From: <threepointone_at_mindspring.com>
Date: Sun, 15 Oct 2006 18:42:48 -0400

Only some mics (generally some electret condensers) need this voltage across
the mic, called bias voltage. These mics have active impedance converting
circuitry, as the electret condenser microphone element itself usualy has a
very high output impedance. Without the impedance converting circuitry, the
capacitance of the cable line will cause the higher-frequency sounds to be
cut off. Higher or lower voltage should not really make a difference in
sound; if I understand correctly, mics that need bias voltage simply won't
work if they don't receive any bias voltage. If you hear differences with or
without the bias voltage, you're probably using a dynamic mic, which
*shouldn't* be used with a bias voltage, as there is a possibility of damage
or changes in sonic characteristics if the mic wasn't designed well.

http://www.shure.com/ProAudio/Products/us_pro_ea_phantom has some good stuff
on this topic, and google probably has even better.

They recommend using a coupling capacitor (i.e. just inline with teh signal)
to block the DC bias voltage. 470uF should be enough for virtually every
dynamic mic, if you like messing around with electronics.
Received on 2006-10-16