Reversing Polarity -- Voodoo or Easy Tweak?

Jeff_jones...Speaking of what I will call "relative" phase (one speaker with respect to the other) the "proper" phase is not always clear. Out of phase signal has a diffuse and directionless quality, and that might be what the recording engineer intended. In a matrix multichannel setup out of phase signal localizes to the rear channels, so reversing one set of speaker wires just swaps front and back speakers. When played back on a two-channel system a source that is intended to be well defined center front (typically a soloist) is a monaural signal (same in both channels). All recordings have some degree of out-of-phase signal, often nothing but ambience. However, there are some exceptions. One good example is the recording by Buffy Sainte-Marie, "The Angel" where out-of-phase signal is used with stunning effect.

I do not suggest that anyone deliberately connect stereo speakers out of phase, but a signal being out of phase is not inherently "wrong", and can be used to great effect when a recording is mastered.

Whoops! I should have said that reversing phase of one channel BEFORE MULTICHANNEL DECODING will swap front and rear. Doing speaker wires in a 2-channel setup will localize ambience, and make the soloist diffuse and directionless.

Herman...Agreed that terminology is commonly sloppy. However, "OUT" of phase means a shift of 180 degrees, which is the same thing as a polarity reversal.

Audiophiles like to worry a lot about the phase shift introduced by filters, as in a crossover network, but, as the phase shift increases beyond the break frequency, the amplitude decreases, so that phase becomes irrelevant.

Herman...You are a bit hasty in saying that the drum sound will be compression followed by rarefaction. It depends on which side of the drum the mic was on. Also, as a disturbance propagates the wave shape changes. Consider, for example a Tsunami, where the initial disturbance is always that the sea recedes, followed by the flood. I have observed a similar effect of a ship bow wave while going through a canal. There must be an explanation, but I don't know it.

Do you have any scope pictures of a mic signal from a drum?

Unlike most audiophile tweeks, the absolute polarity effect, at least superficially, seems to make scientific sense. Also, unlike most tweeks, it is easy and cheap. However, I do suspect that the science might fall apart on closer examination, and the real world usefulness of the tweek is minimal because of what you describe as "recording engineer indifference".

Herman...Both Hi and Lo signals are shifted 45 degrees at X/O, so the woofer/tweeter discrepancy is 90 degrees (for first order). In fact the discrepancy is constant at 90 degrees for all frequencies, but causes most problems around the X/O frequency where both drivers are emitting sound. With a second order crossover, 180 degrees of phase shift, there will be a deep sharp notch in frequency response unless one driver is connected with inverted polarity (or, as some might say, out of phase).That's why I like 24dB crossovers, where the shift is 360 degrees, so that sine waves are back in "phase" if you will pardon the term. Sine waves are a pretty good approximation of musical sounds, at least for a few cycles.

I wish I had access to a storage scope and a mic. It would be very interesting to examine the shape of transient waveforms (like the drum) both close mic'd and distant. Of course, once the signal is played back through a loudspeaker and rerecorded I suspect that any slight difference due to polarity/phase will be unimportant. Very few speakers can reproduce a square wave (original Ohms were one), and those only at relatively low frequency like 1000m Hz.