View Single Post
  #5   Report Post  
Posted to rec.audio.tech
geoff geoff is offline
external usenet poster
 
Posts: 1,812
Default Onkyo Precise Acoustics

On 2/12/2020 5:39 pm, ~misfit~ wrote:
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.

Â*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.Â* Rubber surrounds are (I
believe) both heavier and stiffer than foam surrounds of the same
dimension.Â* 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.Â* 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.Â* 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.)


I remember when I picked up my KEF R107s of TradeMe when opening and
looking down with a torch, I could see right through the two bass driver
surrounds to the bottom of the cabinet !

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.


The butyl on my B110s on LS3-5As after 'just' 40 years-ish.

geoff