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How do you preserve old (but good) foam surrounds?

jhoyt

jhoyt

Incomprehensible space llama
My Technics SB-7000A's have perfect foam surrounds. BUT, they are approaching 35 years old, which is Methuselahesque. Nearly every other pair of these old Technics speakers that I've ever seen have had rotted foam.

So,

Is there a way I can preserve the life of the foam? Kind of like how Keith Richards is old but well preserved?

For starters, the front of the speakers never see the sun, and the backs just barely. The speakers have always been in a climate-controlled environment, never left in a storage shed or barn. They are used nearly every day.

What can I do to preserve them for the future?
 
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jhoyt said:
For starters, the front of the speakers never see the sun, and the backs just barely. The speakers have always been in a climate-controlled environment, never left in a storage shed or barn. They are used nearly every day.

What can I do to preserve them for the future?
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sounds like you are already doing it.

but they will fail eventually.
 
If you want to try the Keith Richards approach, keep it soaked in alcohol. :banana:

Seriously, I don't think there's any way to cure it without losing the nature of the speaker.
 
Ed in Tx said:
I've used this on several speakers, my original foam Realistic Optimus Pro77 I use as computer speakers, a pair of Baby Advents, my 4 HPM-150 woofers first ones I did back in '92, foam all still in good shape, and if there was any change in speaker response I sure could not detect it, a non-issue as far as I am concerned as an actual user of this product. :thmbsp::thmbsp:

http://www.simplyspeakers.com/speaker-repair-cone-edge-sealer-mi-1291fg.html
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If you value your bass response more than the life of your foams, don't use this stuff because it will stiffen up the foam's inherent flexibility and raise resonant frequency. If, OTOH, you value your foam's life more than bass response, then eventually the foam will rot from the underside (if not coated as well) and leave you with a thin film of PVA as your sourround.
 
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The obvious is to keep them in low humidity, and not exposed to too much direct sun light. The problem with the foam I believe, is that they are petroleum based which develops a fungus that breaks them down.
I would really like to know how the foams were done on the early Realistic Mach 1 woofers (4024), because they do not rot. The second version (4029) did rot just like most other brands.
I'm not sure if something else like silicone was added to the foam on the (4024) or if they were just coated. Seems like a coating would peel off over time but there is no sign of that.
If someone could figure out what they used and make replacements the same way it would be a blessing for us speaker collectors. :yes:

My original Mach 1's are from July 1978, and the surrounds have never been replaced. There is no problem with them even getting stiff, or falling apart.
 
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spkrdtr said:
If you value your bass response more than the life of your foams, don't use this stuff because it will stiffen up the foam's inherent flexibility and raise resonant frequency. If, OTOH, you value your foam's life more than bass response, then eventually the foam will rot from the underside (if not coated as well) and leave you with a thin film of PVA as your sourround.
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Have you used it? I have. 21 years ago. HPM-150 woofers X4. No problems. Still work fine. Still flexible. Have lasted twice as long as the originals. I speak from experience.
 
botrytis said:
I speak from a chemists background. anything you put on foam will eventually stiffen up and foam will crack. Also, it has to chemically modify the foam to do it's job. That is a glue and it will stiffen up.

If you value the speakers - don't use it. Changing the foam is best.
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There's a certain amount of risk changing out foam surrounds more than once.

I just went in and checked the foam surrounds of my HPM-150 woofers I put that on 21 years ago, sold by Simply Speakers, coincidentally one of AK's vendors now. Still nice and flexible, no problem at all. Excellent condition, not stiff at all.
 
btw... the stuff Simply Speakers sells is very thin and watery, so it penetrates into the foam and does not make a film on the surface allowing the foam to rot from behind as someone posted.
 
jblmar said:
Do nothing!
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spkrdtr said:
If you value your bass response more than the life of your foams, don't use this stuff because it will stiffen up the foam's inherent flexibility and raise resonant frequency.
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Ditto.

Fortunately for you, the foam surrounds on the SB-7000A are some sort of non-standard formulation that seems to be aging quite gracefully. Lucky, too, because the woofer's a bastard size.
 
I would suggest placing statues of Fu Lu Shou (God of Longevity) near the speakers.

33049.jpg
 
Ed in Tx said:
Have you used it? I have. 21 years ago. HPM-150 woofers X4. No problems. Still work fine. Still flexible. Have lasted twice as long as the originals. I speak from experience.
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I'm sure they are still flexible. It's all relative. However, I'm sure they are not as flexible as before. You may not have noticed the effect is all.
The same stuff was used by many to seal old cloth surrounds whose dope had hardened and flaked off. I've experimented here with this specific problem - treating a surround and accelerating ageing by putting the treated woofer in a low temp oven for awhile and measuring Fs.
Something that does work for cloth surrounds is sold by vintage-AR on *bay. It may also work to preserve foam, but it's VOC's may do more harm to the foam than good. RoyC who posts here knows more about it.
 
I have done measurements of the Simply Speakers product as well a number of other water based "white" compounds advertised for this purpose. While this stuff *may* preserve the foam somewhat, it definitely reduces compliance. Fs increased by 10 to 20 hz (after drying) on every woofer surround I tested it on. This is not at all good for an acoustic suspension speaker.

Unfortunately, the cloth surround sealant sold by Vintage AR will damage foam.

It is best not to apply anything to foam surrounds.

Roy
 
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No oxygen, no UV, no pollutants. Keep them in a pure dry nitrogen environment in the dark. Slow any reactions by keeping the temperature low. I have some drivers in storage that are holding up well in the cool and dark, but it's hard to get any music out of them under those conditions.
 
jsisk said:
I would suggest placing statues of Fu Lu Shou (God of Longevity) near the speakers.

33049.jpg
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I think I'll just go this route, rather than applying any sort of doping. This, and sacrifice a chicken before listening sessions. Should do the trick. Thanks, all, for the good education!
 
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