You folks rock!
I made a set of vents from thin duct aluminum (cut it easily with a pair of Milwaukee Jobsite Offset Scissors). Used the Top Gun template, bent them with some plywood, stuck them on with 3M Outside mounting tape, and it made a huge difference.
The tape is rated for 175 F, so it should be fine. The vents don't even get very warm--probably because the large surface area and use of aluminum makes them able to shed heat easily.
I mounted my vents open upwards instead of downwards, because trapping heat bothered me. That means dust can collect, but I have an air compressor already to (gently) blow gunk out of the Martin Logans, and it will work on the vents too.
I also added a middle vent for the heck of it.
While messing with this, I noticed that pulling the panel a few inches out from the wall dropped the sound even more, so it's definitely a reflection problem. Ironically this means if Panasonic tested in an anechoic chamber, they could have missed it. (This also means adding some anechoic material on the wall behind the panel might help, and I'm going to try that to see if further improvements are possible.)
Probably the air cavity between the main panel body and back, normal plasma electronics buzzing (which you can hear with your ear up against the back air holes), airflows, fans, and flimsy back material conspire to create beat frequencies inside the cavity that are then spewn out the back by the fans. Separators wouldn't (probably) work in that case, because the electronics that need to be cooled can't be separated from the fans (unless the beats come from interactions among the fans, in which case it would be a nice fix, but we'll never know because once the vents work, nobody wants to pursue other solutions).
It's a real shame Panasonic didn't finish the engineering. They were so close. (And it's a horrible shame they gave up on plasma.)
Hope this thing gives years and years of service.
My system? Google for: Martin Logan 420 CLX Descent Stage Summit
Last edited by jimshowalter; 08-30-2014 at 12:04 PM.