Your math is correct, except from 20 Hz and up, I am getting 4 dB above reference, so in my room, a single EP-600 would be about 4 dB below reference from that 20 Hz signal, and about 9 dB from 17.5 Hz.

Another way of looking at this. You own a Corvette already. I was just crazy enough to take my Corvette, by another and send them both to Lingenfelter for extra power.