Doppler Distortion in Loudspeakers
 

Each and every speaker design has it's strengths and weaknesses. But the bottom line on improving sound quality from loudspeakers is the reduction (not possible to eliminate with more than one frequency signal) of intermodulation distortion (IMD). This is often referred to as Doppler or frequency distortion.

http://www.stereophile.com/reference...5yRQcXjcVDA.97