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Re: contact microphones - how?
At 7:48 PM -0800 2/10/02, eileen wrote:
>I'm trying to capture sounds from the inside of a "live" object.
>Someone suggested using a contact microphone. Would this be the
>correct type of mic to use?
It might be, but it depends on the object and what quality of sound
you are after.
>Is a contact microphone able to capture audio? How exactly do the
>vibrations translate into audio? I'm just a little confused on what the
>contact microphone actually does.
A contact microphone is a particular kind of "transducer," just as
any sort of microphone is a transducer. A loudspeaker is another kind
"Transducer" simply means a device that turns one kind of energy or
vibration into another. A contact mic turns the vibrations in a solid
object into small electrical signals that can be amplified. The more
familiar kinds of microphones (what I sometimes call "air" mics) turn
the vibrations of the air into small electrical signals that likewise
can be amplified. It isn't necessary (though it might be helpful) to
know the technical details of these different types of microphones,
but it is important to know to some degree how they behave.
The signal coming out of a microphone is not necessarily the same
thing that you might hear when standing a few feet away from the
object that is being amplified or recorded. Objects radiate different
frequencies of sound in different directions, so if you listen to an
instrument (such as an acoustic guitar) from one location it will
sound differently than it does from another location. Similarly it
will sound a lot different if you put your ear against it.
Putting your ear against a guitar is in many ways similar to putting
a contact mic on a guitar. The quality of sound is very different
from the quality of sound you'd hear from a distance. Another thing
to consider is that putting your ear, or a contact mic) directly in
contact with an object actually affects the sound of the object
because it interferes with the free vibration of the object.
Though this may seem more complicated than you may have hoped, it's
actually an opportunity to learn more about sound and amplification
by listening carefully and thinking about the sound you are trying to
capture and the technology you are using to do the job.
So the answer to your first question about whether to use a contact
mic to capture sounds from the inside of an object is "it depends."
I'm also not sure what you mean by a "live" object. If you mean
"live" as in the case of a live cat, it don't think a contact mic
would do you much good. If you mean "live" in the sense of a vibraing
object (such as a Martha waste basket), then the answer might be
that you can use a contact mic but that you need to be careful where
you attach it in order to avoid damping out the sound. Sometimes you
need to use a combination of techniques to get the "whole" sound
Richard Zvonar, PhD