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AR-11 Tweeter and Woofer "decorative" foam

Pete B

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The subject of replacement foam for the tweeter and the decorative edge around the woofer has been a subject here on the forum. I wanted to point out that most fabrics and foams, if not all, do not completely absorb the acoustical energy that hits them and there is in fact diffraction off the material. It can actually make the tweeter response worse having material very close to the dome as the short distance/delay causes irregularites at higher frequencies. The thin felt tweeter ring commonly available actually makes the response worse. The blue trace in the linked diagram is with no treatment, and the yellow with a 1/8" felt ring:


One issue is that the ring geometry has perfect symmetry and as a result there is no "spread" in the delay causing strong constructive and destructive interference. Some have used a "starfish" cutout pattern to provide some spread in the delay time as can be seen here:

McMaster-Carr is a good source of raw materials:


I'm thinking that a very thin layer of black felt might be the best solution for the woofer frame since it will not deteriorate.

Pete B.

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