I'm really surprised by that sharp increase in 3rd order distortion going into the lower bass frequencies. -27.65dB on D3 is ~4.2% THD, which is comparable to the KSC75 http://www.changstar.com/index.php/topic,231.0.html sub-bass distortion on D3. My personal comparisons against the KSC75 and KSC35 were that the TH-02 mopped the floor with them in terms of sub-bass performance.

Is it possible that the seal wasn't great with that in mind and also the greater perceived bass slam?

I'd be absolutely thrilled if they fit.

The cups are 90mm in diameter, if you have a pair handy and a piece of cardboard you can do a fit test.

Took the baffle out and set it on a foam donut over the microphone. Maybe about 0.7cm above the microphone / coupler plane.
Attached are the results. There definitely is some resemblance to the driver in the cup, although the main peak looks shifted down in frequency about 1.5kHz when the driver has no enclosure behind it. The null is about in the same spot (it really isn't a null, it's actually another peak according to the CSD.)

The ringing wouldn't change - it's very much a driver material, surround, motor characteristic.

BTW. I already damped the baffle, the cup, and the back of the driver with dynamat. Stuffed acoustic fiber in the cups too. No more cavern reverby effect. Also used 1 layer TP between the pad fabric and front of driver. The TP worked better than other materials in reducing the 7-8k peak, while retain as much last octave air as possible.

Measurements forthcoming. It sounds pretty darn good. Unfortunately, I don't think anything can be done to fix the bass distortion.


P.S. I suspect using Jerg technology on the pads may yield some gains in reducing the 1k bump, smoothing things out, and providing a better sense of openness.