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Benefit of high impedance high voltage speakers?

Discussion in 'Electronic Basics' started by Phil Allison, May 4, 2011.

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  1. Phil Allison

    Phil Allison Guest

    "Stretto"
    ** The gauge of wire used inside a speaker to make the voice coil has NO
    effect on efficiency. The same speaker could be produced with impedance
    anywhere from 0.5 ohms to 50 ohms just by altering the wire gauge. The
    important thing is that the same overall VOLUME of copper is used to make
    the coil.

    The voltages that amplifiers deliver to speakers is kept within safe limits
    if the speaker is no more than 8 to 16 ohms.
    A 100 ohm speaker would require dangerously a high drive voltage at power
    levels of 50 watts or more ( ie 70 volts rms) and hence preclude domestic
    use.



    ..... Phil
     
  2. Stretto

    Stretto Guest

    They are obviously not common but what are the pro's and cons? I can't think
    of any cons except the higher voltage. Lower current = more efficient,
    smaller wire, etc...
     
  3. Jasen Betts

    Jasen Betts Guest

    High impedance speakers are common in commercial settings where 100V
    and 70V public address wiring is common. usually ordinary 8 ohm
    loudspeakers are used with a transformer to convert the impedance.

    Often the transformer has a several taps and and switch to select
    between them allowing the volume to be ajdusted at the output
    without using a wasteful L-pad.

    the 8 ohm speaker in combination with the transformer form a high
    impedance speaker.
     
  4. Phil Allison

    Phil Allison Guest

    "Jasen Betts" <

    ** Baaaaaaaaahhhhhhhh..........
    ** Kinda contradicts your first claim.

    ** To what practical advantage ?

    What is special about a "public address" system ?

    And where is the connection with the OP's query ??



    ..... Phil
     
  5. That's a different application. Since the wiring maybe long, it makes
    sense to use higher voltage so the current is lower for the same power,
    and thus the higher resistance accumulated over the longer wires will
    not affect things the way it would if low voltage higher current audio was
    going through those lines.

    Michael
     
  6. Phil Allison

    Phil Allison Guest

    "Globemaker"

    Consider the other issues: insulation thickness, temperature
    variations, and magnetic gap. Imagine a 240 volt speaker driven by a
    common 3 phase power transmission line from the grid . This is a loud
    siren for tsunami alarms. The insulation must be thicker than for
    varnished magnet wire. Thick insulation keeps heat building up to bad
    temperatures. Thick insulation increases the gap between the wires in
    the moving parts and the permanent magnet or electromagnet. Tradeoffs
    between competing physical effects may be calculated.

    ** Wot utter bollocks.




    ..... Phil
     
  7. Stretto

    Stretto Guest

    "Globemaker" wrote in message

    Consider the other issues: insulation thickness, temperature
    variations, and magnetic gap. Imagine a 240 volt speaker driven by a
    common 3 phase power transmission line from the grid . This is a loud
    siren for tsunami alarms. The insulation must be thicker than for
    varnished magnet wire. Thick insulation keeps heat building up to bad
    temperatures. Thick insulation increases the gap between the wires in
    the moving parts and the permanent magnet or electromagnet. Tradeoffs
    between competing physical effects may be calculated.

    -----------------------

    None of the responses give the pro's of high voltage though. Obviously
    higher current = higher temperature = thicker wire and/or insulation, larger
    speaker magnetics, larger transformers, etc. As far as I can tell it is much
    easier to use higher voltage speakers from all perspectives except the high
    voltage itself as it could pose a health hazard.

    So is there any real real cons besides the high voltage itself? If not then
    why do we even use high current(verses high voltage) speakers in the first
    place? Old tube radios used higher voltage speakers(I have a couple of them
    and they are much higher impedances(1k's+). Surely there has to be a reason
    why high current was chosen over high voltage. Best I can guess is that it
    has something to do with efficiency of the magnetics... it's really just a
    guess though.
     
  8. Bob Masta

    Bob Masta Guest

    The other reason (actually *the* reason) for 70V (or 100V)
    PA distribution systems is it issue of impedance matching
    when you have a large and arbitrary number of speakers.

    Suppose you had a typical home-stereo power amp, with a
    minimum recommended load impedance of (say) 4 ohms, and you
    want each channel to drive a number of speakers. If you
    want to drive 2 speakers per channel, you can put two 8-ohm
    speakers in parallel. If you want to drive 4, you can have
    two branches in parallel, each with two 4-ohm speakers in
    series. And so on. But it's a major headache for arbitrary
    numbers (like odd numbers), and it's totally impractical if
    you want to add or remove speakers later.

    With 70/100V distribution you just put all the speakers in
    parallel, with each having its own step-down transformer
    from the high-impedance (and high voltage) distribution
    wiring to a standard 8 ohm (or whatever) speaker.

    See for example
    <http://ticcorp.com/25v_70v_100v_systems.htm>

    (That's not a plug for the company, just the first non-PDF
    that Google came up with.)

    Best regards,


    Bob Masta

    DAQARTA v6.01
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, FREE Signal Generator
    Pitch Track, Pitch-to-MIDI
    Science with your sound card!
     
  9. Stretto

    Stretto Guest

    "Jasen Betts" wrote in message
    High impedance speakers are common in commercial settings where 100V
    and 70V public address wiring is common. usually ordinary 8 ohm
    loudspeakers are used with a transformer to convert the impedance.

    Often the transformer has a several taps and and switch to select
    between them allowing the volume to be ajdusted at the output
    without using a wasteful L-pad.

    the 8 ohm speaker in combination with the transformer form a high
    impedance speaker.

    -------------------
    I suppose high current speakers could have been chosen over high voltage
    speakers because of this reason since putting them in series would require
    unsafe voltages? e.g., if you have 10 speakers at 100V each the total
    voltage then would be 1kV vs around 20V-30V for your average speakers. Of
    course 95% of speakers are not used in PA's so that is not a really good
    reason but who knows...
     
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