Handbook for Sound Engineers

Microphones 493

16.1 Introduction

All sound sources have different characteristics; their
waveform varies, their phase characteristics vary, their
dynamic range and attack time vary and their frequency
response varies, just to name a few. No one microphone
will reproduce all of these characteristics equally well.
In fact, each sound source will sound better or more
natural with one type or brand of microphone than all
others. For this reason we have and always will have
many types and brands of microphones.

Microphones are electroacoustic devices that convert
acoustical energy into electrical energy. All micro-
phones have a diaphragm or moving surface that is
excited by the acoustical wave. The corresponding
output is an electrical signal that represents the acous-
tical input.

Microphones fall into two classes: pressure and
velocity. In a pressure microphone the diaphragm has
only one surface exposed to the sound source so the
output corresponds to the instantaneous sound pressure
of the impressed sound waves. A pressure microphone
is a zero-order gradient microphone, and is associated
with omni-directional characteristics.

The second class of microphone is the velocity
microphone, also called a first-order gradient micro-
phone, where the effect of the sound wave is the
difference or gradient between the sound wave that hits
the front and the rear of the diaphragm. The electrical

output corresponds to the instantaneous particle velocity

in the impressed sound wave. Ribbon microphones as

well as pressure microphones that are altered to produce

front-to-back discrimination are of the velocity type.

Microphones are also classified by their pickup

pattern or how they discriminate between the various

directions the sound source comes from, Fig. 16-1.

These classifications are:

• Omnidirectional—pickup is equal in all directions.


• Bidirectional—pickup is equal from the two opposite
  directions (180°) apart and zero from the two direc-
  tions that are 90° from the first.


• Unidirectional—pickup is from one direction only,
  the pickup appearing cardioid or heart-shaped.

The air particle relationships of the air particle

displacement, velocity, and acceleration that a micro-

phone sees as a plane wave in the far field, are shown in

Fig. 16-2.

16.2 Pickup Patterns

Microphones are made with single- or multiple-pickup

patterns and are named by the pickup pattern they

employ. The pickup patterns and directional response

characteristics of the various types of microphones are

shown in Fig. 16-1.

Figure 16-1. Performance characteristics of various microphones.

Microphone Omnidirectional Bidirectional Directional Supercardioid Hypercardioid

Directional Response

Characteristics

Voltage output

Random energy

Efficiency (%)

Front response

Back response

Front random response

Total random response

Front random response

Back random response

Equivalent distance

Pickup angle (2Q   

for 3 dB attenuation

Pickup angle (2Q   

for 6 dB attenuation

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