B&W electronics 70 User manual

Model70
electronics
B&W
WORTHING. ENGLAND
Tel.Worthing66830
asignificantadvanceon
existingloudspeakersystems

Model70
USERSINSTRUCTIONHANDBOOK
CONTENTS Page
AssemblyInstructionsl
MainsVoltages3
AudioConnections.........4
PositionofSpeakers5
OperationInstructions......6
ServiceandGuarantee7
DesignandDevelopmentStory8
ResponseCurvesandMeasurements...23
SummaryofDetailedSpecification30

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INTRODUCTION.
EachModel70loudspeakersystemcomestoyouintwo
seperatecartons.Thelargercartoncontainsthemain
cabinetandanaccessorybagcontainingplugs,sparefuse
andfixingscrews.Themaincabinetiscompletewithleg
assemblyandelectrostaticpowersupply/filterunit,both
ofwhicharefixedinposition.Thesmallercartoncontains
the701electrostaticunitwhichisreadyforinsertionin
thesocketsprovidedonthetopsurfaceofthemaincabinet.
WARNING.
ITISIMPORTANTTHATTHEASSEMBLYANDINSTALLATION
INSTRUCTIONSBECAREFULLYREADBEFORECONNECTING
THISSYSTEMTOTHEMAINSORAUDIOSUPPLY.
ASSEMBLYINSTRUCTIONS.
Unpackthelargerofthetwocartonsandremovethe
accessorybagfromtheundersideofthemaincabinet.Unpack
theelectrostaticunitfromthesmallercarton.Wesuggest
youretainthespecialPolystyrenepackfromthesmaller
cartonforpossiblefuturetransportationoftheelectrostatic
unit.
Theelectrostaticunitshouldnowbeinsertedinthe
socketsprovidedonthetopsurfaceofthemaincabinet.
Spigotsonbothfeetofthe701electrostaticunitlocatein
thecorrespondingsocketsandtheycanonlybeassembledin
thecorrectmanner.
Havinginsertedtheelectrostaticunitmakesecureby
screwingthroughtheholeprovidedintherearofeachfoot
withthespecialinstrument-headwoodscrewsandcupsincluded
intheaccessorypack.Thesystemisnowready,afterchecking
mainssupplyvoltage,forinstallation.
UNITBEREMOVEDWITHMAINSSUPPLYCONNECTEDORWHILST
THESYSTEMISINOPERATION.

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INSTALLATIONINSTRUCTIONS
MAINS.
BeforeattemptingtoconnectthemainssupplytoyourModel70
pleasecheckyoursupplyvoltageandseethatthisagreeswith
theadjustmentmadetothesystembeforeleavingourfactory.
Asmallredlabelisattachedtothepowersupplypanel
(rearmaincabinet)givingthisindication
AdjustedforEuropean( 200- 240volts§0HzJAC.
AdjustedforAmerican( 110-125volts60Hz.)AC
DuetothegoodregulationoftheEHTpowersupplyadjustment
ofmainsvoltagewillnotnormallybenecessary.Allsystems
aresetbeforeleavingthefactoryforthemarketconcernedas
shownabove.

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(AssemblyInstructions_-_Mains_-__contd.)_ '-
Shouldmainsvoltageadjustmentbenecessarythisiscarried
outbyremovingthepowersupplyandrepositioningonewire
onthemainstransformerterminationboard.Thisworkshould
becarriedoutbyyourdealerwhoisprovidedwiththenecessary
instructions.
Model70requiresconnectiontoanalternatingcurrentmains
supplywiththespecialthreepinplugprovidedwithyour
accessories.Undernormaloperatingconditionsthecurrent
drainisnegligible,theloadbeingonlysome10watts
(onetenththatofa normalreadinglamp)andprovidedthree
corecableisusedformainsconnectionthecorediameteris
innowaycritical.Themainscableconnectionstothethree
pinplugareillustratedinFig.3 below.
Anoutermetalscreenisbuiltintotheelectrostaticunit
forsafetypurposes.Itisimportantthereforetoensure
thatthreecorecableisusedtogetherwitha threepinplug
toyourmainssocket.
AUDIO
Theoutputfromyouramplifierisconnectedviathespecial
2pinnon-reversibleplugprovidedtothesocketmarked
1INPUT' onthepowerunitrearplate.
Thecable(twinortwocore)useafortheaudioleadshould
havelowresistanceandifmorethansaytenfeetofcable
isrequiredforthisleadwewouldrecommendaninnerconductor
of7/029orsimilar.
Whentwoloudspeakersystemsareoperatingforstereo
reproductionitisimportantthattheaudioconnectionsto
the'INPUT'socketarecorrectlyphased.Thered(or
positive)terminalofyouramplifiershouldbeconnectedto
pinoneoftheinputplugonyourloudspeaker.

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AssemblyInstructions- Audio- contd.:-
Ifphasingiscorrectthisisevidentbya relativelysmall
centralimagewhenthelistenerisseatedona centreline
betweentheloudspeakersandbothloudspeakersarefedfrom
amonophonicsignal.Ifphasingisincorrectthesound
imagewillbemuchbroaderandlesswelldefined.A reversal
oftheamplifierorloudspeakerconnectionsfromonechannel
willconfirmthecorrectnessofphasingandillustratethis
point.
POSITIONINGOFLOUDSPEAKERSINLISTENINGROOM.
DuetothewidehorizontaldispersionoftheModel70system
loudspeakerplacingtoobtainanevenstereoimageisnotas
criticalaswithmanyconventionalsystems.Itwillalso
befoundthatthestereoimageispreservedovera wide
listeningangle.Thesuggestedplacingfora pairof
Model70reproducersisillustratedinFig.4 below.
Fig.4.
Itisimportanttorealisethatthebassresponseiscontrolled
underlisteningconditionsbytheroomdimensionsandthe
position(relativetowallsorcornerplacing)"whichthe
loudspeakeroccupies.Thecloserthesystemisplacedto
awallorcornerthegreaterwillbethecouplingtothe
room.Asa generalrulethoseroomswithsimilardimensions
(i.e.a squareroom) arethemostdifficultfromthe
viewpointofobtainingextendedresonantfreebassresponse.
Ifyourlisteningconditionsaresuchthatthebassresponse
isexcessivewithina narrowbandoffrequenciesitmaybe

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itmaybefounddesirabletowithdrawtheloudspeaker
fromthecornerorwallbysometwelvetotwenty-four
inches.
OPERATION,
Attherearoftheelectrostaticunitwillbefounda
removableabsorbentpad,thefunctionofwhichistoreduce
rearradiationinlocationswheretheloudspeakeris
placedclosetoa wallorcorner.Thispadprovidesa
usefulmethodofvaryingthedistributionpatternofthe
electrostaticunitabove400Hz.(lowermid.freguencies)
tosuitbothambientconditionsandtheuser'spersonal
preferanceintermsoftheratioofdirecttoreflectedsound.
Thisabsorbentpadcanbereadilywithdrawnwiththefingers
fromitsrecessintherearofthe701electrostaticmount.
Withtherearpadwithdrawngreaterambiencewillbeexperienced
and,dependingonthereflectivenatureofthewallsand
furnishingsbehindtheloudspeakertherewillbea slight
increaseinsoundlevelabove400Hzwiththeelectrostatic
operatinginthiscondition.Ifitisdesiredtooperate
Model70atveryhighvolumelevelsorwherehighpowered
continoussinewaveinputsareappliedtherearabsorbentpad
shouldbeplacedinposition.
ItwillbeobservedthatontherearpanelofthePowerUnit
thereisa neonindicator.Thisshowsthatmainssupplyis
functioning.Iftheneondoesnotlightupwhenmainsis
connectedthefuseshouldbechecked.A sparefuseisprovided
butrepeatedreplacementshouldnotbemadeandifthis
failsyoushouldconsultyourdealer.
ANCILLARYEQUIPMENT.
Model70probablyaddslessintermsofcolourationand
distortionthananyotherloudspeakersysteminexistance.
Itwillbeanalyticalofthesignalwhichitreceivesand
thereforebenefitsfromusewithancillaryequipmentof
thehighestavailablequality.

from
electronics
manufacturersof
electronic
andacoustical
equipment
THEDESIGN& DEVELOPMENTOF
THEMODEL70
MODEL70,thefirstofourloudspeakersystemswhereall
unitsaredesignedandbuiltwithinourownfactory,represents
whatwebelievetobea successfulattempttoproducea
loudspeakersystemfortheperfectionistwhichisa worthwhile
advanceonexistingsystems.
INTRODUCTION
IncontemplatingthedesignandmanufactureofModel70
certainguidelineswerelaiddownsometwoyearsagoatthe
commencementofthedesignprogramme:-
1)Newthinkingontheacousticaldistributionpattern,
especiallywithinthevitallyimportantmidfrequency
regionof400Hzto5 kHz,aimingtowardsexploring
theadvantagesofa distributionpatternapproximating
tospherical.
2)A midfrequencyunitcapableofhandlinginputpowers
intheregionof25wattsr.m.s.withdistortion
factorstotheorderof0.5%orlower.
3)A reallylowdistortionbassradiatorcapableoftruly
complementingaspects1)and2)abovewithoutoccupying
anundulylargeenclosurevolume.
4)Explorationofthelisteningadvantagesbyincreasing
reverberantto directsound.
5)Allunitsbedesignedandbuiltwithinourownfactory
toensuremaximumqualitycontrolandretentionofthe
exclusiveoriginaldesign.
6)Stylingandgeneralappearancetobeacceptableina
widerangeofdomesticfurnishings.

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ItwasfurtherdecidedthattheconceptofModel70should
beoneofaninternationalproductand,whilstparagraphtwo
detailinga highpowerhandlingcapacitywasconsistentwith
Worldmarkets,certainotherdesignandconstructionalfeatures
werelaiddownasbeingessential:-
a)Thatthesystembeina modularformallowing
easyassemblybyoverseasagents.
b)Thatthebasschamberloading,consistentalways
withtheultimateperformance,berelatively
simpleandcapableofbeingaccuratelycopiedin
distantmarketswhereitisobviouslyuneconomical
toshipcompletesystems.
c)Asanextensionof2)thatallunitsbeeasily
removabletofacilitatespeedyservicinginoverseas
marketswheretechnicalservicefacilitiesare
limited.
DESIGNPERAMETERS
Ithasbeengenerallyacceptedforreasonstoowellknown
toberepeatedthat,ifa loudspeakersystemisaimingat
optimumperformance,thefrequencyspectrumshouldbesplit.
Theprecisedivisionoffrequenciestobehandledbythevarious
unitsandreasonsforthecrossoverfrequencychosenwillbe
discussedlaterinthisrelease,butinitiallyletussurveythe
alternativesdealingfirstwithfrequenciesbelow400Hz.
Thealternativesareelectrostaticormovingcoilunitsand
itwasdecidedatanearlystageinthedesignthatthelatter
methodshowedobviousadvantages.Forexample,onanexisting
fullrangeelectrostaticloudspeakerverycarefulmeasurements
weremadeandtotalharmonicdistortionat60Hzwith15watt
r.m.s.inputwasintheregionof50%.Onanalternativefull
rangeelectrostaticAmericandesignwhichwassampled,the
dimensionsofthisunitweresuchastoexcludeitsuseinthe
majorityofhomeinstallations.Whilsta veryselectedfewmay
acceptpanelsintheirloungesomesevenfeethighandthree
feetWideitwasfeltthatonappearancealonethepoints
discussedintheintroductionwereinnowaycateredfor.
Asa resultoflongdiscussionsbetweenthewriterand
Mr.DennisWarditwasfeltthatthemovingcoilsystemshouldbe

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capableofmeetingtheinitialdesignrequirementssetout
inparagraphthreeabovewithanenclosuresizeofsome2-3
cubicfeet.
Insofarasthemidandupperfrequencieswereconcerned
thechoiceofunitswasthreefold- Movingcoil,Electrostatic
orIonic.ItwillbenotedthattheIonicunitiscurrently
usedinourP2monitor.
AtanearlystageindevelopmentnewalternativeIonic
unitsweremanufacturedinprototypeformwitha viewto
increasingpowerhandlingcapacityandextendingthefrequency
responseat leasttwooctavesbelowthatprovidedby the
existingFaneunit.Whilstcertainprogresswasmade,both
thephysicaldimensionsofthehornloadingandtheR.F.
oscillatorpowerrequirementsshowedthat,althoughimprovement
intheIonicunitwaspossible,thedisadvantageswerethoseof
physicalsizeandadequateR.F.screening.Forinstance,one
prototypehada hornlengthofsometwofeetandanR.F.
oscillatorof70watts,a totallyunmanageablequalitybothin
termsofsizeandadequatescreeningtoprovidefreedomfrom
T.V.I.ForthesereasonstheIonicmethodwasdismissedand
attentionfocusedonElectrostaticandMovingcoilunits.
Althoughconsiderableadvancehasbeenmadeinthedesign
anddevelopmentofMovingcoilunitstheydonot,inthewriter's
opinion,approachtheElectrostatictransducerinsofaraslow
distortion,transientbehaviourorflexibilityofbroadpolar
distribution.
EvaluationscarriedoutbyMr.Harwoodona somewhatsimilar
'stateoftheart'projectand,forthoseinterested,reference
maybemadetothreearticlespublishedin"WirelessWorld"in
1968whereitwasshownthatevenofferinganidealisedMoving
coilunittoa slotradiator,thepolarcharacteristicwasnot
wellmaintainedabove3 kHz.Itwasdecided,therefore,to
explorethepossibilityofmakinganelectrostaticunit,working
fromfirstprincipleswitha viewtocomparativemeasurements
betweentheElectrostaticandMovingcoilunitswhichcouldbe
developed.
Somesixmonthsafterthedesignprogrammewasoriginated
aseriesofprototypeunitswereproducedwhichenableda prime