AKG Acoustics WMS 40 - Manual (Page 91)

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D
EFINITIONS 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).