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Sensitivity of 2000-ohm Headphones

Discussion in 'Electronic Design' started by Reg Edwards, Jul 1, 2004.

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  1. Reg Edwards

    Reg Edwards Guest

    I am writing a program involving an antenna plus two coupled tuned circuits
    plus a matched simple receiver.

    I would like to know, crudely, the audio power input level to 2000-ohm, iron
    diaphragm headphones for a nice, comfortable, not too difficult listening
    level. Such as when the phones are used on a crystal and cat's whisker
    broadcast radio receiver.

    Such headphones are more sensitive than modern 8-ohm varieties. I have a
    pair of 2000-ohm headphones but unfortunately no means of measuring power or
    voltage input.

    Just the number of micro-watts please. At what low power input level does
    speech or music just BEGIN to fade out to a person of normal hearing? Any
    ideas? I could take the average of a few replies.
  2. John Jardine

    John Jardine Guest

    A pair of to hand, WW2, S.G.Brown's D1's, (only 1015 ohms DC resistance
    though) gave a just detectable signal with a 10uV (true rms, 2kHz measuring
    bandwidth) input, (50ohms source). Similar levels for both music and a 1KHz
    sine. I.e about 100 femto-watts!.
    My hearings crap. Good ears would do better.
  3. John Larkin

    John Larkin Guest

    I was just thinking about that the other day. Stray thought trains
    arrived at the question, how can a spark-gap transmitter send a signal
    across the ocean to a crystal receiver, which seems incredible given
    how big the universe is compared to the receiving antenna. But 10 KW
    to 100 fw is a ratio of 1e17:1, which explains a lot. Actually, the
    crystal needs a lot more voltage to rectify, but the whole thing is
    still impressive.

    The 100 fw level is amazing.

  4. Reg Edwards

    Reg Edwards Guest


    John, just the info I was looking for. Thanks very much indeed.

    I first wore a pair of S.G.Brown's phones around 1932 when my father clapped
    them around my head to hear the BBC's Birmingham transmitter on a crystal
    set he had just completed. About 40 years later Mother gave them away to
    the weekly rag and bone man along with a load of father's other old "Junk".
    She didn't even collect the traditional gold fish because she hadn't an
    empty jam jar to keep it in. But I still love her memory.

    I heard prime minister Neville Chamberlain's declaration of war on 3rd
    September 1939 on a pair of S.G.Brown's phones plus a PM1LF 1-valve
    receiver. Five years later I was in the RAF working with the newly-invented
    3000 Megacycle cavity magnetron, the device which led thousands of Lancaster
    bombers to German cities to incinerate their populations. Now every kitchen
    has one. After the war I still used father's phones on incomplete home made
    receivers. I seldom got round to building the loudspeaker output stages.

    Thanks again for your trouble.
    Regards from Reg, G4FGQ
    For Free Radio Design Software go to
  5. Tam/WB2TT

    Tam/WB2TT Guest

    Your 1015 Ohms seems right. I am 99% sure that the 2000 Ohm spec is for the
    two phones in series, which is how they were wired.

  6. Tim Wescott

    Tim Wescott Guest

    Does anybody know if the ones that Antique Electronic Supply sells are
    as good, or do I have to dig for an original pair?
  7. John Jardine

    John Jardine Guest

    (I'm always suitably impressed by the wild numbers attached to space-probes
    received signal powers).
    The spark gap people would also seem to have had the support a much, much
    cleaner aether.
    If a long wire aerial, installed many years ago when I had a radio interest,
    is anything to go by, then the grass on the spectrum analyser baseline
    (0-120megs) is growing at an astonishing (to me!) 2-3dB a year.
    I occasionally wonder where the limits lie. Surely we can't go on pumping
    nearly logrithmically escalating Gwatts of what is essentially 'noise-power'
    into the aetheric void, without some tangible physical or even physiological
    effects turning up. (Maybe we'll find that empty space is non linear :).
  8. John Jardine

    John Jardine Guest

    for both music and a
    No trouble at all Reg. The question piqued my own curiosity. I built up a
    military radio collection. Hence to hand, drawers full of classic headsets,
    mic's etc.
    Your'e going back some there!. Came across a PM1LF article in a volume of
    pre war 'Practical and amateur Wireless'. Often wondered what it would have
    been like to be around at a time when large sections of the population
    enthusiastically pursued technical hobbies and interests, self improvement
    seemed to be the order of the day and people innovated rather than consumed.
    My radio collection tops out at 500MHz with a 'R1359' receiver, believed
    used in the home chain defence network. I/p signal onto a couple of tuning
    rods and straight into a silicon cartridge diode for prompt down conversion
    to some manageable frequency.
    The cavity magnetron invention must have brought tears of joy to the eyes of
    designers doing their damndest to squeeze out just a couple of watts at the
    low UHF frequencies. I'll look at this particular #1359 grey painted Rx,
    ugly, heavy, markedly insensitive and yet know that it has it's own
    (pre-magnetron)particular exact time and place in history.
    I'm eulogising, must move on. Time I found a museum etc, maybe in the
    Yorkshire area that can take the collection. Let other enthusiasts enjoy the
  9. John Larkin

    John Larkin Guest

    I saw a calculation that shows that, extrapolating our present rate of
    energy consumption growth, the surface of the earth will reach
    incandescence about the year 2100.

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