tube amps and electrostatics

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.

Stated differently, is it possible to design a cone speaker that performs well *AND* has benign impedance and phase angle curves? And is also reasonably sensitive??

yes! Roy Johnson of Green Mountain Audio has been doing this for a long time now. He's well known but not an audiophile household name like, say, B&W. But his speakers are all cone-driver types & they are often 6 Ohms & they have very little phase shift in the 200Hz-8KHz band (we're talking 10 degrees or less) & outside this band the phase shift is more but nowhere near the speakers that are members of the Society for the Cruetly to Amplifiers. Green Mountain Audio speakers are easy to drive - a 30W/ch RM10 from Roger Modjeski will drive many of his stand-mount speakers to sufficiently high SPL. The Green Mountain Audio speakers are in the 90dB sensitivity range.
here is a link to his Rio speaker design notes:
http://greenmountainaudio.com/storage/speakers/rio/Rio-Design-Concept.pdf
i realize that no phase plot is given but one can assume from the flatness of the impedance curve that the phase is also relatively flat (note that wild impedance curves & wild phase curves are related - when you see one, you see the other. Do an empirical check to convince yourself).
here's a review of the Callisto speakers on 6moons:
http://www.6moons.com/audioreviews/gma2/callisto.html

The Green Mountain Audio speakers always sound like music on all your genres of music. I recently heard them again at RMAF2013 & they once again delighted. Stereophile gave Green Mountain Audio some very good press:
http://www.stereophile.com/content/marigo-whirls-green-mountain
Roy Johnson on the left (& Marigo Audio Labs owner on Ron Hedrick on the right).

For me speakers from the company are really the best & I can't seem to listen to any other type of speaker as they seem "broken" to me (my understanding is that the Apogee Scintilla also has a 1st order x-over).
No financial or otherwise implied relationship with Green Mountain Audio. Just a happy former owner.
Thanks.

Thanks for this info Georgelofi. The Diamantes were Green Mtn Audio's 1st offering back in 1994. Not a bad start - much better than most other speakers in the market at that time. There has been considerable advance since then & I believe that Roy Johnson has gotten the phase angles down much more so that the newer model speakers are more amplifier agnostic. I think now Roy Johnson is agreeable to the Atma-sphere M60 amplifier driving his speakers.

Hi Atmasphere,
nice to have met you in person at RMAF2013. I always enjoyed listening to the Classic Audio Hartsfield & T1.4 & they were sounding very good with your amps.....

I believe that Roger Sanders has also done a great job with his s.s. amps - ESL Mk2 & Magtech - to drive electrostatic speakers. I listened to his speakers in the Sanders Sound Labs room & I really liked the sonics there as well. So, the s.s. world is not totally shut....
thanks.

Rodman99999,
this debate on MOSFET vs BJT has been duked out before many times & I do NOT want to get into it again. So, I'm writing this with a bit of trepidation -
both your references for MOSFETs seem to deal with MOSFETs used in a high frequency switching application (this is the key here - switching application) where MOSFETs are deemed better power devices than BJTs simply because MOSFETs are all-majority carrier devices (unlike BJTs which are bipolar carrier devices. hence the word "Bipolar" in BJT - both charges exist in this device - majority carriers in the emitter & collector & minority carriers in the base). Today's class-D amplifiers use power MOSFETs in their final output switching stage & for good reason as this stage operates at 10X the max audio frequency & we want to minimize the losses in this stage. For traditional class-A & class-AB power amplifiers, the output stage is NOT being used as a switching output stage; it's being used a continuously-variable analog output stage with high current capacity. I.E. the output stage is a gain stage & not a switching stage. There's a big difference here. You can definitely use power MOSFETs in the output analog stage as we see with Pass Labs, Threshold & many other brands. Not saying it cannot be done....

MOSFETs make better high frequency switches because at high frequencies we worry about the AC losses (CV^2f). These are the losses that are directly proportional to frequency & the parasitic capacitances of the device. Recovery time from off-to-on & on-to-off is also a big consideration in switching application & in MOSFETs this time is less than in BJTs as one does not have to wait for the majority & minority carriers to move from & get back to home base 'coz in MOSFETs there are no minority carriers!
MOSFETs are self-limiting current output-wise (higher temp means higher resistance, which means lower output current. BTW, if you did not realize this - this is negative feedback! But this negative feedback is localized to within the device) & all that is very well.
Output current-wise I also believe that BJTs do a better job - for the same amount of drain (MOSFET) or collector (BJT) current, the gain of the semiconductor device is higher in the BJT than in the MOSFET. Current in a BJT is linear relationship to circuit parameters like Vbe, circuit resitances, etc. In a MOSFET, the drain current has a square-law relationship to gate-source & threshold voltages.
At the very heart of it, the MOSFET is a voltage device (yes, it does convert input voltage to drain current, hence, the transconductance) but, naturally, it is a Field Effect device. And, intrinsically, the BJT is a current device. Yes, applying voltages to the terminals does create high electric fields but the applied voltages are meant to create electron flow (current) in a BJT & not setup a source-drain channel (like in a MOSFET).
MOSFETs have become very good power devices off-lately but I believe that BJts do a better job of high current delivery in analog circuits.