Tweaker's Asylum

Posted by Jon Risch on January 29, 2000 at 08:34:22:

In Reply to: Felt for speaker bafles posted by Rob Bertrando on January 25, 2000 at 20:36:23:

Most felts are not that good for this purpose, as they will reflect a lot of HF energy and cause worse diffraction thanthey are trying to reduce!!

If you must go with the felt, use a low density felt, the wool is better than synthetic fabics, and the thicker the better. 1/8" or 1/4" will not do that much help, at least 1/2" thickness is needed, and 3/4 or 1" is better.

What does work really well is either plain fiberglass (RS used to sell 1" thick fiberglass that was ideal to make a baffle blanket), or a low density polyester batting (the 'Hi-loft' kind). Yes, they look ugly, even compared to the felt, but they are the best, and will not reflect HF's.

Since they are usually available in sheets or rolls, you can cut out a hole for the tweeter and the woofer/midrange, and cover the entire baffle, right up to the speaker grille frame edges, and maximize the diffraction reduction.

Foams can also be used, but they MUST be the proper kind. Neoprene sponge rubber IS NOT any good (nor is the tweeter ring made out of this material sold by a Canadian magazine), nor is mattress foam, etc. It must be the proper density (medium-low) acoustic grade foam, which can sometimes be obtained in sheets.

Jon Risch