enclosure seem larger to the woofer by as much as 20%, even though it occupies some physical space itself. Foam dampens mid/high frequency reflections better than fiber fill, but its too “solid” and actually winds up reducing the apparent box size seen by the woofer. This over damped state leads to a reduction in volume output and raises the point at which the bass rolls off. The same thing can happen when a cabinet is stuffed too heavily with fiber fill.

I usually recommend removing all but one of the foam blocks and filling the cabinets with poly fill [leave one block directly behind the woofer, this damps the crossover components]. The cabinets should be lightly filled, not packed tight. This simple change gives a small but very noticeable boost to the LA’s low end output. Just use regular $3/ 20oz bag poly-fill from your local discount mart or fabric store, the “magic crimped” fill selling for $10/pound works no better.

You can also pick up another dB or so plus some detail by switching out the woofer’s stock filter coil [.8mH] for a heavier gauge low-resistance model. The stock coil is wound from thin gauge wire and has a fairly high resistance, about 0.5 ohm. A good 14ga steel laminate inductor will have less than 0.1 ohm resistance so you have virtually no signal loss through the filter.

[Guest]

DON'T DO IT! At least I wouldn't replace the foam blocks with other fill in the Advents. Yes, The foam blocks were original equipment...I would venture to guess that with all the thinking that went into the design of those speakers, the engineers had a good reason for using the foam rather than a fiberous poly or glass fill. I'm sure that if you would restuff one with a fiber fill and compare the sound to the other one, you would notice some tonal difference. I suppose it wouldn't hurt to try your test with one speaker - if you have the time to do it and let us all know the results - but be sure not to damage the foam removing it from the speaker and take note of how the pieces are stacked inside the cabinet, because I bet you'll wind up putting the foam blocks back in after it is all said and done! Besides, if for some strange, demented reason you would ever want to resell those speakers, they might be less desirable to others if the foam blocks were replaced with "non-stock parts"! I would only consider replacing the foam if it was musty or moldy or deteriorating badly...if it ain't broke, don't fix it - so why attempt to "fix" a work of art?!

Troy