Josephson C720 User manual
JOSEPHSON ENGINEERING, Inc.
329A Ingalls Street, Santa Cruz, California 95060
Tel 831-420-0888 Fax 831-420-0890
http://www.josephson.com
©2008 Josephson Engineering, Inc.
TheJosephsonC720isthelatestintheSeriesSevenrangeoflargediaphragm
side‐addressmicrophones.Itusesadual‐cardioidcapsulewithseparateoutputs
forthefrontandback.Dual‐diaphragmmicrophonessincethe1940’shaveused
asimilarprincipleinternallytoallowtheusertoselectanydesireddirectional
pattern.TheC720allowsgreaterfreedomandversatilitybyprovidinganoutput
ofeachcapsulehalfthroughadiscreteimpedanceconverter/preampstage.
Havingseparateoutputsallowseachoutputtoberecordedindependently,
permittingthepatterntobecontrolledinmixdownratherthanatthesession.
Theusercanmakethepatternchoiceatanotherlocation,oranothertime.
AuniquefeatureoftheC720isits(patentpending)open‐cellmetalfoambasket.
Unliketraditionalmicrophonehousingsmadeofperforatedmetalorscreenwith
reflectivemetalsupportstructures,thishighlyopenmaterialprotectsthecapsule
mechanically,provideselectricalshieldingandsomepopandwindscreening;
nosupportingstructureisnecessary.Afineacousticallytransparentscreen
insidethebaskethelpsprotectthecapsulefrombreathmoisturewhentheC720
isusedasavocalmic.Wewereabletoavoidusingatraditionalsupport
structurebecausethefoamitselfisatoughself‐supportingaluminumalloy.It’sa
highlyopenstructuresothatsoundreflectedbythebasketisnegligible,while
thebasketstillprovidesfullprotectionforthecapsule.Traditionaldesigns
incorporateringsandbarstosupportthegrillematerial,leadingtothereflection
intheleftpicture.Thesereflectionsinturnintroduceacousticresonancesinthe
microphoneresponsewhichcontributetofrequencyresponseanomaliesand
ringing.Maintainingacousticaltransparencyaroundthecapsuleisimportantin
achievingthesonicclaritythatisthismic’ssignature.
TheoutputcableoftheC720terminatesina7‐pinXLRtypeconnector.An
adapterisprovidedtobringfrontandbackoutputstonormal3‐pinXLR
connectors.Eitherthefrontorthebackmaybeusedasacardioidmicrophone–
justplugthecorrespondingconnectorintoyourrecordingchain.
PatternControl
Theusermayaccomplishthesamefunctionprovidedbyatraditionalpattern
controlswitchorbox,byconnectingthefrontandbacksignalsfromtheC720to
twoinputsonamixer.Usejustthefrontsignalorthebacksignalforafront‐or
rear‐facingcardioid.Mixthetwosignalsinphasetomakeanomnipattern,or
flipthephaseoftherear‐facingsignalandmix,tomakeafigure‐8pattern.Any
intermediatepatterncanbemadebymixingthetwosignalsindifferent
proportions.Usethischartasastartingpointforyourownexperiments.
PatternRearPhaseFrontGainRearGain
FrontCardioidNormal0 off
RearCardioidNormaloff0
SubcardioidNormal‐2‐15
OmniNormal‐3‐3
HypercardioidInvert‐2‐15
Figure‐8Invert‐3‐3
Wherethegeometryisappropriate(forinstance,inanambientroompickup)the
C720mayalsobeusedasastereomicrophone,withitstwocloselymatched
cardioidcapsulesfacingleftandright.
AboutDirectionalPatterns
Microphonesachievetheirdirectionalresponsebysubtractingsoundthatcomes
fromsomedirections,fromtheoverallsound.Thisdoesn’tletusfocusabeamof
pickupsensitivityinonedirection,butitdoesallowustosteera“null”inone
direction,andtheresponsetosoundsarrivingfromtheareaofthenullmaybe
reduced20dBormorefromresponsetosoundscomingfromotherdirections.
TheC720allowsallthetraditionalpatternstobeselected,butitsrealadvantage
isinallowingfineadjustmentstobemadetothepatterntosuitthesoundand
theenvironment.
ThebasicpickuppatternsofthetwohalvesoftheC720are“cardioid.”
Sensitivitytosoundarrivingfromthesides,isreducedby6dB(half)compared
withsensitivitytowardthefront.Towardtherear,sensitivityisreducedby20to
25dB.Thepolargraphaboveshowsthisresponse.Towardthetopofthepage
representsthedirectioninfrontofthemicrophone.EachhalfoftheC720hasthis
directionalpattern;oneisfacingforwardandtheotherfacestotherear.
Ifyoumixthefrontandrearsignalsequally,theresultisanomnidirectional
pattern–soundsarepickedupevenlyfromalldirections.Ifyoumixthefront
andrearsignalsindifferentratios,theresultisanomnidirectionaltypepattern
butnotperfectlyeven.Mixingtherearsignalat‐6dBversusthefrontsignal
yieldsthissortofpattern:
Usinglessoftherearsignalmakesa“widecardioid,”“subcardioid”or
“hypocardioid”wheretherearresponsemightbe‐10or‐12dBfromthefront
response.
Invertingthephaseoftherearcapsulesignalproducesthefamilyofpatterns
relatedtofigure‐8orbidirectionalpickup.Withthefrontandrearatthesame
level,butoneinvertedinphase,theresultistheclassicfigure‐8:
Adjustingtherelativelevelofthefrontandrearallowsyoutocontroltherelative
sensitivityofthefrontandback,andalsodetermineswherethenullinthe
patternwillbe.
Ratherthanfocusingonthegraphicrepresentationofthepatterns,it’smost
usefultolistentotheresults.Thinkoftherangeofpatternsfromomniatoneend
ofthespectrumthroughcardioidinthemiddle,tofigure‐8at
theoppositeend.Don’tfocussomuchonwherethefrontofthemicrophoneis
pointing–theresponsetowardthefrontisfairlyuniformforallpatterns.
Anythingfromcardioidthroughthefigure‐8endofthespectrumwillhaveone
ormorenullssomewhereinthepattern,andthedirectionandwidthofthis
“deadzone”makeabigdifferenceintheoverallsound.Asyouchangepatterns,
listentohowtheoverallroomsoundchanges.Ifyou’reworkingclosetothe
microphone,you’llalsonoticethatthebassboostcausedbyproximityeffect
becomesstrongerasyouchangethepatterntowardthefigure‐8endofthe
spectrum.
IngeneralwerecommendthatthetwooutputsoftheC720beroutedtodiscrete
channelsofamultitracksessionrecordingwithoutfurtherprocessing,sothat
anydesiredmodificationtothesesignalsmaybedoneinmixdownwithout
losinganyoftheoriginalinformation.Itdoesn’tmatterwhetherthesource
materialisthetwochannelsfromthemic(mixedduringthesession)orasthey
areplayedbackfromthesessionrecording–thesignalsarestillthesame.But
whileyouaregettingfamiliarwiththemicrophone’scapabilities,trymixingthe
twochannelslive.
Trysomeoftheexperimentsdescribedhere.You’llneedanordinarymixerwith
themicpluggedintotwochannels.Besurethegainissettoexactlythesamefor
bothchannelsandtheEQsettobypass.
Ofcoursethesimplestpickupisjusttousethefrontsignalbyitself.Thisisawell
controlledstandardcardioidpatternandisexcellentforcloseupvocals,detailed
instrumentpickupandlargeensemblerecording.Notehowthesoundcolor
changesasyoumovearoundthemicrophone–moreproximityeffectand
“reach”forsoundsarrivingfromthefront,lesstowardthesides,andasharp
nulldirectlybehindthemic.
Addingsomeoftherear‐facingcardioidsignalallowsthestandardcardioid
patterntobeadjustedtosuitthepickuprequirements.Trysomeexperiments
withyourpickupinareasonablyliveroom,soyoucanheartheeffectofyour
adjustmentsontheoverallpattern.Addingalittlebitoftherear‐facingcardioid
(say,at‐12dBrelativetothefront)willreducethedepthofthenullinthebackof
themic,producingasub‐orwidecardioidpattern–lessdirectionalthanthe
standardcardioid,andwithagreaterlevelofroomambience.Proximityeffectis
reducedtoo,soiftheperformerismovingaroundtoomuchandcausingtonal
shifts,thiscanhelpfixit.Listentotheroomsoundbecomealittlemoreliveand
theoverallpickupalittlemoreopenasyoubringuptheleveloftherearsignal.
Ifyoudothesamethingbutwiththerearsignalinvertedinphase,theresult
becomesmoredirectional(uptoapoint)asyouincreasetheinverted‐rearsignal.
Inthiscasethenulltowardthebackofthemicrophonesplits,forminganullto
eithersideof180degrees.Atabout‐12dBrelativetothefront,ahypercardioid
patternisformed,withnullsatabout140and220degrees.Theoverallrejection
ofreverberantorroomsoundishighestinthisconfiguration,eventhoughthe
nulltotherearofthemicisnotasdeepasinthestraightcardioidmode.You’ll
noticemuchless“roomtone”andagreater“reach”withthemicinthismode,
butwithmorepronouncedlowfrequencyproximityeffect.
AbouttheC720Circuit
LikemostJosephsonmicrophones,theC720usesanalldiscreteclass‐Acircuitto
transformthehighimpedanceofthecapsuletoasuitablelevelforinterfacewith
micpreampsandconsoles.AcascodeFETstagedirectlydrivesaspecialLundahl
outputtransformer,whichusesamorphousmetallicglassasthemagneticcore
material.Theresultisamuchhigheroverloadpoint,evenwhenthemicis
drivinglongcables.Itisthesameaudiocircuitandtransformerfoundin
Josephson’sacclaimede22Smicrophone.TheinternalpowersupplyoftheC720
usesanewelectrostaticcircuitthatprovidescapsulepolarizationchargewithout
theuseofoscillatorsorexternalpowersupplies.
Onlyonechannelofthecircuitisshown.
Thebreakoutcablediagramisshownhereforreference.TheC720willoperate
properlywitheitherfrontorbacksidesofthemicrophoneconnected(orboth).
FullP48phantompowerisrequired.
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
Certificate of Compliance
Josephson Engineering, Inc. certifies that the C720 microphone conforms to the applicable
requirements of the European Union directives as follows:
Machinery 93/68/EEC Exempt – passive sensor
Low Voltage 93/68/EEC Exempt – passive sensor
EMC 93/68/EEC Exempt – passive sensor
RoHS 2002/95/EEC Compliant for Hg, Cd, Cr6,
PBB, PBDE and Pb
David Josephson, CEO
Josephson Engineering, Inc., 329A Ingalls St., Santa Cruz CA 95060 USA
Josephson Engineering, Inc.
Microphone Warranty
Josephson microphones are warranted to be free of defects for five years from the date of
original purchase. If purchase documents are not available, the warranty period begins
when the microphone was shipped from the factory. Josephson Engineering will, at its
option, repair or replace any microphone that fails, providing that it is returned to the
factory prepaid and has not been abused or altered.
There are no user-serviceable parts inside Josephson Engineering microphones.
Disassembling a Josephson microphone will void its warranty.
For service information please contact Josephson at 831-420-0888. Repair shipments may
be sent to:
Josephson Engineering, Inc.
329A Ingalls St
Santa Cruz CA 95060
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