Josephson C720 User manual

JOSEPHSON ENGINEERING, Inc.
329A Ingalls Street, Santa Cruz, California 95060
Tel [phone] Fax [phone]
email [email protected]
http://www.josephson.com
©2008 Josephson Engineering, Inc.

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TheJosephsonC720isthelatestintheSeriesSevenrangeoflargediaphragm
side‐addressmicrophones.Itusesadual‐cardioidcapsulewithseparateoutputs
forthefrontandback.Dual‐diaphragmmicrophonessincethe1940’shaveused
asimilarprincipleinternallytoallowtheusertoselectanydesireddirectional
pattern.TheC720allowsgreaterfreedomandversatilitybyprovidinganoutput
ofeachcapsulehalfthroughadiscreteimpedanceconverter/preampstage.
Havingseparateoutputsallowseachoutputtoberecordedindependently,
permittingthepatterntobecontrolledinmixdownratherthanatthesession.
Theusercanmakethepatternchoiceatanotherlocation,oranothertime.
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AuniquefeatureoftheC720isits(patentpending)open‐cellmetalfoambasket.
Unliketraditionalmicrophonehousingsmadeofperforatedmetalorscreenwith
reflectivemetalsupportstructures,thishighlyopenmaterialprotectsthecapsule
mechanically,provideselectricalshieldingandsomepopandwindscreening;
nosupportingstructureisnecessary.Afineacousticallytransparentscreen
insidethebaskethelpsprotectthecapsulefrombreathmoisturewhentheC720
isusedasavocalmic.Wewereabletoavoidusingatraditionalsupport
structurebecausethefoamitselfisatoughself‐supportingaluminumalloy.It’sa
highlyopenstructuresothatsoundreflectedbythebasketisnegligible,while
thebasketstillprovidesfullprotectionforthecapsule.Traditionaldesigns
incorporateringsandbarstosupportthegrillematerial,leadingtothereflection
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intheleftpicture.Thesereflectionsinturnintroduceacousticresonancesinthe
microphoneresponsewhichcontributetofrequencyresponseanomaliesand

ringing.Maintainingacousticaltransparencyaroundthecapsuleisimportantin
achievingthesonicclaritythatisthismic’ssignature.
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TheoutputcableoftheC720terminatesina7‐pinXLRtypeconnector.An
adapterisprovidedtobringfrontandbackoutputstonormal3‐pinXLR
connectors.Eitherthefrontorthebackmaybeusedasacardioidmicrophone–
justplugthecorrespondingconnectorintoyourrecordingchain.
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PatternControl
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Theusermayaccomplishthesamefunctionprovidedbyatraditionalpattern
controlswitchorbox,byconnectingthefrontandbacksignalsfromtheC720to
twoinputsonamixer.Usejustthefrontsignalorthebacksignalforafront‐or
rear‐facingcardioid.Mixthetwosignalsinphasetomakeanomnipattern,or
flipthephaseoftherear‐facingsignalandmix,tomakeafigure‐8pattern.Any
intermediatepatterncanbemadebymixingthetwosignalsindifferent
proportions.Usethischartasastartingpointforyourownexperiments.
PatternRearPhaseFrontGainRearGain 
FrontCardioidNormal0 off
RearCardioidNormaloff0
SubcardioidNormal‐2‐15
OmniNormal‐3‐3
HypercardioidInvert‐2‐15
Figure‐8Invert‐3‐3
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Wherethegeometryisappropriate(forinstance,inanambientroompickup)the
C720mayalsobeusedasastereomicrophone,withitstwocloselymatched
cardioidcapsulesfacingleftandright.
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AboutDirectionalPatterns
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Microphonesachievetheirdirectionalresponsebysubtractingsoundthatcomes
fromsomedirections,fromtheoverallsound.Thisdoesn’tletusfocusabeamof
pickupsensitivityinonedirection,butitdoesallowustosteera“null”inone
direction,andtheresponsetosoundsarrivingfromtheareaofthenullmaybe

reduced20dBormorefromresponsetosoundscomingfromotherdirections.
TheC720allowsallthetraditionalpatternstobeselected,butitsrealadvantage
isinallowingfineadjustmentstobemadetothepatterntosuitthesoundand
theenvironment.
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ThebasicpickuppatternsofthetwohalvesoftheC720are“cardioid.”
Sensitivitytosoundarrivingfromthesides,isreducedby6dB(half)compared
withsensitivitytowardthefront.Towardtherear,sensitivityisreducedby20to
25dB.Thepolargraphaboveshowsthisresponse.Towardthetopofthepage
representsthedirectioninfrontofthemicrophone.EachhalfoftheC720hasthis
directionalpattern;oneisfacingforwardandtheotherfacestotherear.
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Ifyoumixthefrontandrearsignalsequally,theresultisanomnidirectional
pattern–soundsarepickedupevenlyfromalldirections.Ifyoumixthefront
andrearsignalsindifferentratios,theresultisanomnidirectionaltypepattern
butnotperfectlyeven.Mixingtherearsignalat‐6dBversusthefrontsignal
yieldsthissortofpattern:
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Usinglessoftherearsignalmakesa“widecardioid,”“subcardioid”or
“hypocardioid”wheretherearresponsemightbe‐10or‐12dBfromthefront
response.
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Invertingthephaseoftherearcapsulesignalproducesthefamilyofpatterns
relatedtofigure‐8orbidirectionalpickup.Withthefrontandrearatthesame
level,butoneinvertedinphase,theresultistheclassicfigure‐8:

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Adjustingtherelativelevelofthefrontandrearallowsyoutocontroltherelative
sensitivityofthefrontandback,andalsodetermineswherethenullinthe
patternwillbe.
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Ratherthanfocusingonthegraphicrepresentationofthepatterns,it’smost
usefultolistentotheresults.Thinkoftherangeofpatternsfromomniatoneend
ofthespectrumthroughcardioidinthemiddle,tofigure‐8at
theoppositeend.Don’tfocussomuchonwherethefrontofthemicrophoneis
pointing–theresponsetowardthefrontisfairlyuniformforallpatterns.
Anythingfromcardioidthroughthefigure‐8endofthespectrumwillhaveone
ormorenullssomewhereinthepattern,andthedirectionandwidthofthis
“deadzone”makeabigdifferenceintheoverallsound.Asyouchangepatterns,
listentohowtheoverallroomsoundchanges.Ifyou’reworkingclosetothe
microphone,you’llalsonoticethatthebassboostcausedbyproximityeffect
becomesstrongerasyouchangethepatterntowardthefigure‐8endofthe
spectrum.
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IngeneralwerecommendthatthetwooutputsoftheC720beroutedtodiscrete
channelsofamultitracksessionrecordingwithoutfurtherprocessing,sothat
anydesiredmodificationtothesesignalsmaybedoneinmixdownwithout
losinganyoftheoriginalinformation.Itdoesn’tmatterwhetherthesource

materialisthetwochannelsfromthemic(mixedduringthesession)orasthey
areplayedbackfromthesessionrecording–thesignalsarestillthesame.But
whileyouaregettingfamiliarwiththemicrophone’scapabilities,trymixingthe
twochannelslive.
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Trysomeoftheexperimentsdescribedhere.You’llneedanordinarymixerwith
themicpluggedintotwochannels.Besurethegainissettoexactlythesamefor
bothchannelsandtheEQsettobypass.
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Ofcoursethesimplestpickupisjusttousethefrontsignalbyitself.Thisisawell
controlledstandardcardioidpatternandisexcellentforcloseupvocals,detailed
instrumentpickupandlargeensemblerecording.Notehowthesoundcolor
changesasyoumovearoundthemicrophone–moreproximityeffectand
“reach”forsoundsarrivingfromthefront,lesstowardthesides,andasharp
nulldirectlybehindthemic.
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Addingsomeoftherear‐facingcardioidsignalallowsthestandardcardioid
patterntobeadjustedtosuitthepickuprequirements.Trysomeexperiments
withyourpickupinareasonablyliveroom,soyoucanheartheeffectofyour
adjustmentsontheoverallpattern.Addingalittlebitoftherear‐facingcardioid
(say,at‐12dBrelativetothefront)willreducethedepthofthenullinthebackof
themic,producingasub‐orwidecardioidpattern–lessdirectionalthanthe
standardcardioid,andwithagreaterlevelofroomambience.Proximityeffectis
reducedtoo,soiftheperformerismovingaroundtoomuchandcausingtonal
shifts,thiscanhelpfixit.Listentotheroomsoundbecomealittlemoreliveand
theoverallpickupalittlemoreopenasyoubringuptheleveloftherearsignal.
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Ifyoudothesamethingbutwiththerearsignalinvertedinphase,theresult
becomesmoredirectional(uptoapoint)asyouincreasetheinverted‐rearsignal.
Inthiscasethenulltowardthebackofthemicrophonesplits,forminganullto
eithersideof180degrees.Atabout‐12dBrelativetothefront,ahypercardioid
patternisformed,withnullsatabout140and220degrees.Theoverallrejection
ofreverberantorroomsoundishighestinthisconfiguration,eventhoughthe
nulltotherearofthemicisnotasdeepasinthestraightcardioidmode.You’ll
noticemuchless“roomtone”andagreater“reach”withthemicinthismode,
butwithmorepronouncedlowfrequencyproximityeffect.
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AbouttheC720Circuit
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LikemostJosephsonmicrophones,theC720usesanalldiscreteclass‐Acircuitto
transformthehighimpedanceofthecapsuletoasuitablelevelforinterfacewith
micpreampsandconsoles.AcascodeFETstagedirectlydrivesaspecialLundahl
outputtransformer,whichusesamorphousmetallicglassasthemagneticcore
material.Theresultisamuchhigheroverloadpoint,evenwhenthemicis
drivinglongcables.Itisthesameaudiocircuitandtransformerfoundin
Josephson’sacclaimede22Smicrophone.TheinternalpowersupplyoftheC720
usesanewelectrostaticcircuitthatprovidescapsulepolarizationchargewithout
theuseofoscillatorsorexternalpowersupplies.
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Onlyonechannelofthecircuitisshown.

Thebreakoutcablediagramisshownhereforreference.TheC720willoperate
properlywitheitherfrontorbacksidesofthemicrophoneconnected(orboth).
FullP48phantompowerisrequired.
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C720 Specifications
Type: Dual electrostatic pressure-gradient transducers, cardioid characteristic
Marking: In accordance with IEC 61938
Rated power supply: Phantom 48 ±4 volts, 5 mA per output
Internal impedance: <100 ohms
Rated impedance: 200 ohms
Minimum load impedance: 1k ohms
Free-field and rated sensitivity: 1.7 mV/Pa
Frequency Range: 20-20,000 Hz
Directional characteristics: 2x cardioid
Overload sound pressure: 136 dB SPL at 1000 Hz
Equivalent sound pressure due to inherent noise: 15 dB SPL,
A-weighted rms in accordance with IEC 60268-1