Download Microphones

Microphones
Dynamic and Condenser
Polar patterns
Frequency response
Wireless
How a microphone functions
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Dynamic microphones
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Based on a moving coil of
wire
 Think of the reverse of a
loudspeaker
Sound waves push on a
diaphragm which in turn
moves a coil of very fine wire
through a magnetic field
 Produces current
proportional to the sound
waves
Dynamic microphones
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Usually very robust and durable
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Very often used on stage where rough handling or
dropping is common
Damage is most often caused by breaking
suspension wires
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Two wires which hold the diaphragm and coil in place
Often do not produce a flat frequency
response and not very sensitive to low SPL
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The relatively massive coil of wire takes a great
deal of power to make move
Condenser microphones
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Creates a capacitor using the
diaphragm as one plate.
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Capacitor is used to store an
electric charge. Changing the
distance between plates changes
it’s ability to do that.
Requires the plates to be charged
by an external source
 Battery, phantom power…
As the diaphragm moves, it causes
a ripple in the current from the
phantom power. This ripple is
proportional to the sound waves
Condenser microphone
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Due to the lightweight diaphragm, only small
pressure changes are required to produce an
audio signal.
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Very sensitive to small SPL
Much flatter frequency response than dynamic
Much more susceptible to damage
Requires external power supply to function
Frequency Response
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A graph showing how a specific microphone
responds to different frequencies.
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No microphone is perfectly flat
 Usually not desirable anyway
 Microphones are designed for specific purposes and
frequency responses are tailored for each use
Proximity effect
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Usually only seen on dynamic microphones
As you move the mic closer to the sound source, you get
an increase in the low frequency response.
Trained vocalists will make good use of this effect, the
untrained will make themselves unintelligible.
Frequency Response
Dynamic Vocal Mic
Live Instrument Mic
Condenser Vocal Mic
Studio Instrument Mic
Directional properties
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Every microphone will have a polar pattern
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Description of the sensitivity of the microphone
related to the direction the sound is coming
from
Omni-directional
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Sensitive from all directions
Used for ambient noise recording or where the
sound source is moving and the mic cannot
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Often on lavaliere mics
Sound is often general and unfocused.
Feedback more likely
Omni-directional
polar pattern
Directional properties
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Uni-directional
 Mostly sensitive from one direction and less
from all others
 Cardioid pattern
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Sound is mostly picked up from the front, but
some from the sides as well to allow for some
movement of the mic off axis
Most common pattern, good for general use
Most common on hand held mics
Cardioid polar
pattern
Super and Hyper Cardioid pattern
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Less sensitive to the sides, more sensitive to the
rear
Sometimes called a “shotgun” mic
Very directional
Super cardioid
polar pattern
Directional properties
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Bi-directional
 Sensitive from the front and back and
much less to the sides
 Not much use on stage
Variable directionality
 Polar pattern is adjustable to different
patterns
 Seems like a good idea, but rarely works
perfectly well
Bi-directional pattern
Specialty Microphones
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PCC and PZM microphones
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Collectively known as Boundary microphones
Trade names of Crown International
 http://www.crownaudio.com/mic_web/pcc.htm
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http://www.crownaudio.com/pdf/mics/101062.pdf
http://www.crownaudio.com/mic_web/pzm.htm
Often used as a floor mic to reinforce a large group of
people who are moving
 Musical chorus for example
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Choir microphones
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Small sensitive condenser mics usually hung overhead
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http://www.shure.com/microphones/models/mxoverhead.asp
RF (wireless) microphones
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A microphone which transmits it’s audio signal using
radio frequencies rather than a cable
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The mic has a radio transmitter built into it which transmits
to a receiver off-stage. The receiver then sends the audio
signal to a mixer
Most often in the form of a wireless
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Vocal mic – transmitter is built into the body of the mic
Lavaliere – small mic capsule is clipped onto clothing or
taped to the head (preferred). The mic capsule is wired to
a small pack with the transmitter and batteries.
RF (wireless) microphones
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The frequency that the packs transmit on are
very important
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Usually transmit in the VHF or UHF range and are
susceptible to interference from other radio
sources
Diversity receivers
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MUCH more interference resistant than non-diversity
Involves two separate receivers spaced apart from
each other
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The system will select the strongest signal
RF (wireless) microphones
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Lavaliere mic mounting
 Usually mounted on the center of the forehead or over the ear
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Toupee clips, bobby pins, high quality surgical tape.
Spirit gum only if ALL else fails
Occasionally mounted on clothing
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Traditional use. TV interviews for example
Poor sound quality
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Low frequency boost from being near the chest
Wind or clothing noise likely
Sound level changes as performer moves their head
Boom mounting – a.k.a. “Madonna Mic”
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Mounted on a rig over the ear which puts mic very close to the mouth.
Best sound. Poor aesthetics.
Additional Readings
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http://electronics.howstuffworks.com/framed.
htm?parent=question309.htm&url=http://hom
e1.pacific.net.sg/~firehzrd/audio/mics.html
http://www.mediacollege.com/audio/
Interesting discussion on mic techniques
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http://www.informatik.unibremen.de/~dace/guitar/recording/