"I suspect that some of the low-level articulation advantages attributed to high efficiency speakers is due to their typically being driven by Class A amplifiers which have no crossover distortion]."
The sensitivity/efficiency measurement of speakers is an expression of output sound level for a given input voltage. I am betting that the reason high efficiency speakers "articulate" better at lower levels is that the volume is actually louder at the same dial setting that you used for the less efficent speaker. Unless you have guaranteed that the sound pressure in the room is exactly the same for both tests, it's hard for me to swallow that crossover distortion in a modern class AB amp is to blame.
"Single-ended and OTL tube amps do not suffer from this effect, known as hysteresis."
All magnets suffer hysteresis losses. This includes transformers. OTL amplifiers parallel a bunch of tubes to get the output impedance low enough that a transformer is not required, but every single ended tube power amp I have ever seen has one.
The sensitivity/efficiency measurement of speakers is an expression of output sound level for a given input voltage. I am betting that the reason high efficiency speakers "articulate" better at lower levels is that the volume is actually louder at the same dial setting that you used for the less efficent speaker. Unless you have guaranteed that the sound pressure in the room is exactly the same for both tests, it's hard for me to swallow that crossover distortion in a modern class AB amp is to blame.
"Single-ended and OTL tube amps do not suffer from this effect, known as hysteresis."
All magnets suffer hysteresis losses. This includes transformers. OTL amplifiers parallel a bunch of tubes to get the output impedance low enough that a transformer is not required, but every single ended tube power amp I have ever seen has one.