Microphones Flashcards
Backplate
fixed piece of metal in a condenser microphone; the moving diaphragm in the microphone causes fluctuation in capacitance, yielding a variation in electrical voltage, making our analog audio signal
Boundary mic (PZM)
pressure zone mic; consists basically of an omnidirectional microphone capsule mounted on a plate usually of around 6 inches (15 cm) square or 6 inches in diameter such that the capsule points directly at the plate and is around 2 or 3 millimeters away from it
Directional
having a direct sound, coming from one direction
Bi-directional
figure-8; output produced by sound picked up on rear will be 180 degrees out of phase with identical sound picked up by front lobe; response uniform at all frequencies except for slight narrowing above 10k
Omni-directional
ideally picks up sound from all directions; achieved by leaving diaphragm open at front but closed at back, so it becomes a pressure transducer, responding to pressure change in air waves
Capsule
part of microphone responsible for conversion of sound waves into mic signals
Cardioid
heart-shaped unidirectional microphone pickup pattern; product of omni and figure-8
Coloration
change in the timbre of the sound, usually not desired
Hypercardioid
very directional microphone, rejects sound from sides; leans toward a bi-directional
Condenser mircophone
microphone that uses the difference in capacitance between diaphragm and back plate as a means of transduction; requires phantom power
Diaphragm
moving part of microphone that picks up fluctuations in air pressure around it; movements are converted into electrical representation of the sound wave
Large diaphragm
microphone with a bigger moving plate; typically has the best sensitivity at low levels and a peak in the mid range
Small diaphragm
microphone with a smaller moving plate; good for transient detail, usually called a “pencil condenser”
Dynamic microphone
sturdy microphone consisting of a rigid diaphragm (20-30mm diameter), suspended in front of a magnet; a cylindrical former is attached to the diaphragm and a coil of very fine gauge wire is attached to that; this mechanism sits in the gap of a strong permanent magnet, and when sound waves move the diaphragm, the coil moves in the gap, causing an alternating electrical current in the coil, which creates the electrical output
EIN
equivalent input noise; how noise is specified on mixing consoles, stand-alone mic preamps and other signal processing units with mic inputs, or the amount of noise added to the input signal (since the input signal is variable)
Electret
condenser microphone with a permanent electric charge, eliminating the need for phantom power; power for the head amplifier is supplied usually by a small dry-cell battery in the stem of the mic; since the diaphragm needs to be larger in these microphones, they perform more like moving coil mics
EMI
electromagnetic interference; causes noise in the form of hum or buzz
End-address
microphone with a diaphragm placed perpendicular to the body of the microphone
Gold sputtered
microphone with a very thin layer of gold on its surface, making it a better electrical conductor; allows the diaphragm to be very rigid yet agile for better transient response
Grill
outer protective layer of a microphone, protecting the diaphragm from damage and protecting the listener from the voltage of the microphone
Handling noise
specification for quantifying the sensitivity of a microphone to movement and shock, expressed in dBSPL
Inductor
usually a coil in a moving coil microphone; naturally presents lower opposition to low frequencies and a greater opposition to high frequencies
Lavalier microphone
small microphone designed to be worn on a strap around a person’s neck; usually has low rolloff to increase intelligibility of speech
Lobe
portion of a directional microphone between two null points in the polar pattern
Lobar polar pattern
microphone with the highest possible directionality (ex. cardioid, supercardioid)
Localization
where one perceives a sound to be coming from, based on binaural cues
Maximum SPL
how much volume a microphone can take before it starts to distort audibly
Microphone
electroacoustic device that delivers an electric signal
when actuated by a sound; consists of an acoustic system that supplies mechanical (acoustic) energy to a transducer, which converts the energy into electrical energy
Microphone level
low-level audio signal transmission; the nominal values are typically at least 30 dB below line level
Pad
an input attenuator, usually used for attenuating the mic input signal by something like 20 dB, for situations when the mic is in a field of high sound pressure
Microphone preamp
a device that brings a microphone signal from mic-level to line level (close to 1V)
Moving coil
another term for dynamic microphone
Multi-pattern
microphone that has capability of being switched between multiple polar patterns (cardioid, omni, fig-8, etc.)
Mylar
also called polyester; a tough plastic that is used for recording tape and for diaphragms on microphones
Neodymium
rare-earth metal element, atomic number 60, used in making strong magnets, usually used in dynamic microphones
Omnidirectional
ideally picks up sound from all directions; pressure microphone
Polar pattern
plot of the sensitivity of an audio device as a function of
angle around the device
Piezoelectric
mic pickups that exploit the fact that certain materials, such as a quartz crystal, when physically stressed, emit a very controllable electrical current
Pre-polarized
another term for electret microphones
Calibrated microphone
mic with a defined frequency response; calibration is the process of defining this characteristic of a microphone
Dual-diaphragm
mic with two separate diaphragms; usually used to describe condenser designs where a single mic capsule has two separate vibrating diaphragms mounted parallel to one another, with either a single backplate or two backplates (mounted back-to-back)
Medium diaphragm
mic with a diaphragm around 16mm
Presence peak
a boost in the “attack” range of frequencies, around 2kHz-5kHz, in dynamic microphones, making them useful on drums
Presence
range of a microphone around 5k, usually around vocal range
Pressure microphone
any microphone sensitive to changes in the instantaneous air pressure surrounding it; dynamic and condenser mics in their simplest forms are pressure microphones; a perfect pressure microphone would be omnidirectional
Pressure gradient microphone
microphone that is sensitive to the variation of pressure over a distance rather than to the pressure itself
Proximity effect (bass tip-up)
an increased level of low frequencies when placed close to a sound source, produced in directional microphones
Ribbon microphone
consists of a long thin strip of conductive metal foil, pleated to give it rigidity and ‘spring’, lightly tensioned between two end clamps; opposing magnetic poles create
a magnetic field across the ribbon such that when it is excited by sound waves a current is induced into it
Shotgun microphone
also called line microphone, this is a highly directional microphone that has an acoustical transmission line in front of its active element; fairly long tube (12 to 24 inches long) protruding from its front with a series of holes along
the side; sound coming from directly in front of the unit will enter the holes in succession, and each wave coming into a hole will add in phase to produce the composite sound reaching the transducer; sounds coming from the rear reach the holes in reverse order, and the phasing is such that they cancel each other out on the way to the transducer, resulting in very little or no output; the longer the tube, the more directional the microphone will be
Sibilance
the whistling sound of s, sh, ch, and t noises from vocal signals
Side address
a microphone with the capsule facing to the side of the microphone, such as an AKG C414
Super cardioid
modification of the cardioid microphone to reduce sensitivity to sounds coming from the sides; like a cross between a cardioid and a figure 8 with a large rear lobe; advantage is that it reduces the apparent reverberation by about 1.3 decibels if placed at the same location as a true cardioid
Wide cardioid
microphone with a polar pattern between a cardioid and an omnidirectional microphone
Rolloff
a high- or low-pass filter used on a microphone to reduce low or high frequencies
Self-noise
noise power generated by a microphone in the absence of any input signal
Sensitivity
indication of the electrical output which will be obtained for a given acoustical sound pressure level (SPL)
Transducer
any element that converts energy from one form into another, e.g., from sound pressure to mechanical energy (vibrating membrane/diaphragm) to electrical energy (alternating voltage)
Tube microphone
microphones that use vacuum tubes instead of transistors for power, come with their own proprietary power supply, and do not need to be fed with the console’s phantom power
Velocity microphone
type of microphone that has a polar pattern shaped like a figure 8; for example, in a ribbon microphone the motion of the ribbon is “mass controlled,” or is proportional to the velocity of the air particles
Voice coil
a coil immersed in a strong magnetic field emanating from a permanent magnet; current in the coil causes another magnetic field to be developed, and the two fields interact to cause the force on the coil; current in one direction moves the coil one way, and current in the other direction
moves it the other way, moving the coil in a similar fashion to a waveform
