Re: Carbon microphone amplitude

Walter Harley wrote:
"ehsjr" <ehsjr@xxxxxxxxxxxxxxxx> wrote in message
news:dTQMf.7608$UN1.4908@xxxxxxxxxxx
You guys may not be aware of how a carbon mike works.
You seem to think that the mike generates a voltage.
It doesn't. A voltage must be supplied to it. Sound
varies the pressure on the carbon, which causes its
resistance to vary. That causes the current through
the mike to vary.

What is the typical signal amplitude of a carbon mike?
Meaningless question. A carbon mike is not a source.
Without knowing the source voltage one cannot say what
the amplitude will be. Likewise, without knowing the load
impedance, one cannot say what the amplitude will be.
The signal (and by that I assume you mean the voltage
drop across the mike) is a result of the current through
the resistance of the carbon. That current depends on
source voltage and load impedance, as well as mike
impedance at a given audio level & frequency.

Ed, the OP asked about how much AC voltage is generated across the
mic if he runs a DC current through it and presents it with an
acoustic signal. Since a carbon mic behaves like a variable
resistor, that is an entirely meaningful question: if a DC current is
applied to a variable resistor, the voltage across the resistor will
vary. The unanswered part is "how variable is the resistor"? Does
it vary by 1% before clippping, or 10%, or what? Does the resistance
increase, or decrease, or both, compared to nominal?
Or, you could answer a different question, that still could
reasonably be presumed to be helpful: what sort of circuit might one
typically and usefully employ, to develop an electrical signal from a
carbon mic?
Dan Akers suggested that there's just no way to know. But I suspect
that knowing the answer for "some" specific carbon mic would be more
helpful than knowing nothing at all - even if it's an order of
magnitude away from this one, it's a starting point.

A carbon capsule is likely to be big and went after the advent of electret
mikes into the garbage bin and no sane person will use this technology for
other then close voice pickup and drving a horn speaker directly though a
12V battery, a megaphone without amp. When the OP measured some resistance,
it doesn't mean it is only resistive, but might be an Electret mike which
have about 0.5mA bias current and might on a multimeter show up as some
obscure value.
If the OP would also measure with the test leads crossed the same resistance
it is certainly not an electret mike, exept those with 3 pins where there is
a resistor between supply and output.
--
ciao Ban
Apricale, Italy


.

Relevant Pages

  • The phenomena of apparent negative resistance (but across all voltage ranges and without power sourc
    ... Deborah D.L. Chung's apparent negative resistance in carbon fiber ... toward the high, or positive end, of the voltage gradient. ...
    (sci.electronics.design)
  • Re: Carbon microphone amplitude
    ... You seem to think that the mike generates a voltage. ... What is the typical signal amplitude of a carbon mike? ... if a DC current is applied to a variable resistor, ...
    (sci.electronics.basics)
  • Re: Carbon microphone amplitude
    ... You seem to think that the mike generates a voltage. ... What is the typical signal amplitude of a carbon mike? ... Since a carbon mic behaves like a variable resistor, that is an entirely meaningful question: if a DC current is applied to a variable resistor, the voltage across the resistor will vary. ...
    (sci.electronics.basics)
  • Re: Octane boost - how?
    ... Mike W requests info: ... >Can anyone explain the mechanism by which octane booster>boosts octane? ... Fuels are tested by various methods to determine their ... In any case, the resistance to detonation ...
    (rec.motorcycles.dirt)
  • Re: DC voltage for conventional HO trains
    ... model railroading locos are generally rated for 12VDC for their rated rpm ... barely turn and increasing voltage will make them turn faster. ... http: slash /nav.to slash bobmay ... Mike Lawson wrote in message ...
    (rec.models.railroad)
Quantcast