28 | Chapter 3: Glossary of Terms |
Bus
In audio terms, a Bus is a point in a circuit where many sig- nals are brought together. For example: Most electronic items have a Ground Bus where all of a device’s individual ground paths are tied together. In mixers, we have Mix Busses, where multiple channels’ signals are brought (or blended) together, and Aux Busses, where feeds from channels are brought together to be routed to an external processor or monitor send, etc. In general, the more busses a mixer has, the more fl exible the routing capabilities of that mixer will be.
Capacitor
An electronic component that stores an electric charge. It is formed of two conductive plates separated by an insulator called a dielectric. A capacitor passes AC but blocks DC.
Channel Separation
Relates to crosstalk, or bleed of audio signals from one chan- nel to another. The amount of channel separation is inversely related to the item’s crosstalk spec; i.e. a low crosstalk spec indicates high channel separation.
Circuit Breaker
A resettable device intended to provide protection to electrical circuits. It opens when current fl ows though it that exceeds its current rating.
Clipping
A specifi c type of distortion. If a signal is passed through an electronic device which cannot accommodate its maximum voltage or current requirements, the waveform of the signal is sometimes said to be clipped, because it looks on a scope like its peaks have been clipped off by a pair of scissors. A clipped waveform contains a great deal of harmonic distortion and often sounds very rough and harsh. Clipping is what typi- cally happens when an audio amplifi er output is overloaded or its input over driven.
A Clip Indicator on an amplifi er indicates the presence of clip- ping distortion.
Compressor
A compressor is a device that reduces the dynamic range of an audio signal. First a threshold is established. When the audio signal is louder than this threshold, its gain is reduced.
Crossover Network (Crossover)
An electronic network that divides an incoming signal into two or more frequency bands.
Crossover Slope
High- and
filter at 100 Hz will pass 6 dB less energy at 50 Hz, and 12 dB less energy at 25 Hz. Within the common 1st through 4th
filters there is an endless variety of crossover types including Butterworth,
Crosstalk
Signal bleeding or leaking from one channel of a
Current
Literally, the rate of electron fl ow in an electrical circuit. Cur-
rent is measured in Amperes (or Amps), abbreviated I. Ohms law defi nes current as voltage (V) divided by resistance (R) with the following expression: I=V/R.
Damping Factor
Though technically more complex than this, damping factor is usually thought of as an indicator of how tight an amplifi er will sound when powering bass speakers. A speaker’s driving motor is a coil of wire (called a voice coil) mounted within a magnetic fi eld. As this coil of wire moves within the fi eld a voltage will be induced in the voice coil. If resonant motions of the speaker are not suffi ciently
fier, the speaker output can have an over accentuated or “boomy” bass sound.
From a technical measurement stand point, damping factor is the ratio of the rated speaker impedance to the amplifi er’s output impedance. Low output impedance is the consequence of the amplifi er having substantial negative voltage feedback taken from its output terminals. Properly designed negative feed back not only corrects for output voltage errors induced by the speaker but also produces other benefi ts, including low distortion, low noise (hiss), and fl at frequency response.
DC Output Offset
The presence of DC (Direct Current) at the output of the amplifi er. Any more than approximately 10 millivolts (positive or negative) could be an indication of a problem within the amplifi er.
Decibel
A decibel, a tenth of a bel, is used as an expression of the ratio between signal levels.
One decibel is commonly taken as the smallest volume change the human ear can reasonably detect. Doubling the POWER of an amplifi er results in a 3 dB increase, which is a “noticeable” volume increase. Doubling the VOLUME of a sound is a 10 dB increase.
dBV is decibels relative to 1 volt. dBu is decibels relative to 0.775 volt. dBm is decibels relative to 1 milliwatt.
Distributed Speaker System (Constant Voltage System) A type of speaker system where transformers typically are used at the output of an amplifi er and at each speaker in order to provide a constant voltage (most commonly 70V or 100V) that can be tapped by multiple speakers. These lines can be run great distances with less loss and can have many more speakers on them than typical high current speaker lines. These types of systems are generally employed in situations where an amplifi ed signal must be distributed over vast areas without a need for very high sound level in any one area. This type of P.A. system is typically used in schools, churches, business offi ces, and other commercial facilities.
Dynamic Range
The dynamic range of a sound is the ratio of the strongest or loudest part, to the weakest or softest part; it is measured in dB. An orchestra may have a dynamic range of 90 dB, mean- ing the softest passages have 90 dB less energy than the loudest ones.
EMI
EMI (Electro Magnetic Interference) refers to interference in audio equipment produced by the equipment or cabling pick- ing up stray electromagnetic fi elds. This interference usually
Amplifier Application Guide
