I had noted a high frequency ripple on the MAJ745 speaker input terminals when making some meaurements in the past. I used an HP 34401A 6 1/2 digit multimeter. The frequency was 42.217KHz and the ripple was 17.33mvAC. This is obviously the switching frequency of the bias supply. What I don’t understand is how bias voltage ripple would affect the diaphragm as it is resonant at 22KHz and the response drops off like a rock above that. I suspect that a current probe was used to measure the bias current as measuring 15kv directly is quite risky. I would be interested to know is exactly how the measurements were made.