Specifications

219
GLOSSARY
fig. 6) for several different frequencies (broken,
dotted, solid lines).
Pop Noise
In order to avoid those unpopular pop noises 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 differ-
ence between the sound pressures in front and
to the rear of the diaphragm (called the pres-
sure gradient).
The magnitude of the driving force depends on
the distance between the front and rear sound
entries (see fig. 7), the frequency, and the angle
of incidence and is therefore a directional vari-
able which can be utilized to design directional
microphones. Cardioid, figure eight, or hyper-
cardioid polar patterns can be achieved by
incorporating appropriate sound paths.
Pressure Microphone
If only one side (front) of a microphone
diaphragm 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 pres-
sure being a non-directional (scalar) variable,
the microphone is equally sensitive in all direc-
tions. The resulting polar pattern is called
omnidirectional 1.
Proximity Effect
In unidirectional microphones, as the working
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 diaphragm is vibrat-
ed by the pressure gradient between its front
and rear surfaces and the pressure gradient is
related to the curvature of the wave fronts.
This effect, known as “proximity effect”, begins
to become audible at a few hundred Hz and at
extremely close working distances, the output
level may be up to 15 dB higher at 50 Hz than
at 1 kHz. This corresponds to about 6 times the
normal output voltage.
Reflection
When a signal wave hits an obstacle, it will be
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 (dashdot-
ted line, right-hand half). 150° means
150° left, right, up, and down.
Fig. 6
rear sound entries
Fig. 7
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