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Microphones

• Transducers that convert sound waves into
  electrical signals
• There are several different type of microphones
• Dynamic ??
• Condensing ??
• Carbon granule ??

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Dynamic ??

• The diaphragm??? is moved by changing sound
  pressure
• This moves the coil, which causes current to flow
  as lines of flux from the magnet are cut

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Dynamic ??

• Advantages
• Rugged
• Inexpensive to manufacture
• Tolerates extremely high sound pressure levels
• Requires no power supply
• Disadvantages
• Reduced high frequency performance
• Needs amplification??

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Condensing ??

• A pair of parallel metal plates separated by an
  insulator across which is stored an electrical
  charge
• Charge Q CV
• Moving the plates will change the voltage across
  them causing current to flow in or out of the
  capacitor through the resistor

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Charging the Condensing Mic

• The microphone must have some means of charging
  the plates
• Battery
• Phantom?? powering
• Electret
• The majority of serious recording work is carried
  out with capacitor microphones

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Condensing ??

• Advantages
• No coil and the diaphragm can be made very thin
  (few microns thick) thus light weight and less
  inertia so better high frequency response.
• Capacitor microphones can be made with virtually
  any response pattern.
• Disadvantages
• More complex thus more expensive

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Carbon Granule ??

• When acoustical pressure is exerted on the carbon
  granules, granules are pressed closer together
  which decreases the measured resistance.

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Pickup Patterns

• Microphones can also be classified by their pick
  up patterns
• Omnidirectional ???
• Unidirectional ???
• Bidirectional ??

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Omnidirectional ???

• Pickup of sound equally well within a 360º radius
  around the microphone element

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Omnidirectional ???

• Advantages
• Doesn't have to held directly in front of sound
  source to pick up adequate ?? sound
• Gives a sense of the environment
• Is not affected by slight changes in
  mic-to-source distance
• Provides a natural sound in rooms with good
  acoustics ??
• Is less susceptible?? to handling noise and noise
  created by wind or popping
• Is not subject to the proximity?? effect

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Omnidirectional

• Disadvantages
• Difficult to use in noisy locations
• Susceptible ?? to feedback in locations where
  microphone is feeding a loudspeaker

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Unidirectional (Cardioid)

• Primary pickup of sound from one side of the
  microphone's element
• Wide angle cardioid
• Supercardioid
• Hypercardioid

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Supercardioid
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Supercardioid and Hypercardioid

• - both offers narrower front pickup angles than
  the cardioid
• (115º for the supercardioid and 105 º for the
  hypercardioid)
• - have greater rejection of ambient ???? sound.
• - provide more focused pickup and less room
  ambience ????

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Unidirectional ??

• Advantages
• Discriminates?? against unwanted sound
• Reduces danger of feedback in locations where
  microphone is feeding a loudspeaker
• Picks up very little or no background sounds

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Unidirectional ??

• Disadvantages
• May be subject to the proximity ?? effect
• Must be set correctly to avoid sound source being
  off-mic
• Less natural sound in rooms with good acoustics
• Must take care to avoid covering ports
• More susceptible ?? to wind, popping and handling
  noises
• used to control ambient noise pickup to get a
  cleaner recording.

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Bidirectional ??

• Optimum pickup of sound from two sides of the
  microphone element

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Bidirectional ??
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Bidirectional ??

• Advantage - can be used to reduce number of mics
  in a circuit when two voices are involved in a
  voice-over
• Disadvantage - no separate control over levels of
  talent, so they must maintain proper
  mic-to-source distance and remain on-mic

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Proximity Effect ??

• The closer the sound source is to the microphone,
  the greater the emphasis on the bass??
  frequencies in the sound
• Many microphones are equipped with a bass
  roll-off switch to reduce the proximity ?? effect

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• Proximity effect
• For most unidirectional types, bass response
  increases as the microphone is moved closer to
  the sound source. When miking close with
  unidirectional microphones (less than 1 foot), be
  aware of proximity effect. It may help to roll
  off the bass until you obtain a more natural
  sound by
• 1) roll off low frequencies at the mixer,
• 2) use a microphone designed to minimize
  proximity effect,
• 3) use a microphone with a bass roll-off switch,
  
• 4) use an omnidirectional microphone (which does
  not exhibit proximity effect).

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Condenser Frequency Response
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Dynamic Frequency Response
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Impedance ??

• One important characteristic of a microphone is
  its output impedance
• This is a measurement of the AC resistance
  looking back into the microphone
• Low (50-1,000 ohms, 1kO)
• High (5,000 ohms, gt5kO )

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Low Impedance

• Most microphones used in broadcast applications
  are wired for low-impedance circuits
• Low-impedance circuits have three wire
  connectors a shield and two other wires (hot and
  cold) to conduct the current

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Balanced Systems ??

• Balanced lines are much less susceptible ?? to
  RFI (Radio Frequency Interference) and the pickup
  of the other electrical noise and hum
• In a balanced line, the shield of the cable is
  connected to ground, and the audio signal appears
  across the two inner wires which are not
  connected to ground

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Balanced Systems ??

• Output signal is split into two opposite phases
• Positive and Negative or Hot and Cold
• When returned to the same phase at the amplifier
  input noise is cancelled.

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Phantom Powering

• The standard power supply for microphone is 48V
• DC power is supplied along the signal leads,
  which means no extra cables

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Connectors ??

• Two types of connectors are commonly used with
  balanced systems

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High Impedance

• High-impedance circuits have two wire connectors
  a shield?? and one inner wire
• High impedance makes the signal more susceptible
  ?? to electro-magnetic interference????
• Signal is affected by cable capacitance in long
  runs of cables

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Feedback

• Feedback occurs when the sound from the
  loudspeaker arrives at the microphone as loud or
  louder than the sound arriving directly from the
  original sound source (talker, singer, etc.)

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Accessories for Microphone ??

• Shock Protection
• soft mount one that suspends the microphone in
  an elastic web

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Accessories for Microphone ??

• Pop Filters
• a thin mesh stretched over a circular frame.
• Functions
• remove extra energy comes from sound and prevent
  the moisture ?? .

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Accessories for Microphone ??

• Windscreens
• to reduce wind noise and particle striking the
  diaphragm.
• Disadvantages
• reduce both low and high frequency response.

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Miking Concepts

• Close-Miking
• used in conjunction with a cardioid or
  super-cardioid to focus the pickup pattern on the
  source while simultaneously avoiding any
  significant influence from the surrounding space.
• Distance-Miking
• refers to microphone placement intended to
  incorporate at least some room reflections.

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Minimizing phasing problems

• - Move the microphones in suitable position
• - Check the cables
• - Use the 31 Rule (except X-Y technique)
• - Separate the sound sources
• - Minimize reflective surfaces
• - Avoid boxing microphones in

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Stereo Miking Techniques

• - X-Y miking
• - Blumlein Technique
• - ORTF

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Microphones and Stereo Signals

• Coincident or XY pair
• Right hand microphone picks up sound form left
  stage and visa a versa
• No phase problems as minimal space between
  microphones

Cardioid Microphones
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X-Y miking technique
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Blumlein Technique
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Blumlein Technique

• - takes advantage of the polar patterns inherent
  in bidirectional microphones
• - two patterns are oriented 90 º from each other
  with the positive sides facing the left and right
  sides of the sound source.
• - yields very good stereo separation.
• - picks up significant room reflections

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ORTF Technique
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ORTF Technique

• - emulate the placement of ears in average adult
  human head
• - place two cardioid capsules with 17cm apart at
  a 110º to one another
• - produce the wide imagery and depth common to
  the Blumlein technique
• - the use of cardioids means that the
  configuration captures much less reverberant
  reflection ?????

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Miking Applications

• Vocals
• - large diaphragm capsule is preferred
• - cardioids are typically used with close
  miking
• - distance around 30 to 45 cm
• - Tube microphones and preamps are recommended

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Vocals Group

• Vocals
• For a duet, placing the performers on either side
  of a figure-8 pattern
• For a group, place the singers in a semicircle
  around a cardioid

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Piano

• Use stereo close-miking
• Mic Placements depend on style

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Drums

• Use multiple microphones for different
  instruments
• Difficult in tonal balance

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Amplified Speaker

• - Use a cardioid four to six inches in front of
  the speaker
• - Proximity effect applies here, so closer
  positions yield more low mid frequency
• - The center typically has a more edgy??
  quality, while the outer portions are mellower??

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Acoustic Instruments

• 1. Bridge yields a very sweet sound but the
  performers hand can obstruct the pickup pattern.
• 2. Neck joint yields a nice balance of warm body
  and bright neck, including natural fret and
  finger noises.
• 3. Nut Miking the nut usually results in a
  bright sound. Additionally miking the bridge and
  panning the two microphones hard left and right
  produces an extremely wide stereo effect.
• 4. Audience perspective placing the mic three to
  four feet in front of the performer and level
  with the sound hole in order to capture more room
  sound.

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QUESTION AND ANSWER
End