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There
are various types of microphone we can use, and various different
ways of categorising them. Here we are going to examine the different
technologies that are available, and polar patterns.
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Visit the Studio
tips page to see which microphones work best for different instrument
groups
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Types of Microphone
All microphones are designed to convert acoustic energy into electrical
energy, and all use a diaphragm as part of the process to achieve
this. Having pointed out the common ground, we will now concentrate
on the differences.
There
are basically five different microphone technologies :
-
Carbon - The earliest microphones used carbon dust to interpret
the audio signal. These microphones were commonly used in telephones
and can still be found in some of todays telephones. A current is
run through the carbon dust, the current fluctuates when the carbon
is compressed by sound waves as they hit the diaphragm.
- Crystal
- The crystals used in this type of microphone change their
electrical properties as they change shape. By attaching a diaphragm
to a crystal, the crystal will create a signal when the diaphragm
is vibrated by sound.
- Ribbon
- In a ribbon microphone, a thin metal wire is suspended in a strong
magnetic field. Sound waves move the ribbon which changes the current
flowing through it. This is a type of velocity microphone responding
to air velocity rather than air pressure.
-
Dynamic
- In a dynamic microphone, the diaphragm moves a coil between two
magnets (positive and negative) when sound waves hit it, the movement
creates a small current. more..
-
Condenser - The condenser microphone has been around
for more than a century, and requires an external voltage (phantom
power). A capacitor is created by the diaphragm and a backplate,
they are electrically charged and the movement of the diaphragm
in relation to the backplate causes a varying capacitance, in turn
varying the voltage output. more..
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Please
note that comments on the microphone information pages are opinion
gathered from a variety of different sources. We would urge you
to do your own research before purchasing a microphone.
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The
next category we can use to distinguish between microphones is
Polar Pattern, in other words the characteristics
of the area around the microphone from which an audio signal can
be picked up. And again there are five categories:
- Cardoid
- Strong sensitivity directly in front of the microphone, coupled
with good sensitivity at the sides and rejection from behind.
The pattern earns its name from the heart-shaped pickup area
(as illustrated in Fig 1).
- Supercardoid
- Similar to the cardoid, but with slightly reduced
sensitivity around the sides. The supercardoid pickup range
includes a small area just behind the microphone (as illustrated
in Fig 2).
- Hypercardoid
- This pattern is an even more exaggerated form of the Supercardoid,
with a reduced sensitivity at the sides, and a larger area of
sensitivity at the rear (as illustrated in Fig 3). More directional
than the other two cardoid patterns, and thus used where maximum
isolation between sound sources is required.
- Omnidirectional
- Indicating a microphone that picks up sound equally from all
directions. This is the only microphone not prone to a proximity
effect (undesirable low range interference when a sound source
is too close to the microphone)
- Bidirectional
- A 'figure-8' pattern where sound is picked up equally well
from two opposing directions, without sensitivity at the sides
(as illustrated in Fig 5).This type of microphone may be useful
in an interview situation.
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Fig 1. Cardoid
Fig 2. Super cardoid
Fig 3. Hyper cardoid
Fig 4. Omni directional
Fig 5. Bi-directional
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