Interesting about the 5dB lower figure at home (presumably compared to anechoic space). If you have a citation for that, I'd like to add it to my notes for future reference. Even better, would be curious about how they calculated it so it can be tuned to volumes other than 4K ft^3.
Couple points, per my novice calculations about the bullet point 4:
- To achieve 117 dB at 13ft (~4m) with a sensitivity of 90 dB (i.e., at 1m) would take 8000W for 1 speaker in open space. I.e., must produce 129 dB at 1m
- But for two speakers, additive effects drops down to 4000W per speaker (3dB less, i.e., 126 dB at 1m)
- Still, these values are for open space. To compensate for lack of loss in a closed space, here using the -5dB value you mentioned from THX, this results in 1250W per speaker (121 dB at 1 m)
I think your figure of 2K W per channel is about correct (would be closer to 2500W), but maybe it doesn't take into account the extra sound added by the second speaker, which brings it down to 1250 W/channel. Of course, these are still pretty high values. I still have no idea how does one determine how much power can a certain speaker take before mechanical damage.
