while low-frequency extension is obviously important, i agree that thd is a critical spec for subwoofers. perhaps that's why the vmps subs, when used w/a quality outboard electronic x-over, are such over-achievers at their price-point. vmps' published distortion specs are, if not the lowest in the industry, right up there w/whoever is. most subwoofer mfr's don't even publish their distortion specs.
doug s.