Capt. Zyla wrote:
>
>  I would like to know what is the actual resistance of a microphone that
> one would use as input to a sound board? My understanding is it should be
> low impedance of about 600 ohms. What does one actually measure with an
> ohm meter?

Microphone impedance is not just a simple DC fumction that can be
measured with an ohmmeter, but in fact it is a very complex function
that involves both dc and ac functions and a frequency of operation.
Because a microphone is going to be used over a range of frequencies;
therefore, the impedance is not just one constant value.  However, to
identify AN IMPEDANCE for a microphone, the common standard used is to
measure and calculate the impedance at a set frequency (for voice
circuits, it is typically 1000 Hertz).

And while 600 ohm mics are common, you will find mics with impedances up
to 20,000 Ohms (impedance).  Note: typically, the higher the impedance,
the smaller the output signal of the mic.  But everything has tradeoffs.

As for the input impedance of a sound blaster, I do not know.  But
again, the AC impedance is a function of frequency.  If the manufacturer
is willing to consume power, he may opt for a low impedance input with a
low gain input stage.  But to conserve power, a high impedance input
(20k to 10M ohms) will draw little current but it requires a high gain
amplifier for the same amount of output signal as the low impedance
circuit.  Which is best?  Each has its benefits.

Can you go wrong with a 600 ohm mic?  No.  Should you opt for a higher
impedance mic?  Only if you don't like the quality of sound from it.


>
> john;
>
> Capt. John M. Zyla
> http://www.smart.net/~captzyla
>


--
Jean Bourvic :>))

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