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KLH is redope of surrounds needed?

zls1camaro

zls1camaro

Active Member
Hey I have some KLH 17's I am restoring -- should I assume the driver surrounds should be redoped? How would I evaluate the current surrounds...
I know you can see through the surrounds when held up to the light....
mark
 
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Not necessarily. My Model 6s and Model 30s have not been redoped and sound terririfc. A few years ago I redoped a set of Optimus 1s mainly because the surrounds were dry (but not split or cracked). Afterward, it seemed that the bass response was not as pronounced. The speakers didn't sound bad, but I can't say that they sounded better. So, my advice is leave them alone unless an obvious repair is needed.
 
There is a deal here with re-doping. We know that the Model 17's are an acoustic suspension loudspeaker, so the enclosure must be as sealed as possible. What have you done to them so far?
 
The original doping does deteriorate over decades and air leaks do develop. They do need to be resealed however, here's a dire warning. Get it wrong and you will ruin them beyond repair. The problem is that if the sealant isn't completely pliant, that is if it hardens or cures in any way, stiffening the surround will increase the system F3 and Q. The bass will seem louder but it will not go as low and it will have a peak. What's the right material to use? I don't know. Carl at CSP has some secret formula he says works. Whatever it is, it should be used as sparingly as necessary. Only enough to seal the porous holes and no more.
 
I take a soda straw and masking tape and tape the straw to the surround ridges so as to prevent as much air blow by as possible. You can trim the end of the straw to fit into the peaks & valley as well them tape into place, them blow into the straw. If it is restrictive in several places tested you are probably OK- if it blows through easy thrn you probably need to redope the surrounds with your selected method. I like thinned acrylic putty. Use sparingly so as to avoid altering the "Q" of the driver sustantially Good luck.
DC
 
I redoped the surrounds on my Model 32s, it really helped with low end detail. I used an aircraft grade Neoprene contact cement. I knew from using it at work that I could put it on thin and I would stay pliable for years. If you decide to do yours be very careful, as dc270 said you can ruin your speakers if you get it wrong.
 
This material sold by Ebay's "Vintage AR" is the appropriate material to use to re-seal cloth surrounds.
http://www.ebay.com/itm/ACOUSTIC-RE...553?pt=LH_DefaultDomain_0&hash=item2c68e9b849
It is virtually the same as the original material used by KLH, AR, and Allison. It is also the same compound referred to by Soundminded discussed at the Classic Speaker Pages. Anything else is a crapshoot unless you have the ability to measure the results over time.

It should be noted that most of the old woofers are still sufficiently sealed for low to moderate volume levels. It is at higher volume levels where it can become more of an issue. The cabinets do not have to be completely airtight to work properly.

Roy
 
"Vintage AR's" compound works perfectly. I just used it on a set of KLH 6's and it worked like a charm. The bass response improved dramatically. Recap the 17's if they haven't been already. All caps on the old KLH's are crap and usually non working or way out of spec. With a recap and surrounds redoped the 17's are very musical. Enjoy!
 
I recently picked up a pair of KLH Model 20 speakers (the same as the Model 17s, only in 4 ohm), and after doing quite a bit of research, reading, and listening, I decided that my speakers needed a recap big time, and that they probably needed to have the cloth surrounds re-doped as well.

There seems to be a lot of different materials being used for re-doping the cloth surrounds on these old KLH speakers (as well as their AR kin) and I wanted to use the correct product. My goal was to restore my speakers back to as close to their original performance as possible, and for them to stay that way long term. After much research I purchased some of the butyl cloth surround doping material from RoyC over at the Classic Speaker Pages web site. (I assume he is the same RoyC who posted earlier in this thread as well.) He and the other AR and KLH fans there have done a lot of research and testing of various materials over the years, and have found that this formula is very close to what KLH and AR originally used when they built their speakers back in the '60's. And according to his long term testing, it does not change the compliance of the cloth surround over time. By all accounts this is also the same material that eBay seller vintage-ar sells (no affiliation.) Just do a search for ACOUSTIC RESEARCH CLOTH SURROUND WOOFERS SEALANT KIT, ALSO KLH. It is only $15, and includes shipping, which is the same price I paid for mine.

If you want to take a look at my KLH Model 20 restoration project, here is a link to that thread: http://www.audiokarma.org/forums/showthread.php?t=479559

Good luck with your KLH Model 17s. I just finished mine up this morning and have been listening to them most of the day. They do sound very nice, especially for a nearly 50 year old speaker design. I think I am going to be keeping mine around for awhile.
 
I too restored a set of Model 20's here very recently, and rather than using the AR compound, I used Permatex High Tack Gasket Sealant. Stays pliable, and is pretty easy to work with. Someone I know who worked for Market Speaker (now Midwest Speaker) told me that that is what they used to re-dope cloth surrounds, and it works without issue.

I found that this stuff works, just as he said it would, and it won't harden up either. I figured that I would try it, as I didn't pay anything for these speakers, and presto! Instant fix. Although I do recommend that if you want a professional looking finish, you should take a paint brush dipped in laquer thinner and smooth out the High Tack, but it isn't something that is absolutely required.


Best of Luck!



-Jason



PS-Don't forget to get rope caulk to reseal the woofer. It is also called rope sealant in some instances. Also, I would highly recommend a closed cell foam to re-seal the tweeters.
 
I tried the permatex on a set of Optimus 1's. Was a mistake. The compound that Treker mentioned is what should be used.
 
As "RoyC" and "gbroot" said, go with "Vintage AR"
Larry at "Vintage AR" will be too happy to give you a hand of how to proceed, he welcomes eMail and is extremely helpful. His material to re-seal speakers like, KLH, AR and other has the proper consistency.
 
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The permatex is a very different consistency and seems to harden some.I tried the permatex on some optimus 1's that needed the surrounds redoped.The optimas 1's were "disposable", thus the experiment. The compound that "Vintage AR" formulates remains tacky and is not as "heavy" in thickness. As an experiment, a few months ago I purchased some additional model 5, 23 woofers and used some flexible undercoating sold in a can at auto parts stores on the surrounds. Actually it worked very well and has stayed flexible and did not harden. I swapped the originals back into both cabinets and ordered the "vintage AR". Looking back, my assessment is that the undercoating worked very well and the other compound purchased on ebay from "vintage AR" produced the same results. However, that said, the product ordered on ebay is the one to go with as it is a tried and true formula withstanding the test of time, whereas, my undercoating fix, permatex, and other fixes seen here on AK regardless of results, do not have time behind them.
 
Interesting. A very thin coat was applied, so here is to hoping that it will remain flexible and tacky for many years to come.

I'll have to keep this product in mind the next time I work on a set of ARs or KLH speakers.

Thanks for the tip.



-Jason
 
Permatex (diluted with lacquer thinner) was the first material we experimented with over at CSP a number of years ago, as it contained a butyl compound similar to what we were looking for. Although it remains tacky for awhile, the gasket sealant eventually forms a membrane....which is the problem with virtually all of the compounds discussed in this forum. Once a membrane forms and stiffens, even to a slight degree, fs increases (sometimes dramatically) compromising the design basis of the acoustic suspension woofer. I have tested and measured many compounds over the past 5 years, and negative results have been consistent.
(Actually, a thin application of Permatex is not bad compared to most other materials mentioned along the way.) It is very often better not to apply anything at all, especially if the speakers are not being pushed to higher volume levels.

After input from a number of knowledgeable sources, including Roy Allison (early AR and Allison speakers...who is in his 90's now), I was able to come up with something much like the original compound. It is nasty to make, and is essentially the same tacky stuff manufacturers used to use to treat ("dope") driver cones and domes to modify response characteristics. It is a non-drying butyl compound diluted in toluene.

Due to the high percentage of toluene, and little demand for this kind of compound today, a commercial product of this type is not readily available.

Vintage AR/Larry Lagace is the only "retail" source of the stuff. AK and CSP forum members are welcome to send me a PM for more information.

Roy
 
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Could one use some automotive silicon applied sparingly w/a paint brush? This would be my first thought. Seems that any silicon that would dry to a rubbery state would solve the issue w/o inviting major changes to the speakers' excursion characteristics....
Just a thought-
 
Soundminded said:
The original doping does deteriorate over decades and air leaks do develop. They do need to be resealed however, here's a dire warning. Get it wrong and you will ruin them beyond repair. The problem is that if the sealant isn't completely pliant, that is if it hardens or cures in any way, stiffening the surround will increase the system F3 and Q. The bass will seem louder but it will not go as low and it will have a peak. What's the right material to use? I don't know. Carl at CSP has some secret formula he says works. Whatever it is, it should be used as sparingly as necessary. Only enough to seal the porous holes and no more.
Click to expand...

I re-doped my KLH-5s using, on Merrylander's recommendation, rubber cement, which I haven't seen recommended anywhere else. But it seems to be a material that, though it dries, doesn't harden. My mistake, unfortunately, may have been using two coats (I tried to keep them thin), because I couldn't tell if I got good coverage on the first. The audible results are very similar to your description - louder, not as low, and with a peak.
I did this in conjunction with a recap, and have a post on the concurrent thread about cap break-in. My best hope is that someting will improve with use.
 
HomeBody said:
Could one use some automotive silicon applied sparingly w/a paint brush? This would be my first thought. Seems that any silicon that would dry to a rubbery state would solve the issue w/o inviting major changes to the speakers' excursion characteristics....
Just a thought-
Click to expand...

Thank you RoyC for giving us this valuable in sight. As set of AR 3's will be my next project and will look forward to A/B ing them with the Model 5's.
 
We see an ad for liquid rubber on TV that seals but remains pliant. Anyone have any experience with this material? Does it have any possibilities?
 
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