SL3 sound is 'dim' or dead in the middle of panel.

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bowshocker

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I have a pair of Martin Logan SL3's. One speaker sounds fine, the other is 'dim' in the middle of panel. It sounds normal from a distance but when you run your ear up and down the panel you can tell. I played a white noise track and it was obvious that the top and bottom sounded fine, but the middle was dim or dead. Any ideas?
 
Either the hv charge is not reaching that area at all, or the charge is bleeding off (leaking to stators through conductive dirt in spacers) faster than it can be recharged. For the former, maybe a corroded or warped copper strip is not making good contact with the diaphragm, so try manually squeezing together the middle section at the right side (where the strip runs) to hear if sound returns from there.
 
A similar question was posted on AVSforum, so here is my reply:

Probably the panel has buckled a bit with age and the front to rear seal along the edge of the two stators has separated along that segment leaving no contact path for the signal. There is a copper band that the diaphragm is supposed to be in contact with, but if the seam between the front and rear stators is loose, no contact, thus no sound.

Take the rails of the SL3 and check the panels. Close the gap, then re-seat the rails so they properly press on the panel edges to ensure good contact. The rubber strips on the frame are likely compressed and failed with age, so consider replacing those to help ensure a tight fit. Plenty of tear-down and fixit advice over on the MartinLogan Owners Club site.

It is also probably time for new panels on units of that age, thankfully ML still stocks/makes them and will sell you a pair of brand new panels. Downside is they are not cheap. But will last another 20 years.
 
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