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Glossary of PA Terms - E

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The glossary pages provide definitions for over 1900 PA-related terms. 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. Use of this information is conditional upon acceptance of the Disclaimer on the PAforMusic home page.

Ear buds * Ear mix * Earhook * Early reflections * Ears * Earth * Earth bonding * Earth-compensated * Earth-free * Earth isolator * Earth leakage * Earth lift * Earth loop * Earth rod * Earthy * EBU * Echo * Effects * Effects loop * Effects pedal * Effect return * Effect send * Efficiency * EFI * EFX * EIN * Electret * Electric bass * Electrical safety * Electrodynamic microphone * Electrolytic capacitor * Electromagnetic interference * Electromagnetic wave * Electromotive force * Electronically balanced * Electrostatic discharge * Electrostatic microphone * EMAC * EMC * EMF * EMI * Emulated line output * Enclosure * End-firing * Energise * Ensemble * Envelope * Equaliser (EQ) * Equipotential bonding * Equivalent input noise * Equivalent noise level * ERP * Error correction * Error rate * ESD * ESTA * ETH, Eth * Ethernet * ETS * ETSI * Euro connector * Euro thread * EWM * Exciter * Excursion * Expander * Expansion * Expansion ratio * Exponential horn

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.

Ear buds
A more discrete alternative to headphones, typically used with in-ear monitoring systems and personal entertainment players. Ear buds are a friction fit in the ear canal and so are self-supporting. Different types vary as to how much ambient sound they are designed to keep out. See also Ears (2) and Intraaural.

Ear mix
A slang term for a mix intended to be fed to in-ear monitors, or, less often, for a mix intended to be fed to headphones. See also Ears (2).

Earhook
A device used to attach a head-worn device, usually a miniature microphone, by means of a stiff wire bent around the back of the ear. Or, describes such a microphone. Such microphones are usually radio microphones and are used in conjunction with a bodypack. See also Headset.

Early reflections
Reflections of sound from nearby surfaces, resulting in reflected sound reaching the listener a relatively short time after the direct sound and substantially before the general reverberation of the space. See also Slap echo.

Ears (1)
Apart from the obvious meaning, a slang term for the flanges at the sides of the front face of equipment intended for mounting in a 19 inch rack system.

Ears (2)
A slang term for an in-ear monitoring system.

Earth
Short for either 'safety earth' or 'signal earth'.

Earth bonding
See Bonding.

Earth-compensated
See Ground-compensated.

Earth-free
An alternative term for 'floating'.

Earth isolator
A device which is inserted into an interconnection between items of equipment, whose purpose is to pass the required signal whilst providing galvanic isolation of the signal earth connection, so as to avoid creating an earth loop through that interconnection. The equivalent US term is 'ground isolator'.

Earth leakage
Current that flows in a safety earth conductor from the mains supply. Such unwanted currents typically arise as a result of paths through capacitances between the live conductors of the mains supply and earthed points. These capacitances may be provided intentionally as part of mains interference suppression arrangements, but in any case will exist incidentally between the internal conductors of 3-core power cables and between the internal mains wiring of equipment and earthed chassis.

Earth leakage can be a source of hum and buzz problems where earth loops exist, because the earth leakage currents develop a voltage across the safety earth path impedances and therefore cause voltage differences between different safety earth points in the power distribution system. Such differences in voltage in turn can cause mains-frequency currents to flow in the signal earth conductors of signal cables. As earth leakage can rarely be reduced (except by use of a balanced mains supply), solutions to these hum and buzz problems usually include the avoidance of earth loops as far as possible, and the use of balanced signal interconnections to reduce the effects of them.

Furthermore, the earth leakage currents arising from multiple items of equipment will tend to add up, and if the total value becomes excessive then spurious tripping of RCDs may occur.

Earth lift
On Class I mains-powered equipment, a switch which provides the facility to disconnect the equipment's signal earth from its safety earth, in order to avoid an earth loop. It should not disconnect the safety earth from the parts of that item of equipment which must remain earthed for safety reasons, and so operating an earth lift switch is not the same as using the equipment without a safety earth connection, which would present a serious electric shock hazard.

On Class II mains-powered equipment and on non-mains equipment (such as battery or phantom-powered DI boxes), a switch which provides the facility to disconnect the signal earth connection between other items of equipment, in order to avoid an earth loop. (Such a loop may exist through other signal earth paths, or through safety earth connections to Class I equipment.)

Although operating an earth lift switch should not in itself create a hazardous situation, it is strongly recommended that for maximum safety such switches are only set to the 'lift' position if it is certain that this does not disconnect the only safety earth connection to the signal earth (i.e. a safety earth connection is being provided from other equipment and is certain to remain connected during use). If no safety earth connection is being provided by another path, then a mains earth loop condition does not exist and operation of the earth lift switch is probably unnecessary; to operate it would remove the only safety earth connection from the signal earth, which as well as reducing safety could itself introduce a buzz or hum, confusingly similar to that which would be caused by an earth loop!

An earth lift switch may also be referred to as a 'ground lift switch' (originally a US-only term), and often will have just two positions typically labelled 'Earth' (or 'Ground') and 'Lift'. The 'Earth' position provides a low-impedance connection to earth, and the 'Lift' position provides a complete disconnection of the signal earth path. Note, however, that in the case of equipment which does not provide galvanic isolation (i.e. equipment in which the switch refers to an electronically balanced input or output), the 'Lift' position only breaks the earth path through the signal earth conductor, and a path to earth may remain through the 'live' or 'signal' conductor(s).

In some cases (most often on DI boxes), the earth lift switch has three positions, typically labelled 'Earth' (or 'Ground'), 'Float' and 'Lift'. In these cases the function of the 'Earth' and 'Lift' positions is the same as in the case of a two-position switch, while the 'Float' position provides a 'medium impedance' connection to earth (typically through a parallel resistor and capacitor).

Earth loop
The situation that exists when two or more items of safety-earthed equipment are interconnected (either directly or via other equipment) by signal cables. This creates a continuous 'circular' path of earthy interconnections, made through the safety earth conductors of the equipment power cables and the signal earth conductors of the interconnecting signal cables.

For example, such a situation is likely to occur if a line output of a combo (or other item of Class I mains-powered stage equipment) were connected direct to an unbalanced line input of a mixer. This condition can sometimes result in the addition of hum to the wanted signal(s). An earth loop may also be referred to as a 'ground loop' (originally a US-only term).

The hum occurs because of mains-frequency voltage differences between the safety earths of the interconnected equipment, which arise due to mains earth leakage currents developing different voltages across the impedances of the safety earth conductors involved, and/or due to currents induced into the earth-loop path (e.g. from nearby mains transformers). Such voltage differences result in a voltage difference between the signal earths of the equipment, and therefore add to the voltage of any signals passed between them. Further, they result in the flow of earth currents along the signal earth conductor(s) of the interconnection, which may inductively couple into the signal conductors.

Earth-loop problems may be usually resolved by the appropriate use of DI boxes, earth lift switches, earth isolators, Class II mains equipment, etc. to provide galvanic isolation of signal earth connections and thereby break the loop, and/or by use of balanced or ground-compensated signal interconnections to provide immunity against the earth voltage differences. Additional measures include the use of a technical earth and/or of balanced mains supplies. However, safety earths must never be disconnected, as to do this would create a lethal hazard. See also Pin 1 problem.

Earth rod
A metal rod, usually of copper and about a metre long, which is driven into the ground and connected to in order to provide a local safety earth connection. May also be referred to as an earth spike, or (especially in the USA) as a ground rod or ground spike. In order to provide the required level of electrical safety, it must be verified that the impedance between the earth connection provided by the rod, and the general mass of Earth, is sufficiently low. See also TT.

Earthy
Describes a conductor that, in normal use, possesses a negligible voltage with respect to the general mass of earth, i.e. a conductor which is at essentially earth potential. A conductor at a 'zero' voltage; a signal earth. In an unbalanced connection, it is sometimes referred to as the 'cold' conductor. See also Safety earth. Compare Hot.

EBU
An abbreviation for 'European Broadcasting Union', a body which sets technical standards for broadcasting in Europe. See also AES and ITU.

Echo
An effect unit that simulates a natural echoing of the sound, or which provides an artificial effect of a similar nature. Most units have the ability to provide a single echo or multiple echoes. This effect is also referred to as delay, because an echo is a delayed (and, usually, somewhat modified) copy of the original sound. However, a distinct repetition of the original sound will only be perceived if the delay is greater than about 50 ms. See also Haas effect.

Effects
Devices to modify a signal − usually in such a way as to improve the interest or 'fullness' of the sound. Or, the part of the sound that is added by such devices. Examples would be reverberation, echo, distortion, etc. Frequently abbreviated to 'FX' or 'EFX'. See the Effects page for further information. See also Signal processing and Pedal. Compare Sound effects and Special effects.

Effects loop
The signal path that runs from an effect send output on some item of equipment, through one or more effects units, and back to an effect return input on the original item of equipment.

Effects pedal
See Pedal.

Effect return
An input, of a mixer or instrument amplifier, intended to accept the output signal of an effect unit.

Effect send
An output, of a mixer or instrument amplifier, intended to supply a signal to an effect unit.

Efficiency
A measure of the proportion of the power that is supplied to an item of equipment (its 'input power') that is usefully converted or conveyed by the equipment (its 'output power'), expressed as a percentage. For example, if a particular amplifier is providing 600 W of audio output power and (under those circumstances) is 60% efficient, then it will be consuming 1000 W from the mains supply. The efficiency of speakers and microphones is usually specified in terms of their sensitivity. See also the Amplifier Classes section on the Amplifiers and Speakers page.

EFI
See RCD.

EFX
An abbreviation for 'effects'. (More usually abbreviated to 'FX'.)

EIN
An abbreviation for 'equivalent input noise'.

Electret
See Condenser microphone.

Electric bass
The proper name for a 'bass guitar'.

Electrical safety
See Electrical Safety on the Safety page.

Electrodynamic microphone
Another name for a dynamic microphone.

Electrolytic capacitor
See Capacitor.

Electromagnetic interference
A general term for any interfering signal that is carried as an electromagnetic wave. Such interference may be continuous (e.g. caused by a radio transmission) or momentary (e.g. caused by the operation of a mains switch). Often abbreviated to 'EMI'. See also EMC, RFI and Longitudinal choke. Compare Inductive coupling and Capacitive coupling.

Electromagnetic wave
A more scientific name for a 'radio wave'. The strictly correct term is 'electromagnetic radiation'. See also Radio-frequency.

Electromotive force
Another name for voltage. Strictly, it is the value of a source voltage when no load is connected to that source, i.e. when no current is drawn from it. This term is most commonly used in relation to voltage supplies (such as batteries); when referring to the voltage at signal outputs the terms 'open-circuit voltage' or 'unterminated voltage' are usually employed. Frequently abbreviated to 'EMF'. See also Potential.

Electronically balanced
Describes a balanced input or output that provides balanced operation entirely by means of electronic circuitry, rather than by means of a transformer. The electronic circuitry will always require a source of power, so such an input or output can only be provided by active equipment. Most modern designs of mixer have electronically balanced inputs.

An electronically balanced input or output may alternatively be described as 'transformerless', as it operates without the use of a transformer. For example, if the balanced output of a condenser microphone is described as being transformerless then it achieves the balancing of its output electronically, without the use of an internal transformer.

Advantages of electronic balancing include:

• Good frequency response.
• Good linearity (low distortion).
• Virtually immune to inductively coupled interference (e.g. from nearby mains transformers or from computer displays), without the need for magnetic screening.
• Relatively low cost.
• Relatively small size and weight.

• Cannot provide a truly floating output or input, i.e. galvanic isolation from the equipment circuitry and from earth.
• An excellent common-mode rejection is difficult to achieve, due to component tolerances.
• Poor immunity to high levels of radio-frequency interference.
• Vulnerable to possible damage from large voltage transients, e.g. electrostatic discharges.
• Requires a source of supply power.

Electrostatic discharge
A flow of current from a very high voltage source that is able to sustain that current only very briefly. For example, the current flow from an object (such as clothing manufactured from some types of man-made fibre) that has become statically charged due to friction. Although the current flow is only very brief, the very high voltages involved (often many thousands of volts) can cause serious damage to electronic components, especially semiconductors. Electrostatic discharges can also generate radio-frequency interference, giving rise to the 'crackling' noise commonly referred to as 'static'.

Such very high voltages are able to overcome the insulating properties of insulators (e.g. air), enabling the current to 'jump' a gap between conductors. Such an event can cause permanent damage to nearby insulating material and/or to the conductors. Frequently abbreviated to 'static' or to 'ESD'.

Electrostatic microphone
Another name for a condenser microphone.

EMAC
A trademarked abbreviation for 'extended multiply and accumulate', Mackie's proprietary 32-bit digital stereo effects processor.

EMC
An abbreviation for 'electromagnetic compatibility'. The degree to which items of equipment are immune from the effects of EMI, and/or are designed to reduce EMI effects they might have on other equipment. See also Longitudinal choke.

EMF
An abbreviation for 'electromotive force'.

EMI
An abbreviation for 'electromagnetic interference'.

Emulated line output
A line-level output, found on some combos and heads (especially those intended for guitars), that, when connected to a PA system, is intended to provide a sound similar to that produced by the speaker of the combo (or of the speaker connected to the head). That is, the results are intended to be similar to those obtained by miking-up the speaker, but without the associated problems such as leakage, cost of the microphone, space taken up by the microphone and its stand, etc.. Combos and heads vary in the degree to which the intended objective is actually achieved.

Emulated line outputs can be either balanced (usually at low impedance) or unbalanced (usually at high impedance). If the connector is an XLR then the output is likely (not certain) to be balanced, and if the connector is a jack then it is likely (not certain) to be unbalanced − check the manufacturer's specification. Note that as these outputs are at line level, they are not suitable for direct connection to a mixer microphone input (or to a stagebox) unless the mixer is able to handle such high-level signals on its microphone inputs. (As a general rule, only mixers having 20 dB pad switches usually satisfy this condition.) In other cases, an attenuator or DI box must be used to reduce the level.

Enclosure
The case, housing or cabinet of an item of equipment, especially of a speaker. In the case of a speaker, the enclosure does not simply provide mechanical support and protection for the driver(s), but also affects the sound produced − especially as regards bass response. Speaker enclosures may be sealed to the passage of air (see Sealed box), or may be ported. See also Chassis.

End-firing
Describes a microphone whose maximum sensitivity to sound is at the end of the microphone (rather than at the side). The end-firing design is the norm for PA microphones (with the exception of some types of drum microphones). Compare Side-addressed. See also Polar response.

Energise
To connect to a source of electrical energy, or to activate or switch on such a source so as cause electrical power to flow or to be available. In particular, to connect a mains power distribution arrangement to a source of mains electricity; the distribution arrangement is then said to be 'energised', or more informally, to be 'live'.

Energy
The ability (or potential) to do work. That is, to create heat, light or sound, or to move objects. Or, the amount of work done. Electrical energy is stored in batteries or is obtained from the mains supply or from a generator. Energy is measured in joules: one joule is sufficient to sustain a power level of one watt for a duration of one second. Put another way, if energy is being transferred at a constant rate then the amount of work done (in joules) is the power (in watts) multiplied by the length of time (in seconds) for which that power level is sustained.

Ensemble
A group of instruments that are played at the same time; a term generally used only for small groups of orchestral instruments, and often taken to refer indirectly to the musicians. Or, a group of vocalists.

Envelope
The way in which the level of a musical note changes, from the moment that the note is struck to the time that the sound produced completely dies away. Envelopes of electronically generated sounds are often described using the four parameters attack, decay, sustain and release − for details see ADSR.

Equaliser (EQ)
The facility, of a mixer, amplifier or a dedicated item of equipment, that allows control of the relative level of specific frequency ranges of a signal, whilst leaving other frequencies essentially unaffected. For further information, see the Equalisation section of the Mixing Facilities page.

The most basic equalisers just provide control over bass, mid-range and treble frequencies (loosely referred to as 'tone controls'), whilst more sophisticated units provide a finer degree of control. Most units provide, for each band of frequencies controlled, the facility to both cut (i.e. attenuate) and boost (i.e. amplify) the parts of the signal in that frequency range. Usually the cut and the boost are similar in the extent of control and in the width of the band of frequencies affected; where this is not the case the equaliser is described as asymmetric or non-reciprocal. (An example is where the cut applies to only a narrow band, for notching purposes.)

The term originates from telecommunications, where the purpose of an equaliser is to compensate for inadequacies in the frequency response of equipment, especially of long-distance cables, by providing an 'opposite' frequency response and thus making the overall response through the system substantially flat. It should be noted, however, that in PA work equalisers are more often used to alter the frequency response for artistic purposes rather than to flatten it (with graphic equalisers largely being an exception). See also Sweep EQ, Parametric equaliser, Peaking response, Shelving response, RIAA and Tape equalisation.

Equipotential bonding
See Bonding.

Equivalent input noise (of pre-amps)
An indication of the level of noise that is added to a signal by a pre-amplifier, expressed in terms of the noise level that is apparently added at the input of the amplifier. Note that this figure is usually dependent upon the output impedance value of the signal source that is connected to the input. Often an A-weighted figure is quoted, usually in dBu. Often abbreviated to 'EIN'.

To take advantage of a low EIN value, it is necessary to use a low-noise signal source. For example, if the source is a microphone then it must have a low noise output level. (Microphone noise levels are usually quoted as an 'equivalent noise level' − or 'self-noise' − value, in dB SPL. For details of how to convert this to a value in dBu, for comparison with an EIN value, see Microphone Noise Levels on the Microphones page.)

To arrive at the noise level at the output of the amplifier, the equivalent input noise must be multiplied by the gain of the amplifier (in terms of decibels, this means adding the two quantities).

Equivalent noise level (of microphones)
See Microphone Noise Levels on the Microphones page. See also Thermal noise.

ERP
An abbreviation for 'effective radiated power'. A term used in radio transmission to indicate the level of radio-frequency (RF) power effectively emitted from a transmitter antenna. This value differs from the RF electrical power level provided by the transmitter, due to the effects of cable losses, impedance mismatches, antenna efficiency and antenna gain.

Error correction
A scheme in which additional information is added to a digital signal in order to allow the detection and automatic correction (within certain limits, dependent upon the particular scheme) of bits that are in error (i.e. a 1 instead of a 0 or vice versa). Used extensively in digital recording. See also Bit error rate and Interpolation.

Error rate
See Bit error rate.

ESD
An abbreviation for 'electrostatic discharge'.

ESTA
The Entertainment Services and Technology Association. Their website is www.esta.org.

ETH or Eth
An abbreviation for 'earth'. See Safety earth and Signal earth.

Ethernet
A system for the interconnection of computer-related equipment, especially for the creation of computer networks. Many different variants exist, operating at different data rates and using different cable and connector types. The most common arrangement is 10Base-T and 100Base-T, using UTP CAT 5e cable terminated in 8-pole RJ45 connectors. See also IEEE 1394 and USB.

View ethernet connector (RJ45) image

ETS
An abbreviation for 'European Telecommunications Standard'. Used as an identifying prefix for the telecommunications standards issued by ETSI, which include the allocation of the ISM band for licence-free use of radio microphone and in-ear monitoring systems. See also De-regulated frequency.

ETSI
An abbreviation for 'European Telecommunications Standardisation Institute', a body that devises and issues telecommunications standards for Europe. Its standards have the prefix 'ETS' (see the previous definition).

Euro connector
A vague term for a connector that is used in Europe (especially when not commonly used in the USA). It may be used to refer to many different types of connector, for example the IEC 320 mains connector or the SCART audio-visual connector.

Euro thread
A term for a screw thread that is used in Europe; in PA work it is most commonly used to refer to the 3/8 inch diameter Whitworth thread used for attaching microphone clips (and other accessories such as boom arms) to microphone stands. See also Thread adaptor. Compare American thread.

EWM
An abbreviation for 'ear-worn monitoring' − see In-ear monitoring.

Exciter
An effects unit intended to modify a signal, most often so as to give greater 'body' or more 'cutting edge' to the sound. It usually operates by the judicious addition of appropriate harmonics, particularly even-ordered ones. Most commonly used on lead vocals, and more often used in the recording studio than with live performances.

Excursion
The physical back-and-forth motion of a driver's cone or diaphragm, which is intended to generate sound waves. Or, the extent of such motion.

Expander
A signal processing unit designed to increase the dynamic range of a signal. An expander that applies expansion only when the signal level is below a specific value (the 'threshold') is called a 'downward expander'. See also Compressor, Compander and Noise gate.

Expansion
A process that increases the dynamic range of a signal. The device that provides this function is called an expander, and the extent of expansion provided is called the expansion ratio. Compare Compression (1).

Expansion ratio
A measure of the amount of signal expansion taking place. The ratio control of an expander usually has settings labelled 1:2, 1:4, 1:6 etc, pronounced '1 to 2', '1 to 4', etc. 1:2 means that 1 dB of change in level at the input produces 2 dB of change in level at the output; 1:4 means that 1 dB of change in level at the input produces 4 dB of change in level at the output, etc. (For an explanation of decibels, see the Decibels page.) A setting of 1:1 means that the expander is providing no expansion (i.e. is inactive, or bypassed), whilst 1:Infinity means that it is acting as a noise gate. Compare Compression ratio (1).

Exponential horn
A horn whose cross-sectional area increases exponentially along its length. That is, its area at any given distance from the start of the horn is proportional to some number raised to the power of that distance. This design gives a high efficiency, but the directivity is not constant, increasing with increased frequency. This is not a problem for bass and lower mid-range horns, as the directivity of these frequencies is relatively unimportant. So, this type of horn is useful in those cases. However, at higher frequencies directivity is very important and so constant directivity types are more often used at those frequencies. See also Folded horn.

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This page last updated 24-Jan-2010.