Hi, The originals were foam type surrounds. How noticeable the difference is will be purely dependent on the listener. If you are trying to keep things to the original design then stick with foam surrounds. It would be interesting if you were to do one with foam surrounds and the other with rubber, then see if you can tell a difference. Those are pretty easy drivers to replace surrounds on so it wouldn't be difficult to try. Plus, those being small drivers, the surrounds don't cost much. If you do the test be your and post about it here. -sonavor

The originals were foam, therefore I'd replace them with foam. Changing to rubber will alter the parameters of the drivers and make them sound different. Whether this is an improvement or not is purely subjective.

Specifically changing from foam to rubber will alter the low frequency resonance changing the bass response.

I will try to compare and return with my perspective as I have both. /Pindsen

Foam, where foam was used originally. Repalcing with rubber changes the T/S parameters drastically. If you only had the T/S to compare, you would never suspect it to be the same driver. Martin

What does T/S mean? /Pindsen