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Alternative surround dope ... Lexel

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I just wanted to post that I found an easy to find, easy to use replacement product for Butyl/Toluene as dope for our speaker surrounds that I’ve never seen mentioned. The product is Lexel. It’s an elastic synthetic rubber caulk with properties I believe meet and exceed the Butyl Rubber that KLH used to dope the surrounds in our speakers.

Butyl Rubber is a synthetic rubber falling into a classification of an elastomer (elastic+polymer) which includes natural rubber and synthetic rubbers. There are two main properties of elastomers that we are most concerned with, elasticity and hardness.

After as much research as I could dig up, the butyl rubber caulks that we can get have an elasticity fully cured of around 200-250%. This means you can stretch/displace it to twice the size and it will rebound to it’s original size. Lexel has a listed fully cured elasticity greater than 400%. Twice as elastic as butyl.

As to hardness, the butyl caulks I researched list a hardness, on the “Shore A” scale of around 60. This is compared on most charts to the hardness of the tread of a tire. A pencil eraser is about a 40. Lexel has a “Shore A” measured hardness of 25. Very soft. That’s means it will remain twice as soft as butyl fully cured and is compared to a rubber band on most charts.

Lexel (clear) contains only whatever synthetics rubbers they are using (they don’t say) and two solvents for ease of application that evaporate away. Naphtha and Toluene. It should be easily thinned by adding some more of either or even just some mineral spirits.

Best thing is it is readily available at Lowes or Home Depot and a 5 oz. tube costs about $6. Having a clear is also important to me as my surrounds are the yellow/orange color of the early manufacture and I’d like to keep them that way vs black or white.

I’ll be using it this weekend on my 60’s vintage 17’s but I only have my ears to measure the effectiveness. I’d love some comments or if someone can experiment and measure that would be great too.

P.S. I did find a manufacturer that specializes in commercial butyl rubber sheeting that has a butyl product of Shore A hardness as low as 40 and elasticity of 500% but that still doesn’t match Lexel.

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I would be very hesitant to apply caulk to vintage speakers. Too many other products have been tried and ended up ruining the drivers. AFAIK, Roy's goo is identical to what was originally used and won't cause any issues. It's available from Vintage-AR, so why look for something different?

You do make a good case and have clearly done your homework but I'd be afraid to try the Lexel.

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I agree. I think the Lexel should be investigated, I don't think 17s should be the guinea pigs.

I would say check out some thrift stores and find some no-name crap speakers to try it on. Of course if you don't have the gear to check the Fs before and after you could only go by ear. Not very scientific.

Another low tech test might be to get a bit of Oxford cloth or even T-Shirt material and put some Lexel on it, let it set up and then see if how pliable it is. It should be close to the same as having none on it.

Your 17s won't get much worse if you wait a bit and do tests first.

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I thought I would give my experience after 5 months.

I did redope the surrounds with Lexel. I cut it with Naphtha (zippo lighter fluid) which worked very well. So the solvents were only Toluene and Naphtha with a very flex rubber. It painted on easily and they recommended a week wait. Seeing I cut it and naphtha and toluene both evaporate quickly I only waited 4 days. It sealed the surrounds perfectly. After a few days I tested with frequency generators at it was crisp and clean down to 40hz. It still is and is still as flexible as you can get. I figure these speakers are 1967 vintage by other attributes as I haven't removed the drivers to check yet.

Besides the Lexel I also broke the Cap rule. The original capacitors sound exquisite. I don't know if these speakers were ever used much but I went with "if it isn't broke, don't fix it". The Model 17 crossovers only are there for the tweeter as the woofer is full range. They cut the lows at 1500hz to not damage the tweeters plus some frequency mod but on my speakers everything sounds great so I didn't change them out.

I do highly recommend the lexel cut with naphtha as a surround dope. I guess I'm a heretic.

BTW. A Pioneer SX-780 is their source of sound.

Here is photo

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Nice work, I'm very pleased that we have another alternative!

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