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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: acoustic polarity in multiway speakers (measurement and feeling) posted by dave789 on January 31, 2016 at 10:22:25:
And ideally, run in parallel phase at least an octave either side of it. Good phase tracking through the crossover "region" results in flatter summed response and better integration of the drivers. This, of course, is on a fairly narrowly defined design axis. Listen too much above or below this axis and the phase goes wonky and and bumps and dips appear in the frequency response.
Now, this does NOT mean that both drivers must necessarily connected in the same polarity. With some crossover alignments, notably 2nd order Linkwitz Riley, the drivers will be 180 degrees OUT of phase at crossover frequency IF both are connected in the same polarity. The result will be a deep null or "hole" in the response at that frequency. Reverse the polarity of one driver and they will then sum flat, all though deeper into their respective passbands they will be out of phase with each other and this is what shows up in the step response test.
With a 4th order LR, by contrast, the drivers will sum flat through the crossover region when connected in the SAME polarity, and show a null when one is reversed.
In EITHER case, acoustic phase (which is a complex summation of the electrical and acoustical phase of the individual drivers, the LF box loading, and the electrical phase of the crossover filters) does NOT remain flat, or at the same angle. The acoustic phase of even a single "fullrange" driver ROTATES continuously through its operating band. Some higher frequencies will ALWAYS be "out of phase" with lower ones. Add a second driver and a crossover and the acoustic phase of the speaker system may rotate a full 360 degrees multiple times over its operating range. A 4th order crossover will add another 180 degrees of rotation compared to 2nd order.
How audible is this? The consensus seems to be, "not very," as long as the phase tracks well through the crossover region. That is where the ear is most sensitive to errors and anomalies. If some higher harmonics are in incorrect phase relationship to their fundamentals, which is inevitable even with a single driver, we don't really notice that. If we did, all speakers would be intolerable to listen to!
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Follow Ups
- What matters is that the drivers are IN phase at crossover frequency - Brian H P 12:00:13 02/01/16 (0)
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