After an extended period of searching... Pioneer SE-1000.
Pioneer's first and only electrostatic headphone, similar in appearance to Sony's electrostatic offering from roughly the same time period.
Three units showed up nearly all at once, with one having it's original box and another having the energizer. This pair had neither, and unfortunately sold for the most... and was the first of the three that I heard wind of.
If I tally up every real pair I've ever seen, there are five of them -- one on a Chinese auction site for $Hell.No, one on display in a small local Hi-Fi store, and the three that just sold on Yahoo Auctions. The only other surviving photo is a product render from a European Hi-Fi catalog from the early 1980s. That's it -- no reviews, no product brochure, no official Pioneer catalog. For the longest time, these were nothing but a ghost.
And now here they are.
Since I don't have the energizer, I had to figure out the pinout of the (proprietary) connector manually. It is similar in appearance to a standard 6-pin DIN connector but has brass pins that are presumably rated for much higher voltage and there's some keying on the sleeve to prevent you from plugging it into something awry.
Working around this annoyingly tiny plug took a bit of nerve-racking prodding with a multimeter and some patience, but I was able to map out every pin. I've made this simple diagram in the hopes that it may help anyone else unfortunate enough to find these without the (also proprietary) adapter box.
These are a roughly 60mm x 75mm procedural oval driver, similar to the Stax SR-Lambda in design, with a peculiar earpiece design that pivots separately from the headband joint. The stators are either copper or brass, with a polymer dust cover on the front and a silk one on the back. There's a small gap between the rear cover and the metal mesh, which is filled with the now-coveted micro fiberglass damping pucks that are commonly found in headphones from this time period. The strut through the middle is only for structural support; this is a single-panel, monolithic stat driver.
According to FC2, a Japanese headphone museum with an incredibly helpful website, the diaphragm is a 2.5 micron membrane. I do not know where this spec was taken from, or if it takes the diaphragm coating into account, but it is a little bit on the thick side for a stat of this size. The original SR-Lambda has a 2 micron membrane with coating, and though this driver is wider than a lambda, it is also considerably shorter. The intended bias voltage is unknown, but given the time period it is almost certainly somewhere in the 200V range. They comfortably run off of Stax's Normal Bias standard (230V) with no issues.
I was able to get some preliminary measurements of this headphone using a modified ECA-80 and a pair of cheap and very reflective faux leather earpads I had on hand. I have a pair of period-correct Pioneer pads on the way that will be a much better fit, but for now... I am nearly speechless.
These are
good.