AKG MP 40 User Manual download pdf (Page 91)

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DEFINITIONS FROM A TO Z

GLOSSARY

cates its sensitivity to sounds arriving from

different directions. Omnidirectional micro-

phones “hear” equally well in all directions

while all others prefer sound from one

(unidirectional) or two (bidirectional) direc-

tions. The polar diagram shows the three-

dimensional “hearing performance” of a

microphone as a single curve. It is suffi-

cient to plot only one half of the curve (0°

through 180°) since the other half (180°

through 360°) is symmetrical. In this way,

the directivity can be shown for several dif-

ferent frequencies (broken, dotted, solid

lines).

Pop Noise

In order to avoid those unpopular pop noi-

ses on stage, remember the following:

• Talk across the microphone head.

• Interestingly, pop noises are worst about

2 in. from the mic. So move either closer

or further away.

• Perhaps use an extra foam windscreen.

See “Accessories” section.

Pressure Gradient Microphone

If both the front and rear of a diaphragm

are exposed to a sound field, then the force

that vibrates the diaphragm results from

the difference between the sound pressures

in front and to the rear of the diaphragm

(called the pressure gradient).

The magnitude of the driving force depends

on the distance between the front and rear

sound entries, the frequency, and the angle

of incidence and is therefore a directional

variable which can be utilized to design

directional microphones. Cardioid, figure

eight, or hypercardioid polar patterns can

be achieved by incorporating appropriate

sound paths.

Pressure Microphone

If only one side (front) of a microphone dia-

phragm is exposed to a sound field and the

other (rear) side sealed off by a soundproof

case, the diaphragm will be vibrated by

changes in sound pressure only. Sound

pressure being a non-directional (scalar)

variable, the microphone is equally sensi-

tive in all directions. The resulting polar

pattern is called omnidirectional 1.

Proximity Effect

In unidirectional microphones, as the wor-

king distance decreases, the output voltage

rises more markedly at the low frequencies

than throughout the rest of the frequency

range. This is due to the fact that the dia-

phragm is vibrated by the pressure gradient

between its front and rear surfaces and the

pressure gradient is related to the curva-

ture of the wave fronts.

AKG WMS GLOSSARY

Rear sound entries

Hypercardioid

Ultra-directional

Figure-

eight

Omni-

directional

Cardioid

At 150° off-axis, the sensitivity is

17 dB down (referenced to 0°) at

125 Hz (solid line), and 10 dB down

at 8 kHz (dashdotted line, right-

hand half). 150° means 150° left,

right, up, and down (see diagrams

on the left).

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