Prism Sound Orpheus - Audio Media

Microphone BasicsThe foundation of good microphone practice is technical knowledge. Blažo Guzinaprovides a run-down of the basics for anybody just getting to grips with the wibbly bits...Microphones have different overall physicaland electrical characteristics and areclassifiable into three main groups, basedon the physical principle of converting soundinto an electrical signal: electrodynamic coil,electrodynamic ribbon, and electrostatic (orcondenser) microphones.Dynamic MicrophoneThe electrodynamic moving-coil microphonehas a coil of finely wrapped wire preciselysuspended between the poles of a magnetand attached to a diaphragm. Soundwavesdrive the diaphragm, which vibrates ina high-level magnetic field. In the coil,this movement induces a voltage, whichcorresponds to the sound pressure.Dynamic microphones are very ruggedand handle high sound pressures withoutoverloading. They are reliable and virtuallynever distort the sound signal. They areinsensitive to extreme heat, cold, and highair humidity. Dynamic microphones canusually withstand extreme environmentalconditions such as temperatures from-25°C to +70°C.Ribbon MicrophoneThe electrodynamic ribbon mic has a thinmetal foil in the form of a corrugated ribbonsuspended in a magnetic field. Soundpressure variations displace the diaphragm,in which an electrical current is induceddepending on the amplitude and frequencyof sound. Due to the short length of theribbon compared to the moving coil, itsoutput electrical impedance is less than 1 Ω.This resistance is too low to directly connectto the microphone input of a mixing deskor recorder, so a step-up transformer isneeded to increase the impedance up to the150Ω to 600Ω range.Due to constructional improvements,modern ribbon mics are suitable for outdoorand handheld use. They are prized for theirwarm, smooth, yet delicate sound quality.Condenser MicrophoneThe electrostatic (condenser) microphoneuses a transducer element consisting of avibrating diaphragm (very thin foil) and afixed metal plate (back electrode).These two electrodes make up acondenser (capacitor) charged by anexternally applied voltage (polarizationvoltage) or carrying its own permanentelectrical charge, as with an electretmicrophone.When soundwaves vibrate thediaphragm, the capacitance of thecondenser changes simultaneously, thusproducing an output voltage that varies withthe intensity and frequency of the sound.Condenser microphones usually have aflat frequency response, high sensitivity andgood ability to follow sudden, percussivesound events immediately. This is describedas good transient response.Condenser microphones require animpedance converter in the form of apreamplifier to match the very high outputimpedance to low impedance microphoneinputs. This amplifier fits within the bodyof the microphone in order to prevent hum,noise pickup and the losses of the signallevel due to the length of the circuit from thediaphragm to the amplifier.Phantom PowerCondenser microphones need a DCsupply voltage. Except for battery operatedmicrophones, the voltage usually comesthrough the microphone cable. The positive(+) side of a DC voltage connects to bothsignal wires of a balanced line and thenegative (ñ) side to the cable screen.An exception is the electret condensermicrophone. This type of microphone hasthe polarizing charge stored permanentlywithin the diaphragm or on the backplate.No external power is required to charge thediaphragm.Polar PatternsApart from the basic differences in thephysical principle of operation, the mainfactor that influences the choice of amicrophone is its polar pattern.Polar pattern, also known also aspolar response, is a chart that graphicallyrepresents microphone sensitivity withrespect to the direction of soundwavesarriving at its membrane.A chart is usually plotted in the form ofa 360° polar diagram, with the on-axis 0°direction clearly marked. It is possible toclassify microphones into two main groups,based on their directional characteristics:non-directional and directionalmicrophones.In principle, a non-directionalmicrophone is a pressure-operatedelectroacoustic transducer. Its response toacoustic sound pressure is omnidirectional,meaning that the diaphragm reacts equallyto all soundwaves arriving at its surface,regardless of their direction.A typical example of a directionalmicrophone is a pressure-gradienttransducer. This type has a bidirectional(or figure-of-eight) polar diagram. Thismeans the microphone reacts to differencesin pressure between the two sides of adiaphragm.Ribbon microphones are the mostcommon type with a bidirectional polarresponse. A metal ribbon diaphragm isequally sensitive to soundwaves arrivingfrom front and rear axes.All other known directional patternsare obtainable as a result of a combinationof the aforementioned two main polarpattern types. The number of variations ispractically unlimited.When the outputs of an omnidirectional(pressure) and bidirectional (pressuregradient)pickup pattern are combined, thebest known resulting polar responses thatare obtainable are cardioid, supercardioid,and hypercardioid. Their common name isunidirectional microphones.A unidirectional microphone is mostsensitive to soundwaves arriving from onedirection, in front of the microphone, butsoftens sounds from the sides or rear.The cardioid microphone is sensitive tosounds from a broad angle in front of themicrophone. Generally, it is about 6dB lesssensitive at the sides, at 90° and 270°, and15 to 25dB less sensitive to the rear.40 microphone basics