Capelo makes common speakers sound as good as the World's best and then takes the World's best even higher
If two identical sinusoidal signals are phase-shifted by 90 degrees relative to each other, and each of them suffers the generation of an identical amount of second harmonic distortion along their respective signal paths, when the signals are finally added together, the resultant signal will contain only the fundamental. The second harmonics will be cancelled. Likewise, if the signals are phase-shifted by 60 degrees relative to each other, the third harmonic distortion will be cancelled.
This principle can be applied across an audio frequency band to eliminate harmonic distortion from loudspeakers and amplifiers. The summation occurs acoustically in the air between the loudspeakers and listeners.
Bluacs has worked out how to use this principle to simultaneously cancel both the second and the third harmonic distortion or, if required, any number of harmonics. For example, to simultaneously cancel both the second and third harmonic distortion, four identical channels are required, with separate amplifiers and loudspeakers, and constant phase differences of 60, 90 and 150 degrees across the audio band relative to the reference channel. Bluacs calls this Capelo configuration the “Quad” mode.