Microphone Terminology: I (With Definitions)

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Impedance:

What is impedance and why is it important to microphones? Electrical impedance is the measure of the opposition of current in a circuit when a voltage is applied. It is resistance in AC circuits (also measured in ohms). Mic signals are AC and impedance is a factor when sending a mic signal from a microphone (source impedance) to a preamp (load impedance).

For more information on microphone impedance, check out my articles Microphone Impedance: What Is It And Why Is It Important? and What Is A Good Microphone Output Impedance Rating?


Impedance Bridging:

What is impedance bridging and how does it apply to microphones? Impedance bridging is when the load impedance (input of a mic preamp) is much higher than the source impedance (output of the mic). A load 10 times that of the source is the general rule and maximizes the voltage transfer across the load, allowing a clean transfer of the mic signal.


Impedance Matching:

What is impedance matching and how does it apply to microphones? In electronics, impedance matching is the designing a source’s output impedance and a load’s input impedance for maximal power transfer from source to load. With mics (source) and preamps (load), we’re not so concerned with matching but instead with impedance bridging (for maximal voltage transfer).


In-And-Out Kick Drum Technique:

What is the in-and-out miking technique? In-and-out is a kick drum miking technique that places one microphone inside the kick drum (to capture the beater sound) and another outside the kick drum (to capture the thump sound). The two signals are then mixed together to create a cohesive kick drum sound.


In-Line:

What does in-line mean in reference to microphones? An in-line device is a device inserted between two other devices. With microphones, common in-line devices include filters or amplifiers that are connected “in-line” between the mic and the mic preamp.


In-Phase:

What does in-phase mean in relation to microphones? In-phase means that the phase of two or more audio signals (mic signals) or sound waves align together, causing constructive interference. The greater the alignment of time-based amplitude, the more in-phase two waves are.


Inline Microphone:

What is an inline microphone? An inline microphone is a mic within a headset unit that simultaneously sends and receives audio. Inline microphones are common in broadcasting and telecommunications.

See: Microphone.


INA-3:

What is the INA-3 miking technique? The INA-3 is the 3-mic front array of the INA-5 surround sound miking technique. It has a front cardioid mic positioned 7″ in front of the left and right cardioid mics, which point left and right, respectively, and are spaced 14″ from one another.

INA-3 Drawing

INA-5:

Also known as the ideal cardioid arrangement.

What is the INA-5 miking technique? The INA-5 is a 5-cardioid-mic surround sound miking technique. The center (C), left (L), and right (R) mics point outward and are positioned 7″ from a centre point to the front, left, and right, respectively. The LS and RS mics are positioned 24″ behind the L/R and are 24″ apart, pointing outward.

INA-5

Inductance:

What does inductance mean in relation to microphones? Inductance is present in dynamic microphone capsules. It is the tendency of an electrical conductor (voice coil or ribbon) to oppose a change in the electric current through it. Inductance plays a role in the electromagnetic induction process required for proper transduction in dynamic mics.


Induction:

What is induction and why is it important to microphones? Electrical induction is the process by which an electrical conductor becomes electrified. Microphones are transducers that convert acoustic energy to electrical energy and require induction to do so. Dynamic mic work by electromagnetic induction while condenser mics work by electrostatic induction.


Inductor:

What is an inductor and what is its role in microphone function? An inductor is a passive two-terminal electrical component that works on the principle of electromagnetic induction. In a dynamic mic, the inductor is either the voice coil or the ribbon. When these elements move within their magnetic fields, a voltage (the mic signal) is “induced” across them.


Initial Reflection:

What is an initial reflection and how do initial reflections affect microphones? An initial reflection is the first reflection a sound wave has after emanating from the sound source and adds a sense of space to mic signal. It’s the first echo of the early reflections portion of reverberation and has only bounced off a single surface.


Instrument Level:

What is insturment level? Instrument level is a broad term for the signal level level from electric pickups on/inside instruments. Instrument levels range widely from a few millivolts AC to a few volts AC. DI boxes are often put in-line to convert instrument level signals to mic or line level signals.

To learn more about instrument level and microphones, check out my article Do Microphones Output Mic, Line, Or Instrument Level Signals?


Interference Tube:

What is a microphone interference tube? An interference tube is an extended acoustic labyrinth that yields a lobar polar pattern in shotgun microphones. An interference tube allows on-axis sounds to reach the mic diaphragm unimpeded while causing off-axis sounds to cancel out as they reach the diaphragm with varying amounts of phase shift.

To learn more about microphone interference tubes, check out my article Why Are Some Microphones Long & What Are Interference Tubes?


Internal Microphone:

What is an internal microphone? An internal microphone refers to a mic on the inside of an instrument that acts as an electric pickup. Internal mics are most often of the electret or piezoelectric varieties and provide quick and consistent miking of instruments in recording and sound reinforcement situations.

See: Microphone.


International System Of Units (SI):

What are SI units and why are they important to microphones? The International System of Units (SI units) are the modern form of the metric system and the most common measurement system in the world. SI units help us to make quantitative measurements in microphones to better understand what microphones are and how and why mics perform the way they do.

The base SI units are as follows:

Name:Symbol:Quantity:
AmpereAElectrical Current
KelvinKTemperature
SecondsTime
MetermDistance
KilogramkgMass
CandelacdLuminous Intensity
MolemolAmount of Substance

Other SI units we’re interested in when studying microphones are:

Name:Symbol:Quantity:
OhmsΩElectrical Resistance/Impedance
VoltsVVoltage/Electromagnetic Force (emf)
FaradFCapacitance
SiemensSConductance/Admittance/Susceptance
CoulombsCElectrical Charge
HenryHInductance
HertzHzFrequency
PascalPaPressure
WattWPower
WeberWbMagnetic Flux

Interruptible Foldback:

Also known as interruptible feedback or interrupt for broadcast.

What is interruptible foldback and how does it apply to microphones? Interruptible foldback (IFB) is a one-way communication system from a producer to an on-air talent in television and broadcast. IFB is an intercom circuit with a mix-minus program feed sent to an earpiece worn by the talent that can be interrupted at any time by the producer/director’s microphone.


Inverse-Square Law:

What is the inverse-square law and why is it important to microphones? The inverse-square law states that the intensity of a sound wave (in the air) is inversely proportional to the square of the distance from the sound source. Thus, sound intensity decreases 50% or ~6 dB for every doubling of distance from the sound source. This is worth knowing for better mic placement.


IRT Cross:

What is the IRT cross miking technique? The IRT cross is a surround sound miking technique consisting of 4 cardioid mics positioned in a 20-25 cm (8-10 in) square formation and pointing outward toward their respective corners. The IRT cross resembles back-to-back near-coincident stereo pairs.

IRT Cross

Iso-Booth:

What is an iso-booth and why are iso-booths important for microphones? An iso-booth (isolation booth) is an acoustic space (typically with soundproofing) that isolates one sound source from the others in recording situations. Iso-booths are common for vocals, drumkits, and guitar amps and help tremendously in capturing the cleanest signal possible with microphones.


Isolation Cabinet:

What is an isolation cabinet and why are isolation cabinets important for microphones? An isolation cabinet is like a tiny iso-booth. Isolation cabinets are small acoustic spaces that typically host microphones and guitar cabinets. Iso-cabs greatly reduce bleed when compared to recording multiple instruments in the same room.


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