Speaker's efficiency, sensitivity and impedance

Chris

Efficiency is related to Watts, and Sensitivity is related to Volts.

To supplement Duke, if I may,here are some semantics. Basically,
* efficiency is a measure of how much electrical energy the spkr converts into acoustic energy (very little). It can be expressed in %: this speaker's efficiency is 5% (that high!)

* Sensitivity relates to how much acoustic energy a spkr produces given a specific amount of electrical (potential) energy.

I.e. for a "sensitive" spkr: you give it a little bit of electricity and, being very sensitive, it starts singing

So, the more sensitive it is, the more efficient it will be in the long run. I.e., if it is "sensitive" and plays very loud with very few volts, it is more "efficient" converting electricity into sound.

As you know, impedance is the resistance the spkr "system" has at 1kHz usually.(the actual res changes with frequency, hence the name "impedance" rather than "resistance"). Paraphrasing Duke above, and as a rough rule of the thumb, the lower the impedance quoted, the less "efficient" the speaker.

Is it safe to conclude that the impedance of a speaker gives an indication of the current demand on the amp

That would be very safe! That IS what the impedance actually tells you. It just doesn't tell you the whole story -- but it's a good part of the story!