What are some of the speakers that sound especially accurate and good
with Atma-sphere OTL amps? Some examples would be helpful to illustrate
you're point.
Quad ESLs, Sound Lab ESLs, Classic Audio Loudspeakers (I have T-3s at home), Audiokinesis, Harbeth (some models work better than others, check with us on that one), ProAc, Merlin, Spendor, JM Labs, Most single-driver full range loudspeakers like Lowther, PHY and so on, Sonus Faber (as long as the speaker employs a single woofer), JBL, Altec and many other classic horn systems, Avant Garde, Vandersteen (usually the older ones- some of the newer ones are harder to drive), DeVore Fidelity, Voxativ, Spatial Audio, PureAudio Project, Salk... I can go on for quite a bit! Especially with our smaller OTLs, what you want to look for is that the woofer impedance curve is benign and nominally 8 ohms. So many 2-way speakers work quite well.
What we came to conclude is that flat frequency response is meaningless if the amplifier imparts audible coloration. A good example of that is harshness and brightness caused by low level high ordered harmonic distortion in solid state amps. Its hard to call that 'neutral' when everything you play through it is bright... The reason for this is the ear converts all forms of distortion into tonality (assigning 'bright' and 'harsh' to the higher ordered harmonics) and will favor that over actual frequency response, to such a degree that getting the speaker to be perfectly flat (which appears to be a Sisyphean task anyway) is pointless if the amp causes colorations due to distortion.
If you can keep the harmonic distortion to the lower orders the distortion will be less audible (as the ear is far less sensitive to the lower orders), and there are ways to do that without feedback (the latter of which is often rightly blamed for brightness and harshness in most amplifiers- the reason that is the case is a topic for another thread). If you promote linearity in the amplifier you can achieve fairly low distortion without feedback. Our amps at full power can be as low as 0.5% THD with about 0.05% or less IMD, which is better than a lot of tubes amps running feedback. If you can get the IM and higher ordered harmonics down, that is how you get to 'neutral'.
That is what we've been doing for the last 45 years, but that has also meant that we have to vet the speaker to work with our amps. That's really not all that hard which is why we've been around for so long.