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Old December 3rd 20, 08:08 PM posted to rec.audio.tech
geoff
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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.
>>>
>>> *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.)


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

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