differences between tube and solid state designs

Biomimetic, I can't speak to loudspeaker design at a specific price point, but maybe I can point out one reason why a loudspeaker's job in general is quite a challenge.

Everything in the analog signal path before the loudspeaker deals with three domains: Frequency, amplitude, and timing (or phase).

In addition to variations in these three domains, the acoustic signal generated by the loudspeaker has directional characteristics in three-dimensional space. So the challenge loudspeakers face is at least an order of magnitude greater that that faced by components operating purely in the electrical domain, and indeed we find that a loudspeaker's deviation from "flat" pretty much anywhere in that three dimensional space (including on-axis) is at least an order of mangitude greater than an electronic component's deviation from "flat".

Duke

Well first of all, there are different types of solid state amps, and different types of tube amps.

Areas where different topologies produce different results mostly have to do with their distortion characteristics.

For instance, tube amps soft-clip, which is much less objectionable to the ear that the hard clipping typical of solid state. I think this is the science behind the oft-quote observation that one tube watt = two solid state watts.

Class A/B amplifiers distort in the crossover region (the amp's crossover, not the speaker's), and that's a distortion that (with most A/B amps) happens at very low power levels so it happens all the time but is most noticeable at low listening levels. Class A and Class D amplifiers do not have this distortion. [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].

Now as an aside, note that there is often a negative correlation between low THD numbers and subjectively "clean" sound. In other words, we tend to prefer amps with higher rated THD! The reason is, usually those low THD numbers are arrived at through the use of negative feedback, which in effect trades off high percentages of low-order harmonic distortion for low percentages of high-order harmonic distortion. The ear finds the latter more objectionable than the former. Studies have shown 30% second harmonic distortion to be inaudible with music program material.

One disadvantage a push-pull tube amp has is its output transformer. As the signal changes polarity the field in the output transformer is inverted, and it takes some energy to do this. That energy comes from the output signal. I don't know how audibly significant this is. Single-ended and OTL tube amps do not suffer from this effect, known as hysteresis.

Zero negative feedback Class A amplifiers tend to sound the best because they have the most psychoacoustics-friendly distortion characteristics, assuming they are powerful enough to not be driven into clipping. Such amplifers can be tube or solid state. The day may come when high quality Class D amplifiers are counted in the same category, as they are inherently free from crossover distortion.

All that being said, the audible differences between amplifiers are at least an order of magnitude less than the audible differences between loudspeakers.

Duke