Glossary & Terms
Named after André-Marie Ampère, one of the main discoverers of electromagnetism. The ampere, more commonly referred to as amp, (symbol: A) is the SI unit of electric current. 1 amp (A) = 1 Coulumb of charge per second = 6.2414 million electrons flowing past a point in 1 second. To measure current (I) you divide the voltage (V) by the resistance (R).
“I hear” in Latin. More commonly known as anything pertaining to sound.
A circuit that carries information by means of two equal but opposite polarity signals, on two separate conductors. Concerning microphones this is accomplished generally by using a cable with two conductors and a shield. The advantage of a balanced circuit is that it helps to eliminate stray noise or hum coming from AC lines, lights, or other equipment.
The measure of the electrical effect of a capacitor. The SI unit of measure is the farad, named after Michael Faraday.
An electronic circuit component that has the ability to store and electrical charge. The formula used to determine capacitance is C = Q/V where C is capacitance in farads, Q is the quantity of stored electrical charge in coulombs, and V is voltage. Therefore, stored electric charge can be calculated using the formula: Q = CV. The difference in potential or voltage of the capacitor can be calculated using the formula: V = Q/C
Also known as “voice coil.” The coil is comprised of wire of a specified type and size that is wound to a specified electrical inductance and placed (attached) beneath the diaphragm of the microphone capsule. It is the coil moving within the gap of a magnetic pole piece that transforms the audio sound wave into an electrical signal. This “moving coil” technology is the basis for dynamic microphones.
Also known as a capacitor microphone, operating on the principle of varying the capacitance between two plates: one solid, fixed metal plate and one very thin, flexible plastic diaphragm on to which has been deposited an extremely thin metal coating to make it electrically conductive. When the plates are electrically charged any movement of the diaphragm caused by vibrations in the air will cause the capacitance to change, and this change is then translated into a voltage and amplified to produce an audio signal.
Q (electrical charge in coulombs) = C (capacity in farads) x V (voltage).
The measure of how easily electricity flows along a certain path. The SI unit of measure is the siemens, named after the German inventor Werner von Siemens who is credited with making the first moving coil loudspeaker.
Electric current is the flow of electric charge. Audio signals are always Alternating Current (AC), meaning the current reverses direction each time the signal waveform passes zero. In contrast, Direct Current (DC) from a battery always moves in same direction. The SI unit of electric current intensity is the ampere.
Also known as “moving coil” microphone; based on the principle of electromagnetic induction. When sound enters through the windscreen of the microphone, the sound wave moves the diaphragm. When the diaphragm vibrates, the coil moves in the magnetic field, producing a varying current in the coil through electromagnetic induction, thereby converting acoustic energy into an electrical signal.
Dynamic microphones are robust, relatively inexpensive and resistant to moisture making them ideal for live sound reinforcement.
ELECTRET (CONDENSER) MICROPHONE:
Also known as a prepolarized condenser, whereby the back plate of the condenser is permanently charged. This advantage of an electret is that it can operate on lower voltages, can be battery operated, and can be miniaturized for a wide variety of applications.
Named after Alexander Graham Bell, a decibel is literally one tenth of a bel. The bel is defined as the common logarithm of the ration of two powers. It is a relative term and is always tied to a specific reference.
In acoustics, where 0 dB SPL is referred to as the threshold of hearing, here is a chart depicting various levels of sound in dB and corresponding Pascal.
0 dB = 0.00002 Pa Threshold of Hearing
60 dB = 0.02 Pa Business Office
80 dB = .2 Pa Shop Noise
94 dB = 1 Pa Large Truck
100 dB = 2 Pa Jackhammer
120 dB = 20 Pa Airplane Take-Off
140 dB = 200 Pa Jet engine - threshold of Pain
The thin membrane in a microphone capsule that reacts to incoming sound waves.
In condenser microphones, the measurement in dB of the maximum sound pressure a capsule can handle (before distortion) minus the noise floor (self noise) of the circuitry.
Relative to acoustics, acoustic feedback is the condition that occurs when an amplified sound enters a microphone and is re-amplified until a steady howl or whistle is heard.
The measurement in cycles per second at which sound repeats itself (vibrates).
The range of frequencies that a microphone can reproduce, for example 50 Hz 15 kHz. This figure should also be qualified by a +/-dB measurement such as +/-3 dB or +/- 6 dB. This result can vary dramatically depending on other factors such as +/- dB, proximity of the sound source to the capsule, directionality of the sound source to the capsule, sound pressure level of the sound source.
FREQUENCY RESPONSE CURVE:
An X-Y graph depicting how a microphone reacts to different frequencies. The plot is measured in dB on the vertical (X) axis, and hertz on the horizontal (Y) axis. Results can vary dramatically depending on where the measurements are conducted (free field, anechoic chamber, other), the source of the measurement equipment, proximity of the sound source to the capsule, directionality of the sound source to the capsule, sound pressure level of the sound source.
In electronics, gain is amount of increase in the power or amplitude of a signal by an amplifier. Also called voltage gain and current gain. Gain is usually expressed in decibels.
GAIN BEFORE FEEDBACK:
In a sound system, the level of gain that can be achieved in either the main speakers or the monitors before feedback occurs.
Named after Heinrich Hertz, the SI symbol to indicate frequency at which sound vibrates in cycles per second.
Expressed in ohms, The measure of the total resistance to the current flow in an alternating current circuit. Most microphones are classified as being either high impedance (10,000 ohms or greater) or low impedance (50 ohms to 600 ohms).
The measure of the effect of an inductor. The SI unit of measure for inductance is the henry, named after American physicist Joseph Henry.
The electromagnetic process by which a varying magnetic field causes an electric current to exist in a conductor.
An inductor is a passive electrical component that can store energy in a magnetic field created by the electric current passing through it. An inductor’s ability to store magnetic energy is measured by its inductance, in units of henries. Inductors are sometimes called “chokes” as they are used in audio circuits to filter out unwanted high frequency interference.
An “ideal inductor” has inductance, but no resistance or capacitance, and does not dissipate energy.
Like the decibel, loudness is a relative term. A widely used “rule of thumb” for the loudness of a particular sound is that the sound must be increased in intensity by a factor of ten for the sound to be perceived as twice as loud. A common way of stating it is that it takes 10 violins to sound twice as loud as one violin and then 100 violins to sound twice as loud again.
The ability of a microphone to eliminate unwanted noise coming from the PA system or other instruments on stage.
Named after the German physicist Georg Ohm, the ohm is the SI unit of measure for resistance (R).
Applies to electrical circuits; it states that the current through a conductor between two points is directly proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and inversely proportional to the resistance between them.
The mathematical equation that describes this relationship is: I = V/R where I is the current in amperes, V is the potential difference in volts, and R is the resistance (measured in ohms, also equivalent to volts per ampere).
The SI unit of pressure named after French scientist Blaise Pascal, equal to 1 newton per square meter. International standards have established 1 pascal (Pa) as 94dB SPL. This reference point is now accepted for measuring the sensitivity and signal-to-noise ratio of microphones. In sound, 0 dB or the threshold of hearing is equal to 20 micropascal.
The ability to provide the voltage needed to power a condenser microphone through a standard 3 conductor microphone cable. The source is generally either a mixing console (mixer), a microphone preamp, or a standalone phantom power supply.
see POLAR PATTERN RESPONSE
POLAR PATTERN RESPONSE:
A chart or graph depicting a microphone’s sensitivity relative to the angle of an audio signal at a particular frequency. Types of polar patterns include cardioid, hypercardioid, omni-directional, figure-8, supercardioid and hemicardioid. A typical spec sheet will show the polar pattern of a microphone at a specific frequency of 1000 Hz with 94 dB SPL.
An electronic circuit or device designed to attenuate the output sensitivity of a microphone or microphone preamp. This allows more control at the microphone element and can prevent a loud signal from becoming distorted.
Phase refers to the comparison of two or more given wave forms in time.
When two wave forms arrive at a given space at different times, it can cause some frequencies to cancel each other out. The result can be a thin, unnatural, and incomplete sound. In the case of microphones, when two microphones are placed in close proximity to each other (less than 18 inches apart for example), this phenomenon can occur.
The characteristic of electronic conductors which resists or opposes electric current. See OHM. The reciprocal of resistance is conductance.
An electronic circuit component which resists or opposes the flow of an electrical current. A resistor has no appreciable inductance or capacitance.
Also known as “noise floor”. In condenser microphones, the inherent noise in a circuitry measured in decibels.
Typically microphone sensitivity specifications are derived by producing a 1 kHz tone at a constant sound pressure level of 94 dB (1 pascal). This measurement is a miniscule figure expressed in mV/Pa (millivolts per pascal). The same measurement is sometimes shown terms of a negative dB format which depicts an older standard using 74 dB of SPL (0.1 pascal) instead of 94 dB.
International Systems of Units, the world’s most widely used and oldest system of measurement.
An audio signal is a representation of sound waves in a different form. In microphones, the acoustic signal is converted to an electrical voltage and then converted back to an acoustic signal through the loudspeaker.
SIGNAL TO NOISE RATIO:
In condenser microphones, the ratio of the signal produced at 94 dB relative to the noise floor (self-noise) of the microphone’s circuitry, measured in terms of decibels.
SOUND PRESSURE LEVEL (SPL):
The relative measurement of sound in decibels where 0 dB = 20 micropascals = 0.0002 microbars.
A device that converts one form of energy into another. A microphone capsule, for example, converts acoustic energy to electrical. Conversely, a loudspeaker converts electrical energy back into acoustic.
A device consisting of two or more coils of wire wound on a common core of soft iron or other magnetically permeable material. In audio, transformers are utilized to step up audio voltages from a very low impedance device such as a microphone into a more suitable impedance for mixing boards, recording devices, or mic preamps.
A rapid, non-repeating sound such as is created by the attack of a percussive musical instrument.
The ability of a microphone to capture transients.
A circuit that carries information by means of one signal on a single conductor. Unbalanced cable usually consists of a single conductor and a shield as in instrument cables, coaxial cable, patch cords, and high impedance mic cable.
Named in honor of the Lombard physicist Alessandro Volta (17451827) the volt is defined as the potential difference across a conductor when a current of one ampere dissipates one watt of power.