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Subwoofer variable phase controls? (1 Viewer)

Mark Tranchant

Stunt Coordinator
Joined
May 9, 2002
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126
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)?
 

Saurav

Senior HTF Member
Joined
Feb 15, 2001
Messages
2,174
Yes, AFAIK, they're delay circuits.
And does anyone have any real experience of the benefit over a simple inversion switch
I would think that the benefit would be to compensate for the delay caused by the distance between the sub and the mains. Of course, this compensation can be 'correct' only at one frequency, and will have an increasing error as you move away from that frequency. Ideally, you want to set it so that the 'correct' delay occurs at the theoretical cutoff frequency between your sub and your mains, and assume that the errors in the other frequencies (high freq's for the sub and lower freq's for the mains) would be offset by the attenuation caused by the filter, so they won't make much difference. Or something like that.
This link might have stuff that you could read, maybe some schematics troo, I don't know. I built a crossover for my system, but the URL for that seems to be down right now. The instructions had schematics for 'phase lag' and 'phase lead' circuits (I assume the latter consists of a lag and an inversion).
 

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