Microphones

1
Microphones

• Dynamic and Condenser
• Polar patterns
• Frequency response
• Wireless

2
How a microphone functions

• Dynamic microphones
• 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

3
Dynamic microphones

• Usually very robust and durable
• Very often used on stage where rough handling or
  dropping is common
• Damage is most often caused by breaking
  suspension wires
• 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
• The relatively massive coil of wire takes a great
  deal of power to make move

4
Condenser microphones

• Creates a capacitor using the diaphragm as one
  plate.
• Capacitor is used to store an electric charge.
  Changing the distance between plates changes its
  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

5
Condenser microphone

• Due to the lightweight diaphragm, only small
  pressure changes are required to produce an audio
  signal.
• Very sensitive to small SPL
• Much flatter frequency response than dynamic
• Much more susceptible to damage
• Requires external power supply to function

6
Frequency Response

• A graph showing how a specific microphone
  responds to different frequencies.
• 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
• 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.

7
Frequency Response
Dynamic Vocal Mic
Condenser Vocal Mic
Studio Instrument Mic
Live Instrument Mic
8
Directional properties

• Every microphone will have a polar pattern
• Description of the sensitivity of the microphone
  related to the direction the sound is coming from
• Omni-directional
• Sensitive from all directions
• Used for ambient noise recording or where the
  sound source is moving and the mic cannot
• Often on lavaliere mics
• Sound is often general and unfocused.
• Feedback more likely

Omni-directional polar pattern
9
Directional properties

• Uni-directional
• Mostly sensitive from one direction and less from
  all others
• Cardioid pattern
• 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
• Super and Hyper Cardioid pattern
• Less sensitive to the sides, more sensitive to
  the rear
• Sometimes called a shotgun mic
• Very directional

Cardioid polar pattern
Super cardioid polar pattern
10
Directional properties

• 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
11
Specialty Microphones

• PCC and PZM microphones
• Collectively known as Boundary microphones
• Trade names of Crown International
• http//www.crownaudio.com/mic_web/pcc.htm
• 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
• Choir microphones
• Small sensitive condenser mics usually hung
  overhead
• http//www.shure.com/microphones/models/mxoverhead
  .asp

12
RF (wireless) microphones

• A microphone which transmits its audio signal
  using radio frequencies rather than a cable
• 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
• 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.

13
RF (wireless) microphones

• The frequency that the packs transmit on are very
  important
• Usually transmit in the VHF or UHF range and are
  susceptible to interference from other radio
  sources
• Diversity receivers
• MUCH more interference resistant than
  non-diversity
• Involves two separate receivers spaced apart from
  each other
• The system will select the strongest signal

14
RF (wireless) microphones

• Lavaliere mic mounting
• Usually mounted on the center of the forehead or
  over the ear
• Toupee clips, bobby pins, high quality surgical
  tape.
• Spirit gum only if ALL else fails
• Occasionally mounted on clothing
• Traditional use. TV interviews for example
• Poor sound quality
• 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
• Mounted on a rig over the ear which puts mic very
  close to the mouth.
• Best sound. Poor aesthetics.

15
Additional Readings

• http//electronics.howstuffworks.com/framed.htm?pa
  rentquestion309.htmurlhttp//home1.pacific.net.
  sg/firehzrd/audio/mics.html
• http//www.mediacollege.com/audio/
• Interesting discussion on mic techniques
• http//www.informatik.uni-bremen.de/dace/guitar/r
  ecording/