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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: RE: Let's clear up the phase thing posted by M-dB on November 18, 2016 at 19:32:25:
I think you're mixing up phase and polarity. Lots of audiophiles use the terms interchangeably but they're not. Polarity is binary thing, the signal is either inverted or not inverted. Phase is a continuous quantity that is proportional to time delay at any given frequency. Inverting the signal flips it over, +/- to -/+. Changing the phase from 0 deg. to 180 deg. delays the signal in time by half a period, but does not alter the polarity of the signal. In the special case of a single, continuous sine wave, shifting the phase by 180 deg. produces the same result as inverting the polarity. That's why people get these terms mixed up. But outside of that special case, they are not equivalent.
Here's an example. Suppose a kick drum is recorded with positive polarity. If the rest of the recording & playback chain preserves polarity, the initial impact on the drum will be reproduced with an outward stroke of the subwoofer driver, which produces a pressure wave with a positive leading edge. If instead, the drum is recorded with negative polarity, or if it's recorded with positive polarity but something in the recording or playback chain inverts polarity, then the initial impact on the drum will be reproduced with an inward stroke of the subwoofer driver, which produces a pressure wave with a negative leading edge. If you then add a 180 deg. phase shift, the leading edge is still negative, but delayed in time. A phase shift can't correct a polarity inversion.
The purpose of the phase control on a subwoofer is to match the phase of the subwoofer output with the phase of the main speaker output at the crossover point. If the phase is matched, the two signals will add together. If the phase is not matched, they will cancel each other. In most cases, the subwoofer phase control should be set to where it maximizes output around the crossover frequency as measured at the listening position. If that produces a bass peak at the crossover point, the crossover should be set lower. Once set up properly, it shouldn't be changed from recording to recording because all that would accomplish is to introduce a dip in the bass response due to cancellation.
I don't doubt your experience that some recordings sound better with one subwoofer phase setting and other recordings sound better with a different phase setting. Just keep in mind that you're not correcting the polarity of the recording, just changing your system's output around the crossover frequency.
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Follow Ups
- RE: Let's clear up the phase thing - Dave_K 06:02:15 11/23/16 (1)
- You're absolutly correct, my bad. nT - M-dB 19:36:17 11/25/16 (0)
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