I want to use subwoofer sensitivity specs to try to ensure I design to reach reference levels and/or that they are matched to the output of my main and surround speakers. Anyone know how sensitivity numbers are measured for subs? Are they at the peak driver resonance as shown in the response plots, which are typically well above useful subwoofer frequencies? Or can I assume once they're in a proper enclosure that the published sensitivity will span the usable response?
You should use a modeling program like WinISD or hornresp to plot the SPL of the subwoofer driver in question. Depending on the enclosure type sensitivity will vary greatly over the frequency range of the sub. Another thing to remember is placement will have a large impact on output as well, generally sensitivity is given in 2pi space, (single boundary) Placing the driver near an intersection of two boundaries like on the floor near a wall will usually net +6dB as the radiating space is cut in half, placing it in a corner nets roughly another 6dB.