Watts up with that?

Your speaker isn't a resistor. The REAL part of the complex impedance value is what is doing "work (making music). So be very careful to use the impedance as a resistive load...it is far from that. Speakers are only 5% efficient, so that means the majority of the impedance is imaginary in nature and does not do work.

A reasonable SPL is near 85 dB with 1 watt at 1 meter with a 1 KHz tone. Seems good to me. But, as you increase volume or decrease the frequency, power requirements go up dramatically. To not clip peaks on music (test tones are not dynamic) you aften time need 10 times the average power.

It is this dynamic power requirement that demands attention. When music moves from 1 watt to two watts average, for instance, you need an amp ten time bigger than the last one! A rule of thumb is every 3dB average SPL increase needs twice the power as the previous level. Most music will NEVER see a 30 dB dynamic range for this very reason. No amp can manage it. With digital you could do it, but should you?

If you listen to "normal" SPL around 83 dB and 93 dB peaks (where I listen on most music, and with typical 10dB dynamic range) with 92 dB SPL rated speakers it looks like you should have decent headroom with 30 watt continuous amps as they usually provide more than the instantaneously.

The dynamic range reference is from the AVERAGE SPL, not the minimum. So if your avevrage SPL is 85dB, your peak dynamic range will be 115dB, not a value most systems can manage. Music has to be recorded to be at a comfortable volume WITH the expected dynamic range. If you keep turning down the volume to increase the dynamic range...sooner than later you can't enjoy the music.

...This statement is self-contradictory. An increase from 1 watt to 2 watts IS a 3db increase (as is an increase from 10 watts to 20 watts), and requires twice as much amplifier power (as the second sentence indicates), not an amp that is ten times bigger....
You're right, it should be twice, not ten. Every 3dB is twice the power.

The "real" part of the impedance component is the entire vector sum of the X-over and the driver both. The entire speaker is measured, not just a part of it. Most energy going into a speaker never makes a peep. "Real" power vectors are not reflected, that's why you want them to be large (but they aren't)...they do work. Some of that precious little energy is wasted as heat as you say, but the majority is imaginary in vector.

And no, you can't remove imaginary components of an impedance curve by physicaly moving your physicaly.

... My understanding is that most speakers do not have as much as 10% efficiency. You cited a figure of 5%....

How can an almost pure resistive load be 5%, or even 10% efficient? THAT does not make sense. By definition a resistor consumes the entire load placed across it. Speakers don't so they aren't resistive loads...not anywhere near. Where did the other 90% to 95% go? It's the imaginary component of the speaker fighting the electroniocs, that's where. You have HUGE winds of wire in a magnet and you think that that is mostly resistive when it is driven?

Here are the "real" OSHA numbers for continuous noise, not random, like music, exposure. 85 dB levels with music is far from continuous and is more than fine. My "ear" says the Fletcher Munstrom (spelling) flattens out at about 80dB, where the low end seems linear. The human ear is lousy below about 80 dB for linearity of broad spectrum sounds. We hear around 1-4 KHz at 75 dB OK. That's as nature intended. True, you can "flatten" the sound by EQing to 75dB (remember loudness controls), just don't turn it up much with that EQ active!

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735
TABLE G-16 - PERMISSIBLE NOISE EXPOSURES (1)
______________________________________________________________
|
Duration per day, hours | Sound level dBA slow response
____________________________|_________________________________
|
8...........................| 90
6...........................| 92
4...........................| 95
3...........................| 97
2...........................| 100
1 1/2 ......................| 102
1...........................| 105
1/2 ........................| 110
1/4 or less................| 115

And, Go here;
http://www.stereophile.com/content/dynaudio-confidence-c4-loudspeaker-measurements

Most of a speakers "power" is dissipated at the lower frequencies below 200 Hz and more than 4/5th total isn't uncommon. Here, the graph of C4's clearly shows significant phase departures from "zero" that approach +30 to -50 degrees. It isn't near zero till about 200 Hz in this speaker. Since the majority of the load is mostly reactive below 200 Hz this is a terrible "resistive" load per your conclusion. It is NOT a resistive filament. No where near. It does produce a very reactive signature to the majority of the signal power being applied. This is what your amplifier is fighting against. The numbers at the frequency of the power dissipation peaks show that this isn't as bright of an idea as lighting a light bulb.

As far as the jackhammer example, It's amazing that a device that is intended to crush rocks loses just 1 watt to sound. Sound SPL at a given volume has a measurable power in air that is always the same no matter what produces it. 1KHz at 100 dB SPL is ALWAYS the same power level in-air. It doesn't know who it's mommy is. The energy "used" to launch it varies tremendously in wasted effort, true. The SPL of a jackhammer's frequency range is pretty low and at a pretty high 120 dB SPL so it is amazing that it has a 1 watt sound launch energy value. And the actual "sound" efficiency would be the power going in to make the SPL level coming out (here we'd ignore the jackhammers real job and look at it as a noise maker) right?. How much power is going into a jackhammer relative to the lost energy due to the "sound" escaping from the intended process? Most of the energy is going into the rocks, so it's a pretty lousy speaker for making 120 dB of noise...as it should be.

Al,

I'd like to see the weighted impact of energy distribution across the spectrum to conclude it's a "small" effect. I'm not saying you're wrong, but the laws of physics say the WEIGHTED effects in the frequency range of highest energy can be pretty severe. The lower in frequency you go, the more of the total power that is distributed, and hence, the reactance will really bug an amplifier.

True, the phase angle has to be greater than +/- 45 degrees to me mostly reactive.

True too, where a speaker is mostly resistive the power is tossed as heat. It just seesm to me that 75% of the power is applied across the lower ~200 Hz, where the speaker is most unsettled in impedance. So it isn't necessarilly the "range" of the frequency but the percentage of power supplied AT that frequency. Still, this could be much less than the minds eye thinks looking at the graphs. Stuff can get away from you when we make assumptions (we all know about assumptions).