Those variable phase controls on some subwoofers - are they actually just a delay stage? I can see how the phase of a single note can be varied whilst retaining the information, but changing the phase of a complex, asymmetric music signal doesn't seem possible to my limited brainpower. The only thing I can think is that it is a variable delay stage that has the effect of altering the phase of the important crossover frequencies but actually does what the speaker distance calibration does in the processor. Does anyone actually know how they work, or have a circuit diagram? And does anyone have any real experience of the benefit over a simple inversion switch (pseudo-180deg phase change)?