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Original Message
RE: Soundlab is harder
Posted by Lew on May 4, 2012 at 22:31:32:
Ralph has given a lot of thought to this problem, and I have not. So I leave it to Ralph to comment definitively, but the SL panel is no different from any other full range ESL in that it behaves like a giant capacitor. Thus the impedance is very high at low frequencies. Parameters like mylar to stator distance, bias voltage, size of the panel, etc, all affect the "size" of the capacitative load, but this is why we need the two transformers in parallel or the SL bass transformer alone to get adequate bass response from an A1PX or the like. Direct-drive amplifiers can be designed so as to produce more "drive" or power into bass frequencies and to gradually reduce the drive as frequency increases, so as to deliver power as an inverse complement of the load presented by the speaker. I am sure this is what Acoustat did back in the day; I KNOW that is how the Beveridge dd amplifiers work. So a "crossover network" as we know it should not be necessary. However probably there is some sort of filter that must be built into the input stage. Not as damaging as a conventional speaker crossover, because very low values of capacitance could be used, therefore of very high quality. Ralph?