Those effects will become increasingly pronounced as speaker impedance
in that octave decreases relative to amplifier output impedance,
everything else being equal.
Al, as I mentioned earlier, the impedance curve of any ESL is not a graph of its efficiency (unlike a typical box speaker; this is due to the fact that the impedance curve is based on a capacitor). The fact of the matter is the efficiency curve looks a bit different and often ignores the impedance curve. This is why an amplifier that acts as a voltage source will tend to sound bright on an ESL and might not make so much bass.
none of it negates the fact that ESLs and Magnetics
require a lot of wattage to really sing....
This statement is really questionable. If it were completely true a 15-watt amp would not do so well on Quad ESL57s (but they do- Quad used to make a 15-watt tube amp that was made for the ESL-57). Or a 60-watt amp on Quad ESL63s and Accoustats (we've sold lots of our M-60s to such owners). I've seen 70-watt amps play Sound Labs quite nicely. We sell a good number of our MA-1s (140 watts) to Sound Lab owners. We also have a number of customers running M-60s on Magnaplanars (although they use a set of ZEROs to allow the M-60 to deal with the impedance).
The reason the Sanders needs such a powerful amp is that the speaker is inefficient. This is a conundrum with ESL designers- how to place the diaphragm... closely spaced so its easier to drive (might not handle excursion well)? Widely spaced to handle excursion (will be really inefficient)?
A speaker that **requires** a 900 watt amp to drive it is next door to criminal (and FWIW the Sanders does not seem to need that sort of power). The last thing you want to do with **any** amplifier is make it work hard (such increases audible distortions that make the presentation harsher and less detailed; exactly the opposite of what you want on an ESL). If you've set up your system properly, your amps won't be working hard most of the time.
