FS: Toshiba HR-910 Electret (1979, rare!)
Will Ship To: Anywhere
Selling these rare Toshiba HR-910 Electret Headphones (ca. 1979?) in original box with all accessories:
- Adaptor Unit
- Replacement ear pads (slightly disintegrated)
Both included ear pads (one is an ear-covering and the other an ear-fitting type, as explained in the manual) have started to disintegrate slightly.
The headphones are connected to the adaptor unit which can then be connected to either a headphone amp or a speaker amp using the four speaker terminals. A switch on the adaptor selects the input impedance to better match the amp. The headphones are in perfect working order, the sound is (IMO) natural but thin.
I've included pictures of all pages of the manual so even if you're not buying you can have a look at this rarity.
Can ship anywhere.
Frequency Response: 20-35 kHZ
Sensitivity: More than 104db, 100Vrms input
Distortion: Less than 0.5%, 400 Hz input
Weight: 240g (without cord)
Links with listening impressions:
What are electrets?
"To put it simply, electret headphones are electrostatic headphones. More specifically, they're a type of electrostatic headphone. The only difference is in the method by which a fixed charge is placed on the diaphragm. An electret foil or film is a thin polymer sheet that has been given, and which will retain, an electrostatic charge of a few hundred volts. It would be as if the hard-rubber comb you used to do simple static-electricity experiments at home (picking up tiny bits of paper, making a small stream of water bend) could stay charged indefinitely.
The only mechanical difference between an electrostatic headphone and an electret electrostatic headphone is the material the diaphragm's made of and whether or not there's an electrical connection to it from the outside world, namely from a bias-voltage supply.
From an engineering standpoint, the optimum diaphragm material is a polyester called boPET, biaxially-oriented polyethylene terephthalate film, aka Mylar or Hostaphan or Melinex. Problem is, boPET doesn't make a very good electret. So an engineer must either accept a compromise in the sound, or he can re-engineer the typical electrostatic headphone layout by metallizing a boPET diaphragm and applying the audio signal to it and relegating the electret material to the stators where its inferior mechanical properties won't matter. This inside-out or back-electret design was used by only two manufacturers: Toshiba (most notably the HR 910 and 810; Rotel marketed an OEM version of the 810) and Audio-Technica (the ATH-8, aka the Signet TK33)."
Edited by Case - 5/19/14 at 6:12am