Posted by Al Sekela on November 22, 2002 at 08:47:37:
In Reply to: Re: CLAR~IF~ICATIONS posted by Terry Koehn on November 21, 2002 at 20:10:09:
No, my conclusion is that there is NO amplifier effect on electrostatic speaker damping. The amplifier output impedance can only affect the membrane resonant frequency, and that effect may be negligible compared to that due to normal manufacturing variation and relaxation of the Mylar tension over time. [Heat guns?????!!!!!]
Amplifiers with high output impedance, like OTLs, will deliver bass from electrostatic speakers with just as good damping as the most voltage-source-like Krells. OTL amps will actually deliver more bass power at lower frequencies than such amps, but because of the rising speaker impedance, not because of any loss of damping.
The cone speaker back-EMF is what creates the current that damps the speaker, and the best cone bass performance requires an amplifier damping factor that matches the speaker. Most cone woofers available these days require high damping factors because of the prevalence of transistor amps with high damping factors. If you read the Tomcik article carefully, and reflect on the simple ratios it contains, you will realize that cone woofer efficiency is limited by the practice of high damping factor. Making the woofer magnet stronger would increase efficiency, but would require higher amplifier output impedance to avoid overdamping the woofer. None of this applies to electrostatic speaker bass performance, but it does apply to hybrids with cone woofers.
The Sound Lab website FAQ section contains a good description of the SL approach to utilizing the "drum head" membrane resonance effect to benefit speaker performance. Thank you for supplying information about the amplifiers used by Dr. West to 'voice' the speakers.
By the way, the Beveridge Model 2 speakers incorporated OTL high-voltage amplifiers. I believe this is part of the reason for their magic.