The distortion figures in a sub effect the timbre of the reproduction more than is often realized due to the Fletcher Munson loudness curves. For a simplfied example: a 30 Hz pure sine wave with 10% second harmonic distortion played at around 70 db SPL (think the fundamental from a double bass or contrabasson) will also produce an additional tone at 60 Hz at about 10 db down. However, at that frequency due to the Fletcher Munson effect, the harmonic will be percieved as equally loud as the fundamental which will seriously distort timbral perception. While the effect flattens out at louder volumes even 3% harmonic distortion can shift the perceived timbres of of lower bass instruments (assuming of course that the room distortions don't swamp the lower bass response).
Musical accuracy in subwoofers
I'm hoping some members who are more musically & technically knowledgeable can answer my questions about subs. While sub shopping, web research and sales people make referrence to subs with accurate timbre. The Linn & REL lines were reported to be more accurate than Sunfires in this respect. After playing my sub at a 45-48 hz. crossover without the main speakers, listening leaves me wondering how timbre ( at this low a crossover point) can be an attribute of a sub when most aspects of timbre are a product of higher frequencies. It seems that pitch accuracy, lack of bloat & "overhang," freedom from cabinet resonance, and the ability to tune crossover, volume, & phase accurately are paramount. But timbre?