NHT A-20 User manual

Copyright2001NHTPro,aRecotonCorporationBrand
A-20
OwnersManual
A-20LeftMonitorSerialNumber:
A-20RightMonitorSerialNumber:
A-20ControlAmplifierSerialNumber:

CAUTION
RISKOFELECTRICSHOCK
DONOTOPEN
WARNING:SHOCKHAZARD-DONOTOPEN.
AVIS:RISQUEDUCHOCELECTRONIQUE-
NEPASOUVRIR.
SafetyInstructions--PleaseReadFirst
DETAILEDSAFETYINSTRUCTIONS:
Allthesafetyandoperationinstructionsshouldbereadbeforetheapplianceisoperated.
RetainInstructions:
Thesafetyandoperatinginstructionsshouldberetainedforfuturereference.
HeedWarnings:
Allwarningsontheapplianceandintheoperatinginstructionsshouldbeadheredto.
FollowInstructions:
Alloperationanduserinstructionsshouldbefollowed.
WaterandMoisture:
Theapplianceshouldnotbeusednearwater(e.g.nearabathtub,washbowl,kitchensink.laundrytub,inawetbasement,ornearaswimming
pooletc.).
Ventilation:
Theapplianceshouldbesituatedsothatitslocationorpositiondoesnotinterferewithitsproperventilation.Forexample,theappliance
shouldnotbesituatedonabed,sofa,rug,orsimilarsurfacethatmayblocktheventilationopenings,orplacedinabuilt-ininstallation,such
asabookcaseorcabinetthatmayimpedetheflowofairthroughtheventilationopenings.
Heat:
Theapplianceshouldbesituatedawayfromheatsourcessuchasradiators,heatregisters,stoves,orotherappliances(includingother
amplifiers)thatproduceheat.
PowerSource:
Theapplianceshouldonlybeconnectedtoapowersupplyofthetypedescribedintheoperatinginstructionsorasmarkedonthe
appliance.
GroundingandPolarization:
Precautionsshouldbetakensothatthegroundingorthepolarizationmeansoftheapplianceisnotdefeated.
PowerCordProtection:
Powersupplycordsshouldberoutedsothattheyarenotlikelytobewalkedonorpinchedbyitemsplaceduponoragainst them,
payingparticularattentiontocordsandplugs,conveniencereceptaclesandthepointwheretheyexitfromtheappliance.
Cleaning:
Theapplianceshouldonlybecleanedasrecommendedbythemanufacturer.
Non-usePeriods:
Thepowercordoftheapplianceshouldbeunpluggedfromtheoutletwhenleftunusedforalongperiodoftime.
ObjectandLiquidEntry:
Careshouldbetakensothatobjectsdonotfallandliquidsarenotspilledintotheenclosurethroughopenings.
DamageRequiringService:
Theapplianceshouldbeservicedbyqualifiedservicepersonnelwhen;
Thepowersupplycordortheplughasbeendamaged;or
Objectshavefallen,orliquidhasbeenspilledintotheappliance;or
Theappliancehasbeenexposedtorain;or
Theappliancedoesnotappeartooperatenormallyorexhibits amarkedchangeinperformance;or
Theappliancehasbeendropped,ortheenclosuredamaged.
Servicing:
TheusershouldnotattempttoservicetheappliancebeyondwhatisdescribedintheOperatingInstructions.Allotherservicing
shouldbereferredtoqualifiedservicepersonnel.
CAUTION:Toreducetheriskofelectricshock,donot
removethecover(orback).Nouserserviceablepartsare
inside;referservicingtoqualifiedpersonnel.
WARNING:Toreducetheriskoffireorelectricshock,do
notexposethisappliancetorainormoisture.
Thissymbolwhereveritappears,alertsyoutothe
presenceofuninsulateddangerousvoltageinsidethe
enclosurethatmaybesufficienttoconstituteariskof
electricshock.
Thissymbol,whereveritappearsalertsyouto
importantoperatingandmaintenanceinstructionsin
theaccompanyingliterature.Readthemanual.

RackRail
A-20
Amplifier
FrontPanel
Screws Insulating
Washers
Fig.1:RackMountingDetail
INTRODUCTION:
ThankyouforyourselectionoftheA-20.Yourstudiomonitorsareacriticalelementinthecountless
decisionsmadeduringrecording,mixing,masteringandotherkeyaspectsofaudioproduction.They
mustdeliveratransparent,neutralandrevealingassessmentofsound,sothatyouhavethe
informationyouneedtochooseandplacemicrophones,setEq’s,balancemixes...Inotherwords,deliver
exceptionalproduct.TheA-20iscapableofstateoftheartsonicresolutionandflexibility.Investing
timetolearnabouttheA-20’sfeaturesandoperationwillrewardyouwith thebestpossible
performance.
Ifyourequireassistanceatanytimeduringorafterthesetupprocess,callourCustomerServiceHotLine
at(800)-NHT-9993(648-9993).Youcanalsovisitourwebsiteatwww.nhtpro.comformoreindepth
technicalinformation.Thanksagainforyourconfidenceinourproducts!
GETTINGSTARTED:
TheA-20isuniqueinthatitcombinesadedicatedcontrolamplifierwithloudspeakermonitorcabinets,using
controlledimpedancecablesthatactuallyformpartofthecrossovernetwork.Bydesigningthesystem
asanintegralpackageinthismanner,manyoftheadvantagesofself-poweredspeakerscanberealized
withoutattendantperformancecompromises.However,itmustberecognizedthatthecontrolamp,cablesand
monitorsareaninseparablepackage.
ThefollowingareincludedintheControlAmplifiercarton:
1ea.-ControlAmplifier2ea.-20'MonitorOutputCables
1ea.-6'IECPowerCord4ea.-10-32RackMountingScrews
1ea.-WarrantyRegistrationCard8ea.-PlasticInsulatingWashers
Note:TheA-20mustonlybeusedwiththeA-20ControlAmp,cables,andviceversa!.
TheA-20ControlAmplifiermaybeusedonashelf,ormountedinastandard19”equipmentrackusingthe
screwsandwasherssupplied.Forrackmounting,removeandretainthefourfeetfromthebottomoftheamp
chassisusinga#2Philipsscrewdriver.Twoverticalrackspacesarerequired,butwerecommendyouleave
atleastoneadditionalopenspaceaboveandbelowtheA-20forimprovedcooling,asyouwouldwithany
highpoweramplifier.Fortableorshelfuse,thefourfeetmustremainattachedtoallowforaircirculation.As
astartingpointforspeakerplacement,alignthebackoftheenclosuresparalleltotherearwall,withtheangled
frontsfacingintowardsyou.Formoredetailedspeakerplacementinformationseepage7.
Fig.2TypicalSystemConfiguration
MPOWER
SENSITIVITY BOUNDARY POSITION
+11 +4 -3 -10 FFNF
MF
02
1
SPL TMP VAC
MODE PHONES
A-20 Control
Amplifier
100
Signalflow
.
ToACLine
Signalflow
Signalflow
MonitorOutputCables

SYSTEMCONNECTIONS:
CAUTION:
CAUTION:
CONTROLAMPLIFIERINPUTSECTION:
SPEAKERCABLECONNECTIONS:
MAKEALLCONNECTIONSWITHTHEACPOWEROFF!
CONNECTINGTHEOUTPUTOFTHEA-20CONTROLAMPLIFIERTO
ANYEQUIPMENTOTHERTHANTHEA-20ORC-20MONITORMAY
CAUSEEQUIPMENTDAMAGE.
TheA-20ControlAmplifieracceptsbothbalancedandunbalancedinputsoneitherXLRor1/4”TRSconnectors.
TheseconnectorsarehardwiredinparallelwithintheA-20toallowforconvenientequipmentchaining,butonlyone
signalsourceshouldbephysicallyconnectedtotheunitatanytime.Figure3ashowstheproperwiringschematicfor
eachtypeofconnector.Sincetherearesomanydifferentconnectortypesandsignallevelsemployedbysource
equipment,someexperimentationmaybenecessary,keepinginmindthattheA-20canacceptawiderange
ofsignalsandhasaninputsensitivitycontrolonthefrontpanel.
TheA-20includestwo20’specialpurposecablestoconnecttheControlamplifiertotheMonitors.Whilethese
cableslooksimilartostandardmicrophonecables,theyareconstructedwithlowerandmoreconsistentconductor
impedance.PortionsoftheA-20’scrossovercircuitryarelocatedinboththeamplifierandspeakerenclosures,and
thecablessuppliedareanimportantpartofthiselectricalnetwork.Thisallowsthespeakercablestofunctionasa
neutralandtransparentcomponentinthesystem.Replacingorextendingthesuppliedcableswithanyothertype
willhaveavarying,andonlypartlypredictableimpactonthesoundoftheA-20.Ifyourinstallationrequirestheuse
ofalternativecables,youmayconsultthetablelistingourmeasurementdataonavarietyofcabletypesat
www.nhtpro.comunderthesupportsection.BesuretheyarewiredasshowninFig.3a.Theseconsiderationsaside,
usingthesuppliedcablestoconnectthecontrolamplifierisquitesimpleandstraightforward.Boththeamplifier
andthemonitorsaremarkedwiththeappropriate“left”and“right”channels.FittheXLRconnectorsintothe
correspondingconnectorsonthecontrolamplifierandmonitorsuntiltheconnectorlocks.
WARNING: IFUSINGCABLESOTHERTHANTHOSESUPPLIEDWITHTHISSYSTEM,
BESURETHATNOCONDUCTIORISWIREDTOTHEXLRCASING.
FAILURETODOSOMAYCONSTITUTEARISKOFELECTRICSHOCK.
Fig.3aBalancedWiringDiagram
1
2
3
+(SIGNAL)
-(GND) Shield
SOURCE A-20INPUT
Fig.3bUnbalancedWiringDiagram
NHTPro
MODELA-20CONTROLAMPLIFIER.
SERIALNO:
NHTPro
BENICIA,CALIFORNIA,U.S.A.
A20-A-10001
MADEINTAIWAN G1
CAUTION:
CONNECTINGOUTPUTSTOANY
PRODUCTOTHERTHANA-20or
C-20MONITORSMAYRESULTIN
SEVEREEQUIPMENTDAMAGE.
FUSETYPE:
T9A250VFOR110/120V.
T5A250VFOR220/240V.
50/60Hz-950W
INPUTVOLTAGE
CAUTION
RISKOFELECTRICSHOCK
DONOTOPEN
WARNING:SHOCKHAZARD-DONOTOPEN.
AVIS:RISQUEDUCHOCELECTRONIQUE-
NEPASOUVRIR.
FORCONTINUEDPROTECTIONAGAINST
RISKOFFIREREPLACEONLYWITHSAME
TYPE250VFUSE.
CAUTION:
Fig.4A-20ControlAmplifierRearPanel

USINGTHEA-20CONTROLFUNCTIONS:
POWERINDICATORS:
SYSTEMSTATUSDISPLAY:
SENSITIVITY:
TheA-20controlsaredesignedforutilityandrepeatabilityundervaryingconditions.Youshouldfindtheeffectsofthe
controlssonicallysubtle,withlittleimpactonthebasiccharacterandaccuracyofthespeaker.Weencourage
experimentationtofinetunethesystemtotherequirementsofyourparticularinstallation.
JusttotheleftofthepowerswitchontheA-20ControlAmplifieraretwostatusLED's.Theupper(green)
LEDlightsupindicatingthereisACpowertotheamplifierandthePOWERSWITCHisinthe“on”position.The
lower(red)LEDindicatesaclippingoroverloadcondition.Occasionalflashingofthisindicatorisagentlewarningyou
arereachingthesystem’slimits.IftheredLEDglowscontinually,severeclippingisoccurring.Theinputsignalor
systemgainshouldbereducedtoavoidtheriskofpossiblesystemdamage.
AuniquefeatureoftheA-20ControlAmplifieristheSystemStatusDisplaylocatedinthecenterofthefront
panel.SmallLED’sindicatewhichmodeisbeingdisplayed;greenforaverageSPL,yellowforAClinevoltage,and
blueforheatsinktemperature.Thesquare“Mode”switchtotherightoftheSystemStatusDisplayselects
thedesiredmode.
SPL:Thisisthelongtermaveragesoundpressurelevelcalibratedat2metersfromastereopair,andderived
fromtheamplifieroutputvoltage.Peaksoundlevelsareignored.Thereadoutisdesignedtoinformtheuserof
overalllisteninglevels,andtohelprealizeconsistentmonitoringconditionsfromhourtohour,sessionto
sessionandroomtoroom.Levelsunder68dBareshownas“00”;levelsover120dBareshownas“HI”.
Sincemonitoringlevelhasaprofoundinfluenceontheperceptionofsonics,periodicallycheckingyourlistening
levelshelpstoassureconsistentresults. Makinganefforttocombatlongtermearfatiguecanhelpyouavoid
theheartbreakofharshmorningafterrealities.
VAC:ThisisareadoutoftheACpowerlinevoltagebeingsuppliedtotheA-20.Itisusefulforassuringthat
powerconditionsarecorrectandsufficientforalltheequipmentonthecircuit.Sustainedreadingsbelow110V
maylimityourmaximumoutputlevels,andcouldindicatethattheACcircuitisoverloaded.Continuous
readingsabove125VindicateanACcircuitproblem,whichcouldleadtoamplifierfailure.
TMP:ThisisareadingoftheoutputheatsinktemperatureindegreesCentigrade.Typically,youshouldexpect
thistorunbetween50°Cand80°C,dependingonlisteningandambientconditions.Ifyoufindthatyour
ControlAmplifierunittendstorunhotterthan80°C,itisrecommendedthatyouimprovetheventilationaroundit.
NotethattheA-20ControlAmplifierwillautomaticallyshutdowniftheheatsinktemperaturereaches100°C.
Thiscontrolisusedtochangetheinputsensitivitywithsettingsat;-10dB,-3dB,+4dB,+11dBand(M)uteproviding
noisefree,consistentgainmatchingwithawidevarietyofequipment.Thepropersettingisthelowestsensitivity
possible(highestdBnumber)whichallowsthespeakertoreachthemaximumdesiredoutputwithoutsourceclipping.
Professionaldevicestypicallyspecfulloutputat+4dB,mostconsumeraudioproductsreachfulloutputat-3dB,
andmostcomputersoundcardshaveafullscaleoutputof-10dB.Consulttheowner’smanualforthedevice
connectedtotheControlAmplifierforitsoutputlevelspecificationsandsettheSENSITIVITYcontrol
accordingly.
Fig.5A-20ControlAmplifierFrontPanel
MPOWER
SENSITIVITY BOUNDARY POSITION
+11 +4 -3-10 FFNF
MF
02
1
SPL TMPVAC
MODE PHONES
A-20 Control
Amplifier
100

BOUNDARYCONTROL:
Reflectiveboundaries,suchasfloors,walls,eventabletops,reinforceaspeaker’slowfrequencyoutput.
Conversely,placingspeakersoutintoaroomdecreasesbassresponse.Thehighestlowfrequencyoutputiswith
theBOUNDARYcontrolinthe“0”position,whichassumesnosignificantboundaryreinforcementispresent.
Eachcontrolstepattenuateslowfrequenciesby1.5dB(at50Hz),withrapidlydecreasingeffectabove300Hz.
RefertothediagraminFig.6forinformationonsettingthecontrolappropriately.
POSITIONCONTROL:
Near-fieldmonitoringreduces theeffectofroomacousticsonthesignal,andprovidesgreatersonicdetail.Mid-
andfar-fieldlisteningrevealsaspectsofrecordedambienceandismorerepresentativeofenduse.However,a
speaker’supperfrequencypowerresponsechangeswithdistance,duetoroominfluencesandairabsorption.
TheA-20maybeadjustedforflatresponseatvariouslisteningdistances.Themaximumhighfrequencyoutput
isobtainedwiththecontrolinthe“FF”(far-field)position.Eachcontrolstepattenuates20kHzbyan
additional.75dB(towardsthenear-fieldposition)withnoeffectonfrequenciesbelow3kHz.SeeFig.7for
appropriatePOSITIONcontrolsettingsbasedonlisteningdistances.
0
2
1
02
1
02
1
02
1
BOUNDARY BOUNDARY BOUNDARY BOUNDARY BOUNDARY
02
1
QuarterSpace Quarter/HalfSpace HalfSpace Half/WholeSpace WholeSpace
Fig.6.BoundaryControlSettingsDiagram
1M
0’ 1.5M 2M 2.5M 3M
Near-field Mid-field
ListenerDistance
A-20
Monitor
Far-Field
POSITION
FFNF
MF
POSITION
FFNF
MF
POSITION
FFNF
MF
POSITION
FFNF
MF
POSITION
FF
NF
MF
Fig.7.PositionControlSettingsDiagram

SPEAKERPLACEMENT:
SYSTEMOPERATION:
A-20MONITORSYSTEMCARE:
NEEDHELP?
TheA-20MonitorSystemisintendedtoprovideconsistentperformanceoverawiderangeofplacement
situations.Thisisaccomplishedthroughtheuseofelectricalcontrols,widedispersiondrivers,advanced
enclosuredesignandcarefullychosencrossovercharacteristics.Nevertheless,itisalwaysworthinvestingtime
andeffortexperimentingwithoptimumloudspeakerplacement.Inallcases,A-20Monitorsshouldbesetup
symmetricallyequidistantfromthelisteningposition;theleftspeakerandrightspeakershouldbeatthesame
relativepositionswithrespecttotheprimarylisteningarea.Thisisimportantinorderthehearaproperstereo
soundstage.Thespeakerbafflesangleintowardsthelisteningpositionwiththeloudspeakerbacksparallelto
oneanother.AgoodstartingpointcanbefoundinFigure8below.Ideally,thetweeterheightshouldbeon
axiswithyourears,orslightlyabove.Also,rememberthatnearbyreflectivesurfacescanalterimpulse
response,blurimagingandchangetonality.
TheA-20iscapableofveryhighoutputlevels,especiallywhenlisteninginthenear-field.Protectyourearsanduse
commonsense.Still,everyspeakersystemhasitslimits.Harshbreakupatextremelyhighvolume,orheat
emanatingfromthedriversisanindicationthatthesystemhasexceededitsoutputlimitsandyoushouldlowerthe
playbacklevel.WatchforexcessivelightingofthefrontpaneloverloadindicatorontheControlAmplifier.Speaker
damagemostoftenoccursfromsustainedhighvolumelevels,notfromtransientsoundsorbriefmusicalpeaks.
Exceptfortheoccasionalflatteringcomment,yourA-20Systemneedsnoregularmaintenance.Neverattemptto
cleantheA-20monitordriverunitsexceptforverylightfeatherdusting.TheA-20monitorcabinetsandtheA-20
ControlAmplifierfrontpanelcanbecleanedusingadamp,softcottonclothfirstsprayedwithamild,non-abrasive
glasscleaner.Neverspraythespeakeroramplifierdirectly!Avoidsiliconeandoilbasedcleanersortreatments.
TechnicalSupportcanbereachedseveralways:Telephoneus(800)-NHT-9993(648-9993),E-mailusat:
[email protected],Faxusat:[phone]orwriteusat:NHTPro,527StoneRd.,Benicia,CA94510.Orvisit
ourworldwidewebsiteatwww.nhtpro.com.
ListeningPosition
D
Fig.8IdealMonitorPlacement

SYSTEMSPECIFICATIONS:
PERFORMANCESPECIFICATIONS:
FEATURES/CONTROLS:
Type:Modular,two-piecepowerednear/mid/farfieldmonitor.
Configuration:2-wayacousticsuspension.
Woofer:6.5"curvilineartreatedpaper.Butylsurround.
Tweeter:1"metaldome,textilesurround,ferrofluidcooledanddamped.
MagneticShielding:Partial,12-18”workingdistancefromPCmonitorrecommended.
AmplifierPower:250W(continuousRMS/ch),400W(100mspeak).
PeakAcousticOutput:117dBSPL(100mspinknoise@1M).
Residualhum/noise:<10dBSPL@1M.
SystemTHD@90dBSPL:<0.4%(100Hz~10kHz@1M).
Response+/-2dB:48Hz~20kHz@1M,45Hz~20kHz@2M(1/3oct.sweptnoise)
-6dBLFcutoff:40Hz(in-roomresponse).
LoudspeakerDim./Wgt.:14"hx7.5"wx11.9"d,19lbs.
LoudspeakerMaterials:0.75"MDFw/highpressurelaminate(internal+external).
ControlAmp.Dim./Wgt.:3.5"hx19"wx13.375"d/37lbs.
Connectors:Input:XLR,TRS.
Outputtomonitor:XLR.
Controls:Sensitivity:5position(-10dB,-3dB,+4dB,+11dB,Mute).
Boundary:5position(0.0,0.5,1.0,1.5,2.0representingwalls).
Position:5position,near(1M),near-mid(1.5M),mid(2M),mid-far(2.5M),far
(3M~).
Power:On,off.
Display:Switchable:SPLOutput(68dB~120dB),LineVoltage(90~135VAC),HeatSink
Temp.(20-99C).
LED’s:Power,Overload.
Other:HeadphoneOutput(insertioninterruptsmainoutput).
o
NHTPro
527StoneRd.
Benicia,CA94510
ph:[phone]
fx:[phone]
www.nhtpro.com