Microphone Characteristics
A microphone is a transducer that converts acoustic energy into electric
energy.
The two most common types of microphones are:
Dynamic Microphones
Condenser Microphones
Dynamic
Microphones
- Also
called moving-coil mic.
- This
classification includes ribbon mics (velocity mics).
- Simple
construction, economical.
- Rugged, resistant to hand noise.
- Require no batteries or power supply.
- Standard
equipment used by musical performers.
- Handle
extremely high sound levels.
1. Sound waves strike the
diaphragm.
2. Diaphragm vibrates in response.
3. The voice coil, attached with the diaphragm, vibrates with it.
4. The voice coil is surrounded by a magnetic field created by
the magnet.
5. The motion of the voice
coil in this magnetic field generates the electrical signal.
Condenser Microphones
- Also called capacitor or electret condensor mic.
- More complex than dynamics, tend to be costly.
- Not as rugged as dynamic mics.
- Can be affected by extreme temperature
and humidity.
- Require
batteries or power supply.
- Standard equipment used by film
production.
- Higher sensitivity, provides a smoother, more natural sound,
particularly at higher frequency.
1. Sound waves strike the diaphragm.
2. Diaphragm vibrates in response, changing the space between
itself and the metal or metal-coated-ceramic backplate.
3. The variation of this spacing,
due to the motion of the diaphragm relative to the backplate, produces the electrical signal.
Electrical Impedance / Low-Z & High-Z Mics
- After a microphone changes acoustic
energy into electric energy, the
electric energy flows through a circuit as voltage.
- Whatever resistance that
voltage encounters in the circuit is called impedance.
- Impedance is expressed in ohms.
- Less resistance means lower impedance.
- Low-impedance (low-Z): 600 ohms
or less.
- High-impedance (high-Z): 10,000 ohms
or higher.
- Professionals prefer low-impedance mics.
- Much less susceptible to hum
and electric noise, such as static from motors and fluorescent lights.
- Can be connected to long cables
(over 1000 feet, so says Shure) with negligible loss of sound quality.
- High-impedance mics usually
begin to sound muffled due to a loss of high frequencies when used with a cable longer than 20 feet.
Directionality: Pickup Pattern
á
Omnidirectional
á
Bidirectional
á
Unidirectional
(Cardioid)
1. Cardioid
2. Super Cardioid
3. Hyper Cardioid
Omnidirectional
Mics
- Equal output or sensitivity at all angles.
- It will pick up maximum amount of
ambient sound.
- Should be placed close to the sound
source to pick up a useable balance between direct sound and
ambient sound.
- Cannot be aimed away from undesired
sources such as PA speakers which may cause feedback!
Bidirectional Mics
- Maximum sensitivity at both 0 degrees
(front) and 180 degrees (back).
- Least amount of output at 90 (and/or
270 degree) angles (sides).
- Used for picking up two opposing sound
sources, such as a vocal duet.
Unidirectional Mics:
Cardioid
- Maximum sensitivity at both 0 degrees
(on-axis).
- Least sensitive at the rear (180
degrees off-axis)
- Effective coverage or pickup angle: about 130 degrees.
- Picks up about one-third as
much ambient sound as an omni.
- Isolate the desired on-axis sound from both unwanted off-axis sound and from ambient noise.
Unidirectional Mics:
Super/Hyper Cardioid
- Maximum sensitivity at both 0 degrees
(on-axis).
- Least sensitive direction: 126/110 degrees off-axis.
- Effective coverage or pickup angle: about 115/105 degrees.
- Greater rejection of ambient sound
than cardioid mics.
- Picks up sound directly from the rear:
the rear lobe.
Frequency Response
- The output level or sensitivity of
the microphone over its operating range from lowest
to highest frequency.
- A microphone whose output is equal at
all frequencies has a flat frequency response.
Comparison: Dynamic vs Condenser in frequency response:
- Shure SM58-LC / $99.00
- Unidirectional (cardioid)
- Dynamic microphone
- Shaped
frequency response
- Designed for professional vocal
use in live performances.
- Shure KSM27-SL / $295.00
- Unidirectional (cardioid)
- Condenser microphone
- Flat
frequency response
- Designed for studio use: vocal
and instruments, but rugged enough to use in live performances.