Good questions from Zargon. Also, are the speakers dipolar, front-firing, other? And how far down does their low frequency response go?
Also, I could be wrong but I believe it is more correctly referred to as 1/2 wave cancellation. The path from the speaker to the wall behind it would be 1/4 wavelength at the affected frequency, then another 1/4 wavelength for the reflection to return to the plane of the speaker, where it would be a total of 1/2 wavelength or 180 degrees out of phase with the forward-radiated waveform, resulting in cancellation.
-- Al
Also, I could be wrong but I believe it is more correctly referred to as 1/2 wave cancellation. The path from the speaker to the wall behind it would be 1/4 wavelength at the affected frequency, then another 1/4 wavelength for the reflection to return to the plane of the speaker, where it would be a total of 1/2 wavelength or 180 degrees out of phase with the forward-radiated waveform, resulting in cancellation.
-- Al