Martin Logan CLS panel distortion

Hello Tonnesen - thank you for your answer and forwarding of Jim Power's e-mail. I will attempt "tightening" of the panels in few days.
I will also test my amplifier - need to borrow something more powerful. I am using VAC Renaissance 70/70 so our problem could be related to not sufficient power supply.

Try to examine tubes in your amplifier. If it's old than upgrade or replacement of passive components should probably take place to bring your amp back to tolal balance.

Tonnesen, definitely try another amp before giving up on the panels. I've been driving my IIZs hard for 11 years, 9 of those with an Aragon 4004 and have had no panel distortion issues, just a flattening/hardening of the sound when I push the amp too hard. Just this week I've been auditioning amps to upgrade the Aragon and discovered that the 150W VTL couldn't even begin to drive the CLSs-- major distortion in the upper mids at moderate listening levels. Too bad since the VTL otherwise sounded pretty wonderful.

Those speakers can really drop in impedance at certain frequencies. So, like others have said - check your amp. You may want to check with Martin Logan to see where those dips occur,(if you don't knwo already) and see if that's where your problem is.