Excellent question. It's probably that the timbre issue is the result of semantic confusion. Pitch accuracy coupled with low overhang should result in accurate timbre.
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?