VoR,

You can try 80 Hz or 100 Hz and see if you can hear any difference. Honestly, given the rather minor contributions of Height speakers to the ambient soundfield (compared to the very substantial ambient field generated by your left and right surround speakers), I'd be surprised if you could detect any difference at all between 80 and 100 Hz crossover frequencies.

Regards,
Alan

Alan Lofft,
Axiom Resident Expert (Retired)