foam or felt in the cover

[louped garouv]

so, I know that JBL used a bit of foam in the back cover
of the 244* drivers, which had a tendency to degrade over time...

and Altec used felt in the back cover of the 802 series drivers...


if replacing foam in the JBL drivers,
would it be OK to use felt, as it does not degrade
like the foam would...


pros/cons of each?

other opinions?

[4313B]

Having replaced tons of that nasty foam with more foam I'm going to start looking for some felt. I'm finally fed up with the foam.

[subwoof]

I found a small sheet of the multi-colored mosaic carpet underlayment at a fabric store - it's thickness was almost the same as the 244X foam and it worked well but haven't found any lately..I have also seen it used inside jackets.

I remember that altec used it for some of the 800 series drivers. Have a boatload of drivers in storage and it's time I found some more of it. When I do I will post the info.

sub

[grumpy]

... I've used the same material..., time will tell if it was a good idea.
I'd be interested to hear how your 800-series Altec's have fared.

[badman]

Mc-master carr sells F11, F13, etc. felt (you want the heavy wool content) that is appropriate for the task. Members in soCal are welcome to pick up a small piece from me if it's more convenient, I've got enough to share. You can use a lot of this stuff though, so if you want more than a couple driver's worth you should just order some. It makes great baffle treatment (absorbtion before the diffractive cabinet edges).

[grumpy]

Good to have a source (or two ). Thanks for the reference and kind offer!

[herki the cat]

Having replaced tons of that nasty foam with more foam I'm going to start looking for some felt. I'm finally fed up with the foam.

Been there !!___ In 1972 a co-worker in RCA Camden bought a huge roll of "Sound Coat Inc., Acoustic Foam, 2 " by 6 ft by 20 ft costing him $400, which we were going to share. We never found time to stuff this junk-goop into a kit, of his__ two, & my__ four, RCA LC9-A horns.

Thirty years later in my friends garage, this huge roll of "sticky muck" collapsedto to the floor & the poor guy's hair turned White! We were gratefull this sticky melt-down did not occur around our priceless drivers and the inside surfaces of our horn enclosures..

Foam is worse than you think. Most foams are made from polyurethane which ultimately reverts to a liquid sticky state similar to the parent polyurethane paint finish-genere . The sticky foam crumbs disloge & do move around__ not a good idea around exquisite, priceless LE 175, LE 85, & the 2420 professional driver aluminum diaphragms, which are no longer available from JBL. For the 375 & 2440 drivers, the replacement diaphragms cost some $250 each if you are lucky to find stock.

Felt damping against titanium diaphragms in the 2425 / 2426 drivers sounds like a better choice__ By all means, wool felt is ideal & it is available from professional Artists Etching-Press Supply Sellers & other industrial sources.
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cheers, herky the cat

[robertbartsch]

I don't care too much for foam surrounds that also melt with time.

[sonofagun]

"Most foams are made from polyurethane which ultimately reverts to a liquid sticky state similar to the parent polyurethane paint finish-genere."

The foam I use does not disintegrate or rot - is an improved formula.

Course, you should allready know that