It's interesting to listen to the Acoustats playing through their crossover without powering the subs. This way you can hear more clearly exactly what the Acoustats are doing.
With 121Hz crossover, the Acoustats sound like a tweeter. Zero bass.
With 84 Hz crossover (now LR48), the acoustats sound a little thin but still like a full range speaker.
I brought up two versions of Polyvtsian Dances on Friday Night, and played them as loudly as I could with the new notch filters in place.
No buzzing or rattling whatsoever. It's looks to me like the 84Hz crossover is safe.
On Sunday I tried to duplicate the buzzing problem with "A Story Within A Story." I couldn't make it buzz anymore, even with the notch filters turned off.
Perhaps by operating the Acoustats with a lower crossover, they have "broken in" and loosened up so they don't buzz anymore at 116 Hz.
Actually I should probably go back and test Polyvtsian Dances without the notch filter too.
It does seem that the octave from 100Hz to 200Hz has pretty weak output, particularly from 110-170 Hz.
Taking out the notch filters doesn't change much (surprisingly) but does make the output just noticeably weaker.
I had been motivated to replace the notch filters with "dynamic EQ" filters that activate only for signals loud enough to cause the buzzing. But I can't know how to set up the dynamic filter if I can't reproduce the problem it is supposed to fix.