Electro-Voice Foam Surround

Non JBL example but have wondered with them all. This is a photo I lifted from an auction.
I own a pair of these and just recently re-edged them (that's why I don't have a photo) with some of Rick Cobb's surrounds. The old surrounds had a shiny treatment on them; I never knew for sure who applied it, now thanks to this photo I know, EV did. And you can see the marks in it, that it was applied after the fact (not just the way their surrounds looked to begin with).

These drivers run in a ported box. Can anyone tell me why they applied a sealer or dressing on their foam surrounds? These 12"s with foam edges are fairly rare for EV, or so I have heard/read. Mine are in monitors (indoor), Sentry 500s, same as the photo.
Was/is this treatment a carryover from musical instrument/sound reinforcement and foldback use? (drivers exposed to the elements).
Any reason I should treat them?
Thanks

Thomas

http://i.ebayimg.com/images/g/YAAAAO...rN/s-l1600.jpg

I don't know what it is, but M&K used it as well, and I think Velodyne too. It could be there to prevent foam rot. In the case of the M&K,(volkswoofer), the foam disintegrates behind the coating anyway.

I have a pair of 2234Hs that have been re-foamed in a similar fashion....curious as well.

I expect it was to extend the life of the foam. My parents had EV Interface A speakers. Both the woofers and the passive radiators rotted away. The passive radiators completely fell apart since there is no voice coil spider. Unfortunately, my Dad threw them away, they probably could have been fixed. I've got a pair of Interface C speakers, the 10" woofer surrounds have never rotted. I'll take a closer look at them, they might have a butyl rubber surround.

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Originally Posted by dr_gallup

I expect it was to extend the life of the foam. My parents had EV Interface A speakers. Both the woofers and the passive radiators rotted away. The passive radiators completely fell apart since there is no voice coil spider. Unfortunately, my Dad threw them away, they probably could have been fixed. I've got a pair of Interface C speakers, the 10" woofer surrounds have never rotted. I'll take a closer look at them, they might have a butyl rubber surround.

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I think you (and Don C) called it.
I wrote a well regarded speaker man, in my opinion the best, Bill LeGall of Millersound.

http://www.millersound.net/indexfl.htm

His feelings were as follows:

I don’t know what was the exact reason, but here are some choices for you to ponder:They may have felt that the foam required further damping (I don’t)Slow-down the time it could take until it rots, as it was urethane foam (Slightly likely)They may have felt the foam was porous (It could only be slightly porous and wouldn’t matter in a ported system)They may have felt it needed to be slightly more elastic and/or stiffer (I doubt it)Don’t bother to coat the surrounds.Best RegardsBill

When I was working at Kenwood in the early 2000s, some of our high-power 10" and 12" car subwoofer drivers had surrounds that looked like that. They were made from stuff called "Meltoam", which was basically thick foam that had the top and bottom surfaces melted. The benefit was supposed to be added strength, yielding higher power handling while retaining foam's low Fs. Sort of a combination of foam and rubber. Never heard 'em; have no idea about performance or long-term robustness. (Can't remember the model numbers—that was a dozen years and several employers ago; had to do a brain dump of no-longer-useful information between each.)

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Originally Posted by hsosdrum

When I was working at Kenwood in the early 2000s, some of our high-power 10" and 12" car subwoofer drivers had surrounds that looked like that. They were made from stuff called "Meltoam", which was basically thick foam that had the top and bottom surfaces melted. The benefit was supposed to be added strength, yielding higher power handling while retaining foam's low Fs. Sort of a combination of foam and rubber. Never heard 'em; have no idea about performance or long-term robustness. (Can't remember the model numbers—that was a dozen years and several employers ago; had to do a brain dump of no-longer-useful information between each.)

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The stuff on the EVs was clearly applied after the fact; not a part of the surround itself as manufactured, definitely a topical application. Was obvious during the re-edge job as well.
If your monitor's resolution is high enough you can see the brush marks in the photo; they are very easy to see in person.

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Originally Posted by hsosdrum

Sort of a combination of foam and rubber.

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It's Flubber!