Microphone Theory Transducer types Pressure / Pressure Gradient Understanding specsLecture originally compiled by Brani Gerun (SAE Institute Sydney). Content developed and arranged by Craig Herbert (SAE Institute Sydney) and Dr Eve Klein (University of New England, Armidale). Used and adapted with permission.

Transducer: definitionTransduction - DefinitionAcoustical energyMicrophoneElectrical energyBandwidthResponse to low levels / high levelsResponse to transientsOutput levelColouration

Brief HistoryHistory1927: Sir Charles Wheatstone uses the word to describe a mechanical stethoscopeMicro (small) Phone (voice)1683: Microphone appears in the dictionary to describe hearing aids1867: Bell laboratories the liquid transmitterDiaphragm at base of cylinderMetal pin connects diaphragm to cup belowCup contains an acid solutionResitance varies between the pin and cup, as the pin moves up / down with the diaphragmAny electrical voltage submitted to this resistance will vary accordingly

Brief HistoryHistory1878: David Hughes invents the carbon microphoneCarbon granules are encased behind the diaphragmVoltage passes through themAs they vibrate, the global resistance varies Which in turn varies the voltageAny electrical voltage submitted to this resistance will vary accordingly

Brief HistoryHistoryWestern Electric 394Late 1910s: First condenser microphone developed by Wente at Bell Labs.RCA 4AA

Brief HistoryHistory1928: Georg Neumann launches the CMV3

The worlds first ever mass produced condenser microphone.9cm diam40cm high

Condenser: large / small diaphragmTransduction principle Condenser(source: Neumann.com 2004 [online]Front addressSide address(source: Neumann.com 2004 [online]Higher self noiseLower self noiseLower sensitivityHigher sensitivityHigher SPL handling capabilityLower SPL handling capabilityHigher Frequency rangeLower Frequency rangeHigher Dynamic rangeLower Dynamic rangeSmaller / stiffer membraneLarger / looser membraneSmall influence on sound fieldLarge influence on sound field

Frequency range off axis responseFrequency range off axis responseAKG C414(source: akg.com 2004 [online]

Frequency range off axis responseFrequency range off axis responseAKG C414(source: akg.com 2004 [online]

Frequency range off axis responseFrequency range off axis responseAKG C414(source: akg.com 2004 [online]

Frequency range off axis responseFrequency range off axis responseAKG C414(source: akg.com 2004 [online]

Rode NTG2

Shotgun microphone

Shotgun pickup pattern

Other mic specs Max SPLOther mic specs max SPL(source: audiotechnica.com 2004 [online]

Boundary microphones - PZMsPZMsDouble pressure

Parabolic microphoneParabolic microphone

Dynamic : moving coilTransduction principle Dynamic(source: kiopo.com 2004 [online](source: wikimedia.org 2004 [online]Electromagnetic inductionNo need for external powerHigh SPLLow output level (1 to 5 mV / Pa)Bad High Frequency response (16 to 17k)RobustBad Transient responseCheapHigh self noise Withstands relative humidity

Dynamic : RibbonTransduction principle Dynamic(source: cybergeo.com 2004 [online]No need for external powerGood High Frequency response ( 18k)Cant handle high SPLVery fragileGood Transient responseSensitive to humidity(source: wikimedia.org 2004 [online]Low output level ( 1 mV / Pa)Electromagnetic induction

Condenser(source: kiopo.com 2004 [online]Needs some form of powerGood High Frequency response (> 18k)Cant handle high SPLFragileGood Transient responseSensitive to humidityHigh output level (15 - 40mV / Pa)High handling noise(source: Neumann.com 2004 [online]Low self noiseSwitchable polar patternsPower SupplyAKG SE-300 B WITH 10 dB pad !! Variable capacitance

3:1 Rule of Mic Placement.When using two microphones to record a source, normally you will get the best results by placing the second mic three times the distance from the first mic that the first mic is from the source. An example: If the first mic is 1 foot from a source, the second mic should be placed 3 feet from the second mic. Using the 3:1 Rule will minimize phase problems created by the time delay between mics.This rule originated when engineers were micing multiple sources in the same vicinity. The same principle applies. If you are recording two different sources of sound, their respective microphones should be at least three times further apart than they are close to their respective sources. Keep in mind that rules are meant to be broken; you may prefer the sound created by ignoring the 3:1 Rule experiment and let your ears be your guide! (Source: http://www.sweetwater.com/insync/31-rule-of-microphone-placement/ Accessed: 3/2//13)

The 3 to 1 ruleTo avoid phase cancellation issuesDD

How Do Microphones WorkBasically all microphones have a diaphragm that vibrates when hit by sound waves. The vibration of the diaphragm is translated into an electrical signal that corresponds to the variation in the sound wave. That is why it is necessary to clean the diaphragms in your mikes on a regular basis as a build-up of dust, spit etc. will impede the vibration of the diaphragm and thus distort or colour the sound

The Dynamic MicrophoneIn a Dynamic microphone, also referred to as a moving coil microphone, the capsule is rather like a speaker in reverse. The cone is the diaphragm and it has a coil attached that is suspended in a magnetic field. When the diaphragm vibrates the coil creates an electrical current. This is an entirely passive circuit as the magnet can be a permanent one so no external power is required.

Dynamic MicrophonesTypically have a cardioid pickup pattern

The Condenser MicrophoneOn the other hand the Condensor microphone has two plates, one fixed and one moveable, that are each charged with a polarising voltage that creates a capacitor. The vibration of the plates creates a change in the distance between them which changes the capacitance and thus the sound wave is converted into an electrical current. In this case external power is required as there is an electrical circuit required to produce the polarising voltage. Because the current obtained is so small an amplifier circuit is also included.

The Condenser MicrophoneThus when using Condenser mikes an external power supply is required. This can be either a stand alone power supply for one or more mikes or it can be fed to the microphone from the console down the microphone cable and is commonly referred to as Phantom Power and is now standard at 48 Volts.All new consoles have that facility and usually consists of an on and off switch on the rear of the console or is an on/off option on each module.Don't worry about sending phantom power to a dynamic microphone, it won't blow it up as the circuit is inactive in a dynamic microphones.Condenser Microphones can have variable pickup patterns.

The ElectretAn Electret Microphone is also a Condenser microphone except that the charge on the plates is created by a permanent electrostatic charge.Therefore an external polarising voltage is not required but once again the voltage obtained is small so an amplifier is usually built in and powered by an internal battery. Electrets are often thought of as the cheap cousin to the condenser mike because the material required to hold the charge on the diaphragm is heavier but good electrets can sound fine.Have a fixed pickup pattern.

The RibbonThe Ribbon Microphone consists of a thin metal ribbon that is placed in a magnetic field. The vibration of the ribbon within the magnetic field induces a current that is proportional to the variation in the sound wave. This is also a passive circuit as the magnetic field can be created by a permanent magnet.

The RibbonThe Ribbon Microphone consists of a thin metal ribbon that is placed in a magnetic field. The vibration of the ribbon within the magnetic field induces a current that is proportional to the variation in the sound wave. This is also a passive circuit as the magnetic field can be created by a permanent magnet.

Ribbon DirectionalityRibbon microphones are typically bidirectional, meaning they pick up sounds equally well from either side of the microphone.

Microphone Techniques for the guitarMicrophone positioning demonstrations for the guitarAdditional examples from Neumann Audio Contest CD-ROM (2003)

L-R check

The following slides feature performances by Raphal Nol

Sound categoriesSound categoriesFour types of sounds:

Acoustic guitar

Electric guitar clean sound

Electric guitar - crunch sound

Electric guitar distortion sound:-)

Acoustic Guitar The Acoustic GuitarTerminology:Sound HoleSound BoxBridgeNeckSound Board

Recording the Acoustic GuitarAcoustic Guitar - MicrophonesTypical microphones:

Any good quality condenser

Small membrane,Large membrane,

Recording the Acoustic GuitarAcoustic Guitar Recording techniquesTowards the Bridge Towards the neckIn front of the holeThe fact that its not the same mic on all 3 takes definitely has an impact on the final sound, but all 3 being high quality microphones, that would only factor in at about 5%

Recording the Acoustic GuitarAcoustic Guitar Recording techniquesIn front of strings, angled towards holeAbove the shoulderGain not compensatedLiveTowards the Bridge Towards the neckIn front of the hole

Recording the Acoustic GuitarAcoustic Guitar Recording techniques: DIYou can also DI a guitar that is equipped with a piezzo pickupMic recordings for comparisonYou can always combine DI and Mic source

Recording the Acoustic GuitarAcoustic Guitar Recording techniques: XY PairIn front of strings, angled towards holeIn front of the holeStereo recording with a 90 XY PairreminderreminderSame recording in MONO

Acoustic Guitar Room AcousticsAcoustic Guitar Room AcousticsInfluence of the room on distant recordingsAbout 50cmAbout 1mAbout 2mLive

Electric GuitarElectric Guitar Components that make up the soundComponents responsible for final sound: The body (solid / hollow / semi-hollow)Pickups: simple or double (humbucking) / Tone controls

Pre-amp and Amp

Speaker(s)The artist would have made these 4 choices according to his own criteriaThe engineers job is to record this sound as truthfully as possible.

Electric Guitar - BodyElectric GuitarSemi-hollowSolid body

Electric Guitar - pickupsElectric GuitarpickupsSelectorswitchVolumeTone controlVolume

Electric Guitar Amp headElectric Guitar - Heads

3 different guitars playing through the same comboElectric Guitar CabinetElectric Guitar Head-Cabinet stack / ComboThe same guitar playing through 3 different stacks / combosROLAND Jazz ChorusMARSHALL Stack JIM KELLEY ReverbES 335 Jazz GuitarPaul Reed SmithStratocaster 66

Electric Guitar - combosElectric Guitar - CombosOther tone variationsFender vs Mesa BoogieFender Strat vs Gibson ES

Recording the Electric GuitarElectric Guitar MicrophonesTypical Microphones:Shure SM57AKG C414AKG C451Beyer M88Sennheiser e609Neumann M149etc...

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesPositioning in front of the speaker: Sliding an SM57 from centre to edge

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesPositioning in front of the speaker: Sliding an SM57 from centre to edge

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesLocate the centre of the speaker dome. Flash light can help

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesTwo types of amplification setup:Integrated: comboHead + Cabinet(a.k.a. stack)Yeah, I know, a Marshall 4x12 with a Peavey head.Thats all we had in the house for the picture!A combo may have several speakers!

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesHow to record a cabinet with several speakers:Mic on just one speakerAlways ask the guitarist if he/she is aware of one or several dodgy speaker cones on his cabinet, so you dont point your mic on that one!

Electric Guitar - clean sound - C414Electric Guitar Recording techniques - / clean sound C414CentreMid-wayEdgeMid-way, angled towards domeWith no gain make-up

Electric Guitar - clean sound SM57Electric Guitar Recording techniques - / clean sound SM57CentreMid-wayEdgeMid-way, angled towards domeC414With no gain make-upC414C414C414

Electric Guitar Front/BackElectric Guitar Recording techniques - / front-backWhy not take advantage of the open back of some designs?Phase on the rear mic can be inverted or not, to suit your taste

Electric Guitar - clean sound - DIElectric Guitar Recording techniques - DIWhy go through Amps and speakers if youre after a clean sound???High Z inputOr any DI box

Electric Guitar - clean sound DI + MicElectric Guitar Recording techniques - DIYou can of course combine mic AND DITo console Mic InputTo consoleMic Input

Electric Guitar - DIElectric Guitar Recording techniques - DIWhy go through Amps and speakers if youre after a clean (or distorted) sound???

Electric Guitar - DistortionElectric Guitar Recording techniques - DistortionC414 dead centreSM57 dead centre

Electric Guitar Recording TechniquesPositioning in front of the speaker: Sliding an SM57 from centre to edgeElectric Guitar Recording Techniques

Electric Guitar Recording TechniquesElectric Guitar Recording TechniquesPositioning in front of the speaker: Sliding an SM57 from centre to edge

Electric Guitar Distortion - SM57Electric Guitar Recording Techniques Distortion - SM57CentreMid-wayEdgeMid-way, angled towards domeWith no gain make-up

Electric Guitar Distortion SM57Electric Guitar Recording Techniques Distortion - SM57Sliding the second SM 57 backLive

Electric Guitar Distortion SM57Electric Guitar Recording Techniques Distortion - SM57Sliding the second SM 57 backLive

Electric Guitar Distortion Front/RearElectric Guitar Recording Techniques Distortion Front/RearBack mic phase normalMic in front and rearBack mic phase inverted

Electric Bass Guitar - microphonesElectric Bass Guitar - microphonesTypical Microphones:

Any mic made for high levels and low frequencies:

Sennheiser MD 421AKG D112Beyer M88Sennheiser e602ElectroVoice RE20Shure Beta 52etc

Electric Bass Guitar - speakersElectric Bass Guitar - speakersThe speaker behaves in the same way as for a guitarCentre (dome)Edge (rim)Mid-way

Electric Bass Guitar micing up a cabinetElectric Bass Guitar micing up a cabinetYoull sometimes find a tweeter driver to handle the higher frequenciesThe mic will therefore be placed mid-way between the HF driver and one of the LF drivers

Electric Bass Guitar micing up a cabinetElectric Bass Guitar micing up a cabinet!!Mega Goliath : 8x 10Often times, a DI recording will sound betterMy advice: record BOTH DI and Mic

Electric Bass Guitar DIElectric Bass Guitar DIMost Electric Bass amp heads sport a DI output

Electric Bass Guitar - soundsElectric Bass Guitar sounds

**Discuss faithfulness of electrical signal *Lawsuits between these two inverters, most notably for the invention of the telephone. Emile Berliner, Amos Dolbear, Thomas Edison, Elisha Grey, Henry Hunnings, and, of course, Alexander Graham Bell. In 1887, the U. S. Supreme Court decided, through a series of appeals, that Bell invented the telephone.*They hissed constantly due to random movement of the carbon particlesDistortion, peaks here and there, limited frequency responseThe horror.. the horror*Telephone and Microphones go hand in hand*The development of telephone technologies and microphones go hand in hand.*Small is considered less than 16mm / Large is considered from 20mm onwardsFont Fire Side Fire*TOLERANCE**Watch out for rear lobe !!!110 for stage monitors when using hypercardioids (SM58, etc)**Directivity : shotgunLF response poorDirectivity proportional to length of diffraction tubePhase shifting network cancellation by summing of different times of arrival when off axis*0.5 % THD*Directivity : hemisphericalLow freq response proportional to size of boundary*Directivity : shotgunLow freq response proportional to diameter of parabola*Weight and size of mobile partsSelf induction creates natural compression at higher SPLsAcoustic port to balance pressure inside/outside capsuleNeodymium magnets *Step-up transformerPhantom Power !!!!!!*Invented by Georg NeumannMention improvements in last 2 decades (high SPL, tolerance to humidity, )Price. Not as expensive as one might thinkInternal PADEXPLAIN POLARISING CURRENT / PRE AMPLIFIER / EXPLAIN ELECTRET / EXPLAIN VALVE********Watch for phase issues when combining 2 sources containing the same wave form******Hi gain input Low gain inputPower attenuators (power breakers)******Before you do anything, locate the centre of the speaker cone. Sometimes it is difficult to see the centre, it is good idea to have a flash light in your tool box.*******Loop or parallel out in reality, either jack can be used !!!!*************Make sure you set the DI output to be PRE EQ *Double bass / upright bass