tube amps and electrostatics

George, I happen to enjoy reading many of your posts in other threads. But I feel compelled to politely suggest that Ralph Karsten (Atmasphere) and Al (Almarg) are among the most respected A'gon members. Both are EE techies. And Ralph is the gent behind Atmasphere as in the "designer" and maybe the owner too.

In short, you're taking on some pretty heavy-duty guys. I suggest you back down and carefully re-read what Ralph and Al posted. I happened to think that what they wrote makes sense.

Ralph and Al, the discussion begs the question of how can one know whether an ESL was voiced to be driven by a tube versus SS amp. Obviously Sound Lab ESLs were designed to be tube friendly, ergo Ralph's comment that his amps have been coupled with Sound Lab ESLs for years. Is it the same old answer -- call the manufacturer and ask?? Or try to determine the type of amp that was used by the manufacturer to display the ESLs at shows??

Seems to me that what gets a bit dicey is the case where the ESL is coupled with a cone/dynamic speaker to cover LFs. Then we're back in the soup with "rock and roll" impedance curves.

Folks, let's try to remember this is a just a cool hobby and we're all friends.

Cheers,

Bruce

Al, I don't mind; and, thanks. I think your comment "Which of those two kinds of amplifier/speaker interactions results in the most correct acoustic output from the speaker is a separate question, however." is particularly valuable and relates to another issue that you bring up, perspective.

As I said previously I tend to let those more technically astute explain these interactions, but after a lot of years in this hobby I am convinced that part of the reason that some of us "are at loggerheads" (besides ego and stubbornness) is that there are still aspects of sound and music and the perception of those that the technical doesn't fully explain. I would like to offer some thoughts about this from my perspective.

In my experience, and almost without exception, systems assembled with the stated goal of "linearity" don't sound the way that live music sounds. More times than not the result is sound that is tipped up in the highs and lean through the midrange compared to the sound of acoustic instruments. The argument that there is too much variability in the sound of live to establish a benchmark is nonsense; there is much more that is consistent than there is that is different. Most of music takes place in the midrange and most audiophile systems sound too lean in this range without enough fullness and image density particularly in the lower midrange. I can't remember how often I have heard comments about a system lacking bass when there really was no true bass content in the music and what the listener was missing was the appropriate fullness in the lower midrange and, perhaps, upper bass that gives music much of its power. "Linear" highs will often result in upper partial information that is not well integrated with the fundamental frequency and add excessive "presence" to the highs.

"Brightness" is an interesting descriptive term in that it is often confused with "texture". I have heard many systems (or recordings) that are described as "bright" which I would describe as harsh or grainy but definitely not bright. In fact I have heard systems that are dark and harsh (usually ss based) and others that are bright and overly smooth (usually tube based). Incorrect texture is what I hear oftentimes with ss amps driving electrostats and not necessarily excessive brightness (even when the sound is too lean, giving the illusion of brightness), and that is the main reason that tubes driving electrostats usually sound more natural to me: the fullness and image density of the midrange and the proper integration of harmonics with their fundamentals creating a texture and clarity that is much closer to the sound of live acoustic instruments even if, in absolute terms, the sound does not measure as "linear"; whatever that is.

" The argument that there is too much variability in the sound of live to establish a benchmark is nonsense; there is much more that is consistent than there is that is different. "

Agree with Frogman on this. All live music has certain things in common. Patterns emerge and can be recognized with experience.

Also with the commonly accepted mindset that documented or measured technical specs and parameters are insufficient to tell the whole story regarding how well overall any playback system delivers the illusion of being real to individuals.

Its the twilight zone of home audio, that which cannot be explained fully based on scientifically established or otherwise known facts, that helps keep things interesting in that one never knows exactly what one will encounter until one encounters it. And each case will be just enough different most likely to still matter.

Just remember that the twilight zone is a prime feeding ground for charlatans and other purveyors of (intentional) disinformation as well. None of those in this discussion though, I would say. Misinformation (unintentional) is more prevalent as well.

Ralph and Al, the discussion begs the question of how can one know whether an ESL was voiced to be driven by a tube versus SS amp. Obviously Sound Lab ESLs were designed to be tube friendly, ergo Ralph's comment that his amps have been coupled with Sound Lab ESLs for years. Is it the same old answer -- call the manufacturer and ask?? Or try to determine the type of amp that was used by the manufacturer to display the ESLs at shows??

That's easy. Most of the ESLs intended to be driven by transistors tend to have very low maximum impedances. For example MLs tend to be 4 ohms in the bass. When you figure that the typical ESL varies by 10:1 in impedance from the bottom octave to the top, that means that the MLs should be about 0.4 ohms at 20KHz, and a number of them are.

However by use of a set of ZEROs you solve this problem, as I have mentioned before. Let's take the example of the ML and its 0.4 ohm impedance at 20KHz. The ZERO has taps that set up the amplifier load at 16 ohms, assuming that the speaker load is 4,3 or 2 ohms. If you are using the 4 ohm tap that 0.4 ohm load will look like 1.6 ohms. If the tube amp employs negative feedback it will have no trouble making this work with flat (linear) bandwidth. If the tube amp lacks feedback, you might have to use the 2 or 3 ohm tap, and it will still work quite well.

So really what it comes down to is whether the tube amp makes enough raw power that might be suitable to drive the speaker. IME, the Accoustat is a good example. Some versions of the Accoustat, as mentioned earlier in this thread are high impedance, meaning a little OTL like our M-60s can drive them fine across the entire band. Other Accoustats have that dreaded low impedance and require the use of the ZEROs. A good friend of mine had a set of Accoustats like that, and he used our M-60s with a set of the autoformers. The amps made plenty of power- and the setup was in a room 17' by 24', and we never clipped the amps.

The point here is that one must not confuse efficiency with the impedance. The ZERO is a problem-solver here- it allows almost any tube amp to effectively drive almost any ESL, provided the amp makes enough power in the first place.

Rodman99999, Thanks, I think I see what you mean.

Ralph and Al, the discussion begs the question of how can one know whether an ESL was voiced to be driven by a tube versus SS amp.

Bruce, altho' you've directed the question to Ralph & Al, just my 2 cents: since ESL behave like (giant) capacitors which have impedance inversely proportional to freq, wouldn't it always be true that ESLs are almost always voiced with tube amps (not saying that you cannot or should not use a BJT-based power amp if you want to)? Barring those like Sanders Sound Lab ESLs where the impedance is deliberately kept low so as to use a s.s. power amp.