Handbook for Sound Engineers

496 Chapter 16

phones because they discriminate between signal and
random unwanted noise. This has many advantages
including:

• Less background noise,


• More gain before feedback especially when used in
  the direct field,


• Discrimination between sound sources.

The cardioid pattern can be produced by one of two
methods:

1. The first method combines the output of a pressure
   diaphragm and a pressure-gradient diaphragm, as
   shown in Fig. 16-10. Since the pressure-gradient
   diaphragm has a bidirectional pickup pattern and
   the pressure diaphragm has an omnidirectional
   pickup pattern, the wave hitting the front of the
   diaphragms add, while the wave hitting the rear of
   the diaphragm cancels as it is 180° out-of-phase
   with the rear pickup pattern of the pressure
   diaphragm. This method is expensive and seldom
   used for sound reinforcement or general-purpose
   microphones.
   2. The second and most widely used method of
   producing a cardioid pattern is to use a single
   diaphragm and acoustically delay the wave
   reaching the rear of the diaphragm. When a wave
   approaches from the front of the diaphragm, it first
   hits the front and then the rear of the diaphragm
   after traveling through an acoustical delay circuit,
   as shown in Fig. 16-11A. The pressure on the front
   of the diaphragm is at 0° while on the rear of the

Figure 16-7. Cardioid pickup pattern. Courtesy Shure
Incorporated.

Figure 16-8. Supercardioid pickup pattern. Courtesy Shure
Incorporated.

Figure 16-9. Hypercardioid pickup pattern. Courtesy

Sennheiser Electronic Corporation.

Figure 16-10. Two-diaphragm cardioid microphone.

Input Output

Input Output

Diaphragm

movement

Sound

Front wave

Rear

Sound

wave

Pressure

gradient

cartridge

Pressure

cartridge