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Date: | Thu, 10 Dec 1998 23:07:53 -0800 |
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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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