I get 70dBA (92dBC) at 20Hz from dual 500v4 at reference level in my 4200 cu.ft. unsealed room. The subs are 1/3 away from side walls and 32" out from the front wall.

The figures above are about 10dB low according to calibrated readings from others who use the same meter as I do.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated