AKG Acoustics WMS 40 - Manual (Page 92)

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D
EFINITIONS FROM
A
TO
Z
GLOSSARY
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 reflected, i.e., bounce off the obstacle's
surface at an angle equal to the angle of
incidence.
Remote Antenna
Antenna that is connected by a special
antenna cable to the antenna input socket
on a receiver rather than directly to the
antenna input socket.
Room Radius
In a room within which a sound is genera-
ted, e.g. by a loudspeaker, every point is
characterized by its own unique ratio of
direct sound and sound reflected from the
walls.
The distance from the sound source at
which the direct and reflected sound ener-
gies are equal is called the “room radius”.
Outside the room radius the overall sound
pressure level is constant throughout the
room in the form of a “diffuse sound
field”.
Sensitivity
A microphone's output voltage at any given
sound pressure level. A more sensitive
microphone will sound louder at the same
gain setting (the feedback risk being pro-
portionately higher). High sensitivity (con-
denser microphones) is needed to drive the
mixer adequately when far miking quiet
sound sources.
Sensitivity is commonly given in mV/Pa or
dBV (referenced to 1 V/Pa) and measured
at 1 kHz.
Here are some examples:
D 58
0.7 mV/Pa (-63 dBV)
D 190 1.6 mV/Pa (-56 dBV)
C 1000 S 6.0 mV/Pa (-44 dBV)
C 535 7.0 mV/Pa (-43 dBV)
C 451 EB comb 9.5 mV/Pa (-40.5 dBV)
C 460 Bcomb ULS/61 10.0 mV/Pa (-40 dBV)
C 562 BL
20.0 mV/Pa (-34 dBV)
Shadow loss
Signal loss which occurs in wireless trans-
mission if an obstacle blocks the line-of-
sight transmission path between transmit-
ter and receiver.
Signal Loss
Signal loss in a cable may be due to ohmic
resistance, dielectric leakage or radiation
loss.
Signal-to-noise (S/N) Ratio
The S/N ratio is the difference between the
reference sound pressure level of 94 dB
(1 Pa sound pressure) and the equivalent
noise level. Contrary to the equivalent
noise level, a lower S/N ratio means higher
noise and therefore a narrower dynamic
range.
Squelch
Electronic circuit that switches the recei-
ver off when the received signal is too
weak so the associated extraneous noise
and the self-noise resulting from the recei-
ver being switched off will be inaudible.
The squelch threshold is usually user ad-
justable within a preset range.
Tone coded squelch, tone code squelch, tone
squelch
These terms denote a circuit that will open
the audio path only when it detects a
system-specific tone within the demodula-
ted signal. This tone is higher than
20 kHz, the upper end of the range of
human hearing, and is added to the audio
signal by the transmitter.
Total Harmonic Distortion (T.H.D.)
A measure of the non-linear distortion of a
signal (e.g. a sine wave) that occurs when
a microphone or input is overloaded pro-
ducing harmonics (overtones) at multiples
of the fundamental frequency.
Transient
Temporary change in voltage or current
occurring as a voltage or current source is
switched on or off, e.g., a transistor con-
trolled by a pulse signal.
Transient Response
The ability of a microphone to follow sud-
den sound events immediately. Transient
response depends on diaphragm mass,
transducer damping factor, etc.
Types of Microphones
Microphones utilize different electroacou-
stical principles to convert sound energy to
electrical energy:
1. Carbon Microphone A microphone using
a flexible diaphragm which moves in
response to sound waves and applies a
varying pressure to a container filled
with carbon granules, causing the resist-
ance of the microphone to vary corre-
spondingly
2. Piezoelectric microphone A microphone
in which deformation of a piezoelectric
bar by the action of sound waves gen-
erates an output voltage between the
faces of the bar. Also known as “crystal
microphone”.
3. Magnetic microphone A microphone
employing a diaphragm acted upon by
sound waves and connected to an arma-
ture which varies the reluctance in a
magnetic field surrounded by a coil.
Applications include miniature micro-
phones for hearing aids and guitar
pickups.
4. Dynamic microphone A conductor (coil
attached to diaphragm, ribbon) flexibly
suspended in the field of a fixed magnet
is vibrated by sound waves. This indu-
ces in the conductor an AC voltage that
varies in step with the sound waves.
5. Electrostatic microphone A flexible dia-
phragm and a fixed electrode together
form a two-plate air capacitor whose
capacitance varies in step with the
sound waves that vibrate the dia-
phragm. Also known as “capacitor
microphone” or “condenser micro-
phone”. In electret microphones one of
the electrodes carries a permanent
charge.
UHF
Ultra High Frequency
VHF
Very High Frequency
Vibrational Noise
In addition to air-borne sound, micro-
phones also pick up mechanical noise
such as impact, footfall, handling, or cable
noise. Such unwanted noise can be re-
duced by special design features (trans-
ducer shock mount, compensation systems,
bass cut)
Vocal Microphone
A microphone specifically designed for
vocal use on stage. It incorporates a pop
screen, a transducer shock mount to re-
duce handling and impact noise, and is
particularly rugged so it will survive the
occasional drop from the stand.
Many vocal microphones have an upper
midrange (3 to 8 kHz) peak to make the
voice cut through. In the studio, vocals are
ideally recorded from 30 cm (1 ft.) or even
farther, usually with condenser micro-
phones.
Wavelength
The distance between two consecutive
peaks (or troughs) of a sine wave.
AKG WMS GLOSSARY