AKG Acoustics WMS 40 - Manual (Page 89)

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D
EFINITIONS FROM
A
TO
Z
GLOSSARY
Crosstalk
The undesired coupling of signals from one
channel to another channel.
dB SPL
Decibel Sound Pressure Level. A measure
of the sound level referenced to 20 µPa
(the sound pressure corresponding to the
threshold of human hearing). A 6-dB
increase in SPL would sound about twice
as loud.
Deep Fade
Massive decline of received signal strength
due to cancellation of the carrier in multi-
path transmission situations.
Directivity Factor
The directivity of a microphone can be
expressed in terms of the amount of sound
energy it absorbs out of a diffuse sound
field. The directivity factor indicates how
much less sound energy is absorbed by a
directional microphone than an omnidirec-
tional microphone.
Distortion
Dynamic microphones virtually never dis-
tort the signal. To be precise, their distor-
tions at very high sound pressure levels
(<130 dB) cannot be measured because
loudspeakers are incapable of reproducing
such levels distortion free. For this reason,
we state no maximum SPL for dynamic
microphones.
However condenser microphones with their
built-in preamplifier may overload at high
sound levels. When close miking (from a
few inches) loud instruments such as
drums or trumpets the microphone sensiti-
vity should be reduced. With the C 535,
simply use the preattenuation switch.
Directional Antenna
Antenna whose sensitivity is highest within
a limited angle in front of the antenna.
Directional antennas are used mainly where
standard receiving antennas cannot be
mounted within the range of the transmit-
ters so the transmitter signals must be
picked up from greater distances (e.g., in
open-air arenas).
Diversity
Reception technique that ensures clear
reception even in difficult environments.
Diversity receivers use several antennas for
the same carrier frequency and some
models use several receiving sections, too.
Downtime
Period of time during which a system is
inoperative.
Dropout
Momentary loss of signal due to squelch
operation or interference.
Dynamic Microphone
A coil attached to a diaphragm is driven by
the sound waves and vibrates between the
poles of a magnet. This movement induces
in the coil a voltage which corresponds to
the sound pressure. Dynamic microphones
handle high sound levels without overloa-
ding and are very rugged. They require no
operating voltage. Dynamic microphones
from AKG are designated by the letter “N”
in front of the model number. Also known
as “moving coil microphone”.
Electret Condenser Microphone
Condenser microphone that needs no pola-
rization voltage. Instead, a special metali-
zed plastic “electret foil”, in which a per-
manent electrical charge has been stored
by application of heat and a high polarizing
voltage, is used either for the diaphragm or
the fixed electrode. The latter type is called
“back plate electret microphone”.
Electromagnetic Wave Spectrum
Range of frequencies of electromagnetic
radiation.
Environment
Dynamic microphones will generally stand
up to extreme environmental conditions
such as temperatures from -25 °C to +70 °C
and high humidity.
Condenser microphones, however, are sus-
ceptible to humidity and condensation.
When an object is damp and colder than its
environment, condensation water will form
on its surface. Drops of condensation water
inside the transducer or high-impedance
preamplifier will cause crackling noises.
Storing condenser microphones:
1. Store the microphone in a dry and warm
place. It should never be colder than its
environment. If it has been transported
in a cold car or van, allow it to warm up
before use.
2. The supplied silica gel absorbs humidity.
It will maintain this property as long as
you keep it in the sealed package and
may be regenerated in the oven if neces-
sary.
3. Be sure to protect condenser micropho-
nes from rain when using them outdoors.
Equivalent Noise Level
Since condenser microphones incorporate
a preamplifier, they introduce a low amount
of self-noise which appears at the micro-
phone output as an unwanted signal volta-
ge. This noise voltage is measured using
standard weighting filters and the result
stated as the equivalent noise level in dB.
An equivalent noise level of 20 dB, for
instance, means that the self-noise of the
microphone is as loud as a sound at 20 dB
SPL (see dB SPL).
Noise level in quiet recording studio:
A low equivalent noise level means that the
microphone's self-noise is low. The self-
noise voltage is weighted either conforming
to IEC 268-1 and DIN 45 405 using the
filter according to CCIR 468-3 with the
“quasi-peak” value being quoted, or in
accordance with IEC 651 or DIN 45 412
using the A-weighting curve with the rms
value being quoted. Studio engineers seem
to prefer the CCIR weighting while A-
weighting is still accepted as well.
ERP
Equivalent Radiated Power,
a measure of a transmitter's RF output.
Far-Near Difference
The difference between the shortest and
the longest distance between stage and
antenna.
Inside a bass
drum 3 cm
(one inch)
from the head
Tom-toms
3 cm (one in.)
distance;
60 watt guitar
amp, at 30 cm
(12 in.)
distance
Loud vocals,
at 15 cm
(6 in.) distance
Acoustic
guitar,
chords
strummed with
plectrum, at
40 cm (16 in.)
Acoustic
guitar, at
40 cm (16 in.)
played
“fingerpicking”
Noise level in
an average
city apparment
Threshold of
hearing
Loud vocals,
measured in
front of the
mouth;
threshold of
pain
Congas, 2 cm
(one in.) from
the head
Cowbell at
10 cm (4 in.)
distance
Saxophone,
trombone,
played p,
at 40 cm
(16 in.)
distance
Piano, played
pp, at 1 m
(3 ft.) distance
Whispering at
distance of
10 cm (4 in.)
quiet conver-
sation at 1 m
(3 ft.) distance
Noise level in a
good sound-
isolated studio
140 dB
130 dB
120 dB
110 dB
100 dB
90 dB
80 dB
70 dB
60 dB
50 dB
40 dB
20 dB
0 dB
➂
AKG WMS GLOSSARY