This explains in simple language many terms used in PA industry. We are stil expanding this section. Please email us any questions that you would like us to answer.

• Amplifier- Sound equipment that converts the low voltage, low current signal from a tape deck, mixer etc. into a higher current signal suitable for driving speakers. See Power Amplifier, Crossover.
• Ampere -The unit of current, abbreviated Amp.
• Bi-Amplification
  1) A way of optimizing the efficiency of a speaker system by separately amplifying the High Frequency (HF) and Low Frequency (LF) portions of the sound signal and sending them down two pairs of cables to the speaker. Multipin Speakon connectors have been developed to do this.
  2)The process of having of having low-frequency speakers and high-frequency speakers driven by separate amplifiers.
• Boom Stand - A microphone stand equipped with a telescoping support arm to hold the microphone.
• BPM - An abbreviation of Beat Per Minute (the number of steady even pulses in music occurring in one minute and therefore defining the tempo).
• Bridging amplifier -most professional amplifiers have two channels built inside. By bridging you are combining the output of each channel into one. In bridge mode both channels of the amplifier are run in 'push-pull' configuration and the load (loudspeakers) are wired between +ve of amplifier channel 1 and +ve of amplifier channel 2. Bear in mind that a bridged load presents half the load impedance to each channel. That is, 4 ohm bridged load presents a 2 ohm load to each channel. Normal minimum load impedance limits apply. In other words do not attempt to run a 2 ohm load in bridge as this will present a 1 ohm load potentially activating the amplifiers short circuit protection.
• Cable, 1/4 inch
  An unbalanced cable most often used for instruments and patch cords. Commonly referred to as "guitar cords".
• Cable, TRS - A less common balanced cable that has 3 different contacts on its 1/4 inch connectors. Most headphone jacks are a good example of a TRS (Tip-Ring-Sleeve) connector. These are sometimes used instead of the more common XLR connection.
• Cable, XLR - A balanced cable used for low impedance microphones and sometimes for connections between some parts of the PA. Commonly referred to as a "mic cord".
• Cardioid Pattern - A microphone pick up pattern, which has maximum pick up from the front, less pick up from the sides, and least pick up from the back of the diaphragm.
• Clipping - Distortion of a signal by its being chopped off. An overload problem caused by pushing an amplifier beyond its capabilities. The flat-topped signal has high levels of harmonic distortion which creates heat in a loudspeaker and is the major cause of loudspeaker component failure.
• Compressor
  1) Effect used to squash the sound together. Used properly, it can take the edge off or your sound. Used improperly, it can take the life right out of your system and make it sound like an MTV mix.
  2) A piece of sound processing equipment that ensures all wanted signals are suitably placed between the noise and distortion levels of the recording medium. It evens out the unwanted changes in volume you get with close-miking, and in doing so, adds punch to the sound mix. A Limiter is used to stop a signal from exceeding a preset limit. Beyond this limit, the signal level will not increase, no matter how loud the input becomes. A Limiter is often used to protect speaker systems (and human ears) by preventing a system from becoming too loud.
• Condenser Mic (Capacitor Mic) - A microphone that uses the varying capacitance between two plates with a voltage applied across them to convert sound to electrical pulses. Condenser microphones need a power supply to provide the voltage across the plates, which may be provided by a battery within the case of the microphone, or it may be provided from an external phantom power supply. A condenser mic is more sensitive and has a faster reaction to percussive sounds than a Dynamic mic and produces a more even response. See Electret Mic.
• Compression Ratio - How many dB the input signal has to rise above the threshold for every one dB more output of a compressor or limiter.
• Compression Driver The unit that feeds a sound pressure wave into the throat of a horn (in a horn loudspeaker). Compression driver reproduces the high frequencies.
• Condenser Microphone - A microphone which converts sound pressure changes into changes of capacitance. The capacitance changes are then converted into electrical voltage variations (an audio signal).
• Compressor  - A signal processing device that does not allow as much fluctuation in the level of the signal above a certain adjustable or fixed level.
• Crossover (Active) - A rack mountable processor unit used to separate frequencies leaving the soundboard into high's, mids, and lows with different outputs for each. This allows the system to work more efficiently.
• Crossover (Passive) -Used inside of full range speaker cabinets to separate highs, mids, and lows and send them to their respective speakers within the each cabinet. These are not as efficient as active crossovers because they require all frequencies to draw from the same source of amplification.
• Diaphragm - A thin flexible membrane or cone that vibrates in response to electrical signals to produce sound waves. Distortion is usually referred to in terms of total harmonic distortion (THD) which is the percentage of unwanted harmonics of the drive signal present with the wanted signal. Generally used to mean any unwanted change introduced by the device under question.
• Distortion - Usually undesirable result of overloading sound equipment. Reducing the levels can remedy the situation.

• db - decibel, measure of loudness.
• Dynamic Mic-Robust type of microphone which picks up the sound on a diaphragm connected to a coil of wire which moves within a magnet. An alternating current is induced into the wire which provides the electrical output. Most dynamic mics have low output impedance of 200 Ohms. See Condenser Mic.
• Equipment Rack-A cabinet with rails (or free standing rails) that have holes to accept screws at standard spaces (see rack spacing) and used to house outboard gear.
• Feedback
  1) The delayed signal sent back to the input of a delay line, used in repeat-echo effects.
  2) The pickup of the signal out of a channel by its input or the howling sound that this produces.
  3) In an amplifier, the phase reversed output signal sent back to its input, reducing gain but also distortion and noise.
  4) This occurs when the sound coming out of the speakers goes back into the microphones, then back out the speakers, then back into the mics...and so on. This can build very quickly to a point where everyone in the room is holding their ears and screaming at you. It can also cause damage to the PA.
• Fidelity- The recording or reproduction quality.
• FOH (Front of House) -Refers to the speakers that face toward the audience. Also called the "main" speakers.
• Foldback - term for the signal sent to the stage monitors in a live performance.
• Folded Horn - A speaker design where the speaker points back into the cabinet and bounces around finally coming out large ports in the front. It is intended to maximize low frequencies in a relatively small cabinet.
• Front Loaded- A speaker cabinet where the speaker faces out toward the front.
• Frequency Range- The range of frequencies over which an electronic device is useful or over which a sound source will put out substantial energy.
• Frequency Response- How sensitive an electronic device (mic, amplifier, speaker, etc.) is to various frequencies; often communicated with a graph.
• Horn
  1) The part of the speaker that emits midrange and higher range frequencies.
  2) A speaker or speaker enclosure where sound waves are put into a narrow opening (by a speaker cone or driver) and the narrow opening flairs out to a larger opening.
• Impedance
  1) A term for the electrical resistance found in a/c circuits. Affects the ability of a cable to transmit low level (e.g. sound) signals over a long distance. Measured in Ohms. Speakers are rated according to power handling capabilities (Watts, W) and impedance (Ohms).
  2) The total opposition offered by an electric circuit to the flow of an alternating current of a single frequency. It is a combination of resistance and reactance and is measured in ohms. Remember that a speaker's impedance changes with frequency, it is not a constant value.
  3) The opposition to alternating current.
• Loudspeaker - Device for converting the electrical signal from an amplifier back into sound waves, most commonly by vibrating a paper cone. Most speaker systems are composed of a number of sources - each designed to handle a specific range of frequencies. See Tweeters and Woofers, Bi-Amplification.
• Low-Pass Filter -A device that rejects signal above a certain frequency and passes signals that are lower in frequency.
• Mic Preamp- An amplifier to boost the low-level audio signal out of a microphone up to line level.
• Mid-Range Frequencies - The audio frequencies from about 250 Hz through 6000 Hz.
• Mixer
  1) A console, or other device that blends audio signals into composite signals and has a small number of outputs.
  2) A section on a console that does this function.
  3) In Europe, a fader.
  4) An engineer or technician who mixes, especially a live sound mix at a performance.
• Mono- Shortened from Monophonic and meaning that there is only one sound source or the signal was derived from one sound source.
• Mute Switch- A switch which turns off a channel, takes out a track signal from the monitors, or which turns off the entire monitor signal.
• Noise Gate- A piece of sound processing equipment that reduces background noise by muting a sound signal when it falls below a certain level, restoring it when the level increases again. Must be used on vocal microphones with care, because it may cut the signal off, although the vocalist is still singing quietly. Also known as an Expander.
• Noise Filter- A filter used which passes only signals with the intended audio frequencies thus eliminating noise signals at other frequencies.
• Ohm- The unit of opposition to current flow.
• Omni- Directional
  1) In microphones, picking up evenly from all directions.
  2) In speakers, sending out evenly in all directions.
• Open Circuit
  1) Having a break in a conductor or, for another reason, not having a complete path for electrons to flow.
  2) Said of an amplifier, having nothing feeding the input.
• Out Of Phase
  1) Being similar to another signal in amplitude, frequency and wave shape but being offset in time by part of a cycle.
  2) 180 degrees out of phase or having opposite polarity.
• PFL - These buttons allow you to boost or isolate individual channels in the headphones.
• Phantom Power- Some condenser microphones require a power supply in order to operate. If this supply is not from a battery within the microphone body, it is known as a phantom power supply. It is usually 48 Volts DC (can be 9 - 52 volts from most mics), and is supplied either by a separate battery pack, or by the sound desk. The supply is termed "phantom" because it is "invisibly" carried down the same microphone cable as the sound signals.
• Phase Cancellation - The energy of one waveform decreasing the energy of another waveform because of phase relationships at or close to 180 degrees.
• Pitch Control - Facility on some sound playback devices for changing the speed of playback, and thus the pitch or frequency of the sound, to match an existing sound, or to fit a particular timeslot. Some Professional CD players have tempo controls which speed up the playback, and then compensate for the resulting increase in frequency using a pitch change. This results in the ability to match the beat of a CD in a disco situation, without the "Pinky and Perky" effect.
• Polarity
  1) The condition of being positive or negative with respect to some reference point or object.
  2) The direction of flow of electricity either negative to positive or positive to negative. Matching polarity between different amplifiers can greatly reduce hum and the risk of elictrical shock. Most amps come equipped with a "polarity switch".
• Rack  - A cabinet of standard width (19") into which various components can be bolted. Racks are ideal for touring equipment, are neat, and they allow easy access to the rear and front panels.
• Rack Ears - Mounting brackets that can be attached to equipment to make the equipment able to be housed in a standard equipment rack.
• Rack spacing - 1 rack space (1RU) is equivalent to 44.4mm. Most professional amplifiers are 2-3 rack spaces and 19" wide designed for rack mounting.
• RF Interference- The induction (generation of current by magnetic lines of force cutting a conductor) of RF signals (usually broadcast by television and radio stations) into audio lines causing noise, buzz and static. Also see the term TV Interference.
• RMS rating (also known as continuous rating) - Abbreviation for root mean square. When shopping for PA equipment always ask for RMS rating of the speakers. In audio there are three rating systems, RMS, Program, Peak. Program rating is approximately twice the RMS rating, and Peak is almost twice the Program rating ie. if speaker is 100W RMS this can be equivalent to 200W Program or 400W Peak !!!
  
• Shielded Cable - Cable that has a shield around an inner conductor or inner conductors.
• Shock Mount - An elastic mount for the microphone that reduces movement of the microphone when the stand moves (because of floor vibrations from footsteps, etc.).
• Short (Short Circuit) - A direct connection between two points in a circuit that (usually) should not be connected.
• Shotgun Microphone - A microphone with a long line filter (a tube that acoustically cancels sound arriving from the side) to make the microphone pick up much better in one direction than in any other direction.
• Speakon Connector - A type of shielded, locking multipin speaker connector which can safely carry the high currents from an amplifier needed to drive large speaker systems. Available in 4- or 8-way types, and ideal for bi-amplified systems. The cable version of the connector is male, and the panel mount connector is female.
• SPL - An abbreviation of Sound Pressure Level, referring to a pressure of .0002 microbar, considered to be the Threshold of Hearing (lowest level where people begin hearing sound).
• Tweeter
  1) A speaker designed to reproduce the higher frequencies only.
  2) A small driver unit designed to produce only high frequencies.
  3) Part of a speaker system designed to handle the high frequency part of the signal.
• Two Way Speaker - A speaker system with separate speakers to reproduce the lower frequencies (woofer) and to reproduce the higher frequencies (tweeter).
• Unidirectional - A pick-up pattern which is more sensitive to sound arriving from one direction than from any other.
• Wireless Microphone - A microphone with a transmitter inside of its case that transmits a signal to a receiver off of the stage area.
• Woofer
  1) A speaker that is designed to reproduce bass frequencies only.
  2) A drive unit operating in the bass frequencies only. Drive units in two-way systems are not true woofers but are more accurately described as being mid/bass drivers.
  3) Part of a speaker system designed to handle the low frequency parts of the signal.
• XLR - Multipin metallic audio connector. (3 pin for normal sound use, 5 pin for DMX, Colour Scrollers etc.). Sometimes called Cannons after the original manufacturer. See balanced line. The UK standard for wiring the 3 pin connector is as follows: Pin 1 (Screen), Pin 2 (+ve / "hot"), Pin 3 (-ve, "cold"). (Xternal, Live, Return).