-september.org> e715e3ec   
   From: shaun.at.pukekohe@gmail.com   
      
   On 1/12/2020 1:28 pm, gregz wrote:   
   > 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   
   >   
      
   Oxygen alone will break the foam surrounds down so it doesn't matter if you   
   use them or not, they   
   last 20 - 30 years max depending on the thickness of the material. (Unless   
   they're stored in an   
   oxygen-free atmosphere.)   
      
   Rubber surrounds can last 50 years. However if they're stored and not used for   
   a decade or so   
   they'll go hard and brittle. Also UV light and/or excess heat will cause   
   similar degradation.   
   --   
   Shaun.   
      
   "Humans will have advanced a long, long way when religious belief has a cozy   
   little classification   
   in the DSM"   
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