So what is the customer to do. Well the best guide is to find the low point of the speakers impedance curve. Many manufacturers quote the minimum impedance. Then use these formulas to determine how much current a given amp will provide into that impedance. That is the easiest way to find out the point at which his amp is likely to run out of gas supplying that speaker. If the phase angles present a difficult load it still may not be as good as he thinks.
Impedance vs frequency, and especially phase vs frequency curves seem to be exclusive to reviewers from reputable AV magazines. So you are absolutely right, what is the customer to do? The high current hype has already done enough to confuse people and create misconceptions around forums such as this. Now we (I admit I started it this time) are talking about the effects of the phase angles also.
You made a good point about voltage being important too. Theoretically a speaker that has lots of
high impedance peaks could well be more difficult to control than one that has a lower nominal impedance spec but a much flatter curve across the 20 to 20,000 Hz spectrum.
To summarize, may be we can agree on the following:
1. Everything being equal, 4 ohm nominal speakers are more difficult to drive than 8 ohm nominal speakers.
2. Everything may not be equal; the nominal impedance specified for a speaker does not always tell the whole story. To be sure, one also has to refer to manufacturer's (or reliable reviewer's bench tests) impedance/phase angles vs frequency graphs.
3. Speakers with high impedance peaks on its impedance vs freq. graph could also make it more difficult to control.
4. Talking about high current in isolation is not always useful (tempted to say meaningless). Voltage, current, impedance, power dissipation are inter-related. You cannot have current without voltage, regardless of how low the impedance is.
5. If you have enough power, you don't have to worry about any of the above.
6. While more power is always better, at low to moderate (caution: it depends on how one defines “moderate”) volume, speakers can sound just as good with lower power amps, e.g. $4,500 Luxman 20W amp, many low power tube amps, etc. There could be exceptions if we are comparing amps of different classes, i.e. class, A, A/B, B, D etc.
Regarding the phase angle (due to the complex and dynamic nature of speaker's impedance:inductive, capacitive, resistive) thing, I suggest we can just size our amp according to the speaker’s impedance characteristics, listening habits, room acoustics and then may be multiply what we come up with by say 1.5 times give or take. As others posted many times before, get 200 WPC and be done with it. If you must spend all your money on an expensive lower power amp, then you are going to have to find that “easier” to drive/control speakers. I think now I am done on this one. Thank you all!
