Re: Carbon microphone amplitude
- From: ehsjr <ehsjr@xxxxxxxxxxxxxxxx>
- Date: Thu, 02 Mar 2006 07:08:17 GMT
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?
You don't even know if he has a carbon mike! Then you post
the above and call it an "entirely meaningful" question?
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.
Balderdash. The OP is *guessing* he has a carbon mike.
If he does not then what good is it posting "the answer"
(if one existed) concerning a specific carbon mike?
You mention 'the answer for "some" specific carbon mic'
There is no "the answer ...", for crying out loud. It depends
on external (to the mike) circuit elements: the load and the
source. "The answer" does not exist.
What you are suggesting is to give the op something that
doesn't exist, for an unknown circuit for an unknown mike.
Misleading the op that way is not helpful.
Ed
.
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