Using tube amp with electrostatic speakers.

I'm going to assume the original Quad ESL is not amongst those considered "really not very neutral". That would be quite silly.

Tomcy6, what Ralph is saying that relates to your first question is that the very low impedance at 20 kHz is a byproduct of M-L’s decision to avoid extremely high impedances at low frequencies. The maximum power capability of nearly all solid state amplifiers decreases dramatically as the load impedance increases to high values, and therefore what M-L was trying to avoid was forcing the customer to use much more powerful solid state amplifiers than their designs require. Especially given that most music contains most of its energy in the lower part of the spectrum.

In contrast, depending on the specific design a tube amp will often be able to supply more power into high impedances than into 8 ohms, up to a point, and in any event whatever falloff may occur in its maximum power capability into impedances that are above a certain level (but still within reasonable limits) will almost always be much less than in the case of a solid state amp.

So M-L’s choice of impedance characteristics works in the direction of making their speakers more practical choices for users of solid state amps, since less powerful amps can be used than would otherwise be the case, while making them less friendly to tube amps than would otherwise be the case. While also, to some degree, adversely affecting amplifier sonics in both cases, as Ralph indicated.

Regards,
-- Al

@tomcy6

I think your skepticism, in general, is well placed. I've seen speakers who have crossovers DELIBERATELY designed to be hard to drive.  That's not the case with electrostatics however.

Plug: Has anyone seen my LM-1 monitor kits? Easy to drive, completely neutral, and free designs. :)

There's just no way to avoid the impedance dropping at the top when you are making an ESL. The entire panel is basically a capacitor, as opposed to a dynamic speaker which is an inductor + resistor. That's one of the main reasons Roger Sanders got into offering amps specifically designed to be excellent with ESL speakers.

I have however read about some radical designs where ESL's are driven from tube amps WITHOUT a transformer. Those who hear them say they are breathtaking. The amps are carefully designed around the ESL's though.

Not all panel speakers are the same though. The old Apogee's did have a ridiculously low impedance but it was relatively flat.

Best,


Erik

^^ to further build on that, many transistor amps can't continue to increase power into low impedance loads like 0.5 ohms. Further, the speaker cable itself becomes a significant factor when dealing with impedances like this!!

This works in ML's favor to help tame high frequencies, because the impedance curve of any ESL is not also an efficiency curve. What I mean by this is that if you put a watt into the speaker at its four ohm impedance level for a given output you should not be seeing 8 watts into the 0.5 ohm impedance level to get that same output level.

It is this 10:1 impedance ratio which is why tube amps are usually favored on ESLs as they tend to be less bright and there is a better ability to play bass. The brightness in this case is a simple frequency response error caused by a solid state amplifier's tendency to act like a voltage source (which is another way of saying that it tries to put out the same voltage regardless of what the load impedance is). By setting the impedance as low as they have, ML has limited the ability of most amps to be too bright, but I suspect various users will find that a lot depends on the amp and the speaker cables.