Why are high efficiency speakers preferred for low volume listening?

Matching inefficient speakers to capable amps can overcome the loss of low volume dynamics that happens to us with large speakers. 

Something I can speak first hand to. 

My wife is a nurse and works nights, sleeps during the day.  Our bedroom is directly above the listening room.  Fully half the time I listen to my system when she is sleeping.  My Maggies (84 db sensitivity) at low volume give me so much detail and even dynamics that it full out surprises me almost every time!  I've had guests comment on exactly the same surprise that such low level listening can produce such detail.  I also have two REL subs hooked up and the bass at low volumes is ever present.  I fully believe it is a mix of electronics and speakers and I cannot agree with the statement that high efficiency correlates to quality listening at low volumes - Not on my system anyway.

OP,

thanks for catching my memory lapse and I really am referring to port/no port, omni-directional, controlled directivity.

here a KEF, there a Revel, any where you go ...

you wrote

"so I was thinking that if one was low level listening with an adequate amp, the sensitivity wouldn’t be that critical."

I absolutely agree, in theory, assuming no mis-match of equipment/space/placement/frequency distribution ’received’ at listening position. which is: an impossible assumption/comparison.

my friend’s little KEF Reference 1’s needed some serious juice (spl 81, sealed, no ports), made a great 1st impression. His mono block beasts burnt out after a while. Bass only down to 90 hz admitted to in those days. He built a table with an enormous down firing sub to that system after a while, I’m afraid to remember 30".

KEF Reference 1, sealed, no port, spl 81db

Add a port (other KEF, Revel, .....), sensitivity goes up a bit, all the way up to 86db hah, and bass performance goes lower a bit, however, now you have a much higher amount of indirect secondary ..... sound waves.

you also quoted:

"they are not finicky as far as placement." (about the ported Revels).

I think, when a port is involved, any/all locations already involve so much reflected sound ....., whereas, no port, front emanation, the placement(s) make a more discernable/measurable difference, so .... ported is less finicky isn’t necessarily a good thing.

..........................................

this becomes academic, a choice has to be made for a small room, many small ported speakers sound very enjoyable with or without a sub.

low volume is a separate issue

and there is no getting around the established facts that at the least low bass needs to be boosted at low volumes, ideally 'progressively boosted' as volume lowers.

Where's Wally? Where's Ray?

Play some Jazz, Ray Brown with others or his trio. Lower the volume, ... lower some more, where's Ray? For me, it is maintaining the Bass Player in Jazz that maintains involvement when listening at low volume. Otherwise it quickly becomes un-involving background music.

No matter how much we want to avoid the truth regarding 'loudness compensation'' (because so much modern equipment lacks solutions for it), success depends on both understanding and being equipped to solve the requirement.

you youngsters: get thee vintage features:

"Amplifiers often feature a "loudness" button, known technically as loudness compensation, that boosts low and high-frequency components of the sound. These are intended to offset the apparent loudness fall-off at those frequencies, especially at lower volume levels. Boosting these frequencies produces a flatter equal-loudness contour that appears to be louder even at low volume, preventing the perceived sound from being dominated by the mid-frequencies where the ear is most sensitive."

"Loudness compensation boosts low and high frequencies when listening at low levels so that the ear perceives an overall flatter (substitute accurate for flatter here) sound pressure level. This helps quiet sounds be easier to hear, and prevents loud sounds from overwhelming the listener."

I frequently see high efficiency speakers suggested for those who listen at "low levels." And is this another area that actually is "how easy the speaker is to drive (as related to its nominal impedance)" that is more important than the actual sensitivity number?

@immatthewj Efficiency (sensitivity) is important but so is the impedance and phase angles the amplifier must deal with.

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

So if you want to get the most out of your amplifier dollar investment, its best served by a speaker of 8 Ohms or more, if high quality sound is your goal. Its a pretty weak argument for 4 Ohms just because some amps can play only 3dB louder (which isn't remarkable to the ear).

Its harder to find high powered amps that actually sound like music as opposed to electronics. 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. 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.

FWIW Dept.: My speakers (Classic Audio Loudspeakers) are 98dB, 16 Ohms and flat to 20Hz. They are also some of the most revealing speakers I've heard.