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3-to-1 Rule When using multiple microphones, the distance between microphones should be at least 3 times the distance from each microphone to its intended sound source.
Absorption The dissipation of sound energy by losses due to sound absorbent materials.
Active Circuitry Electrical circuitry which requires power to operate, such as transistors and vacuum tubes.
Ambience Room acoustics or natural reverberation.
Amplitude The strength or level of sound pressure or voltage.
Audio Chain The series of interconnected audio equipment used for recording or PA.
Backplate The solid conductive disk that forms the fixed half of a condenser element.
Balanced A circuit that carries information by means of two equal but opposite polarity signals, on two conductors.
Bidirectional Microphone A microphone that picks up equally from two opposite directions. The angle of best rejection is 90 degrees from the front (or rear) of the microphone, that is, directly at the sides.
Boundary/Surface Microphone A microphone designed to be mounted on an acoustically reflective surface.
Cardioid Microphone A unidirectional microphone with moderately wide front pickup (131 degrees). Angle of best rejection is 180 degrees from the front of the microphone, that is, directly at the rear.
Cartridge (Transducer) The element in a microphone that converts acoustical energy (sound) into electrical energy (the signal).
Clipping Level The maximum electrical output signal level (dBV or dBu) that the microphone can produce before the output becomes distorted.
Close Pickup Microphone placement within 2 feet of a sound source.
Comb Filtering An interference effect in which the frequency response exhibits regular deep notches.
Condenser Microphone A microphone that generates an electrical signal when sound waves vary the spacing between two charged surfaces: the diaphragm and the backplate.
Critical Distance In acoustics, the distance from a sound source in a room at which the direct sound level is equal to the reverberant sound level.
Current Charge flowing in an electrical circuit. Analogous to the amount of a fluid flowing in a pipe.
Decibel (dB) A number used to express relative output sensitivity. It is a logarithmic ratio.
Diaphragm The thin membrane in a microphone which moves in response to sound waves.
Diffraction The bending of sound waves around an object which is physically smaller than the wavelength of the sound.
Direct Sound Sound which travels by a straight path from a sound source to a microphone or listener.
Distance Factor The equivalent operating distance of a directional microphone compared to an omni directional microphone to achieve the same ratio of direct to reverberant sound.
Distant Pickup Microphone placement farther than 2 feet from the sound source.
Dynamic Microphone A microphone that generates an electrical signal when sound waves cause a conductor to vibrate in a magnetic field. In a moving-coil microphone, the conductor is a coil of wire attached to the diaphragm.
Dynamic Range The range of amplitude of a sound source. Also, the range of sound level that a microphone can successfully pick up.
Echo Reflection of sound that is delayed long enough (more than about 50 msec.) to be heard as a distinct repetition of the original sound.
Electret A material (such as Teflon) that can retain a permanent electric charge.
EQ Equalisation or tone control to shape frequency response in some desired way.
Feedback In a PA system consisting of a microphone, amplifier, and loudspeaker, feedback is the ringing or howling sound caused by amplified sound from the loudspeaker entering the microphone and being re-amplified.
Flat Response A frequency response that is uniform and equal at all frequencies.
Frequency The rate of repetition of a cyclic phenomenon such as a sound wave.
Frequency Response A graph showing how a micro-phone responds to various sound frequencies. It is a plot of electrical output (in decibels) vs. frequency (in Hertz).
Frequency Response Tailoring Switch A switch on a microphone that affects the tone quality reproduced by the microphone by means of an equalization circuit. (Similar to a bass or treble control on a hi-fi receiver.)
Fundamental The lowest frequency component of a complex waveform such as musical note. It establishes the basic pitch of the note.
Gain Amplification of sound level or voltage.
Gain-Before-Feedback The amount of gain that can be achieved in a sound system before feedback or ringing occurs.
Gobos Movable panels used to reduce reflected sound in the recording environment.
Harmonic Frequency components above the funda-mental of a complex waveform. They are generally mul-tiples of the fundamental which establish the timbre or tone of the note.
Hypercardioid A unidirectional microphone with tighter front pickup (105 degrees) than a supercardioid, but with more rear pickup. Angle of best rejection is about 110 degrees from the front of the microphone.
Impedance In an electrical circuit, opposition to the flow of alternating current, measured in ohms. A high- impedance microphone has an impedance of 10,000 ohms or more. A low-impedance microphone has an impedance of 50 to 600 ohms.
Interference Destructive combining of sound waves or electrical signals due to phase differences.
Inverse Square Law States that direct sound levels increase (or decrease) by an amount proportional to the square of the change in distance.
Isolation Freedom from leakage; the ability to reject unwanted sounds.
Leakage Pickup of an instrument by a microphone intended to pick up another instrument. Creative leak-age is artistically favourable leakage that adds a "loose" or "live" feel to a recording.
Maximum Sound Pressure Level The maximum acoustic input signal level (dB SPL) that the microphone can accept before clipping occurs.
NAG Needed Acoustic Gain is the amount of gain that a sound system must provide for a distant listener to hear as if he or she was close to the unamplified sound source.
Noise Unwanted electrical or acoustic energy.
Noise Cancelling A microphone that rejects ambient or distant sound. NOM - Number of open microphones in a sound system. Decreases gain-before-feedback by 3dB every time NOM doubles.
Omnidirectional Microphone A microphone that picks up sound equally well from all directions.
Output Noise (Self-Noise) The amount of residual noise (dB SPL) generated by the electronics of a con-denser microphone.
Overload Exceeding the signal level capability of a microphone or electrical circuit.
PAG Potential Acoustic Gain is the calculated gain that a sound system can achieve at or just below the point of feedback.
Phantom Power A method of providing power to the electronics of a condenser microphone through the microphone cable.
Phase The "time" relationship between cycles of differ-ent waves.
Pickup Angle/Coverage Angle effective arc of coverage of a microphone, usually taken to be within the 3dB down points in its directional response.
Pitch The fundamental or basic frequency of a musical note.
Polar Pattern (Directional Pattern, Polar Response) A graph showing how the sensitivity of a microphone varies with the angle of the sound source, at a particular frequency. Examples of polar patterns are unidirectional and omnidirectional.
Polarization The charge or voltage on a condenser microphone element.
Pop A thump of explosive breath sound produced when a puff of air from the mouth strikes the micro-phone diaphragm. Occurs most often with "p", "t", and "b" sounds.
Pop Filter An acoustically transparent shield around a microphone cartridge that reduces popping sounds. Often a ball-shaped grille, foam cover or fabric barrier.
Presence Peak An increase in microphone output in the "presence" frequency range of 2,000 Hz to 10,000 Hz. A presence peak increases clarity, articulation, apparent closeness, and "punch."
Proximity Effect The increase in bass occurring with most unidirectional microphones when they are placed close to an instrument or vocalist (within 1 foot). Does not occur with omnidirectional microphones.
Rear Lobe A region of pickup at the rear of a super-cardioid or hypercardioid microphone polar pattern. A bidirectional microphone has a rear lobe equal to its front pickup.
Reflection The bouncing of sound waves back from an object or surface which is physically larger than the wavelength of the sound.
Refraction The bending of sound waves by a change in the density of the transmission medium, such as tem-perature gradients in air due to wind.
Resistance The opposition to the flow of current in an electrical circuit. It is analogous to the friction of fluid flowing in a pipe.
Reverberation The reflection of a sound a sufficient number of times that it becomes non-directional and persists for some time after the source has stopped. The amount of reverberation depends on the relative amount of sound reflection and absorption in the room.
Rolloff A gradual decrease in response below or above some specified frequency.
Sensitivity A rating given in dBV to express how "hot" the microphone is by exposing the microphone to a specified sound field level (typically either 94 dB SPL or 74 dB SPL,). This specification can be confusing because manufacturers designate the sound level different ways. Here is an easy reference guide: 94 dB SPL = 1 Pascal = 10 microbars. To compare a microphone that has been measured at 74 dB SPL with one that has been measured at 94 dB SPL, simply add 20 to the dBV rating.
Shaped Response A frequency response that exhibits significant variation from flat within its range. It is usu-ally designed to enhance the sound for a particular application.
Signal to Noise Ratio The amount of signal (dBV) above the noise floor when a specified sound pressure level is applied to the microphone (usually 94 dB SPL).
Sound Chain The series of interconnected audio equip-ment used for recording or PA.
Sound Reinforcement Amplification of live sound sources.
Speed of Sound The speed of sound waves, about 1130 feet per second in air.
SPL Sound Pressure Level is the loudness of sound relative to a reference level of 0.0002 microbars.
Standing Wave A stationary sound wave that is rein-forced by reflection between two parallel surfaces that are spaced a wavelength apart.
Supercardioid Microphone A unidirectional micro-phone with tighter front pickup angle (115 degrees) than a cardioid, but with some rear pickup. Angle of best rejection is 126 degrees from the front of the micro-phone, that is, 54 degrees from the rear.
Timbre The characteristic tone of a voice or instrument; a function of harmonics.
Transducer A device that converts one form of energy to another. A microphone transducer (cartridge) con-verts acoustical energy (sound) into electrical energy (the audio signal).
Transient Response The ability of a device to respond to a rapidly changing input.
Unbalanced A circuit that carries information by means of one signal on a single conductor.
Unidirectional Microphone A microphone that is most sensitive to sound coming from a single direction-in front of the microphone. Cardioid, supercardioid, and hypercardioid microphones are examples of unidirec-tional microphones.
Voice Coil Small coil of wire attached to the diaphragm of a dynamic microphone.
Voltage The potential difference in an electric circuit. Analogous to the pressure on fluid flowing in a pipe.
Wavelength The physical distance between the start and end of one cycle of a soundwave.