PR’s Data (old):

Fs = 21.08 Hz
Qms = 8.6400
Qes = 0.4595
Qts = 0.4363
Vas = 371.70 Liters
Cms = 3.706E-4 M/N
Re = 3.19 Ohms
BL = 11.89 N/A*
Sd = 0.0845 Sq. Meters
Mms = 0.15379 Kg
Ref Efficiency = 0.728 %
Predicted Output = 90.82 dB/1W/1M
Predicted Sensitivity =  94.82 dB/2.83v/1M
Xmax = 7.11 mm

*Notes indicate that the BL crosscheck was “ok”, but we
  do not have the exact data.