It's the curves from the entire speaker. You put the speaker on a turntable and rotate it horizontally and take measurements. You rotate the microphone for vertical angles. The measurements are frequency sweeps across the audible range. You generate 234,389 curves and drink your face off and smoke the good stuff for 20 days straight to make sense of all of them. Then when you do, you go to the DSP and tweak all the filter coefficients, and then go back to the chamber and do it all over again until you have the angelic curves Ian posted.

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