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AR2a woofer coil rub. What to do?

fiddlefye

fiddlefye

AK Subscriber
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I have a great looking pair of AR2a's that I picked up last summer. When I got them they were producing sound from the woofers but from nothing else. Of course the rheostats were shot and that would have to be dealt with. Then it turned out that some of the mid drivers were in pretty sad shape. I was kindly sent some replacements. Next pull apart the rest of the speakers to get at the controls. In checking one of the woofers (cloth surrounds) it became apparent (which I had not heard during my brief audition last summer) that the voice coil in one of the woofers is rubbing.

So, what to do? Is it common for the spiders in these drivers to sag over time? How do I tell if this is the case or it it was over-driven sometime? Neither the mids nor tweeters show any sign of such damage. If the spider has indeed sagged would it work to flip it 180º as I did with the "active radiator" in my Vandersteen 2Cs or would it have to somehow be rebuilt?

I seem to be getting one foot up the hill on this project and then slip back down with the next step. Sage advice needed.
 
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I'm no expert at all, but I have done a few re-foam projects on some of my speakers. I was very careful to be sure that the new surrounds were glued in perfectly centred so that the voice coil did not rub. Is it possible that the sub had a new surround put on it but not centred properly? If so, I would redo the repair and make sure it is centred. Before you go though that kind of trouble flipping the speaker 180 is a good idea. That is an easy test, and if it works you may be good to go. Check it with a very low frequency test track, or by moving the driver by hand. I like the by hand method, just be sure you are not adding any forces that are not axial or your test may be ineffective. Good luck.
 
Gtyler said:
I'm no expert at all, but I have done a few re-foam projects on some of my speakers. I was very careful to be sure that the new surrounds were glued in perfectly centred so that the voice coil did not rub. Is it possible that the sub had a new surround put on it but not centred properly? If so, I would redo the repair and make sure it is centred. Before you go though that kind of trouble flipping the speaker 180 is a good idea. That is an easy test, and if it works you may be good to go. Check it with a very low frequency test track, or by moving the driver by hand. I like the by hand method, just be sure you are not adding any forces that are not axial or your test may be ineffective. Good luck.
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Nope, no new surround. It is a cloth surround, original and in good condition. I used to 180 flip with the "active radiators" in my Vandersteens about 3 or 4 years ago and they have been fine ever since. Ok, let's hope for the best then.

I was wondering if this was a common issue with that particular woofer?
 
Have you redoped the cloth surround? If not, that may be the solution as well as turn the 180. Check with RoyC. He is the resident AR expert.:yes:
 
gbroot said:
Have you redoped the cloth surround? If not, that may be the solution as well as turn the 180. Check with RoyC. He is the resident AR expert.:yes:
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What does one use for doping? The last thing I doped was some tissue in building an RC aircraft about 40 years ago. :D
 
fiddlefye said:
What does one use for doping? The last thing I doped was some tissue in building an RC aircraft about 40 years ago. :D
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There is a compound sold by Vintage AR on ebay that RoyC helped develop that is very similar to what the surrounds were doped with out of the factory. I would not recommend redoping with anything else as bad things can happen. The reason for redoping the surround is that on older speakers with cloth surrounds i.e. AR's,KLH's, and a few others the dope over the years wears off which changes the excursion of the woofer as well as air leakage through a porous surround can occur.
 
gbroot said:
There is a compound sold by Vintage AR on ebay that RoyC helped develop that is very similar to what the surrounds were doped with out of the factory. I would not recommend redoping with anything else as bad things can happen. The reason for redoping the surround is that on older speakers with cloth surrounds i.e. AR's,KLH's, and a few others the dope over the years wears off which changes the excursion of the woofer as well as air leakage through a porous surround can occur.
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Makes sense as well as it being undoubtedly part of the strength of the surround in terms of support. I'll flip the driver on the other side and leave for a bit and see if it settles and doesn't scrape then?
 
I just don not have enough experience to tell if this woofer is toast or not. Anyone reasonably local who might be able to have experience with this type of driver and be able to tell me if it is salvageable or not?
 
The AR-2/2a/early 2ax woofer with the cloth surround is having glue issues these days. The glue bonds between the masonite ring of the surround as well as that of the spider are failing. It is the most likely cause of the voice coil rub.

The fix often requires complete removal of both masonite rings/cone assembly...and then cleaning, shimming, and re-gluing. I've completed a number of these in the past few months.

See photo of works in progress

Roy
 

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RoyC said:
The AR-2/2a/early 2ax woofer with the cloth surround is having glue issues these days. The glue bonds between the masonite ring of the surround as well as that of the spider are failing. It is the most likely cause of the voice coil rub.

The fix often requires complete removal of both masonite rings/cone assembly...and then cleaning, shimming, and re-gluing. I've completed a number of these in the past few months.

See photo of works in progress

Roy
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This makes a lot of sense to me. How to check for this or would one simply need to pull things apart to judge? I have to say that in the case of these particular speakers it seems to my unlikely that the woofer was over-driven as the remaining drivers are undamaged, at least in that sense (some of the original mids were decaying, different matter). I would have thought the tweeters would have been the "canary in the coal mine" in that regard. I also doubt that the speakers were ever paired with any amp that had enough oomph to push matters to that extreme. They most certainly were never party to any heavy rock sessions.
 
fiddlefye said:
This makes a lot of sense to me. How to check for this or would one simply need to pull things apart to judge? I have to say that in the case of these particular speakers it seems to my unlikely that the woofer was over-driven as the remaining drivers are undamaged, at least in that sense (some of the original mids were decaying, different matter). I would have thought the tweeters would have been the "canary in the coal mine" in that regard. I also doubt that the speakers were ever paired with any amp that had enough oomph to push matters to that extreme. They most certainly were never party to any heavy rock sessions.
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I am certain the cause has nothing to do with the woofers having been abused or overdriven. Another area where I have seen deteriorating glue lately is where the voice coil is glued to the woofer cone. This can be inspected and fixed, if necessary, when the the woofer is apart for the other issues.

These problems are also showing up in the larger, 12 inch cloth surround woofers found in the AR-1, 3, and early 3a.

Roy
 
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