When dealing with microphones, one
consideration which is often misunderstood or
overlooked is the microphone's impedance rating.
Perhaps this is because impedance isn't a "critical"
factor; that is, microphones will still continue to
operate whether or not the best impedance rating is
used. However, in order to ensure the best quality
and most reliable audio, attention should be paid to
getting this factor right.
If you want the short answer, here
it is: Low impedance is
better than high impedance.
If you're interested in
understanding more, read on....
What is Impedance?
is an electronics term which measures the amount of
opposition a device has to an AC current (such as an
audio signal). Technically speaking, it is the
combined effect of capacitance, inductance, and
resistance on a signal. The letter Z is often
used as shorthand for the word impedance, e.g. Hi-Z
Impedance is measured in ohms,
shown with the Greek Omega symbol Ω. A
microphone with the specification 600Ω has an
impedance of 600 ohms.
What is Microphone Impedance?
All microphones have a
specification referring to their impedance. This
spec may be written on the mic itself (perhaps
alongside the directional pattern), or you may need
to consult the manual or manufacturer's website.
You will often find that mics with
a hard-wired cable and 1/4" plug are high impedance,
and mics with separate balanced audio cable and XLR
connector are low impedance.
There are three general
classifications for microphone impedance. Different
manufacturers use slightly different guidelines but
the classifications are roughly:
(less than 600Ω)
(600Ω - 10,000Ω)
(greater than 10,000Ω)
Note that some microphones have
the ability to select from different impedance
Which Impedance to Choose?
High impedance microphones are
usually quite cheap. Their main disadvantage is that
they do not perform well over long distance cables -
after about 5 or 10 metres they begin producing poor
quality audio (in particular a loss of high
frequencies). In any case these mics are not a good
choice for serious work. In fact, although not
completely reliable, one of the clues to a
microphone's overall quality is the impedance
Low impedance microphones are
usually the preferred choice.
Matching Impedance with Other
Microphones aren't the only things
with impedance. Other equipment, such as the input
sound mixer, also has an ohms rating. Again, you
may need to consult the appropriate manual or
website to find these values. Be aware that what one
system calls "low impedance" may not be the same as
your low impedance microphone - you really need to
see the ohms value to know exactly what you're
A low impedance microphone should
generally be connected to an input with the same or
higher impedance. If a microphone is connected to an
input with lower impedance, there will be a loss of
In some cases you can use a
line matching transformer, which will convert a
signal to a different impedance for matching to