Grexx,
I don't wish to deter your experiments but it will certainly screw up the dispersion traits of the tweeter, which are exemplary. I think you will lose much of the clarity and transparency that distinguish the M60s/M22s from competitor's speakers. Besides, using the felt is akin to making the speaker into a tone control--to compensate for source material that is badly recorded. What if you play a CD that has dullish mids or highs? Are you going to remove the felt?
Why not try using a treble control for a few dB reduction if a CD or DVD is strident? That's what those controls are for. . . and I agree that tone controls are not always effective but at least you are not permanently altering the speaker's frequency balance and dispersion traits.
Axiom goes to great lengths to make the M60s as "linear" as possible--as smooth and flat across the musical spectrum--so that really good recordings will have as natural, transparent and uncolored reproduction as possible. We do many blind listening tests with listeners of different ages and normal hearing acuity, and the balance of the M60s is as close to ideal as we can make it.
And there might be a heat-dissipation issue at high volume. The dome actually radiates much of the heat generated in the voice coil. That's why titanium/aluminum dome tweeters are so more linear at very high SPLs than the old plastic, silk, or cloth dome tweeters.
Regards,
