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In Reply to: yes, I don't doubt that it rolls off posted by Ralph on June 15, 2012 at 12:15:44:
You wrote, "The reason I ask is if there is self inductance, then its impedance should be going sky high if its not influencing the impedance at 20KHz. But all I have ever seen of ESLs is that impedance goes down as frequency increases. That really suggests to me that while the transformer may not be making any output, its still loading the amp and for no good purpose unless you like heat. Am I way off the mark??"
Here's the way I think of it, right or wrong: (1) Yes, I think the impedance of the speaker as seen via the bass transformer alone would by "sky high" at 20kHz, but no, I did not measure the bass tranformer alone (with no treble transformer in parallel) above 2kHz, because it was going straight up to the sky already at that frequency. I did it only from 20Hz to 2kHz in log intervals. Did someone else put out some data to the contrary? (2) I think the reason the speaker has a low impedance at very high frequencies is by far mostly to do with the speaker itself and its capacitative nature. So, when the speaker is seen by the amplifier, almost entirely reflected via the treble transformer at high frequencies, the impedance will be very low. The effect of the transformer should be a constant, related to the turns ratio, at all audio frequencies. I think R West himself recently wrote that the speaker is ~1600pF capacitor. (Can't remember, was some number between 1600 and 1900. These capacitances seem too low to me; I thought K Covi calculated the M1 as a 2uF capacitor.) Figure the impedance of a 1600pF capacitor at 20kHz and then divide that by the square of the turns ratio of either the SL toroid (75:1) or the AU90 (90:1). Gosh, I think the result would not correspond to reality, too high Z.
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Follow Ups
- RE: yes, I don't doubt that it rolls off - Lew 14:30:02 06/15/12 (0)
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