Posted by Al Sekela on February 17, 2003 at 10:18:47:
In Reply to: Re: Soundlab Aura's Vs. Rotel 1090 posted by Chuck on February 16, 2003 at 17:43:44:
Sorry about my mistake regarding the Rotel. The specs are impressive, and mean this amplifier is built with a very large power supply.
Electrostats are not easy to understand because they respond to voltage, not current. The high impedance at lower frequencies results from the capacitive nature of their load. They are "voiced," if you will permit this audiophile term, with this property in mind, and will give their intended bass response with a constant-voltage amplifier if that is how they were designed. The "power" calculated from the load impedance is largely reactive power, where the current is not in phase with the voltage. The amp has to handle the substantial bass currents phase-shifted by almost 90 degrees as part of its job of maintaining the fidelity of the voltage signal. Even though the bass impedance of the speaker is higher, typical music signals have much larger bass voltage levels compared to the treble.
This all means you need to have an amp that will handle the very low (capacitive) impedance at high frequencies without oscillating or burning out the output devices. The bass is less of a burden for such an amp, but, depending on how the feedback (if any) is accomplished, may still favor transformer or OTL tube amps over transistor amps for the best sound.