Why did Vintage SEAS Rubber Surrounds Hold Up Fine For Over Lifetime?

[zastin17]

Something that I was curious about, is the Rubber Surrounds used on Seas drivers.

Used on the 1960s Beovox Line, and Dynaco Line of Speakers aswell.

As you know, rubber this age is almost never going to be ok. Its usually dry, cracked, melted, or anything in-between.

I have seen many of these speakers, and not 1x of them has had a single sign of that Rubber surround going bad after 60+ years!!! its as pliable and brand new as Rubber can get!!! But its infact 50+ year old Rubber and that is kind of blowing my mind thinking about it.

WHAT IS THIS ""MAGICAL"" RUBBER? And why was it not used for Rubber belts, capstans, everything else? Makes me think a bit about that a bit.

Is it even a Rubber?

 

[alteclipsch]

I'm no chemist, but I believe the surrounds you're discussing are butyl rubber, a synthetic elastomer used in many, many applications that call for durability, flexibility, and resistance to chemicals. So much better than foam, but more expensive, that's why foam is so popular, even in premium speakers (unfortunately). IMO.

 

[Lavane]

Marantz used butyl rubber surrounds with some of the speakers they made. The Imperial 6's I have still sound good and the butyl surrounds have held up well.
I did.rotate them 180° when I got them. They can sag a bit over a long period of time.

 

[jdurbin1]

The popularity of foam as a material for surrounds isn't just down to cost, it provides the designer a lot more options for tuning than other materials like butyl rubber. It's generally more tunable, in short - makes it easier to nail exactly the mechanical compliance desired for a specific tuning.

John

 

[bowtie427ss]

Neoprene, and santoprene were both used for speaker surrounds at some point.

 

[elitopus]

When I was into car audio 20 years ago I remember subwoofers having santoprene surrounds was a thing. It might not have been new then but it was popular on the nicer drivers.

 

[Tom Brennan]

I'm no chemist, but I believe the surrounds you're discussing are butyl rubber, a synthetic elastomer used in many, many applications that call for durability, flexibility, and resistance to chemicals. So much better than foam, but more expensive, that's why foam is so popular, even in premium speakers (unfortunately). IMO.

Foam can have superior cone damping to rubber and that's why some companies use it. Years ago I was in a speaker building club and at a meeting a driver designer from Jensen built and tested drivers that were identical save that one had a foam surround and the other rubber. The driver with the rubber surround showed a resonant response peak lacking with the foam surround.

Harry Olson's famous RCA LC1 coaxial driver used a foam ring in the surround to damp resonant behavior of the cone.

 

[Yodathedog]

I have a pair of original AFS L400s I bought back in the early 70s that are still useable today with the original woofers and their original surrounds.

But I don’t think the OP’s question is being answered. Why has this rubber survived for so many years?

 

[alteclipsch]

I don’t think the OP’s question is being answered. Why has this rubber survived for so many years?

I didn't mean to derail this thread by adding my thoughts about the pros and cons of foam vs rubber. What I should have said was synthetic rubber inherently has properties that resist deterioration from light, oxygen, ozone, etc., that foam doesn't. That's why it's used in roofs, tires, and speakers. It just lasts.

And I'll stand corrected on foam's positive effects on speaker behavior. But I still don't like materials that deteriorate quickly, so I've never owned foam speakers. I don't think I'm really missing anything.

 

[elitopus]

Honestly, unless someone here worked at Seas or Scanspeak around the time the drivers for the Dynaco A25 etc were manufactured, and knows what rubber they used and why, we’ll probably never know the exact reason. Just that it’s good quality rubber.

 

[WaynerN]

Foam was used in many acoustic suspension speakers (AR, Advent, etc). Oddly, I have some ported models that have the same foam surround. What the heck????

 

[alteclipsch]

Foam was used in many acoustic suspension speakers (AR, Advent, etc). Oddly, I have some ported models that have the same foam surround. What the heck????

I doubt foam surrounds would be exclusive to sealed cabinets. The way I see it, foam is primarily a suspension, not just a sealer, similar to cloth, paper, and rubber.

 

[Yodathedog]

I doubt foam surrounds would be exclusive to sealed cabinets. The way I see it, foam is primarily a suspension, not just a sealer, similar to cloth, paper, and rubber.

Many Polk speakers use rubber surrounds and many of their speakers are ported.

 

[WaynerN]

Well, early models of ARs used a doped cloth surround, but was replaced by foam because it was more compliant. For ported versions, it may have been merely a cost of manufacturing consideration (as time went on).

 

[bowtie427ss]

Well, early models of ARs used a doped cloth surround,

It was the best they had at the time.

but was replaced by foam because it was more compliant.

Certainly foam is also much more uniform(in compliance) across it's circumference, and more stable across varying environmental conditions.

Doped surrounds can be quite variable, there's really no precise way to determine if a surround has too much, or too little. The viscosity of doping compound can vary with temperature, and in hot climates surround dope can get loose enough to migrate under the force of gravity.

Even though most foam has a finite lifespan, i think it was a significant improvement over doped surrounds for most pedestrian applications.

 

[WaynerN]

Well of course, that is why AR went with the foam after a period of time. I have an AR-4x and AR-2ax that still had the doped surrounds. My original AR-2ax that I bought back in the early 70s (like maybe 1973) had foam by then. My current ARs have plywood cabs, newer ones were MDF.

 

[nefertem7]

My current midrange drivers are from Scanspeak in my home speakers and I have Bravox system in my car all use composite rubber surround