Last month I briefly touched on 'absolute polarity' in the context of playing music recordings. A related issue - one that's understood far less than simple polarity - is phase coherence, the idea that maximum fidelity is attainable only when the playback of a recording matches as closely as possible the complex phase relations that originally impinged on a microphone. In other words, an accurate recreation of an acoustic event occurs only when cascading waveforms emanating from a loudspeaker recreate the cascading waveforms that came from the performing musicians. It's a simplistic assumption that on first consideration seems both a reasonable approach to high fidelity and a laudable design goal. It's also one that at various periods has obsessed audio engineers and hi-fi enthusiasts alike, to the point where it was once a recurring marketing ploy, brand names such as Phase Linear and Phase Technology having an implication that meticulous attention to phase coherence yields higher levels of playback realism than might otherwise be possible. It's still an article of faith for some people in this industry. Until earlier this year I worked with a fellow who fervently believes that only coincident drivers (with tweeter in the throat of the woofer) are capable of launching phase-accurate waveforms into free air. It's a charming, harmless belief that ignores the reality of natural phase relations, recording practices, and the design and construction of loudspeakers.
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