| Glossary of PA Terms - W
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The glossary pages provide definitions for over 2680 PA-related
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In the list below, the most commonly looked-up terms
are in bold, lighting-specific terms are in
and video-specific terms are in
Wall wart *
Wash light *
Weighted noise measurement *
Weighting filter *
Wet hire *
White Book *
White noise *
White space *
White space device *
Wire gauge *
Wired microphone *
Wireless microphone *
Wireless system *
Wiring classes *
Wiring harness *
Wiring loom *
Wiring regulations *
Word clock *
Word length *
Working lights *
The definitions for these terms are given on the assumption of
their use in the context of PA systems; many of the terms have
more general meanings when used in a wider context. Where more than
one definition is given for a term, the definitions are numbered
(1), (2) etc.
Some of the
definitions themselves use terms (such as "signal") in
a specific way − most of these are links (just the first time
they are used, in each definition), so just click on them to see
the meanings that are intended.
An abbreviation for watt.
Note that due to font conversions, on some web pages the Greek
capital letter Omega, the symbol for ohm,
may be displayed by your browser as a 'W'; it should look like
a horseshoe shape with a flat base, which, if your browser displays
it correctly, now follows: Ω.
See Acoustic wadding.
A slang term for an external
power supply unit,
for converting mains to
in the form of a somewhat larger-than-normal
engages directly with a mains
outlet, as compared
to one in the form of a stand-alone unit equipped with
a mains lead terminating in a standard mains plug.
Such devices must of course incorporate the
appropriate type of mains plug for the specific
country of use, and must provide a low-voltage
output whose characteristics are suitable for
the equipment to be powered by them.
The name derives from the fact that
these units generally project outwards from a
wall-socket outlet more than does a standard
mains plug. For further information see
A term used in the film industry to refer to the background
sound made by a crowd of people.
Describes a sound lacking in harshness.
See also Clarity and
A lantern that gives
an even illumination of a relatively large area of the
stage. See also Fresnel.
The unit of power,
named after James Watt. One watt represents a
transfer of energy
at the rate of one joule
In a DC
circuit, the number of
watts dissipated in a
particular part of the circuit is the
flowing through that part of the circuit multiplied by the
across that part.
In an AC circuit, provided that
the voltage and current are
in phase with each other
(i.e. unity power
the number of watts dissipated in a particular part
of the circuit is the
RMS current (in amps)
flowing through that part of the circuit multiplied by
the RMS voltage
(in volts) across that part.
For more information on power and power
See also VA.
The 'shape' that would be made by a
signal if its
were plotted against time, for example if the
signal were displayed on an
The term often refers to a signal having a repetitive
shape (such as a
in which case the waveform has a specific
its waveform may be identified from a single
See also Square wave
and Crest factor.
The distance occupied by one
cycle of a
wave, as it travels though some
medium (such as air).
The wavelength of sound
waves in air can be of great importance when considering
cancellation effects and other phenomenon such as
Wavelength is inversely proportional to
the wavelength in metres can be calculated by dividing
the velocity (speed) of the wave (in the relevant medium)
in metres per second by its frequency in
For information on the calculation of sound
wavelengths in air, see
Speed of sound.
As the velocity of electrical
signals is extremely
high, the wavelength of electrical
signals is very large and not usually of any relevance.
However, the wavelength of electrical
signals can be of importance, most particularly in
relation to antennae.
An abbreviation for
See also SDIF.
A slang term for a
(because these are usually wedge-shaped).
See also Slant.
A measurement of noise
level in which the noise
signal is passed through a
before the measurement is made. The reason for doing this
is usually to take account of the differing
sensitivity of the
human ear to different
sound, so that the value of
the measurement corresponds more accurately to the level
of noise that would be perceived by a person listening to it.
The filter is usually an A-weighted type,
but CCIR weighting is
sometimes encountered − for further details see
Weighting. See also
Noise Levels on the
The process of attributing a different
significance, or 'weight', to the different
within a complex sound
signal. The purpose of
this is usually to simulate the natural weighting
given by the human ear to different frequencies,
so that a measurement of the sound or signal
level may be made which
correlates more accurately with its
loudness, as it would be
perceived by a person with healthy hearing.
However, the situation is complicated by the fact that
the weighting naturally applied by the human ear varies
according to the loudness of the sound. At low levels of
loudness, the ear has a rather poor response to
improving quite rapidly until an optimum response is reached
at around 2.5 kHz; as the
frequency continues to rise the response then slowly falls
off again. At high loudness levels however, there is
a much better response to bass frequencies, and the response
is fairly flat from around
200 Hz to 6.5 kHz.
Therefore the weighting applied to the sound or signal
to be measured needs to take account of the loudness at
which the sound will be heard. For this reason,
three different types of weighting have been specified,
corresponding to the three standard loudness values of
40, 70 and 100 phons.
These weightings are derived from the 'equal loudness'
measurement work on human hearing undertaken by Fletcher
and Munson, and are defined by specification
IEC 651 (or DIN 45412). They are as follows:
A-weighting, corresponding to the response of the human
ear at 40 phons. This is the most common type, and
is most frequently encountered in the measurement of
(because noise in PA systems is
usually at a low level of loudness).
To achieve this response a
centered on a frequency of
2.5 kHz is used;
increases steadily as the frequency falls below 2.5 kHz
(20 dB attenuation at
and increases much less rapidly as the frequency rises
above 2.5 kHz (10 dB attenuation at 20 kHz).
B-weighting, corresponding to the response of the human
ear at 70 phons. This type is the least commonly
encountered. It has a similar high-frequency response to
A-weighting, but has a rather
less severe attenuation of low frequencies.
C-weighting, corresponding to the response of the human
ear at 100 phons. This type is suited to
level measurement in loud environments such as rock
concerts, dance clubs and noisy industrial environments.
This has a similar high-frequency response to
but has a far less severe attenuation of low frequencies.
Another type of weighting, generally used only in noise
measurement (especially of
'CCIR weighting', specified
by CCIR 468 (or DIN 45405). For further
information on microphone noise levels, see
Noise Levels on the
Note that, when a weighting is used in the measurement of a
signal (or noise) level, there
is an implicit assumption that, overall, no modification
of the frequency response (or other modification such as
distortion) occurs in
the system between the point of measurement and the
sound waves that are eventually heard (or that would
Note also that the term 'weighting' is occasionally used to
refer to the response given by equalising filters such
as those used in the recording and playback of
analogue recordings −
see RIAA and
equalisation − though to avoid confusion this
usage of the term is best avoided.
A filter specifically
designed to give more emphasis (or 'weight') to certain
within a signal,
usually in order to simulate some natural filtering
effect such as the response of the human ear. Such filters
are most often used in the measurement of
levels and in the measurement of
types of filter will give different weight to each
frequency, and so will give a different result to the
measurement. For more detailed information see
Describes a sound laden with
Hiring of equipment (usually a complete system) from a
hire company, that includes the personnel to assemble and
operate it, as compared to hire (usually of individual items)
on a 'self assemble and operate' basis.
Compare Dry hire.
Feedback at a high audio
See CD standards.
A particular type of noise,
remains constant over the entire audible
range. More accurately, frequency bands of equal
bandwidth contain the
same amount of noise power.
See also Pink noise
and IEC noise.
Refers to unused parts of the
typically fairly narrow sections such as those between
television channels. Some
systems are designed to locate such spaces and operate
at frequencies within them (subject to licensing
A general term for any wireless device (e.g. a
system) that is able
search for white space
in order to select the
at which it will operate, or in order to give the user
an indication of which such frequencies are apparently
available for use. May be abbreviated to WSD.
See IEEE 802.11.
Describes an effect which has
a strong stereo component.
See also Width.
Describes a signal
(often noise) or
equipment (often a filter)
having a relatively large
A term used to describe the extent to which sounds
within a mix deviate
from a central position in the
'Width' is sometimes an adjustable
parameter of stereo
However, the actual 'width' experienced by a listener
will depend on a number of factors, particularly upon
their distance from the
as compared to the distance between the Left and Right
speakers. See also Pan,
Wind (musical instruments)
See Woodwind and
A coil of wire within electromagnetic components
such as a
electric motors. The term is not usually used for
the coils of speaker
(see Voice coil).
For further information on transformer windings see
A device, usually made of acoustic foam, that is placed
over the sound aperture of a
microphone to reduce the
unwanted popping noises that
result from plosives
(and, in outdoor events, to reduce wind noises) without
significantly affecting the quality of the
wanted sound. Also known as a 'sock' or a 'pop filter'.
See also Basket.
The moving electrical contact of a
It contacts with the track
of the potentiometer.
A flexible single
conductor whose length
is very much greater than its diameter, usually having
or coating. It is used to provide a path for an electric
to equipment or within a
cable, and may be stranded or
solid-cored. A wire within a cable is more usually referred
to as a core of the cable.
Non-technical personnel frequently use the term 'wire' to
refer to a complete cable, but this usage is deprecated by
The amount of current that can be safely carried by a
wire is determined by its gauge
and by other factors such as the type of
insulation it has and the ambient temperature when
A microphone that is
connected to the PA system
by means of an attached cable,
rather than via a
wireless link. Alternatively
termed a cabled microphone. Compare
Describes equipment that is is able to send or
receive a signal
by a means other than through a
cable, most commonly by
use of radio-frequency
transmission or reception.
A separate transmitter and receiver unit that communicate
with each other wirelessly.
Most commonly refers to a
microphone system, in which case the
may or may not be included as part of the system.
A person whose job is to install
cables and make the
required connections to them.
See Classes of wiring.
harness, Wiring loom
See BS 7671 and
BS 7909 (UK) and
Electrical Code (USA).
An abbreviation for 'Working Load Limit', the maximum
loading (expressed as a
weight) that can safely be supported
by a chain, rope, truss, hoist,
etc., under the most advantageous conditions
(working environment, method of use, etc.).
The WLL value is typically specified
by the manufacturer of the equipment, and so cannot take
into account factors relevant to specific real-life
conditions of use. A
assessing the specific usage situations may need to
assign an SWL value that is
less than the WLL value. So effectively the WLL value
is a maximum possible SWL value, that applies only under
WLL values incorporate a suitable
safety factor to
allow a substantial margin between between the quoted
value and the minimum loading at which the equipment
might be expected to fail − generally at least
a factor of 8 for these kinds of equipment.
For further information on safety see the
An abbreviation for 'Windows Media Audio', a
digital audio file
format suitable for playing on PCs, personal audio
Describes a particular class (or 'section')
of orchestral musical instruments, including the flute,
piccolo, clarinet and oboe. (Note that these instruments
are not necessarily made of wood.)
A driver which is designed
specifically to handle bass
frequencies. It is used
in a bass bin and as the
low frequency driver in
"wuffer". See the
Amps and Speakers page for
Compare Tweeter (but
also see Horn (1)).
The smallest meaningful unit of
digital information in a
particular system, for example, one sample of a
single channel of an
It consists of several bits,
often comprising one or more complete
indicates the rate at which
are conveyed or processed in a
So, its frequency
is the same as the sampling rate.
See also Bit clock and
to digital conversion.
The number of bits in
In an equipment
an item of equipment that is normally (or is currently)
fulfilling the relevant task. Or, rarely, the singular
of the next definition.
A slang term for
Generally used in the plural because there would
rarely be just one of such lights.
Or, of course, the plural of the previous definition.
Lights which are not used during a performance, but only
to provide light for the crew
during the rigging
and de-rigging of the system.
In a purpose-built performance venue they may be permanent
fixtures; otherwise they are mobile equipment and are usually
the first items to be rigged and the last to be de-rigged.
The process of arranging a
cable into a compact series of
circular loops (a coil),
for the purpose of convenient storage or transport.
Typically, in order to avoid damage to the cables by
kinking, a specific coiling technique is used such as the
Wrapping is also known as 'coiling'.
An abbreviation for
'white space device'.
An abbreviation for 'wide extended graphics adaptor'.
A standard interface
for the connection of display
equipment (such as monitors and projectors) to
computers. The standard gives a resolution of
1280 pixels horizontally
and 800 pixels vertically. Note that this format gives
aspect ratio of 16:10
(most usually employed for the integrated
LCD displays of laptop
See also VGA,
The most commonly encountered standards, their resolutions
and aspect ratios are tabled under the entry for
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This page last updated 05-Sep-2017.