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These are photos of the headphones that I use in my ham shack. As you can see, the dark gray foam rubber inside is deteriorating, and I need to replace it. It appears to be open-cell foam "rubber" between 1/8" and 3/16" thick.

One of the headphones has had little use (bought it as a spare) and shows the original size of the hole centered around the element's sound holes.

They are military surplus communications phones with just the right frequency response for SSB ham radio use.

That foam is holding the elements in place. Notice that one element where there is almost no foam left is loose. However, it is not particularly stiff. That may or may not be because it is so deteriorated.

Does it matter what kind of foam is needed to replace this deteriorating stuff? Regardless, where can I get it? (It doesn't matter what color it is.)

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    $\begingroup$ type probably doesn't matter much – the differences in attenuation at these thicknesses will, if at all, be measurable at highest audible frequencies. Where to get it – no idea, but I'd check DIY Speaker community forums for supplier of audio materials. $\endgroup$ – Marcus Müller Mar 2 at 20:16
  • $\begingroup$ Thanks @MarcusMüller. Do you have a link? $\endgroup$ – Mike Waters Mar 2 at 20:23
  • $\begingroup$ Everytime I take these phones off, some of that foam sticks to my ears. :-( I have always had oily skin. Maybe that's contributing to the foam's deterioration. $\endgroup$ – Mike Waters Mar 2 at 20:25
  • $\begingroup$ best I could find $\endgroup$ – Marcus Müller Mar 2 at 20:36
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    $\begingroup$ Whatever you replace it with, do not bother to cut out the hole over the speaker element. It is not necessary for such a thin absorber and is likely contributing to the degradation $\endgroup$ – Chris K8NVH Apr 14 at 12:49
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Out of left field - If function is the only cause and fashion isn't an issue, use a couple of black cotton socks. On my headphones the plastic outer pieces are removeable. I cut the ends off two socks, slid them over the phones and my wife sewed them in place. Comfortable, although the seams do show a little. I don't care! Cost nothing and works fine!

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Audiophiles like to replace those plastic and foam earpads with a velour product such as this:

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If red doesn't suit you, there are other choices. There are several vendors for this type of product, with Brainwavz Audio as one example.

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To directly answer your question, the exact-replacement material would be open-celled polyurethane foam with a density of about 2.0 lb/ft^3 (30 kg/m^3). This can be found at just about any foam outlet store.

Alternatives:

  • It does not have to be polyurethane but I have found polyurethane to be far more durable than other foams.

  • The density can be adjusted; heavier foams will provide a little more absorption at lower frequencies and a little less at higher frequencies.

  • Open-celled foam is better for sound absorption than closed celled foam

Having said that, I understand the function is to reduce reverberation in the air space between the outer shell and the ear. For that, the best sound absorbers are fibers rather than foams. So a non-woven fiber such as Thinsulate or even a few cotton balls would work better than a foam. Materials such as this can be found in old coats or gloves.

@Doc 's suggestion of cotton socks is an excellent one. A little bit of absorption is lost due to the woven nature of the fibers, but it is still a very good absorber.

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