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A Microphone
is a generic term that refers to any element that transforms acoustic energy
(sound) into electrical energy (electricity (audio signal).
How we Hear!
How Hearing Works
Click on picture to enlarge
Picture 1. Sound waves enter the ear canal and vibrate against the
tympanic membrane
Click on picture to enlarge
Picture 2. The intensity level of sound is measured in decibels The
hearing threshold (level at which humans begin to perceive sound) is 0 dB. When
a sound reaches upwards of 120 dB, it is above the threshold of pain (point at
which most people begin feeling pain). Everything in between can be heard by a
human with normal hearing.
What do former President Bill Clinton and Pete Townsend of the Who have in
common?
Answer!
Types
of Microphones
Dynamic microphones
- A dynamic microphone takes advantage
of electromagnet
effects. When a magnet moves past a wire (or coil of wire), the magnet induces
current to flow in the wire. In a dynamic microphone, the diaphragm moves either
a magnet or a coil when sound waves hit the diaphragm, and the movement creates
a small current.
Condenser microphones
- A condenser microphone is essentially
a capacitor,
with one plate of the capacitor moving in response to sound waves. The movement
changes the capacitance of the capacitor, and these changes are amplified to
create a measurable signal. Condenser microphones usually need a small battery
to provide a voltage
across the capacitor.
Condenser
microphones need a source of power to impress the charge on the capacitor.
One of three methods is used. Either a battery will be inserted inside
the microphone, a permanent charge is retained on the diaphragm or back
plate, or phantom power is used.
Phantom power is the supply of power through the ground cable of an XLR
cable. Ranging from 9 volts to 52 volts, typically 48 volts,
this power can be put into the cable either from a mixer, a phantom power
box or a battery pack. A mixer might have a button that allows phantom
power through the ground cable. A phantom power box is like an
intermediate component between a mixer and a mic. It is a box connected to the
mains that essentially just puts a charge on the ground cable. A battery pack
does exactly the same thing, but works only with batteries instead of mains
power.
Guide
to Microphones
Older Microphones Explained
Ribbon microphones - In a
ribbon microphone, a thin ribbon is suspended in a magnetic field. Sound waves
move the ribbon which changes the current flowing through it.
Carbon microphones
- The oldest and simplest microphone uses carbon dust. This is the technology
used in the first telephones
and is still used in some telephones today. The carbon dust has a thin metal or
plastic diaphragm on one side. As sound waves hit the diaphragm, they compress
the carbon dust, which changes its resistance. By running a current through the
carbon, the changing resistance changes the amount of current that flows. See How
Telephones Work for more information.
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