Slam possible with Tubes instead of SS ??

FWIW Sound Labs have a high impedance at low frequencies which is why tube amps are preferred if you want them to play bass right. You can get them to play bass with transistors, but I think you will find that the way to do that involves having the speaker too close to the rear wall so you get some reinforcement. The problem is you wind up with a one-note bass.

The high impedance we are talking about is enough that a 600-watt transistor amp will only make 75-150 watts at certain bass frequencies. Sound Labs like some power though, so you really need about 150-200 watts to really make them play.

This is a good example of what I was talking about with regards to Sound Lab- if you are going to use transistors you need something that has a lot of power. 600 watts is about the minimum.

Now if you do your math, one thing that becomes apparent right away is that a speaker that needs 600 watts must be really inefficient. But that is not the case here- you need that power because in a transistor amplifier they won't be able to make nearly that power into the lower frequencies.

Mrtennis, yes and I think I have mentioned it before. ESLs have high impedance at low frequencies and low impedance at high frequencies.

Transistor amplifiers double power as you cut the impedance in half, which is another way of saying **their power is halved has you double impedance**. The ESL 63 has an impedance of 45 ohms in the bass. Your typical 200-watt transistor amp can only make about 40 watts or so into this impedance, and Quads actually *do* want some power.

By contrast a tube amp looses far less power into these higher impedances! Consequently only the bigger transistor amplifiers can keep up with a tube amp on a speaker like this.

The frequency response anomaly is related. First off, ESLs are a Power Paradigm technology. That is to say, since they do not have a box and associated resonance, they are not expecting that the amplifier be capable of constant voltage. see
http://www.atma-sphere.com/papers/paradigm_paper2.html
for more information.

Since the amplifier cannot make much power into high impedances and since it also wants to make a lot of power into low impedances, most transistor amplifiers will have a tilted tonality favoring the highs when used on most ESLs. The use of feedback helps reduce this problem, but does not eliminate it, and since the use of feedback makes almost any amplifier brighter, there is no good fix for it except to avoid transistors with ESLs.

Most ESL manufacturers want their speakers to work with transistors because its a bigger market, so you see a number of them making ESLs (Quad, excluding the 57 and 63, Martin-Logan, King, Innersound) with very low impedances to try to get around this problem. Its not a good solution though so even if you have one of these speakers you will still hear this phenomena with transistors.