-september.org> e715e3ec   
   From: zekor@comcast.net   
      
   Dave Platt  wrote:   
   >> I have some nice speakers made with remnants from Parts Express excess. 8   
   >> inch woofers have a rubbery type surround. Just in the last two years the   
   >> surrounds started breaking what looks like tearing apart. I have redone the   
   >> two sets with rubber replacements think they are working well. Just   
   >> wondered if anyone knew what type of rubber they used. I guess they were   
   >> made in late 80s by Onkyo, so that would be about 30 years old. The driver   
   >> was on the front cover of a Speaker Builder Magazine with Keith Johnson.   
   >   
   > From what I've seen, speaker surrounds are most commonly made either   
   > of a closed-cell foam, or of butyl rubber.   
   >   
   > They are not necessarily interchangeable.  Rubber surrounds are (I   
   > believe) both heavier and stiffer than foam surrounds of the same   
   > dimension.  Their weight, and lower compliance can change the acoustic   
   > characteristics of the speaker - quite possibly enough to de-tune the   
   > speaker/enclosure relationship and throw off the speaker's frequency   
   > response.  This would be more of an issue with vented/ported/   
   > bass-reflex enclosures than with sealed (acoustic-suspension) systems.   
   >   
   > Rubber surrounds seem to have a longer lifespan than foam surrounds,   
   > but they can go bad over time.  I had to replace the rubber surrounds   
   > on a pair of 4" drivers in some Optimus AV mini-monitors - I believe   
   > they'd been used outdoors, and sunlight and heat had caused the rubber   
   > surrounds to become stiff and brittle.   
      
   Someone on this group might have known about these drivers. I don't have   
   many rubber surrounded speakers, but these were a first for me. All of hese   
   drivers seem to have failed about the same time regardless of use,   
   including being in original shipping container.   
      
   Greg   
      
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