We should reject hard-to-drive speakers more often

High power class D amps more than make up for the difference in dynamic contrast between low and high efficiency speakers. High efficiency speakers have way worse problems than thermal compression.

@jon_5912 Rather than innuendo, could you be specific about ’way worse problems’?

If any amplifier is properly designed and operating properly, it will not add dynamic contrast to the signal. The signal itself is the source of dynamic contrast. Loudspeakers only take away from that; if you value dynamic contrast, using a speaker that has the least thermal compression will bring you closer to your goal. In this light, ESLs have the least thermal compression owing to no voice coil at all; a close runner up is higher efficiency loudspeakers, in particular those that employ field coils (since the magnetic field in an electro-magnetic loudspeaker does not sag when current is applied to the voice coil).

Some argue that SETs are the most ’dynamic’ of all amplifiers, but if you use a sound level pressure meter you find out that isn’t true- its really distortion on the leading edge of transients interacting with the way the ear perceives loudness that causes this impression.

Amplifiers cannot ’make up the difference’ in terms of dynamic contrast.

My experience with ESL’s says that this low impedance (1/3rd of an Ohm) in the upper octave is quite noticeable and often pushes owners to beefier solid state amps.

@erik_squires FWIW, about 90% of our MA-2 (a 220Watt class A triode OTL) production are running on Sound Lab ESLs. Tubes work quite well with ESL57s, ESL63s and ESL98s. Most solid state amps behave as a voltage source and since ESLs in general tend to have an impedance curve that varies by about 9:1 or 10:1 from the bass region to the highs, quite often a voltage source will sound bright as the amp doubles its output again and again as frequency is increased.

For this reason, some ESL producers make their speakers low impedance in the bass and nearly a dead short in the highs, limiting the ability of the amp to drive the higher frequencies (partly due to the speaker cable impedance becoming a significant portion of the source impedance).

Even then, brightness is an ever-present danger with such amps, particularly if they have distortion rising with frequency.

I think the answer to that is the so-called Hoffman’s Iron Law

@lanx0003 Exactly!

@atmasphere  - I'm trying hard not to use absolutes.  I'm sure your amps do fine!

Rather, I think ESL's bring a lot of other qualities to the listening experience which makes us swant to overlook the hard to drive aspect.

We buy ESL's in spite of the low impedance, not because of it.

So far nothing perfect has ever been found by humans in this Universe and from my understanding of physics if it did exist all molecules in our universe would be equally distributed thus we wouldn't exist. It's all variables and compromises in any human endeavor these perfect loudspeakers could never exist since perfection itself doesn't exist. As far as rejecting lower eff that's more of a taste and experience or bias issue hi- eff low- eff most can have a good system built around them if you embrace strengths and mitigate known issues. If one wants dynamics, large image size, great transient response, and the ability to run off lower power but can accept a bit of size, different appearance from audiophile standards and can handle the limited market options or you can DIY, Hi Eff would be the logical choice. If you want what almost all audiophiles use and approve of, like to have many easy-to-source options, enjoy large power or need a small speaker. Low-Eff may be the best choice for you. There are still loudspeakers that are neither low or high eff those also may be worth checking out if you feel you want a bit of both worlds.

speakers make the sound we hear in our rooms... and wonderful sound is what we are striving for in our rooms

speakers should be evaluated when performing at their best, which is properly set up in room, driven by a suitable amp to get peak performance (or something very close to it) from them

efficiency of the speaker, and the requisite amp, are all part of the tradeoffs to get the sound we really want

all others things equal, yes, easy to drive, efficient speakers are nice to have... but it is foremost about the sound... that is the big dog that wags the tail of efficiency and amplification

we buy ESL speakers because we like how they sound, realizing we need the right amp...