These were brought over by Milos as well. From what I've read and heard, these were the first electrostatic headphones available, and were put on the market around 1960. This particular sample might have driver imbalance and one driver pad was not attached. I eventually placed the pad on the driver, but measured without it... Maybe if there is a next time I'll measure them again properly.

These were driven by an SRM-T1... And it struggled like hell to do so. It could not reach 90 dB SPL at all. I think I saw 85 dB SPL when the volume was all the way up on the most efficient driver, and the T1 (and/or the SR-1) distorted heavily. If I get the chance I'll probably shot for a 50 or 55 dB measurement.

Anyhow here is what I got out of them (disregard the imbalance magnitude since we played with the volume given the difficulty to drive these, and one driver did not have pads... can't remember which one now):

Frequency Response:



Distortion Right:



Distortion Left:



CSD Right:



CSD Left:



This is a ~50 year old historic headphone and it was built like a tank. It still puts out sound.