B&W electronics dm70 User manual

B&W
DM70
Instruction
manual
testcertificate
andguarantee

DM70
B&WDM.TrademarkofB&Welectronics

Contents
1.GeneralDescription
2.TheListeningRoom
3.Installation— unpackingandconnection
4.Installation— Siting
5.Ancillaryequipment
6.Specification
Page
2
3
5
10
12
13
B&Welectronics
MeadowRoad• Worthing
England-BN112RX

Generaldescription
andintroduction
TheDM70isa precisionmonitorloudspeakerfordomesticandprofes-
sionaluse,builttoveryhighstandards.
Thisloudspeaker,employingthecombinationofdynamicbassdrive
unitinconjunctionwithanelectrostatictransducerforthemid-range
andupperfrequencies,iscapableofmostrealisticreproductionofboth
speechandmusicprogrammematerial.Becauseofitslowdistortion,
wideandbalancedfrequencyresponse,andrelativefreedomfrom
colouration,itwillbeanalyticalandmaywellrevealshortcomingsin
programmematerialanddefectsinancillaryequipmentwhichan
inferiorproductwouldmask.
Wehopethatthisinstructionbookwillhelpyoutoassemblewith
ease,andinconnectingandplacingyourloudspeakers,andwehave
quitedeliberatelyrestrictedtheseinstructionstobesimpleandnon-
technicalwhereverpossible.
Foranexplanationofunpackingandassemblingyourloudspeakers
(eachDM70system,excludingstands,ispackedintwocartons)refer
tosection3 ofthisbooklet.
IncommonwithallB&Wloudspeakersystems,theDM70issubjected
tostringent,qualitycontrolthrougheverystageofmanufactureand
dispatch.IndividualfrequencyresponsetestsaremadeoneveryDM70
duringmanufactureandbeforedispatch,andweprovideyouwitha
calibrationcurvewiththeguaranteeregistrationcard.
Providedtheinstructionsarefollowed,yourloudspeakershouldgive
youmanyyearsofcompletelytrouble-freeservice.Intheeventofany
querywewouldaskyoutoadoptthefollowingprocedureifservice
isrequired:—
England,Scotland& Wales:
Contactthedealerfromwhomyoupurchasedtheloudspeakers.
AllotherCountries:
Contactourdistributorforyourcountry—nameandaddresssupplied
fromourfactoryifindoubt.
B&Whaveappointedagentsthroughouttheworld,selectedwithgreat
caretogiveyouthebestpossibleservice.Shouldyouhaveanyreason
tofeeldissatisfiedorifanyqueriesarise,wewillbepleasedtoassist
whereverpossible.

Thelisteningroom
Mostpeoplehaverelativelylittlecontrolovertheirlisteningroomin
termsofsizeorshape,butastheenvironmentinwhichtheloudspeaker
isusedplayssucha bigpartinthequalityofsoundwehear,some
commentsonroomcharacteristicsmaybehelpfulbeforeweproceed
insection3.
Therearetwoaspectsoflisteningroomswhichwillmostwidely
influencesoundreproduction: Thebasicdimensionsoftheroomand
largeitemsoffurniturecontrollingthelowerfrequencies;anditemsof
softfurnishingtogetherwithwallandothercoveringsaffectingthe
middleandupperfrequencies.
Allroomshaveresonances,andsoindeeddoestheconcerthall,but
inthecaseofthelatterthesearesolowinfrequency,andbydesign,
sowellspacedthattheyaddambienceratherthancolouration:The
worstexampleina listeningroomorstudiowouldbetheunlikely
eventofalldimensionsbeingthesameandtheroomforminga cube.
Thebestcasebeinga relativelylargeroomwherealldimensionsare
different.Fortunatelytheworstexampleisrarely,ifever,encountered
butwherea choiceispossibleasbetweena squareorrectangular
roomthelatteristobepreferredastheroomresonances— knownas
eigentones— occuratspacedfrequenciesandarethereforeoflower
amplitude.
Themostpronouncedeigentonesoccuratlowfrequenciesbelow
approximately200Hz.Inadditiontotheseeigentonesthereisanother
importantinfluencetheroomhasovertheloweroctavesofreproduced
sound.Duetotherelativelysmalldimensionsoftheloudspeakercom-
paredwithwavelengthsofsoundintheloweroctaves,theradiation
patternordistributionofsoundatthesefrequenciesiseffectively
spherical.Whenoperatinga loudspeakerina room,thissphereof
soundiscontained,toa greaterorlesserdegree,dependingonposition
withina seriesofplainsurfacesformedbythewalls,floorandceiling.
Thisproducesa factorknownas'roomgain'anddoesinfactmake
thelowerfrequenciesconsiderablylouderthanif,forinstance,the
loudspeakerwereoperatedintheopenair.
Asa resultofresearchcarriedoutintothe"roomgain"andhowthis
affectsloudspeakerperformance,thestandoftheDM70hasbeen
specificallydesignedtogiveoptimumresultsovera rangeoflistening
conditions.
Beforeleavingthewayinwhichtheroomaffectsthelowfrequency
partofthesoundspectrum,a wordshouldbesaidontheconstruction
Thelisteningroom

Theidealisa solidlybuiltgroundfloorroomwitha concretefloor.In
roomswherethereisa boardandjoistfloorthiswillplaya partin
bothaddingtobassgainandroomcolouration.Thesuspendedfloor
actsasa supplementarybassradiatoroperatingatthemainresonance
oftheroom.Ifyourlisteningroomhasotherthana solidfloorand
youaretroubledbyexcessiveorresonantbassresponseasa result,
positioningyourloudspeakerawayfromthecornerswillassist.
Thesubjectofpositioningyourloudspeakersisdealtwithinsection
4,butbeforeleavingthelisteningroomwewillmentionitseffecton
middleandhighfrequencies.
Thesoftfurnishings— chairs,curtainsandcarpet,togetherwithwall
andceilingcoveringsarethemainfactorsgoverningtheperformance
ofa roomatmiddleandupperfrequencies.Positionofcupboards,
bookshelvesandotheritemsofwallfurniturealsoplayanimportant
roleinthesepartsofthespectrum.
Aroomwithinsufficientsoftfurnishingwillgivea hardorsteelytonal
qualitytomiddleandupperfrequencies,withstringssufferingespecial-
ly.A roomwithtoomanysoftfurnishings— anover-dampedroom—
willsounddullandlifeless,a somewhatsimilareffecttoputting'top
cut'onyouramplifiertonecontrol.
Theidealmid/highfrequencyreverberationtimes( a measureof
acoustic'brilliance'or'dullness')aresomewhatsubjective,but
generallya goodbalancecanbeobtainedbyopposinga reflective
surfacewithanabsorbentone.Asanexampleceilingsareusually
bareandreflectiveandthiscanbewellbalancedbya fittedcarpet.An
unbrokenwallfacinglargewindowareascanbebrokenbya bookcase
ontheoppositewall.
Whenfurnishinga newroomwhichistobeusedforlisteningto
reproducedmusic,itisusuallywiseinitiallytounderdamptheroom
andthenaddabsorbentarticlesafterthecorrectbalancehasbeen
determined.

Installation-
unpackingandconnection
ForsafetyintransporttheDM70Improvedsystemispackagedin
threecartons,foreachloudspeaker:—
Carton1 Maincabinetwithfittedpowersupplyunit.
Carton2 Twometalstandsforthepairofloudspeakers.
Carton3 The"702"electrostaticunitcomplete.
WARNING
ITISESSENTIALTHATTHEASSEMBLYANDINSTALLATION
INSTRUCTIONSBECAREFULLYREADBEFORECONNECTING
THISSYSTEMTOTHEMAINSORAUDIOSUPPLY.
Unpacking.Unpackthelargestcartonsandremovetheaccessory
bagtiedtotherearofthepowerpackatthebackofeachcabinet.
Thisbagcontainsallnecessaryhardwareandspares,suchasfuses.
Thesmallerpackagesshouldthenbeunpacked.Itisa worthwhilepre-
cautiontosavethepolystyrenepiecesinwhichtheelectrostaticunits
arepackedincaseofanyfuturetransportation.
Thestandsmaynowbefittedtothebaseofthecabinetsbymeans
ofthemetalboltsprovidedwhichwillmatewithsealedcaptivenuts
insidethebaseofthecabinet.
Mains.BeforeattemptingtoconnectthemainssupplytoyourDM70
checkthatyoursupplyvoltageagreeswiththeadjustmentmadeto
thesystembeforeitleftourfactory.

Fig.1
RearviewofContinental
powersupply,showinglabel
indicatingthepowersupply
voltage.Thepowersupplyfor
theStandardversionissimilar
butrotatedthrough90
degrees.
Theregulationofthepowersupplyissuchthat,normally,noadjust-
mentwillbenecessaryandtheunitissetforthecountryofdestination,
e.g.EuropeanorAmerica,etc.If,afterhavingmadethischeckonmains
supply,itisnecessarytoadjustthemainsvoltage,pleaserefertothe
abovediagramandreadtheinstructionsregardingtheremovalofthe
powersupplyfromthecabinet.
Adjustmentofmainsvoltagesetting.
ITISIMPORTANTTODISCONNECTTHEMAINSPOWER
SUPPLYANDAUDIOFEEDFROMAMPLIFIER(IFCON-
NECTED)BEFOREATTEMPTINGTOREMOVETHEPOWER
SUPPLYUNITFROMTHECABINET.
Fig.2
Showsa 70Cpowersupply
unitremovedfromthe
cabinet.

.
Toremovethepowersupplyunitfromthecabinet,unscrewthefour
screwsatthesideoftherearpaneloftheunitandwithdrawit,un-
pluggingtheaudiooutputtothebassunit.(Ifthe701electrostatic
unithasalreadybeenfittedtothecabinet,itwillbenecessaryfirstto
removethis,byreversingtheassemblinginstructionswhichfollow.)
Thevariousadjustmentstothemainsvoltageselectorareself-
explanatory.Re-insertthepowersupplyunitintothecabinet,securing
bymeansofthefourscrews.
FinalAssembly.Havingmadethechecks,andadjustments,if
necessary,the701electrostaticunitmaynowbefitted.Withthe
cabinetsecuredtoitsstand,theelectrostaticmaynowbeinserted
intothesocketsonthetopofthecabinet.Spigotsonbothfeetof
the701locateincorrespondingsocketsandtheycanonlybeassem-
bledinthecorrectmanner.Havinginsertedtheelectrostaticunit,
makeitsecurebyscrewingdowntothecabinetthroughtheholein
therearofeach701footwiththescrewsprovided.
Connection.UNDERNOCIRCUMSTANCESSHOULDTHE701
ELECTROSTATICUNITBEREMOVEDWITHEITHERTHEMAINS
SUPPLYORTHEAUDIOFEEDFROMTHEAMPLIFIERCONNECTED.
Withthesystemcompletelyassembled,connectionmaynowbemade
tothenecessaryalternatingcurrentpowersupply— thepowerdrain
isnegligible.Connectiontothemainsismadebythethree-corecable
provided,thestandardcolour-codingofwhichis:—
YELLOW/GREEN— EARTH
BROWN— LIVE
BLUE— NEUTRAL
FORCOMPLETESAFETY,ITISIMPORTANTTOUSEA THREEPIN
SUPPLYMAKINGA SOUNDEARTHCONNECTION.
Theoutputfromyouramplifiershould,ofcourse,beconnectedtothe
AUDIOINPUToftheloudspeaker— locatedonthebackpanelofthe
powersupplyunitConnectionismadetotheterminalsockets,either
byconnectingbaredwirestothebindingposts,orbyusingstandard
4mm."banana"plugs,orsimilar.Theterminalsarecolour-codedred
andblackandtheseareconnectedtothepositiveandnegativeloud-
speakeroutputsrespecrtively.ofyouramplifier.

Itisadvisabletokeeptheseriesresistanceofconnectingcablesas
lowaspossiblebyusingreasonablyheavygaugecables.Ourrecom-
mendationsare.—
Loudspeakersunder10metresawayfromamplifier:use16/0.2mm.
Loudspeakersover10metresawayfromamplifier:use24/0.2mm.
Phasing.Thecentreimageandcorrectspreadinstereophonicre-
productionrelieson"inphase"componentsofsoundofequalampli-
tude,anditisessentialtocheckthatyourloudspeakerandother
itemsinthe"reproducingchain"arecorrectlyconnected.Ifother
itemsinthechain,suchaspick-upcartridge,etc.,arecorrectlycon-
nected,thenthemethodofconnectionoftheloudspeakersasoutlined
abovewillbecorrect.However,thereisa simpletestworthmaking:—
Feedbothchannelsofyoursystemwitha monophonicsource,e.g.
monoradio,a monorecord,ora stereophonicsourcewiththefunction
selectorofthecontrolunitofyouramplifierswitchedto"A+ B",
"Left+ Right",or"MONO."Ifphasingiscorrect,then,whenlisten-
ingfroma centralpositionbetweentheloudspeakers,thesoundshould
appeartoemanatefroma relativelysmallareabetweentheloudspeak-
ers.Ifthephasingisincorrect,theimagewillbebroaderandspread
acrosstheareabetweentheloudspeakers.(Commercialgramophone
recordsareavailablewhichillustratethis"phasing"procedure,should
thereremainanydifficultyordoubt.)
Ifphasingofanyitemisincorrect,reversalofanyoneitemwillcorrect
thefault.
Operation.Attherearofthe701electrostaticunitwillbefounda
removableabsorbentpad,thefunctionofwhichistoreducerear
radiationinlocationswheretheloudspeakerisplacedclosetoa wall
orcorner.Thispadprovidesa usefulmethodofvaryingthedistribution
patternoftheelectrostaticunitabove500Hz.tosuitbothambient
conditionsandtheuser'spersonalpreferenceintermsoftheratioof
directtoreflectedsound.Thisabsorbentpadcanbereadilywithdrawn
withthefingersfromitsrecessintherearoftheelectrostaticmount.
Withtherearpadwithdrawn,greaterambiencewillbeexperienced—
dependingonthereflectivenatureofthewallandfurnishingsbehind
theloudspeaker— therewillbea slightincreaseinsoundlevelabove
500Hz.withtheelectrostaticunitoperatinginthiscondition.Ifitis
8

JI
desiredtooperatetheDM70atveryhighsoundlevels,orwherehigh
poweredcontinuoussinewaveinputsareapplied,therearabsorbent
padshouldbeplacedinposition.
ItwillbeobservedthatontherearpanelofthePowerUnitthereis
aneonindicator.Thisshowsthatthemainssupplyisfunctioning.If
theneondoesnotlightwhenthemainsisconnected,thefuseshould
bechecked.A sparefuseisprovided— butrepeatedreplacements
shouldnotbemade— andifthisfailsyoushouldconsultyourdealer.
ThecontinentalDM70isprotectedoninputwithfuses,accessibleon
therearpanelofthepowersupply(seefigure1 page6).Thecorrect
valuesare1.5ampforthefusemarkedTreble,and2 ampforthe
fusemarkedBass.

AlthoughinthecaseoftheDM70(duetoitsremarkabledispersion
characteristic)positioningisnotascriticalaswithmanyconventional
loudspeakersystems,thissystemisquitea substantialpieceof
furnitureinitsownright,anditisworthwhiletakingcareinsitingthe
loudspeakersinthemostacceptablepositions,bothvisuallyand
acoustically.
Itwillbefoundthatthestereoimageispreservedovera widelisten-
ingangle,andthesatisfactorylisteningarealargerinthecaseofthe
DM70thanwithmostconventionallydesignedloudspeakers.
Exampleofsitingsofa pairofDM70'sanda pairofconventional
Loudspeakersareillustratedinfigure3.
Fig.3 Listeningareashownhatchedin.
Asimpleguidetositing.
1.Itissuggestedthatininitiallayouta flexibleleadisused,andthe
positionsoftheloudspeakersexperimentedwithonfamiliarmusic
untila naturalbalanceisobtained.Permanentinstallationmay
thenbeundertakenaftertheexactpositionshavebeendecided.
2.Bassresponsewithinthebottomtwooctaveswillvarywiththe
positionsoftheloudspeakersrelativetoanyplanesurfaces.
Minimumbasswilloccurintheunlikelyeventoftheloudspeakers
beingsituatednearthecentreofa room.Conversely,maximum
bassresponsewillresultshouldtheloudspeakersbetightly
"coupled"tothecornersoftheroom.
10
10

3.DuetothewideandbalancedhorizontaldispersionoftheDM70,
theirhorizontalpositionwillnotbecritical.Wewouldnormally
suggestthatindomesticroomsofnormalsizetheybenotcloser
thaneightfeet(2.5metres)apart,orseparatedbymorethan
fifteenfeet(4.5metres)togiveanevenandsolidstereoimage.
4.Thefinalpointforconsiderationiswhethertoplacetheloud-
speakersparallelwiththewallorsurfaceortoanglethemtowards
thelisteningarea.Thegoverningfactorsarethedistancebetween
theloudspeakersandthedistanceofthelistenersfromthem.
ConsiderablelatitudeisofferedinthecaseoftheDM70,but,asa
generalrule,theanglebywhichtheyshouldbeturnedisincreased
thefurthertheyareapartandthecloseryouareseatedtothem.

Ancillaryequipment
Becauseofitsexceptionallygoodfrequencylinearityandrelative
freedomfromcolourationanddistortion,theDM70iscapableofex-
tremelyfaithfulreproduction,providedthatthesignalfedtoitisof
theveryhighestquality.A monitorloudspeaker— andtheDM70is
sucha high-qualitysystem— isthereforeanalyticalandwillreveal
faultsinancillaryequipmentandprogrammematerialwhichcouldwell
bemaskedbyaninferiorloudspeaker.
Itisnotappropriateinthisinstructionbooktorecommendspecific
itemsofancillaryequipmentandfortunatelythereisa widerangeof
topqualityequipmentavailable.Ingeneralterms,however,itiswise
tomatchthequalityofthevariousitemsinthereproducingchain.A
goodguidebeingtospendapproximatelyequalamountsonthepick-
uparmandmotorcombination;ontheamplifierortuner/amplifier;and
ontheloudspeakers.
Thepowerratingrequiredoftheamplifierwilldependonthesizeof
yourlisteningroom,onthepreferredlisteninglevel,aswellasonthe
sensitivityoftheloudspeakers.TrueRMSoutputsofbetween25and
100wattsperchannelwillmeetallrequirements.
VolumeandTonecontrolSettings.Thecorrectoperationofthese
controlsisimportantifrealisticreproductionistobeobtained.Deal-
ingfirstlywithvolumecontrolsetting:itisimportanttosetthevolume
controlofyouramplifieratsucha levelastorecreatetheoriginal
levelofsoundthatwouldbeheardintheconcerthallorplaceof
originalliveperformance.
Formanyreasonsitmaynotalwaysbepossibletolistenatoriginal
soundlevels.Forthisandotherreasons,tonecontrolsareprovided.
Theactualtonecontrolsettingswilldependona numberoffactors
toonumeroustodetail.Asa generalguide,orchestralmusicwill
requiresomebassliftandlittle,ifany,treblecontrolwhenplayed
belownaturallevel,speechwillrequirebasscutandslighttreblecut
whenplayedabovenaturallevel.Betweenthesetwoextremesthere
aremanysettingswhichwillbequicklydeterminedbylistening.
12

Specification
GeneralDescription
B.& W.DM70isa hybriddesignemploying
exclusiveModel70111-elementwidedis-
persiondoubletelectrostaticunit(patent
no.1239658),DW13/70highpowerlow
distortionmovingcoilbassunitwithcom-
plexcrossoverandfilterunitanddividing
network.Relativesensitivitiesbetweenthe
dynamicandelectrostaticunitsareaccu-
ratelyequalisedbya massiveautotrans-
former.
Thevitallyimportantmiddleandupperfre-
quenciesarehandledwithouttheattendant
phasedistortionassociatedwithcrossovers
inthisregionandtheexceptionallywide
dispersionofthesefrequenciesgivea much
greaterdegreeofstabilityofthestereo
image.
AlternativeCabinetstylingsareavailablebut
bothofferanextremelyrigidcritically
dampedinfiniteenclosurewithlowsystem
resonance.Thebassdriverisa nocom-
promiseunitcapableofhandlinghighpower
withextremelylowdistortionandemploys
aspeciallybracedconeassemblywithdamp-
ingpadsatcriticaldampingpointsandthe
exclusiveB.& W.triplesuspension.
DetailedSpecification
DriveUnits
DW13/70.Thislowfrequencyunit,ofnom-
inalpistondiametertwelveinches(305mm)
isofsizeconsistentwiththeenclosure
volumeandmethodofacousticloadingused.
Theresultingsystemresonanceis40Hz.,
theunititselfhavinga freeairresonanceof
approximately28Hz.
Theconeisformedfromlongfibrepaper
material,withmassadjustmentanddamping
(todiscourageconebreak-up)providedby
criticallypositionedrectangularsectionof
syntheticrubberattachedtotheconeface.
Themassiveceramicmagnetassembly,in
conjunctionwiththelowimpedanceofthe
voicecoil,ensureshighdampingleadingto
excellenttransient-handlingcapacity.
Electrostaticmid-andhigh-frequencyunit.
The701electrostaticmodule(patentnum-
ber1239658)coversallaudiofrequencies
above500Hz.3yvirtueoftherelatively
smallverticaldimensionoftheunit,the
verticaldistributionisexcellentinthemid-
frequencyregionandthecurvedgeometry
oftheelevenintegratedmodulesineach
701providesverywideanduniformfrontal
radiationofsound,witha strongrear
radiationpatternwhichcanbecontrolledto
suitambientconditionsorpersonaljudge-
ment.
Intermsofdistortion,newstandardsare
setandreferencetothefigures,inthe
followingpages,showingharmoniccontent
willdemonstratetheextremelylowlevels
ofthecommonlytroublesomeoddharm-
onicsathighsoundpoweroutput.
Thepowerhandlingofthismid-highfre-
quencyunitconfirmsresearchfindingsthat
itiswithinthemid-frequencyband(say
500Hz.to5 kHz)thatmaximumpoweris
applied.Theconceptofthe701electro-
staticunitprovidescoverageofallaudio
frequenciesabove500Hz.reducinginter-
modulationdistortionandDopplereffect.
13
DW 13/70 Bass Unit

Aprimedesignpointofthe701isthatitis
free-standing.Thismakesitpossibleeasily
toremovetheunitintheeventofdamage
etc.,andservicebeingrequired,thusavoid-
ingthetransportationofentireheavyand
bulkysystem.
CrossoverandFilterUnit
The500Hz.crossoverfrequencybetween
theDW13/5bassunitandthe701electro-
staticunitensuresthatboththesetransducer
elementsoperateovertheiroptimumfre-
quencyranges.Carehasbeentakeninthe
designofthelow-passsectionofthefilter
toensurethatmaximumamplifierdamping
maybetransferredtothebassunitbythe
useofheavygaugecopperintheseriesin-
ductor,overa ferritecore.Inaddition,an
impedance-andlevel-controllingtransformer
formsa partofthebassunitfilter.
Thepowersupplyandhigh-passfilterfor
the701electrostaticunitissolidlyand
safelyhousedina steelcase.Themainslead
iscaptive,forsafety.
Cabinet
Thecabinetisconstructedof25mmchip-
board;inthecaseofthe"Continental"
version,thecurvedfrontformedfrom19mm
plywood.Thegrillematerials(earthedmetal,
frontandrearfortheelectrostatic)have
beenchosentogiveminimaldeterioration
oftheacousticperformance.
The"Standard"versionofthecabinetis
availableinteakorwalnutveneersanda
choiceofwalnutveneerorsatinwhitefinish
forthe"Continentals."
AcousticLoading
Theacousticloadingforthebassdriveunit
isofthe"infinitebaffle"type,synthetic
dampingmaterialbeingusedtoachieve
optimumsystem"Q".A resonance-control-
lingremovablepadisfittedtotherearof
theelectrostatic.
Sensitivity
17wattsintonominalimpedancerequired
toproducea soundlevelof95dB.atone
metreat400Hz
PowerHandling
TheDM70issuitableforhighqualityamp-
lifierswithtrueRMSoutputsofbetween
25and100watts,withdoublefusepro-
tectiononC andCAversions.
14
Electrostatic Unit model 701

STANDARD
CONTINENTAL
Dimensions.
Weight:Weightwithstand:45.4kg.(100lbs)
Standard
OverallHeight(onStand)31i " (808mm)
OverallWidth32"(815mm)
OverallDepth15"(382mm)
Continental
OverallHeight(onStand)32s"(820mm)
OverallWidth26s"(680mm)
OverallDepth151"(390mm)

FrequencyResponse.On-Axis± 5 dB.60Hz.to15kHz.
Onaxisresponseofa productionsampleDM70takeninFt& D AnechoicChamber.
B& K equipmentusedthroughout,withtype4133microphoneat1 metre.
CrossoverandFilterUnit.IndividualAcousticoutputfromeachDriveUnit,showing
Crossoverfrequency.
PolarDistribution.+ 3 dBenvelopetoon-axisfrom20Hzto20kHzover60degreearc.
DM70responsefor30degreearcand60degreearcs.
16

Impedance.Nominalimpedance8 ohms.Notgreaterthan30ohmsorlessthan4 ohms
20Hzto9 k.Hz.,theimpedanceminimumoccurringina frequencyregionofverylow
musicenergy.
PlotofimpedanceofproductionsampleofDM70.
Distortion.Harmonicanalysisplottedagainstfrequency
Contentof2nd.and4th.Harmonics.
Contentof3rd.and5th:Harmonics.
17

TransientResponse.ToneBurstoscillogramstakenatone-thirdoctaveintervalsinou
ResearchAnechoicChamber.MicrophonetypeB & K 4133.
31.5Hz40Hz50Hz63Hz80Hz
100Hz125Hz160Hz200Hz250Hz
315Hz400Hz500Hz630Hz800Hz
1kHz1.25kHz1.6kHz2.0kHz2.5kHz
3.15kHz4 kHz5 kHz6.3kHz8 kHz
10kHz12.5kHz16kHz20kHz
18