 www.paformusic.info |
Glossary of PA Terms - 0-9 |
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
- If you have arrived here by clicking on a linked term on another page of this site, it may take a moment before your browser jumps to the definition of the term that you clicked on; thank you for your patience. (If there's still no movement after a few seconds, you may have encountered a broken link; please report it.)
- If you have arrived here from a search engine, or by clicking on an alphabet letter on another page of the Glossary, then click on your required term in the list below.
The glossary pages provide alphabetically-listed definitions for over 2270 PA-related terms. If you're not sure what term you are looking for, then the structured list of topics on the Training page may be a useful place to start, as there are links from there to many of the Glossary entries.
If you can't find the term you are looking for, or would like any of the existing definitions to be expanded, please email me − likewise of course if you find any errors in the links etc.
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.
As PAforMusic is a UK-based site, this glossary uses British spelling and the definitions reflect British usage and engineering practice. However where differences exist between British and American terminology, they are generally noted in the relevant entries. The most significant differences are listed under American terminology.
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 (and then use your browser's 'Back' button to return to where you were).
Use of this information is conditional upon acceptance of the Disclaimer on the PAforMusic home page.
0 dB * 0HLS * 1-legged * 1 microphone technique * 1 note bass * 19 inch rack system * 100 volt line * 1080i * 1080p * 2-pi space * 2-TK * 2-TRK * 2-track * 2-way * 3 dB point * 3-phase * 3-to-1 rule * 3-way * 4 mm connector * 4-pi space * 5.1 * 57 * 58 * 5th * 5th-order * 7.1 * 70 volt line * 720p * 75 ohm interconnection
0 dB (1)
When applied to the level of a
signal, 0 dB
refers to the agreed
reference level
of that signal. Although this may be referred to as the
signal's 'zero level', it does
not mean the complete absence of any signal.
When 'dB' is followed by other characters, those
characters usually indicate the applicable reference
level. Common examples of such reference levels are:
- 0 dB SPL − A sound pressure level of 20 µPa (= 200 pbar).
- 0 dBu − A signal voltage of 0.775 V RMS.
- 0 dBV − A signal voltage of 1 V RMS.
- 0 dB FS − A full-scale digital signal level.
- 0 dBm − A signal power level of 1 milliwatt.
0 dB (2)
When applied to the setting of a
level control such as a
fader, 0 dB
refers to the reference setting of that control.
On some level controls of some equipment, this is the
setting at which the relevant section of the equipment
provides unity gain.
For further information see the
Decibels page.
0 dB (3)
When applied to the setting of an
EQ control (including a
band of a
graphic equaliser),
0 dB refers to the setting that has no effect on the
signal
being equalised (usually the mid-position of the control).
See also Flat.
For further information on decibels see the
Decibels page.
0 dB (4)
When indicated on a level
meter, 0 dB indicates a
signal
level that is equal to the
relevant reference level. For meters that indicate
the level at
line-level
outputs, a list of the
most common reference levels used is
given below. Consult your equipment handbooks to check
which 0 dB output reference level is applicable
to your equipment.
- +4 dBu − Most professional equipment
- 0 dBu − Some professional equipment (e.g. some Mackie mixers)
- −10 dBV − Most consumer/amateur equipment and some semi-pro equipment
- 0 dB FS − Digital equipment
1-legged
See One-legged.
1
microphone technique
See One
microphone technique.
1 note bass
See One note bass.
19 inch
rack system
A metal (usually steel) mounting system for equipment.
Each item of equipment is secured to the rack by bolts
through flanges (or 'ears') at the left and right edges
of its front panel. The bolts are usually 15 mm
M6 types. Plastic washers are often used
under the bolt-heads, to protect the flanges from damage.
The arrangements for the bolts to screw into vary between
different types of rack, and include:
- removable caged nuts which clip into holes in the vertical strips located at each side of the front of the rack. The nuts may be installed, as required, at fixed intervals in order to accommodate equipment of differing front panel heights.
- nuts that are captive in slots incorporated in the vertical strips. The nuts are free to slide up and down, in order to align with the holes in the flanges of the equipment to be fitted.
- threaded steel bars located behind, or incorporated into, the vertical strips. These allow the insertion of bolts at any of the standard positions.
All front panel heights are a multiple of 1.75 inches (approximately 44.5 mm), referred to as a vertical unit or U. The total width of the equipment front panels (including the flanges) is 19 inches (482 mm), which is the reason for the name given to this racking system.
100 volt line
A particular type of arrangement for the connection of
passive speakers
to the power amplifier
driving them, specifically
developed to meet the requirements of
public address
applications. This arrangement is able to
accommodate a relatively large distance between the
speakers and the amplifier (sometimes up to several
hundred metres), while avoiding significant
power
losses resulting from the
resistance
of the interconnecting
cables. It also allows the
connection of a large number of speakers to each
amplifier output.
It works by supplying a substantially higher voltage to the speakers than is typically used in the low impedance speaker interconnections used in conventional PA applications. This means that the current flowing in the speaker cables (known as lines) is much reduced, resulting in much less power loss in them. In the UK the nominal voltage used is 100 volts RMS. In the USA the value is 70.7 volts RMS, and the system there is known as a '70 volt line' or as a 'constant voltage' system.
A system of this type requires a specific type of power amplifier providing one or more 100 volt outputs, appropriate cabling suitable for the high voltages present, and speakers that accept a 100 volt line input. These speakers (which usually have a relatively low power rating) are equipped with a transformer which steps the voltage down to a value suitable for the driver(s). The transformer often has several taps, which are usually marked with power ratings such as 5 W, 10 W, 15 W and 20 W. The effect of selecting a higher-power tap is that a lower impedance is presented to the line by the speaker, and so a larger current is drawn from it. The speakers are always connected in parallel to the line, which is often looped from speaker to speaker. The total connected load (usually specified in watts) must not exceed the drive capability of the amplifier, or damage to the amplifier may result.
This arrangement is generally used only in public address installations (whether fixed within buildings or for outdoor sports events and the like), where a large number of low-power speakers, located over a wide area, are to be connected to a centrally located amplifier. Historically, these types of speakers were often designed for cost-effective reproduction of voice frequencies only (rather than music), with maximum efficiency being given higher priority than sound quality. Therefore, in the past 100 V line systems have gained a reputation for poor audio quality. However, systems providing much improved audio quality are now available.
The term 'constant voltage' derives not from the output voltage of a particular amplifier of this type being constant in use, but from the fact that, in contrast to 'normal' (i.e. low impedance) amplifiers, two amplifiers of this type that differ in their power output capability do not differ in their maximum voltage output − their difference in maximum power output is accounted for solely by a difference in the amount of current that they are able to supply. This means that, when additional speakers need to be added to a system, the amplifier can be upgraded to a higher-powered model without affecting the power level supplied to the existing speakers. See also Installation speaker.
2-pi space
See Half space.
2-TK, 2-TRK
An abbreviation for
2-track.
2-track
An alternative term for
stereo.
A name often given to a stereo
input on a
mixer, intended for
a playback connection from a stereo audio player
(e.g. a CD player); often labelled '2-TK' or
'2-TRK'. Such inputs are often
equipped with a reduced set of facilities (especially
as regards equalisation
and routing) as compared
to a channel strip.
2-way
Describes a speaker
equipped with two different types of
driver, each handling
a different frequency
range. Typically, the two types of drivers will be
woofers to handle the
low (bass) frequencies
and horns to handle the
high (treble) frequencies.
Such speakers
usually include a passive
crossover to
direct the bass and treble frequencies to the appropriate
drivers, but may also be equipped with separate
inputs
to allow bi-amping.
Similarly, a speaker that incorporates three different types of driver, handling three different frequency ranges (low, mid-range and high) is described as a 3-way speaker. See also Concentric.
3 dB point
See Cut-off
frequency.
3-to-1 rule
The rule-of-thumb that recommends that when two or
more microphones are
used to pick up different
sound sources,
the distance between the microphones should be
at least three times the distance between each microphone
and its respective sound source. Or, to put it another
way, the microphones' distances from their respective
sound sources should be no more than one third
the distance they are from each other.
This is to ensure that each sound source is picked up predominantly by just one microphone, and so minimise the extent of undesirable comb filtering effects which can occur when a sound source is picked up at similar levels by two or more microphones whose outputs are subsequently mixed. See also Microphone technique.
4 mm connector
A single-pole
connector sometimes used
(in pairs) for speaker
connections, so-named because the
nominal diameter of the
male prong is 4 mm.
Some 2-pole speaker connectors employ a pair of 4 mm
prongs mechanically linked; in this case the prong
centres are normally 0.75 inches
(approximately 19 mm) apart.
Usually the female
connector can be unscrewed by hand for alternative use
as a binding post.
The male connector is commonly referred to as a
banana plug.
These connectors are now deemed unsafe for use in a domestic environment because they will fit into unshuttered European-type mains outlets (e.g. Schuko), which would result in a serious shock hazard (its replacement for domestic use is the BFA connector). See also Speakon.
4-pi space
See Full space.
5.1
The multichannel digital audio
scheme developed by
MPEG to provide a
surround sound
capability for films in many formats,
including
DVDs, tape and celluloid.
Also used in some high definition
television (HDTV) broadcasts. It incorporates five
full-range
(20 Hz to
20 kHz)
channels, for the
left front, right front, centre front, left rear
and right rear speakers,
and one sub-bass
(20-120 Hz) channel, hence the designation '5.1'.
A 4-pole 3.5 mm
jack
connector is
sometimes used for 5.1 digital connections. See also
7.1 and
AC-3.
57
A slang term for a Shure SM57
microphone.
58
A slang term for a Shure SM58
microphone.
7.1
A multichannel digital audio
scheme similar to the 5.1
scheme but with the addition of 'Left Side' and 'Right Side'
channels.
70 volt line
See 100 volt line.
75 ohm
interconnection
See Impedance-matched.
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
There are no more definitions on this page. (The space below is to facilitate linking to the last few terms above.)
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Visited count:
since 16-Aug-2000
This page last updated 05-Jan-2012.