I guess I'm the oldest of the old guys on this list. I inherited some high impedance headphones from my father who used them when he built crystal sets in the 20s. Naturally, I used them for my own crystal sets. These babies had 30,000 ohms impedance. 3000 ohms impedance would have been considered low impedance at the time.
They had essentially the same construction as telephone receivers, but with much finer wire in the windings and a lot more turns. The basic construction had a permanent magnet with the coils wound around it. A flat steel disk was held at a slight distance from the magnet by the construction of the earpiece. I don't remember the sound being particularly bad, but there was no hi-fi around for comparison. The telephone used throughout the late 19th century and most of the 20th century was mostly an Edison invention rather than that of Bell's. Bell's was utterly impractical. An external current source with the carbon microphone gave the phone enough power to be used over distance. Patent problems with Bell in Britain made Edison come up with what I consider his cleverest invention, the electromotograph. Hardly anyone has heard of this remarkable gadget, but I built one way back when and was suitably impressed. It consists of a rotating wet chalk cylinder with a metal stylus riding in contact. The stylus is connected to a diaphragm. The consumer complaint about this device was that it was too loud. I could be heard throughout a room and thus prohibited private conversation. On Tuesday, September 15, 2020, 01:09:20 PM UTC, William Beaty <bi...@eskimo.com> wrote: On Mon, 14 Sep 2020, Frank Znidarsic wrote: > > with this arrangement I can unplug them. These earphones are of a 3000 > ohm high impedance design. The voice coil goes over a fixed magnet. > The magnet operates on a thin steel armature with no electrical > connections on it. The sound is very tinny and awfull The Radiola III > actually sounds much better with modern low impedance earphones. I wonder how those differed from earpieces in telephones of the time? Back then, everyone just took the "receiver" out of telephones. See Nikola Tesla's 50-microvolt radio receiver pdf below. When actually built, it turned out to be an amplifier element, with multiple LC circuits giving it "regen" bias, plus even a local BFO oscillator so that CW Morse would be heard as beeps. The Corums measure its gain as orders better than any receiver before Armstrong's regen/superregen receivers. Tesla's receiver, a parametric amplifier, slow-rotating coherer http://www.teslasociety.com/teslarec.pdf Tesla kept it secret, unpatented. The plans appeared in "Colorado Springs Notes" found in the 1970s. (The museum in Beograd had them, but wasn't releasing them until forced to publish, since the notes would harm Tesla's reputation of never taking notes, but only using his photographic memory! sheesh.) > There I am hoping to live to see the upcoming modern age of the low > impedance high fidelity loud speaker. Try these 1925-era science-project magazine PDFs, with loudspeaker ads. (Note that some of those science projects appear to be "lost technology" which only appears in these pdfs, but weren't published in all the Popular Electronics or Scientific American project magazines. The "matter disintegrator" project, making weird carbon compounds from methane feed into a rotary spark-gap, probably was producing Fullerenes and diamonds in gram quantities! The Experimenter https://worldradiohistory.com/The_Experimenterr.htm More, earlier: https://worldradiohistory.com/Electrical_Experimenter.htm > When you find something like this from the incipient age of electrical > communication and get it working, you realize how short of a time that our > modern electrical age has existed. > > Frank Znidarsic > > > http://www.angelfire.com/scifi2/zpt/temp/OutOf1923.jpg > > (((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))) William J. Beaty https://electricatechnology.com beat...@gmail.com CTO, Inventor, Research Engineer bi...@amasci.com 206-762-3818 vm 5459 Wilkinson Rd, Langley, WA 98260-8700
