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Foam surrounds. What were they thinking?

 
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Lee in Montreal
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PostPosted: Fri Jul 23, 2010 6:45 pm    Post subject: Foam surrounds. What were they thinking? Reply with quote

My Calindas, Cantatas and 105/2s have perfect woofer surrounds, despite being 25 to 30 years old. Any B110, B200 or B300 is in new condition despite their age. On the other end, you got 104/2s and 107s with rotten woofer surrounds. What separates them? Rubber surrounds on one hand and foam on the other.

I just bought four 1985-vintage B300B and the surrounds are like new. I wiped the membranes and surrounds with alcohol to remove grim and dust and they look like I just bought them.

So, the big question is: what quality of cocaine were the designers at Kef snorking at production meetings (remember the mid-1980s?) when they decided to use foam surrounds on woofers when they already had proven rubber surrounds already in production? Wink

We want the name of whoever approved that... Wink
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Kef Calinda - since 1979
Kef Cantata - since 2009
Kef 105/2 - since 2009
Evo 105/2 - in the build


Last edited by Lee in Montreal on Fri Jul 23, 2010 7:16 pm; edited 1 time in total
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proffski
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PostPosted: Fri Jul 23, 2010 7:07 pm    Post subject: Re: Foam surrounds. What were they thinking? Reply with quote

Surround compliance is part of the complex design criteria.
Just about every famous loudspeaker manufacturer has suffered this problem, I doubt if the foam rot was forseen or anticipated.

The surround has more duties than merely keeping the cone in place.
If you can find a copy of "High Performance Loudspeakers" by Martin Colloms it is explained well in laymans terms.

Most amateur DIY loudspeaker builders I know own this veritable bible as of course does yours truly.

http://www.amazon.ca/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=High+Performance+Loudspeakers&ih=20_9_0_0_0_0_0_0_0_1.124_171&fsc=-1

The price range of the book on Amazon Canada is amazing! Shocked
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audiolabtower
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PostPosted: Fri Jul 23, 2010 9:38 pm    Post subject: Reply with quote

we talked about this in a previous thread, and I made much the same point. They came in with coupled cavity loading, and Speakerguru explained that this form of loading needed a lightweight diaphragm with low resonance freq - hence the foam surround with paper cones. They were all taken by surprise at how relatively quickly the foam deteriorated compared to the previous generation pvc surrounds.

Do any models still use foam surrounds nowadays?
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proffski
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PostPosted: Fri Jul 23, 2010 10:00 pm    Post subject: Reply with quote

I still have a pile of original Son Audax foam surround drivers and the foam is perfect.

But, they are still in their boxes with no sunlight creeping through or household vapours, and they are in room with no central heating either!

Now I'm curious as to how long the ones I used in my friends centre speaker will last as well as the ones I made for the schools physics department? Confused
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audiolabtower
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PostPosted: Sat Jul 24, 2010 3:20 pm    Post subject: Reply with quote

proffski wrote:

But, they are still in their boxes with no sunlight creeping through or household vapours, and they are in room with no central heating either!


good point, so if there's no uv inside a coupled cavity, heat/humidity and vapours? or just age?

Maybe age, my Spendors have a plywood cutout for the grill, covered in 1/4in of foam under the BBC tygan?/vynair? type grill, and after nearly 30 years that foam is crumbling.

Yet the polyester damping foam inside the Spendors and Kef References is still rigid and perfect, although coarser than that grill bulking foam.
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proffski
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PostPosted: Sat Jul 24, 2010 4:13 pm    Post subject: Reply with quote

I have seen foam rot inside loudspeakers a plenty, including KEF!

By far the worst were other makers units using reflex tuning in a household full of smokers, they reeked! The foam just turned to crumbs.
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audiolabtower
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PostPosted: Sat Jul 24, 2010 5:34 pm    Post subject: Reply with quote

that's interesting, smoke must be an accelerant? My speakers have never seen smoke from new, so eventually age must be the eventual limiting factor. Interestingly the Spendor grill foam is much softer than the internal damping foam, presumably this makes it more vulnerable in comparison since the BC1s are also reflex and open to the surroundings.

I see that few Kef104s (which I once had) have their grills intact either.
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TL 200
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Location: Emmer-Compascuum The Netherlands

PostPosted: Sat Jul 24, 2010 6:26 pm    Post subject: Reply with quote

audiolabtower wrote:
that's interesting, smoke must be an accelerant?


Talking about accelerants, my brother owned a pair of AR 28 S, two way bookshelf speakers.
When repainting the livingroom he put them in a spare bedroom for safety. Sadly enough he stored a jar with thinner in which he saved his paintbrushes overnight in that same small bedroom.
You can guess what happenend to the surroundings....... first they were very sticky, after "drying" a while they crumbled.
I've replaced them with a couple of B-200's i had for spare, the AR's never sounded that good before. Now they're all busted because of some stupid DC-pumping Sansui Sad
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rossalator
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PostPosted: Thu Sep 30, 2010 4:25 pm    Post subject: Reply with quote

Hi people, im a newby here.

Just a quicky on the subject of foam rot, i have this pair of dantax "studiopower metal cone" speakers, well aware they are awful sounding , i brought them for £2 off a boot sale in awful condition, i basically needed a speaker i dont care for to use with my electronic drums.... these things have two 8" with foam and a 4" also with foam, the cabs had been in a very damp place and the boxes all swelled, still wet inside...with the bottom of one flapping open ...

i basically bodged the boxes, glue and screws to hold them together so they dont fall apart while i use them..... had them a year and decided to replace the tweets and sort out the terrible crossover, they sound alright now and 3 years down the line the foam is still intact ! they take some stick as well !

i dont get it, if any surround should have rotted it should be these !?!
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audiolabtower
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PostPosted: Thu Sep 30, 2010 9:23 pm    Post subject: Reply with quote

Hi, have you any idea how old they are? Maybe age is the primary factor, but secondary factors like smoke and chemical vapours act as accelerants. If the foam is relatively new (compared to the 20 or 30 years we are talking about here) maybe moisture and "clean" water vapour does not affect that badly in the short term? Still an interesting story Smile
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Pyrrho
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PostPosted: Tue Jul 19, 2011 4:43 am    Post subject: Reply with quote

rossalator wrote:
Hi people, im a newby here.

Just a quicky on the subject of foam rot, i have this pair of dantax "studiopower metal cone" speakers, well aware they are awful sounding , i brought them for £2 off a boot sale in awful condition, i basically needed a speaker i dont care for to use with my electronic drums.... these things have two 8" with foam and a 4" also with foam, the cabs had been in a very damp place and the boxes all swelled, still wet inside...with the bottom of one flapping open ...

i basically bodged the boxes, glue and screws to hold them together so they dont fall apart while i use them..... had them a year and decided to replace the tweets and sort out the terrible crossover, they sound alright now and 3 years down the line the foam is still intact ! they take some stick as well !

i dont get it, if any surround should have rotted it should be these !?!


Supposedly, many manufacturers now treat foam such that it will not fall apart with time, or at least not for a very long time. I have been told that "foam rot" is really a fungus eating the material, and consequently, environmental factors affecting the fungal growth affects the rate of decomposition. The "treatment" of the foam is a fungicide. Thus, if one buys a quality replacement that is so treated, when one gets one's speaker refoamed, it should last indefinitely.

I have some relatively new speakers that supposedly have treated foam that is supposed to last indefinitely, and I had some speakers refoamed with foam that is supposed to last indefinitely. But it is all too recent for me to have any real way of knowing if I have been lied to or told the truth. If I am still around in 20 years, I should have a good idea by then whether or not they are lasting better than foam surrounds of the past.
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ColinR
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PostPosted: Wed Jul 20, 2011 7:42 pm    Post subject: Reply with quote

I would suggest foams from Speakerbits of Melbourne Australia.
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