Doppler shift . Clearly, those audiophiles desiring to experience true purity of sound(at least those who hear differences in interconnects and speaker wires)would be required to use an individual speaker for each separate frequency up to at least 20,000Hz in order to avoid intermodulation effects; of course the wave form distortion of each individual frequency caused by driver excursions might still leave them unfulfilled, although a step closer to nirvana.

-----------------------------------

Enjoy the music, not the equipment.