Why are high efficiency speakers preferred for low volume listening?

@immatthewj  IME its best to have the amplifier loafing for a living. They will produce the best sound they can that way and its always audible- smoother and more detailed (as well as measurably lower distortion, which is why 'smoother and more detailed'). 

@atmasphere  , well, it does not seem to sound like (to me, anyway) as if it is straining, but by loafing, are you thinking that it would prefer being in 100 wpc ultralinear versus the 50 wpc triode mode?

I feel that my preamp (Cary SLP 05) has a lot of gain (and probably some of that is because I am using the balanced ins and outs) so I rarely move the volume knob  much past 9 oclock to achieve my desired listening level, but I realize that this does not necessarily mean that the amp is not working harder than maybe would be optimal.

@immatthewj No, I was more suggesting the idea that if the speaker were 91 dB instead of 86, that the amplifier would be doing far less work. You could get the same sound pressure you do now with 1/4th the power. So your 50 Watts would be much closer to 'unlimited power' and distortion would be lower; therefore more transparent.

@immatthewj No, I was more suggesting the idea that if the speaker were 91 dB instead of 86, that the amplifier would be doing far less work. You could get the same sound pressure you do now with 1/4th the power. So your 50 Watts would be much closer to 'unlimited power' and distortion would be lower; therefore more transparent.

Ah, now I've got you, @atmasphere  .  That makes sense.  And I suppose that is what I was thinking about when I posted this question.  

@immatthewj, The importance of speaker efficiency: The article below is from 1962 and is as relevant today as it was then. Another advantage, with higher efficiency speakers,  is greater head room with a given amount of amplifier power. In my opinion, a high powered amplifier that can drive lower impedances will never be a proxy for a speaker's lack of true efficiency see here.

Mike

@atmasphere Wrote:

For that reason higher efficiency is good whether played at a lower volume or not since it can take advantage of lower powered and (hopefully) more musical amps.

All amplifiers make more distortion into lower impedances. This distortion is audible- don't fool yourself.

Its that first Watt of most amps that is usually the most important so if your amp has a good first Watt, you can see that a speaker of higher efficiency will be more able to take advantage of that.

I agree!