What is your take on high efficient speakers vs. low efficient speakers?

In my opinion high efficiency for larger rooms. Less efficient for smaller. It all depends on the room which affects the over all sound. Klipsch  Horns in a 12x12 would sound awful.  In a 20x20 wonderful.  Also depends what's in the room.

While it may not be optimal, I’ve heard large horn systems in some really small rooms that sounded very good.  Check out Japanese audio magazines and you will see large horns in tiny Japanese apartments.  Japanese people are very considerate and would not be inclined to bother their neighbors so they would play their systems at low volume.  It is at LOW volume that horn systems shine.

Bass gives a foundation. This is a very big disadvantage of high efficiency design. 

Not to mention that many just don't tolerate horns.

Anyway, it's amp-speakers unit in a particular room, right.

Hi @sns ,

You mentioned a very important question.
Most low power DSET (45, 2a3, 300b,...) made today and before designed for very easy load and very hight sensitivity speakers file full range Lowther, Fostex, Voxativ,...
But in therm of pik volume these amplifiers can work for midsize room and ~95dB sensitivity speakers like big JBLs and Tannoys. But in the real live they don’t work properly even with more sensitive Klipsch and vintage Altec speakers.
The main design issue is weak power supply and weak driver tubes. The only SET amplifier I know (probably there are another) that don’t have these issues is Coincident Frankenstein.

I have been using a good DIY 300B DSET (6sn7 input, 6f6 driver) since 2006 with Altec 604E. This combination played nice but it had pronounced genre preferences. It was good for small jazz and classical groups, great for vocals but disaster for any kind of electronic music, rock, fusion jazz.
When I increased capacitors value and quality (oil capacitors) in the power supply and divided the right and left channels PS by resistors. It dramatically improved bass, dynamics and separation on bass heavy complicated, congested music. My solution is not optimal as my stereo amplifier uses one power transformer, rectifier and choke. Monoblock solution should be significantly better.
But the bottom line - the main issue in DSET in combination with big woofer 15" speakers is not lack of power but lack of ability to produce enough current. And the reason for this is not enough powerful power supplies. To drive 15" speakers some audiophiles go in the direction of big 845, 211 DSETs, but I’m not sure that this solution is the only one. 2a3 or 300B with a good big power supply can be another very good and more affordable one.

Regards,

Alex.

Lower efficiency speakers gives designers much more opportunity to “voice” things. At least that’s my uneducated opinion.