tube amps and electrostatics

Mapman, most Class D's I know off and some I have tested are greatly troubled by loads that go under 3-4ohms, and ESL's can dip to below 1ohm.

Cheers George

GEorge,

I think you are right about that in general, from what I have read.

Still, not all Class D amps are created equal. I think I have read of some cases where they have worked well with very low impedances in some cases. It would be a concern, but you never know for sure till one tries. I'm wondering if anyone has?

Al, as most here already know, is one of the more knowledgeable contributors on this website. I feel really fortunate that we often agree :)

Al did indeed get it right, as usual. The problem you often run into when trying to use solid state with ESLs is not enough bass and too much treble. When you look at the impedance curve of nearly any ESL, its easy to see why- it is common that the amplifier will be trying to make nearly 10x more power at 20KHz than it might be at 50Hz!

The thing is, as pointed out earlier, the ESL has a low impedance at high frequencies due to its capacitive nature and *not* because it is less efficient at that or any other frequency. It is the latter fact that is often understood by many, (apparently) including Georgelofi; this is why his comments can be safely ignored.

Of course there is not nearly as much energy at 20KHz, but the result is easily heard as brightness. That, coupled with the normal brightness associated with solid state amps (due to odd ordered harmonic distortion) is why such amps do not usually make the best choice for ESLs- even those meant for transistors.

"That, coupled with the normal brightness associated with solid state amps'

That is a massive overgeneralization, and should be totally ignored.

"its easy to see why- it is common that the amplifier will be trying to make nearly 10x more power at 20KHz than it might be at 50Hz!"

Doesn't mean it's giving 10x the spl at those frequencies, it means it's staying linear and a have a flat frequency response into those load/s and frequencies.
If that were the case nearly every Solid State amp with good current ability would blow ESL's sky high at high frequencies, get real!

Cheers George

Here is what is real... the feedback used in transistor amps is what keeps them from destroying the speakers. That same feedback is also one of the things that makes a transistor amp bright. It can do that to tube amps too, but tubes can run with less or even zero feedback and have good HF bandwidth even on ESLs.

It appears that George and I are at loggerheads. I have in the past had difficulty taking much George has posted with anything other than a grain of salt, as often (as we see in the post above) the *math gets ignored.*

He is the only one I know of to challenge a technical comment made by Al.

If we can see an ESL efficiency curve that shows that the efficiency of the speaker drops with the impedance curve, I would be willing to concede he had a point. But no such curve exists. What information that does exist suggests that any ESL has the same efficiency at 10KHz that is does at 50 or 100Hz.

There is also personal experience. Something like 80% of our MA-2 production over the last 23 years has been for Sound Lab installations. During that time, we have sold a lot of amps to customers with Quads, Acoustats, Audiostatic and King ESLs. In that time its been really obvious when we encounter an ESL that is designed for transistors- the highs are muted as George suggests. The thing is, that does not happen with *all* ESLs, only some, and there is a fix for that- the ZEROs as I mentioned earlier.

Also in this case I was careful to use the word 'associated' in my comment that he quoted (which excuses it from being a generalization, instead it is a statement taken from the experiences of many people).

Its my opinion that George is grinding an axe.