What causes phase shifts...Sean?

They are caused by reactive energies introduced by inductors and capacitors, if you are talking about voltage and current. Capacitance makes the current lead and inductance makes the voltage lead. each one in its pure form introduces a minus or plus 90 degrees of phase shift. Otherwise, it is in varying amounts dependant on the quantity of resistance in the system as a root-sum-square function. Any basic electronics book will describe all this in detail in the first chapter or so and will go into series and parallel network combinations of each so you can see the effects. Often times in audio, the cap and inductor are parasitics (they are unintentionally added to the system, essentially due to the second law of thermodynamics) in which case their values are small and so their effect is small as well. Most of the phase shift is due to circuit components in the amplifier although Energy Star is now requiring power factor correction which brings them in phase for anything over 75W. Perhaps audio designers have found a loop hole to avoid doing this since it does add significant harmonics if done efficiently - but I am not sure on this point. My work involves high-power nonlinear circuit design in which case this is a big issue. Anyway, I would refer to an electronics book (Hazen's Exploring Electronic Devices is an excellent basic book that all audio people interesting in circuit design should own IMO) since diagrams will facilitate comprehension to a great degree. Arthur

I just ordered a reference grade book on electronics that is supposed to be both excellent and very easy to understand. If it turns out that it is as good as all of the hype says it is, i'll post something listing the name and good places to pick it up. Only problem is that this book is not cheap, but would be well worth the investment if it can help those that are interested in really learning more about this subject. Other than that, Aball did a nice job on that one : ) Sean
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Other than electrical elements which inherently cause phase shift (and enables passive x'overs to work), there are: room reflections and delays to waveforms introduced by A/D and D/A converters, microphone placement, wiring losses, RF/EMI, processors, mixers; anything that comes in contact with a signal has the potential of screwing with the timing relationship.

A good reference with more info than you'll know what to do with:
"Acoustical Engineering" -Harry F. Olson, 1991.

From what I have read, the most common cause is in the crossovers of 98%+ of speakers ... one driver ... as I understand it the mid-range or tweeter ... is wired reverse phase to the other drivers with anything other than a first order (-6dB per octave) crossover.