Smooth treble

Hi Chris, yes, that's right. FWIW tubes in general make less odd-ordered harmonics so its a lot easier to build a smooth sounding system by using them.

Tubes are so linear that it is possible to build circuits that use zero amounts of loop negative feedback. Although feedback reduces distortion, it will actually increase the odd orders that our ears use as loudness cues. This gives the equipment that uses negative feedback a sheen or harshness that it would not have otherwise, although with most transistor designs, not using feedback is not an option.

Rleff, does that answer your question?

In my book 'smooth' is two things- a lack of high frequency emphasis (however we are not talking about anything being rolled off), and a lack of odd-ordered harmonics, which is the source of 'jagged' sound that others here have referred to.

Odd-ordered harmonic content is often described as 'hard', 'brittle', 'harsh', 'clinical', sometimes 'overly detailed' (which is impossible if there is no brightness) and now 'jagged'.

You can have smooth and a lack of detail, but in my book when a change in the system causes smoothness and **increased** detail, then you are on to something. The smoother, the more detailed without losing speed, the closer you will be to the recording itself.

Dazzdax, to answer your question about the differences between the Sound Lab and the Apogee, IMO/IME the Sound Lab is likely the better performer of the two, given that you have the ideal amplifier to driver either one, which could be two very different amplifiers!

The reason I say this is that the Sound Lab has a powered system for moving the diaphragm and the Apogee relies on a permanent magnet. All magnets in all speakers have a certain amount of sag when the amplifier puts power to the diaphragm to make it move (BTW this is why Alnico magnets are preferred in cone systems as they sag the least and consequently sound better). IOW the powered electrostatic field of the ESL will not sag while the permanent magnet system will. The cone speaker equivalent of this is the field coil; so far I've not heard of a field coil-powered magnetic planar, and that would be an interesting speaker project...

The powered system offers greater impact and greater detail, often with associated smoother sound, IME.

Otherwise I would expect very similar performance overall, if it is possible to rule out the amplifier in the equation, which I am not sure is possible.

Opus88, its all about the rules of human hearing. Most people think about 20hz to 20KHz as the most important, but the most important is the ability to tell how loud a sound is. We use odd-ordered harmonic content to do that.

When electronics do not take this into account, they sound harsh...