Richard Clark $10,000 Amplifier Challenge - Why Couldn't Anyone Pass this Test??

IMO it is a somewhat misleading oversimplification to categorize the ESL57 as being either an easy load or a difficult load.

It is a difficult load in the sense that its impedance descends to low values in the upper treble region, due to the capacitive nature of the impedance. Although even in that region its impedance is not nearly as low as the sub-1 ohm impedances of some other electrostatics, such as many of the Martin-Logan designs.

However, that difficulty is of course mitigated by the fact that most music contains relatively little energy in the top octave, where the impedance is particularly low.

It is an easy load in the sense that damping factor is a non-issue **with respect to bass control,** as Atmasphere indicated, because of its high impedance in the lower parts of the spectrum.

However, it will be a load that is **revealing** of amplifier differences, not only because of its transparency and musical resolution, but because differences in damping factor among different tube amps, and also between tube amps and solid state amps, will have tonal consequences.

Damping factor is inversely proportional to an amplifier's effective output impedance.  (I add the word "effective" to indicate that I am referring to output impedance taking into account the effects of whatever feedback may be present). The interaction of the amp's effective output impedance and the speaker's wide variations of impedance over the frequency range will certainly have tonal consequences, especially among different tube amps, and between tube amps and solid state amps. Less so among different solid state amps, since their effective output impedance is near zero in most cases.

In any event, the bottom line with respect to the tube-friendliness or lack thereof of the ESL57 is perhaps indicated by the fact that it was designed before solid state amps existed.

Regards,
-- Al
 

@erik_squires   

+1 the link you gave states this about Quad:

"The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases. This makes the Quad ESL a bad choice for single ended tube (SET) amplifiers."

@almarg    

+1 that is what I stated I even clarified that damping equates to  "(output impedance)" 

" They need about 15 Watts of the best amplification you can get your hands on."

" The Quads will play up to about 100 dB, which is much louder than I play music even when playing loudly. "

" The second downside is that they are a difficult load for the amplifier to drive. They are highly reactive loads (primarily capacitive). Their impedance drops as the frequency increases. This makes the Quad ESL a bad choice for single ended tube (SET) amplifiers. "

I think I can figure out why this guy isn't an authority, desperate or not.

All ESL panels I know of follow this descending impedance curve, which is a problem for a lot of amplifiers since most amplifier’s have rising impedance at the upper end of the frequency spectrum, resulting in an overall significant net loss of output.

This is in addition to current limiting, which thanks to music being bass heavy, is less of a concern.

Tube amplifiers rarely have the low output impedance (anywhere) that solid state amps do so they start at a disadvantage.

However this is all basic electrical / and voltage dividing theorems. The final choices about matching any given amp to any given speaker has to include the speaker’s acoustic output and room.

Given the impedance curves of the amps and speakers you can predict reliably that amp X’s electrical output will drop 6 dB at 20 kHz with a given speaker, but I can’t tell you if you’ll like it. :)

Best,


E