M-Audio Microphone Microphone Design

Chapter 1
Microphone Design
While all microphones are designed for the common purpose of converting variations in sound
pressure to electronic signals, different technologies have their benefits depending upon the
application.This chapter examines the merits of different design types,capsule sizes, polar patterns,
electronics and more.
Microphone Types
The three main types of microphones in common use today are dynamic,ribbon and condenser.
Each has unique attributes appropriate for different applications.
Dynamic microphones
The dynamic or moving-coil microphone is the easiest to understand.It is the classic technology
taught in grade school as the inverse of the common speaker. A plastic or metal diaphragm is
attached to a copper coil that is,in turn,suspended in a magnetic field. Sound pressure waves hitting
the diaphragm cause it to move, and with it,the coil within the magnetic field. The resulting
magnetic fluctuations translate to electrical fluctuations
generally corresponding to the physical fluctuations of the
original sound wave.
Due to the requirement of attaching the coil directly to the
diaphragm,dynamic diaphragms are thicker and, therefore,less
sensitive than the ribbon and condenser microphones
discussed shortly.These same design considerations also give
the ability to take the greatest amount of sound pressure
before distorting, as well as the greatest amount of physical
abuse. Dynamics are also the easiest and least expensive to
make.Dynamics also to tend to color the sound in the range of
about 5k to 10k,and star t to sound thinner when more than
about a foot away from the source.
For these reasons,dynamic mics are most often found in
the average stage situation. After all,live performance
environments are much more likely to subject mics to
torture such as high volume, sweat,the elements, shock
and being dropped.In the studio, dynamic mics are most
often used to close-mic drums due to the possibility of
wayward drum sticks.Large-diaphragm dynamics are often
used on kick drums due to high sound pressure levels and
low-frequency content.
Ribbon microphones
Ribbon mics are another form of dynamic microphone distinct from the moving-coil variety.A very
thin metal ribbon suspended between the poles of a powerful magnet moves in response to sound
waves, thus cutting through the magnetic field and inducing a flow of electrons.The resulting
low-voltage output is typically fed to a step-up transformer and sent down the mic cable.The
extreme thinness of the ribbon makes this type of mic the most sensitive,especially at very low
sound levels.They are most often used in close-miking situations and, because they are also the
most fragile and costly mic design, ribbons are typically reserved for very controlled conditions.
Like moving-coil dynamics,ribbon mics color the sound in a way that is often employed to warm
up brassy sounds.(Ribbons are a great choice for recording sax, for example.) They also tend to
output signal
voltage
coil
fixed magnet
+
-
metal ribbon diaphragm
fixed magnet
output signal voltage
+
-
ultra -thin diaphragm
solid backplate
capacitance
output
signal
diaphragm
In dynamic mics, sound pressure moving the
diaphragm causes the attached voice coil to interact
with a magnetic field to produce an electric signal
output signal
voltage
coil
fixed magnet
+
-
metal ribbon diaphragm
fixed magnet
output signal voltage
+
-
ultra -thin diaphragm
solid backplate
capacitance
output
signal
diaphragm
In ribbon mics, sound waves cause a thin metal
ribbon to move within a magnetic field to produce
a current
Choosing & Using Microphones
3