JBL 4671 User manual

InstructionManual
MotionPictureLoudspeakerSystems:
AGuideToProperSelectionAndinstallation
A.Introduction: B.SystemsforSmallerHouses:
Inrecentyears,JBLhasemergedasthepredomi-
nantmanufacturerofloudspeakersystemsforthemo-
tionpicturetheater.Ourproductsaretobefoundinthe
mostprestigiousscreeningroomsanddubbingtheaters
inHollywood,includingWarnerHollywoodStudios,Glen
GlennSound,TheBurbankStudios,UniversalStudios,
andTodd-AO.Therecentinstallationofa JBLsystemin
theGoldwynTheateroftheAcademyofMotionPicture
ArtsandSciencesrepresentsa benchmarkforourcom-
pany.Ourcomponentshavealsobeenselectedby
Lucasfilm,Ltd.,fortheirTHXtheatersystem.
ThereareseveralreasonsforJBL'ssuccessinmo-
tionpicturesound.Foremosthereisourconceptofflat
powerresponse,whichresultsinanorderofimprove-
mentinsoundcoverageinthetheater.Second,our
componentsareofprovenreliabilityandhaveextended,
inherentlysmoothresponse.Inaddition,wemanufac-
turecomponentsforallaspectsoftheatersound.JBL's
systemsareverycosteffectivewhencomparedtothe
ventedhorn/multicelldesignsofearlieryears.
Thismanualisintendedforboththeaterdealersand
prospectivepurchasersoftheatersystems.Itwillbeuse-
fulasa guidetotheselectionandinstallationofsystems,
anditwillprovideconsiderabletheoreticalbackground
forthespecifyingengineer.
1. A SummaryofHouseTypes:
Byfar,mostofthetheatersconstructedtodayare
relativelysmallrectangularrooms.Theyareusuallybuilt
ingroupsknownasmultiplextheatersforeconomicrea-
sons. Mostofthesetheatersaremonophonic,witha sin-
gleloudspeakerbehindthescreen,andseatingcapacity
rangesfrom200upto500.
2. GeneralAcousticalCharacteristics:
Motionpicturetheatersaregenerallyacoustically
"dead" rooms,withreverberationtime,eveninthe larg-
esthouses,notexceeding1.25seconds.Inmostmulti-
plextheaters,reverberationtimesareontheorderof0.5
seconds.Theshortreverberationtimeensurescleardia-
logthroughoutthehouse.
Themostcommoninteriortreatmentoftheatersis
double-foldvelour,whichmaybeplacedonthesideand
rearwalls.Thiswillprovidefreedomfromunwantedre-
flections,butitdoesnothingtoisolateonemultiplex
spacefromtheadjacentone.Here,thearchitectmust
relyonsolidblockwallsforgoodisolation.
Anyunusualacousticalproblemsshouldbereferred
toa qualifiedacousticalconsultant.

3.SoundLevelRequirements:
Normalpeaklevelsof85dBSPLarecommoninthe
theater.A minimumheadroomlevelabovethisfigure
wouldbe10dB;thatis,thesystemshouldbecapableof
handlingpeaksupto95dB-SPLWhereverpossible,
JBLrecommendsthata headroomfigureof15dBbe
designedintothesystem.
Thefollowingfactorshavebeentakenintoaccount
indeterminingsystemandamplifierchoiceforvarious
housesizes:
a.Roomvolume
b.Roomboundary
c.Reverberationtime
d. Systemsensitivityandpowerrating
e.Systemdirectivityindex
4. RecommendationsforVariousSizeTheaters:
A.Fortheatersseatingupto200patrons;volume
approximately1700cubicmeters(60,000cubicfeet):
*Preferredsystem:Model4673(directradiatorLF)
Powerneededfor100dB:46watts
Recommendedpoweramplifier:JBL6230in
bridgedmode(300wattsinto8 ohms)
Characteristics:Broad-bandsensitivity97dB,one
wattatonemeter;500-HzcrossoverintoBi-Radialhorn;
integralpowerresponsecorrection;smoothresponse
downto45Hz;idealqualityforbothdialogandmusic;
shallowprofile.
*Alternatesystem:Model4671(directradiatorLF)
B.Fortheatersseatingupto350patrons:volume
approximately2800cubicmeters(100,000cubicfeet):
*Preferredsystem:Model4670B
Powerneededfor100dB:30watts
Recommendedpoweramplifier:Singlesectionof
JBL6230(75wattsinto4 ohms,theimpedanceofthe
low-frequencysectionofthe4670Bsystem.)
Characteristics:Sensitivity,100dB,onewattatone
meter;500-Hzcrossoverformostnaturaldialogand
musicquality;integralpowerresponsecorrection;LF
responsesmoothdownto45Hz;shallowprofile
'Alternateventedhornsystems:Models4672Aand
4674A
Powerneededfor100dB:30watts
Characteristics:Mid-bandsensitivity,103dB,one
wattatonemeter;LFresponselimitedduetohorn load-
ing; tobespecifiedwhereavailableamplifierpoweris
limited(typically,50wattsorless)
C.Fortheatersseatingupto500patrons:volume
approximately4500cubicmeters(160,000cubicfeet):
'Preferredsystem:Model4670B
Powerneededfor100dB:50watts
Recommendedpoweramplifier:singlesectionof
JBL6260(300wattscanbedeliveredinto4 ohms,the
impedanceofthelow-frequencysectionofthe4670B
system)
Characteristics:Sensitivity,100dB,onewattatone
meter;500-Hzcrossoverformostnaturaldialogand
musicquality;integralpowerresponsecorrection;
smoothresponsedownto45Hz;shallowprofile
Powerneededfor100dB:46watts
Recommendedpoweramplifier:JBL6230in
bridgedmode(300wattsinto8 ohms)
Characteristics:Broad-bandsensitivity,97dB,one
wattatonemeter;800-Hzcrossoverwithintegralpower
responsecorrection;smoothresponsedownto45Hz;
slightlylessrealisticondialogthanrecommendedsys-
tem; shallowprofile
'Alternateventedhornsystem:Model4674A
Powerneededfor100dB:50watts
Characteristics:Mid-bandsensitivity,103dB,one
wattatonemeter;LFresponselimitedduetohorn load-
ing; shouldbespecifiedonlywhereavailableamplifier
powerislimited(100wattsorless)
*Alternateventedhornsystems:
Models4672Aand4674A
Powerneededfor100dB:23watts
Characteristics:Mid-bandsensitivity,103dB,one
wattatonemeter;LFresponselimitedduetohorn load-
ing; tobespecifiedwhereavailableamplifierpoweris
limited(typically,50wattsorless)
ThesystemsdiscussedaboveareshowninFigure
1 A,andtypicalfree-fieldresponsecurvesareshownat
BandC.
2

FIGURE1.SYSTEMSFORSMALLERHOUSES
FIGURE1A.LINEDRAWINGS
4671
PMAX=
150W
SENSITIVITY:
97dB,
1W,1 M
4673
PMAX=
150W
SENSITIVITY:
97dB,
1W,1 M
4670B
PMAX=
300W
SENSITIVITY:
100dB,
1W,1 M,
4672A
PMAX=
150W
SENSITIVITY:
103dB,
1W,1 M
4674A
PlVlAX=
150W
SENSITIVITY:
103dB
1W,1 M
FIGURE1B.ON-AXISRESPONSEOF4670B (2TT LOADING);
HIGH-FREQUENCYPOWERRESPONSE
CORRECTED.
3
dB
Relative
Response
FrequencyinHz

FIGURE1C.ON-AXISRESPONSEOF4674A (2TT LOADING);
HIGH-FREQUENCYPOWERRESPONSE
CORRECTED.
5.Installation of thesystems: FIGURE2.MOUNTINGTHESYSTEM
A.GeneralComments: A.PositionBehindTheScreen
JBL'stheatersystems are shipped tothe dealer in
componentform.Everyattempt is made to ship the
componentscompletesothatthesystemscan be readily
assembled. All componentsshould be inspectedprior to
beingsent outto thejobsite.Wiringinstructions forall
theatersystems are included inthe dividingnetwork
package.
Manydealerswillwant to takeadvantage of thefact
thatcertainJBLtheaterlow-frequencysystems are
availableloadedfrom the factory.These are:
4647(consisting of 4507loadedwith2225H)
4648(consisting of 4508loadedwith 2-
2225H)
Further, the 4671 OK isa factorypreassembledver-
sion of theutilitysystemwith an oakvinylenclosure and
browngrillecloth.
V3 •SCREEN
B.PhysicalConsiderations:
,ABSORPTIVE
'MATERIAL
STAND
IF
NECESSARY
MOUNTING
OFSCREEN
LOUDSPEAKER
Mounting the systembehind the screen is shown in
Figure2A. The preferredlocation is two-thirdsthedis-
tance upthe screen,andthis may require a platform.
Details of this are shown atB.
4
LF
HornLoading
LF
ReflexLoading
dB,
RelativeResponse
Frequencyin Hz

ELPlatformDetails
Framedimensions
slightlylargerthan
bottomofenclosure.
Topcovered
V2" thickplywood.
Frameandlegs,2x4
lumber
Braces1 x 4 lumber.
Bracingrequiredon
foursides.
AllJBLtheatersystemsmustbeorientedasshown
inFigure 1 A.Inparticular,themodels4670Band4675A
shouldNOTbeassembledwiththelow-frequencyenclo-
surelyingonitsside.
FIGURE3-INSTALLINGTRANSDUCERS
ANDCOMPONENTSINSYSTEMS
Theloudspeakershouldbeplacedona densefoam
rubberpadorsectionofcarpetsothatitcannotpossibly
rattlewhendrivenathighlevels.Whentheloudspeaker
isplacedonanelevatedsupport,itisadvisableto
anchortheloudspeakerwithfourormoreangleironsso
thatitcannotpossiblyshiftposition.
Thebackwallbehindthescreenshouldbecovered
witha soundabsorptivematerial.
1. High-frequencyHornAiming:
Figure3 showsdetailsofmountingthecomponents
inthevarioussystems.Notethatthehigh-frequency
hornsareaimedstraightoutintothetheater.JBLhas
foundthatthismountingwillbebestformostinstalla-
tionsforthereasonsshowninFigure4A.Sincetheoff-
axisresponseofournewhornsisquiteuniformoutto12
kHz,wecantradeofftheinversesquarelossesinthe
roomwiththeoff-axishornlossestoprovidemoreeven
front-to-backcoverageintheseatingarea.
ANGLEIRON
5
A.

FIGURE3,Cont'd
6
HORN/DRIVER
SCREWEDINPLACE
PANELREMOVED
B.
C.4 WOODSCREWS*
INTOFRONTEDGES
OFLFENCLOSURE
"Use#10x2flat-headPhilipswoodscrew;pre-drillholeswithVa"bit.
D.MOUNTINGLFTRANSDUCERSIN4507,4508,
AND4518 E.MOUNTINGLFTRANSDUCERSIN4550BKA
AND4560BKA

FIGURE3,Cont'd
H.(Seenoteintextconcerningpolarity)
INCLUDED
WITH
NETWORK
INSERT
T-NUTS
#6
SCREWS
TERMINALBOARD
PLATEREMOVED
FROMINSIDE
F. G.
For4671,4672A,4673,4674A: For4670B:
3115A
311OA
J.
7

FIGURE4.PROPERAIMINGOFHIGH-FREQUENCYHORNS
A.INVERSESQUARE,OFF-AXISTRADE-OFF
0°(Maximumoutput)
FIGURE4B.CADPDISPLAY;HFHORNAIMEDSTRAIGHTAHEAD
Screen!
HFHorn
10' high
12'
2kHz
8

FIGURE4C.CADPDISPLAY;HFHORNAIMED10°DOWN
Screen]
HFHorn
10'high
12'
2kHz
Furtherevidenceofthisbenefitisshowninthe
CADP(seereference)coverageplotshownatB.Here,
thefront-to-backvariationincoverageisonly5 dB,and
thismeansthatthemajorityofpatronswillreceiveexcel-
lentcoverage.Comparethiswiththecoverageshownat
C.Here,wehavetiltedthehigh-frequencyhorndownby
only10degrees!Theresultingcoveragevariationhas
increasedto8 dB.
Onlywherethereisa pronouncedrake(8degrees
ormore)tothefloorshouldthesystembeangledslightly
upwardtowardtheback wall. Thiscanbeaccomplished
byplacinga stripofwoodbeneaththefrontedgeofthe
loudspeaker.
C.WiringConsiderations:
AllJBLnetworkandtransducerterminalsarecolor
codedsothatconsistentpolarity(phase)ofallsystems
isassured.
Inthefollowingsystems,allconnectionsbetween
transducersandnetworksshouldbebetweenlikecoded
terminals.Inotherwords,redtored,andblacktoblack:
high-frequencysectionshouldbewiredinreverse
polarity:
4670B
4673
Thereasonforthishastodowiththeprecise posi-
tioningofthehigh-frequencydriverwithrespecttothe
low-frequencyacousticcenter.Thereisone-halfwave-
lengthshiftatthecrossoverfrequencyinthesesystems
whichrequiresthepolaritychangetomaintainproper
summationwiththelow-frequencysection.
Wiringfromtheprojectionboothtothescreen loud-
speakersshouldconformtolocalcodes.Thewiregauge
selectedshouldbesuchthatelectricallossatthe loud-
speakerdoesnotexceed0.5dB.Formostapplications
insmallerhouses,AWG#12(2.053mm)copperwire
willbesufficient.ThetableshowninFigure5 showsthe
wireresistanceforvariousdoublerunsofcopperatvar-
iousgauges.For8-ohmloudspeakers,thetotalwire
resistanceshouldnotexceed0.552ohms.
FIGURE5.TABLEOFWIRELOSSES
4671
4672A
4674A
Inthefollowingsystems,thelow-frequencysection
shouldbewiredredtoredandblacktoblack,butthe
WIRERUN(DOUBLE;COPPER)
NO. 10
NO .12 NO .14
NO .16
NO. 18
10M (33')
.02
.032
.05 .08
.125
20M (66') .04
.064
.10
.16
.250
30M (100')
.06
.096
.15 .24
.375
40M (132')
.08
.128 .20
.32 .500
50M (165') .1
.160 .25
.40
.625
60M (200') .12 .192 .30
.48
.750
FOR 8HLOAD, LINE RESISTANCESHOULDBE0.552ORLESS.
9
Nornalizeddirectfield.

Themodels4670Band4675Ahave4-ohmlow-
frequencysections,andthetotalwireresistanceshould
notexceed0.276ohms.
C.SystemsforLargerHouses:
1. GeneralComments:
Theclassofhousesconsideredherewillallhave
multichannelsystems.Seatingcapacitymaybeaslittle
as500andaslargeassomeoftheoldmoviepalacesof
yesterday.Therearefewofthelatterleft,exceptinlarge
metropolitanareas.Forthemostpart,thelargertheaters
havebeenconvertedintomultiplextheaters.
Thenumberofloudspeakersbehindthescreenwill
beeitherthreeorfive,andtherewillalwaysbea sur-
roundchannelconsistingofsixormoresmaller loud-
speakersarrayedonthesideandrearwalls.
ThesesystemswillbecapableofplayingDolby
films, andthird-octaveequalizationwillbeemployed,as
partoftheDolbyequipment,toadjustthesystemtothe
roomaccordingtoa standardresponsecurve.
Ingeneral,theclassofaudioequipmentusedin
theseinstallationswillbetheequalofthefinestequip-
mentspecifiedforhigh-qualitysoundreinforcementsys-
temsinauditoriumsandconcerthalls.
DONOTmixdifferentsystemsinthemultichannel
screenloudspeakerarray.Notonlywilltherebe dif-
ferencesinpowerhandling,theremaybepolarity dif-
ferences,andthesewilladverselyaffectstereophonic
performance.
Wewillnowcoverindetailtherequirementsfor
thesesystems.
2. SystemRecommendationsforLargeHouses;
500to2000seats;volume14,000cubicmeters
(500,000cubicfeet):
*Preferredsystem:Model4675A(directradiator
LF)
Powerneededfor100dB:90watts
Recommendedpoweramplifier:JBL6260,one
loudspeakersystemperchannel(300wattsinto4 ohms)
Characteristics:Broad-bandsensitivity100dB-
SPL, onewattatonemeter;JBL'smostpower-flatand
accuratesystem;useslargeBi-Radialhornforprecise
90-by-40degreepatterncontroldownto500Hz;integral
powerresponsecorrection;extendedresponsedownto
45Hz
Forverylargehousesandforthehighestdegreeof
performanceinprofessionaldubbingtheatersand
screeningrooms,the4675A-2maybespecified.Werec-
ommendthatbiamplificationbeseriouslyconsidered
withthissystemforoptimumperformance.Thebroad-
bandsensitivityofthe4675A-2is103dB,onewattat
onemeter.
*Alternateventedhornsystems:
Models4676B-1and.4676B-2
Powerneededfor100dB:80and53watts,
respectively
Recommendedamplifier:JBLmodel6260,one
channelperloudspeakersystem(300watts)
Characteristics:Mid-bandsensitivity,106and109
dB-SPL,respectively;recommendedforretrofitinlarge,
olderhouseswherea completeconversiontoall-new
hardwareisnotfeasible.LFresponserollsoffbelow80
Hz
Thesystemsdiscussedinthissectionareshownin
Figure6A.ResponsecurvesareshownatB andC.
3.Systemimplementation:
A.Electricalconsiderations:
Thesystemsintendedforlargerhousesmaybe
implementedwithJBL's3160high-levelnetwork,with
wiringasshowninFigure7AthroughB.
However,foroptimumperformance,werecommend
biamplificationusingtheJBLmodel5234Aelectronic
dividingnetwork.The5234Aisavailablewitha 500-Hz
cardwhichcontainshigh-frequencypowerresponse
correction. Implementationofbiamplificationisshownin
Figure7C.
Thechiefvalueofbiamplificationisthereductionof
intermodulationdistortiononpeakprogramsignals.Fur-
thermore,largerpoweramplifiersmaybespecifiedfor
theLFsectionsthanthoseindicatedforusewiththe
high-leveldividingnetwork.
10