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In Reply to: RE: Magneplanar MG-II panel vibration problem at low frequency posted by neolith on December 03, 2016 at 18:08:21
The socks are currently off. The tweeter wires have been replaced (along with crossover caps). The banana peels and some spots on the bass panels have been fixed. The Mylar diaphragm panels are solid riveted to the frames.It's definitely the infamous slap. It happens in both speakers, at exactly the same heavy mid-bass passage. It happens on the bottom parts of panels, where the distance between cross-braces is the largest.
Someone on AK forum posted Magnepan instructions on how to adjust clearance between Mylar diaphragms and magnets, but it's a scary procedure (pushing onto the cross braces "evenly" through the Mylar, essentially bending the magnets away from the diaphragms.
One thing I cannot examine are those cross bars, as the Mylar diaphragms frames are riveted (not stapled) to the speaker frame. Those rivets are very well made, no vibrations or movement.
Edits: 12/03/16Follow Ups:
I never had a "slap" with my IIb, IIIa or 3.7i. OTOH I listen almost exclusively to classical music and jazz and very little bass heavy sources and usually well below 90 db (typically peaks below 85db). It would seem to me that increasing the bend in the metal panel might not help as it would just reduce the stretch of the mylar, probably by the same amount as the increased spacing. Is the buzz at a frequency that allows a cut-off and use of a sub, although from your picture it looks like you may already have a sub in place. Perhaps talking to Wendell at Magnepan may be helpful - I have gotten good response from him but others may beg to differ. FWIW I thought my IIb's actually had a deeper bass response than my IIIa's.
I married the perfect woman. The downside is everything that goes wrong is my fault.
I'll wait a bit before trying to bend those magnets. Something just doesn't add up with that idea. I'll fix my Carver M-1.5t in the meantime, so to be sure that if I give them enough power, maybe this pair won't slap.
So just a quick update - bending was a no-help at all. I followed Magnepan instructions that someone posted on AK - apply 100-170 lbs through a towel onto the crossbars (from the Mylar side).
Made zero difference. Popped some staples where the outer frame is stapled, had to fix that...
Oh well. And I was running Rotel RMB-1075 amp, which according to S&V magazine goes into clipping around 260 Watts per channel into 4 Ohms. I wasn't clipping obviously, but I was playing close to reference level on the preamp.
I'll put these together and get rid of them. I just don't know what else I can do to this pair.
I don't know if it is a realistic option shipping wise, but Magnepan could fix them.
Unfortunately, by the time I crate and ship these from Canada to USA, I'll probably be able to buy 3.6R for the same cost.
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