Microphones

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Microphones

• EL2071 Audio 2

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A microphone is

• a transducer a device that changes one form of
  energy into another
• Sound Electrical signal

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Three types of mic

• Dynamic
• Ribbon
• Condenser

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Dynamic microphone

• Operates by electromagnetic induction

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Ribbon microphone

• Operates by electromagnetic induction

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Condenser microphone

• Operates on an electrostatic principle

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Condenser mics

• True condenser diaphragm and backplate charged
  from a circuit built into mic.
• Electret condenser diaphragm and backplate
  charged by electret material in d. or b.
• Sound equally good, true is preferred but costs
  more
• Need a power supply battery or

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Phantom power

• 12-48 volts DC
• Usually supplied from mixing desk

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Whats inside
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Characteristics

• Condenser
• Wide, smooth frequency response
• Detailed sound, extended highs
• Omni-type has excellent low frequency response
• Transient attacks sound sharp and clear
• Preferred for acoustic instruments, cymbals,
  studio vocals
• Can be miniaturized

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Characteristics

• Dynamic
• Tends to have rougher response, but still quite
  usable
• Rugged and reliable
• Handles heat, cold, high humidity
• Handles high volume without distortion
• Preferred for guitar amps and drums
• If flat response, can take edge off brass and
  woodwind

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Characteristics

• Ribbon
• Prized for its warm, smooth tone quality
• Delicate
• Complements digital recording

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Polar patterns
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Polar patterns

• Omnidirectional sounds from all directions
• Bidirectional sounds equally from two directions
  in front and from behind
• Unidirectional sounds from one direction in
  front
• Cardioid, Supercardioid, Hypercardioid

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Polar patterns
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Characteristics

• Omnidirectional
• All-around pickup
• Most pickup of room reverberation
• Not much isolation unless close
• Low sensitivity to pops
• Low handling noise

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Characteristics

• Bidirectional
• Front and rear pickup, side sounds rejected
• Good for two-part vocal groups
• Good for across table interviews
• Maximum isolation of an orchestral section if
  miked overhead

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Characteristics

• Unidirectional
• Selective pickup
• Rejection of room acoustics, background
• Good isolation
• Up-close bass boost

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Frequency response

• Range of frequencies that it will reproduce at an
  equal level
• Most instruments 80 Hz to 15 kHz
• Bass 40 Hz to 9 kHz
• Brass and voice 80 Hz to 12 kHz
• Piano 40 Hz to 12 kHz
• Percussion 300 Hz to 20 kHz

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Frequency response

• Shure SM58

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Other terms

• Low frequency/bass roll-off
• Impedance (Z)
• SPL Sound Pressure Level
• Sensitivity
• Self-Noise
• Signal-to-Noise Ratio

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Impedance (Z)

• Effective output resistance at 1 kHz.
• 150-600 ohms is low
• 1000-4000 ohms is medium
• above 25 kilohms is high.

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SPL Sound Pressure Level

• A measure of the intensity of sound. Max. spec of
  120 dB is good
• 135 dB is very good
• 150 dB is excellent.

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Sensitivity

• Output voltage a mic produces when driven by a
  certain SPL.
• High-sensitivity mic puts out a stronger signal
  (higher voltage) than a low-sensitivity mic when
  both are exposed to an equally loud sound.
• Low-sens. mic needs more mixer gain than a
  high-sens. mic more gain more noise.

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Self-Noise

• Electrical noise or hiss a mic produces itself
• Usually referred to as A-weighted
• 18 db SPL or less is excellent
• around 28 dB SPL is good
• around 35 dB SPL is fair but not good enough
  for quality recording.

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Signal-to-Noise Ratio

• Difference between mics sensitivity and its
  self-noise.
• Higher the SPL of sound source at mic, higher its
  S/N ratio.
• Usually given as SPL of 94 dB, S/N ratio of 74 dB
  is excellent 64 dB is good.

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Microphones

• EL2071 Audio 2