JBL L100 CENTURY User manual

L100 CENTURY INSTRUCTION MANUAL

Excellenceisanelusivequality.It'ssoeasytorecognizeyet
sodifficulttoattain.
JBL craftsmenhavebeeninvolvedintheartofsoundfor
morethana generation — signal andsource,woodand
fabric, transducersandacoustics —all ofit.
Today thesecraftsmencontinuetoperformtothemost
rigid standardsanycraftsmencansubmitto:thosethey
imposeuponthemselves.
JBL loudspeakersarecarefullyengineeredinstruments,
painstakingly craftedandassembledtowatchmakers'
standards.JBLenclosuresexpresstheexcitementofcreative
design; theyareelegant, solid and flawlessly finished. JBL
transducersandelectronicsofferwhathasbeen
characterizedbydevotedmusiclistenersasthe
"incomparableJBLsound"
By followingthefewsimplesuggestionscontainedin
this booklet,youcanlookforwardtosuperbhighfidelity
reproduction that will retainitsclarityandrealismyear
after year.
Development of theCentury 1
PerformanceCharacteristics 2
Specifications 3
ConnectingtheL100 5
Placement 6
Listening RoomAcoustics 7
Adjusting theSystem 7
PowerCapacity 9
SystemComponents 10
ComponentRemoval 12
TheCenturyEnclosure 14
In Case of Trouble 15
Service 17
Summary 17
For Additional Information 17
JBLcontinually engages in research relatedtoproductimprovement.
New materials,productionmethodsanddesignrefinementsareintroduced
into existingproducts without notice asa routineexpressionofthat
philosophy.Forthisreason,anycurrentJBLproductmaydifferin some
respect from itspublisheddescriptionbutisalwayswarrantedtoequal or
exceed theoriginaldesign specifications unlessotherwisestated.

Themostdemandingrequirements for loudspeaker
excellence come from recordingstudios. The playback
monitor isthe standard by whichrecordings are judged—
from initial microphoneplacementthroughmixing,dub-
down andonto final mastering.
JBL's reputationforbuilding the ultimate in accurate full
sizemonitorsprompted a group of engineers from leading
recordingstudios to request a new,compactcontrolroom
monitor. Therequirementswerestringent:unprecedented
power-handling capacity,highacousticoutput without
distortion, smoothfrequencyresponsethroughout the
entire audiospectrum —all within a cabinetlimited to1.6
cubic feet in volume. The size limitation was dictated by
today'ssophisticatedrecordingtechniqueswhichoften
require that as many as24 separate monitorloudspeakers
belocated ina singlecontrolroom.
After twoyears' work, many conferences, modifications
and final fieldtesting, the productarrived. Itwas
introduced bythe ProfessionalDivisionandwas an
immediate success. Thenew JBL systemwassoon
established asthe standard for compactstudiomonitors
throughout the industry.Studiosswitching toJBL
equipmentincludeAngel,Capitol,DeutscheGrammophon
Elektra, EMI,London/Decca,MGM,RCA,Reprise,
Vanguard and WarnerBros.
DEVF.IDPMF.NT OFTHECF.NTURY
1

When itwasfoundthatmusicians,engineersandother
discriminating professionalsinincreasingnumbers
purchasedthestudiomonitorforhomeuse,JBLintroduced
the L100Century—acousticallyidenticaltothestudio
monitor, yetofferingprovocativestylingappropriatetothe
home environment.
Truncated pyramidsoftheQuadrex2 grilledramatizethe
unique lineageandadvancedengineeringoftheL100
Century. Newmethodsofsculptingsemi-rigidfoam
material gaveJBLthefreedomtoexploretexture,colorand
shape.Thisreticulated(open-pore)foam—substantiallythe
same materialusedforqualitymicrophonewindscreens—
hasbeenproventotransmitsoundas well aseventhemost
acousticallytransparentgrillecloths.Thegrilleframeand
loudspeakersystemenclosurearefinishedinhandrubbed
oiled walnut onallfour sides andcanbeplaced
horizontally orvertically.
Whether playedatbackgroundmusicleveloratconcert
hall volume,theperformanceoftheL100loudspeaker
systemisrichandrobust.Lowfrequencyreproductionis
solid andwell-defined,avoidingthe"boominess"of
unnatural accentuation.Midrangematerial,theheartofthe
audio spectrum,isreproduced with theincredible crispness
and presence whichhavelongbeencharacteristicofJBL
loudspeakers. High frequencysoundsaredelineated with
utter clarityandtransparency.Moreover,theinherent
smoothnessandlackofdistortionoftheL100Century
virtually eliminateauralfatigue,evenafterlisteningtothe
systemformanyhours.
To accuratelytesttheloudspeakersystem,a setof
evaluation parameterswasdevelopedandspecifications
derived from measurementsmadeunderstandard
laboratory testconditions.TheL100wasmountedinthe
measured center ofa large flat baffleina reverberation-free
environment, anda calibrated condenser microphonewas
suspendedata specifieddistance from thesoundsource.All
electronicequipmentwas checked andcalibratedbefore
tests wererun.
Due tothewide-anglesounddispersioncharacteristicsof
the loudspeakersystemcomponentsinstalledintheL100,
frequencyresponsemeasuredupto45°off-axis,
horizontally orvertically, does notdeviatemorethan6 dB
from on-axisresponse.
A dual-traceoscilloscopewas utilized tocomparea
50-Watt RMSinputat50Hzdirectly with theacoustic
output ofthesystem.A laboratorymicrophonewas
connecteddirectlytotheoscilloscopeandthedisplay
photographed. Thelefttrace,representingthegenerated
low frequency input, isidenticaltotheoutputtrace,
demonstrating theverbatimsignalreproductionoftheL100.
Sustainedperformanceatthisintensity would notbe
encounteredduringnormaluse.A 50-WattRMStestsignal
is farmore difficult fora speaker toreproducethanitsrated
2

capacity of50 Wattsprogrammaterial,speciallyinthe
lowestregister of theaudiospectrum.Nevertheless, it can
be seen thattheL100produces a virtually perfectreplica of
theinputsignal.
A number of compact loudspeakersystemscanhandle
largeamounts of power;othersarehighlyefficient.JBL
productsareuniqueintheirability to combineboth
attributes.TheL100Century,forexample, will convert a 1-
Watt input of "whitenoise"1into a soundpressurelevel of
78 dBata distanceof 15 feet? This is approximatelytwice as
loud as ordinaryconversationandrepresents a comfortable
listening level,demonstratingthattheL100delivers
substantialoutput from very little inputpower.
JBLattributesmajorimportance to thevalidity of
publishedinformation.Ratherthanrepeattheambiquity of
mosttechnicalspecifications,JBLhastraditionallyrefrained
from listingdataforwhich no widely accepted test
1. "White noise" is a rigorous test simulating average
musical program material under laboratory conditions. It
provides a controlled means of energizing all the
transducers of a loudspeaker system simultaneously. "White
noise" encompasses all audible frequencies just as white
light includes all the colors of the visible spectrum.
Produced in the laboratory by a signal generator, "white
noise" sounds very much like the hiss heard between FM
radio stations.
2. A decibel (dB), in this context, is a unit expressing
relative loudness of sound. Three dB is approximately equal
to the smallest change in loudness of program material
ordinarily detectable by the human ear.
Comparison of input and output signals.
3

procedurehasbeenestablished.Inthe absence ofsuch
standardsanywell-equippedlaboratorycanlegitimately
produce a varietyoffrequencyresponsecurvesfor a
loudspeaker,dependingontheconditionsselected.AtJBL
the final analysisconsistsofextensivelisteningsessions.
Although laboratorydataareanintegralpartofthe
process,thetrainedear is theultimatecriterion.The success
of thisphilosophy is reflectedintheenthusiastic acceptance
of JBLsystemsbyrecordingstudioengineers,producersand
performers —professionalswhoseartisticachievementsare
closelyrelatedtotheequipmenttheyuse.
PowerCapacity* 50Wattscontinuousprogram
Nominal Impedance 8ohms
Crossover Frequencies
1500and 6000 Hz
Efficiency 1 Wattinput produces 78 dBSound Pressure Level
(Note: 75-80 dB is a comfortable listening level.) at a distance of15'
Low Frequency Loudspeaker
Nominal Diameter 12
inches 30 cm
VoiceCoil3-inch(7.6cm)edgewound copper ribbon
MagneticAssemblyWeight 6.75pounds3.1kg
FluxDensity
10,400 gauss
Sensitivity** 42dB
MidrangeTransducer
Nominal Diameter 5
inches 13cm
VoiceCoil 78-inch(2.2cm) copper
MagneticAssemblyWeight 2.75pounds1.2kg
FluxDensity
16,500 gauss
EIA Sensitivity 46dB
High Frequency DirectRadiator
Nominal Diameter 1.4
inches 3.6cm
VoiceCoil %-inch(1.6cm) copper
MagneticAssemblyWeight 1.6pounds0.7kg
FluxDensity
15,000 gauss
Sensitivity (averaged above 2 kHz) 47dB
Finish OiledWalnut
Grille ColorOptions
Ultra Blue,ChocolateBrown
orBurntOrange
Dimensions 14y4"x23y2"xl35/8"
deep
36x60x35 cm deep
ShippingWeight 55lbs25kg
*Basedon a laboratorytestsignal.SeePowerCapacitysectionforamplifier
power recommendation.
:*Sincethemajor
portion oftheenergyreproducedbythelowfrequency
loudspeakerliesbelow800Hz,thisspecificationhasbeendevelopedby
using a testsignalwarbled from 100-500 Hz,ratherthantheconventional
1-kHz sinewavetestsignalon which theEIAsensitivity rating isbased.
4

IMPORTANT: Whenconnecting or disconnecting
loudspeakers from anamplifier,theamplifiermust be
turned off. Making connections while theamplifier is
operating couldseriouslydamagetheloudspeakersystem
and void the warranty.
Eighteen-gaugeinsulated wire (ordinaryhousehold
lampcord) is the minimum sizerecommendedfor
loudspeakerconnectionsup to50 feet.Beyondthisdistance,
heavier gaugeinsulated wire is recommended; 16-gauge
from 50 to100feetandl4-gauge from 100to200feet. If
lampcord is used,wirescan be differentiatedbynotingthat
one of theinsulatingjackets is smooth, while theotherhas a
distinct ridge.Byconsideringtheridgedjacket"red"andthe
smooth jacket"blacky wiring connectionscan be made asif
using color-coded wire.
Connections to theaudiopowersourcearemadeusing
the twopushbutton terminal postslocatedonthe back of
the loudspeakersystemenclosure.TheholesinJBL terminal
postsdonot allow theconnecting wire to pass alltheway
through, preventingthepossibility ofa short to theother
terminal post orto nearbyelectricalconductors.
To make a secure connection,stripapproximately Vi inch
of the insulation from theend of the wire, push down the
spring-loaded terminal postcap,insertthebare wire into
the exposedopening of the terminal postandrelease.
(Insertion of the wire into theopening will be easierifthe
stripped wire is first tinned with a soldering tool andsolder.)
Locatetheloudspeakeroutputterminalsonthe back of
the receiverorpoweramplifier.For each loudspeaker
system, connectthe wire from theblack terminal post to the
amplifier output terminal labeled"common""ground" or
( —), andthe wire from thered terminal post to the
remaining 8-ohmspeakeroutput?
Note thatmanyamplifiershave a chassis grounding
terminal which is usuallyisolated from theother
connectors.Thisshouldnot be confused with the"ground"
designation sometimesusedtodescribetwo of theterminals
in each setofloudspeakerconnections.
The specified8-ohmimpedance rating isa nominal figure
which suggests a connection giving themostefficientpower
transfer betweenamplifierandloudspeakersystem.
However, 4- or16-ohmamplifierterminalscan be used
without danger.
VL/_f.<!'OT'E:To maintain consistentpolarity with
other JBLloudspeakersystemmodels,currentLlOO's
(commencing with serialnumber 47100 andeasilyidentified
3. Connecting hoth speakers as described will insure proper
"in phase" operation; i.e., their cones will respond to a
monophonic signal by moving simultaneously in the same
direction, and not opposite to each other. Inadvertent out-
of-phase operation (which occurs when one set of speaker
wires is reversed with respect to the other) will not harm the
system, but may cause some acoustical "cancellation" which
will have the audible effect of reducing low frequency response.
5

bythefoam ring surroundingthehighfrequencydirect
radiator) arereversedinpolarity with respect to earlier
units. If earlyandcurrentLlOO'sare utilized inthe same
room, as in a quadraphonicinstallation,theearlyunits
should be connected"out of phase" with thecurrentLlOO's.
Thus, if thewires from thenegativeterminals of the
amplifier areconnected to theblackinputterminals of early
LlOO's, thenegativewiresforcurrentLlOO'sshould be
connected to theredinputterminals.In a quadraphonic
installation, twoearly or currentLlOO'sshould be used as
the front or rearloudspeakersystems,ratherthan as left- or
right-hand pairs.Similardifferencesmayexistwhen JBL's
areused with loudspeakersystems of othermanufacturers.
In suchinstances,consultyourJBL Audio Specialist.
Although JBLloudspeakershave a widesounddispersion
pattern, the final sound of thecompletedinstallation is
affected by thelocation of theenclosure within thelistening
environment. If possible,experiment with placement of each
loudspeakersystembeforedecidingon a final arrangement.
For the best possiblestereoperformance,thetwo
loudspeakersystemsshould be arrangedsymmetrically on
each side of thelistener. Asa general rule, a personsittingin
the usuallisteningpositionshouldsee an angle of about 40°
betweenthetwosoundsources.Thedistance from one
loudspeakerenclosure to theother is determined by their
distance from thelistenerand by the 40° "listeningangle'.'
Loudspeakersmay be positioned at anyheightabovethe
floor, althoughlocatingthehighfrequencydirectradiator
nearearlevelusuallygivesthemostrealisticsuggestion ofa
live performance. Bass response will be augmented if the
enclosuresareplacednearadjacentroomsurfaces,such as
in a corner or on a wall nearthefloor or ceiling.
6
1. Depress colored button, exposing hole in terminal post.
2. Push stripped end of lead wire into hole and release
button. Never apply twisting force to the terminal post.

The soundreflecting or soundabsorbingqualities of the
listening room will affectthesoundquality ofa loudspeaker
system. Roomacousticscan be tested by listening to the
echo ofa sharpsound,such as handclapping.
A roomhavinglargewindows,paneledwallsand a
hardwood floor or ceiling will be acoustically "live" and
will echo noticeably. A roomcontainingoverstuffed
furniture, carpetedfloors or drapedwindows will be
acoustically"dead"and will echo very little or not at all.
Ideally, thereshould bea reasonablebalancebetween
absorptivematerialandsoundreflectingsurfaces. If there
aretwolargereflectingsurfacesfacing each other,the
"bounce"betweenthem will makesoundsruntogetherand
the music will lack definition. Large, flat wall surfaces
should be brokenup with bookshelves,drapesor screens.
The L100 is provided with a Presence controltoregulate
the relativeloudness of themidrangetransducerand a
Brilliance control to adjustthevolumelevel of thehigh
frequencydirectradiator.Thesecontrolsadjusttheoutput
of thecomponentloudspeakers to achieverealistictonal
balancein a variety of roomconditions.
LOUD-
SPEAKER
LOUD-
SPEAKER
LISTENING
PORTION
7
40° "Listening Angle"
Sound energy from each loudspeaker blends to form a
stereo "wall of sound!' The stereo image will be intensified
and the area of best stereo perception increased if the two
systems are rotated slightly toward the preferred listening
position.

Thecontrolsarecalibratedintermsofa laboratory
standardreferencelevel,indicatedbya "0"onthe
instruction plate.Whenboththe Presence andBrilliance
controls'aresetatthislevel,theloudspeakersystem will be
adjustedforbalancedperformancecharacteristicsina
reverberation-freeenvironment.Sincemostlisteningrooms
possess varying degrees ofhighfrequencyabsorptionand
reflection, someadjustmentofthecontrolsisusually
preferred.
Theloudspeakersystemshouldbeadjustedwhile
reproducingnormalprogrammaterial with theamplifier
tonecontrolssetatthemiddle(generallyreferredtoas
"flat") position.Beginbyplacingbothoftheloudspeaker
systemcontrolsatthereferencelevelandlisteningtoa
yariety ofprogrammateriallongenoughto become
accustomedtothesystem'sperformance.
After theearhas become attunedtothe"0"setting,
evaluatethe presence andbrilliancequalitiesofthe
loudspeaker'sperformance.Themostvalidevaluation will
beobtainedbylisteningtotheloudspeakerplayed
monaurally. (Thiscanbeaccomplishedinstereoor
quadraphonicinstallationsbysettingtheamplifiermode
control formonauralreproductionandusingthebalance
control to select theindividualloudspeakersystemtobe
adjusted.)Theevaluationshouldbemadewhileseatedin
thenormallisteningposition.
To arriveatthespecificsettingfor each oftheloud-
speakersystemcontrols,proceedasfollows:
1. Setthe Presence controlat"0"androtatetheBrilliance
control totheextremeleftofitstravel.This will attenuate
high frequencyperformancesothattheear will perceive
only thebalancebetweenthelowfrequencyloudspeaker
andthemidrangetransducer.
2.Ifmidrangematerial—suchas violin, pianoorguitar—
seems too close oroveremphasized,usea coinorscrewdriver
to reducethesettingofthe Presence controlbyrotatingitto
theleft.Conversely,ifmidrangematerial seems toodistant,
increasetheoutputofthemidrangetransducerbyrotating
thecontrolclockwise.
3.Oncethe Presence controlhasbeenadjustedtoprovide
themostpleasingbalancebetweenthelowfrequencyand
midrangetransducers,settheBrilliancecontrolat"0'.'If
high frequencymaterial— suchascymbals,bells,triangles,
violin overtonesorvocalsibilants—seemtooprominent,
lower thesettingoftheBrilliancecontrol.Ifgreaterhigh
frequencyoutputisdesired,increasethesettingofthe
control.
After each setofadjustments,againlistentoa varietyof
program material until theearhas become attunedtothe
new characteristicsandcancomparethemtotheprevious
performanceofthesystem.Oncethe Presence and
Brilliance controlshavebeensetforthemostpleasing
overall results,andthe exact placementof each loudspeaker
8

hasbeendetermined,compensationfordifferencesin
individual recordingsshould be made with thetonecontrols
on theamplifier or receiver.
The specifiedpowercapacityindicatesthecontinuous
program powerlevelthatcan be accepted bya JBL
loudspeakersystem without damage.Itspeakpower
capacity is considerablygreaterthanthecontinuousrated
value, as indicatedbytheremarkabletransientresponse of
JBLloudspeakersystemcomponents.TheL100 will
reproducecleansound at comfortablelisteninglevelswhen
driven byanamplifierhavinganoutput ofas little as10
Watts RMSperchannel?However,forreproduction of the
full dynamicrange of contemporaryrecordings at high
volume, a qualityamplifierdeliveringupto150WattsRMS
perchannel will provide optimum performance.Innormal
high fidelity applicationsanamplifiershouldnever be
operated with itsvolumecontrol at maximum,however,
suchanamplifierhasthereservepower necessary for
accurate reproduction of transients,whichcanreach
momentary peaksequivalent to tentimestheaverage
power level.
If distortion is heard,one or more of thesoundsystem
components is operatingbeyonditscapacity(assuming each
component is properlyadjusted)andtheoverallvolume
level of thesoundsystemshould be reduced.Inalmostall
cases, theacousticlevelgeneratedby a JBLloudspeaker will
become noticeablydiscomforting to theearbeforethe
loudspeakercan become damagedby excessive power from
4. The RMS (root mean square) rating of amplifier power is
the most stringent method currently used in the audio
industry. An amplifier rated at 60 Watts RMS per channel,
for example, is generally considered to he a high-powered
unit. The same output expressed in terms of "Music Power"
would be 160 Watts.
9
Presence and Brilliance controls are conveniently located on
the front of the enclosure, behind the removable grille
assembly.

the amplifier.There is virtually no danger of damaging a
JBLloudspeaker ifitis operated within the following
guidelines: 1)the signal from the amplifier,regardless ofits
rated power, is notdistorted; 2)the amplifier is notdriven
into clipping(another form of distortionwhich occurs
when the poweroutputlimitations ofthe amplifiercircuitry
are exceeded); and 3)the powercord or audioconnectors
arenotinserted or unplugged while the amplifier is
operating.
However, a powerfulwiderangeamplifier can
accidentallydamageanyloudspeakerundercertain
conditions. For example,rewinding a taperecorder with the
playbackvolumeturned upcan generate"squeals"powerful
enough to burnout the highfrequency unit. Similarly,
..powerful lowfrequencypulsesextending down into the
subsonicrange can eventuallydamage the lowfrequency
loudspeaker. If thephonographpickup is accidentally
dropped with the volumecontrol full up, orifthe system is
played veryloudly with excessive bass boost,nearly the full
rated power ofthe amplifier canbe channeled into
dangeroussubsonicenergy.
The componentsused in every JBL product are designed
and produced byJBL personnel to exactingstandards. JBL
loudspeakerframes are massive rigid structures.Magnetic
assemblies are preciselymanufactured of low-reluctance
iron, energized by large,highgrademagnets.Voicecoils are
held to within one turn of designspecifications.Stamped
frames, punchedmagneticstructuresandmass-produced
voicecoils would be less expensive;however, the resultant
loss of structuralintegrity,magneticforceandacoustic
efficiency would tend to degrade low-distortion
performanceandtransientresponse—qualitiesthathave
become JBL hallmarks.
LOW FREQUENCY—Bass reproduction is accomplished by
apowerful12-inch,long-excursionloudspeaker.Its3-inch
edgewound copper ribbonvoicecoil,massivemagnetic
assemblyandlargeAlnico V magnetenablereproduction of
powerful bass fundamentals with ease. Thevoicecoildrives
amolded cone, carefullydamped with an exclusive JBL
formulation, Lansaplas, to preventspurious resonance and
provide smoothperformancethrough the vital midrange
region. Itis thisdampingcompoundwhichgives the cone
its white color.Theshallow,curved cone provides uniform
wide-angle distribution of soundenergythrough the full
low frequencyrange; the viscous-dampedsuspensionallows
extremely longexcursion without distortion.Efficiency and
dynamic range are furtherincreased bytheuseofan
enclosurehaving a tunedportfor optimum bass
performance.
10

MID RANGE—The midrangeregion,whichincludesvocal
overtones and strings, is reproduced bya precision5-inch
transducerpossessingpeak-free, uniform sounddistribution
both on- and off-axis.Extremesensitivity and highpower
handling capacityallowgreaterundistortedacousticoutput
than any othersmall cone loudspeaker. The unit is
separatelyhoused within the mainenclosure to prevent
acousticalinteraction with the low frequencydriver andto
optimize the superiorresponsecharacteristics ofthe
transducer.
Themidrangetransducer is driven bya 7/8-inchcopper
voicecoilimmersed inan intensemagneticfieldprovided
by a massive2.75-poundmagneticassemblyenergized by
an Alnico V magnet. The coil is coupled toa molded cone
having a viscous-dampedsuspension to preventspurious
resonance. The entiremovingassembly is rigid, yet
exceptionallylight — a combinationpermittingoutstanding
transient reproduction.
HIGH FREQUENCY-Information above 6000 Hzis
reproduced bya 1.4-inchdirectradiatorenergized bya 1.6-
pound magneticassembly. Its 5/8-inchcoppervoicecoil is
unusually large in relation to cone size,providing
exceptionalefficiency and transientresponse. The precisely
formed cone assembly is suspended atits outer edge byan
impregnatedclothtermination to insurelinearity and
absorbspuriousresonance. The entiredynamicstructure is
surrounded bya ring of densefoamdampingmaterial to
preventunwantedradiation and reflections.
Thesmallradiatingsurface ofthe cone and centerdome
isresponsible forthe widehighfrequencydispersion
pattern, assuringthat each listenerhears the sametonal
balance and blend of direct and reverberantsound. The
result isa precisiontransducerprovidingexceptionally
transparenthighfrequencyreproductioncharacterized by
clarity and precisedelineation of even the mostcomplex
treblewaveforms.
DIVIDING NETWORK-Allocation of each segment ofthe
full musicalspectrum tothe appropriatetransducer is
determined bythe frequencydividingnetwork. As with all
JBLdividingnetworks, the unit installed inthe L100 is
carefully designed and tested to complement the exact
characteristics oftheJBL transducers with which itistobe
used.Transitionbetweenspeakers is accomplished
imperceptibly and without degradation ofthe linear
responsecharacteristics ofthe system.
Thefunction ofa precisiondividingnetwork is
considerablymorecomplexthanmerelyfeeding low and
high frequencyinformation tothe appropriatereproducers.
Sincebothloudspeakersoperatethrough the crossover
region, the controlexerted bythe dividingnetwork is
vitally important tothe totalsound ofthe loudspeaker
system. The circuitvalues of JBL.dividingnetworks are
adjusted so thatacousticoutput of each transducerremains
smooth and uniform through the crossoverregion,assuring
that the superiorperformancecharacteristics ofthe
11

completeloudspeakersystemaremaintainedthroughthe
full audiospectrum.Thus,the effects of individual speaker
characteristics,impedancefluctuations,andthephysical
separation of theindividualsound sources arealltakeninto
accountinthecompletesystemdesign.
TheL100networkpermits full control of tonal balance by
regulating thepowerfed to themidrangeandhigh
frequencyreproducers.Thecontrols do notappreciably
affectthecrossoverfrequencies,nor do they limit theupper
frequencyresponse of theloudspeakersystem.
If it should become necessary to removetheloudspeaker
systemcomponentsfortesting or repair,disconnectthe
loudspeakersystem from theamplifierandproceed as
follows:
GRILLE—The grille is secured to theenclosure by dowel
pinslocatednearthefourcorners of thegrilleframe. To
removethegrille,grasptheframe at bothtop or both
bottom cornersandgently pull theassemblyaway from the
enclosure.Toreplacetheassembly,reposition it on the
enclosureandapplylightpressure to reseat thegrilleframe
on thedowelpins.
When replacingthegrille be surethatthelargecircular
cutout on theunderside of thegrilleframe is locatedover
the12-inchlowfrequencytransducer. Align thedowelpins
with thematchingholesinthegrilleassemblyandgently
applypressure at thecorners of theframeworkadjacent to
thedowels.Notethatone of thedowelpins is offset to
insurethatthegrillecanonly be replacedwhenpositioned
correctly.
TheJBLemblem is secured to thegrillematerial by hook-
and-pilemountingtape. It can be lifted from thegrille,
12
Loudspeaker System Components
12-inch Low Frequency Loudspeaker
5-inch Midrange Transducer
1.4-inch High Frequency Direct Radiator

rotateci and pressed lightly back into position to read
correctlywhether the loudspeakersystem is placed
horizontally or vertically.
LOW FREQUENCY— Place the enclosure on its back ona
cleanpaddedsurface. The low frequencyloudspeaker is
mounted from the front of the bafflepanel and held in
place by fourPhillips-headscrewsthreaded into T-nut
fasteners,which are anchored on the back of the panel.
Carefully unscrew the machinescrews without applying
pressurethatmightdislodge the T-nuts.When the mounting
screwshavebeenremoved,gently lift the edge ofthe
loudspeakerframe from the bafflepanel,disconnect the
wires at the bindingposts and remove the loudspeaker from
the enclosure.
M1DRANGE—The midrangetransducer is held in place by
four woodscrews at each corner of its frame.Carefully
remove the screws, lift the unit from the enclosure and
disconnect the leads at the pushbuttonbindingposts.
HIGH FREQUENCY—The highfrequencydirectradiator is
secured to the enclosurebafflepanel by woodscrews at
each corner of its frame. The unit is removed by carefully
taking outthe mountingscrews and lifting the complete
assembly out of the enclosure. The two leads from the
dividing network can then be disconnected at the tab
connectors on the back of the frame. The sealinggasket
should be reusedwhen the unit is replaced.
DIVIDING NETWORK—The dividing network is installed
behind the bafflepanel and held in place by fourscrews and
T-nuts. To gain access to the network,remove the
transducers as previouslydescribed, pull the wire leads
from the midrangesub-chamber,carefullypeel off the
serialized foil nameplate,remove the wire nutsconnecting
the networkleads to the terminalbindingposts at the back
of the enclosure,remove the mountingscrews, and lift the
network out through the low frequencyloudspeaker
opening. Note:Malfunction of the network is highly
unlikely. Since the nameplate is generallydestroyedduring
removal, itis not recommendedthat the network be
removed simply forthe purpose of inspection.
REPLACEMENT— Reverse the removalprocedure to
replace the loudspeakersystemcomponents.Mounting
screwsshould be tightenedevenly to avoid the possibility of
frame warpage, and justenough to prevent air leaks
between the components andthe enclosure. Avoid excessive
force.
Although JBL loudspeakers are extremely ragged, thecone
andothermovingparts are subject to accidental damage.
Exercise extremecautionwhenusing a screwdriver or other
tools in theirimmediatevicinity.
13

WIRING — Whenreconnectingthe wire leadsbetweenthe
dividing networkandthecomponents,observethepolarity
shown below.
The L100Centuryenclosure,embodyingtheprinciplesof
fine furniture designandconstructionthathavemadeJBLa
leaderintheindustry,complementstheacoustic
characteristicsoftheloudspeakersystem.Itutilizesa ducted
port extendingthroughthebafflepaneltoprovidethe
properloadontheloudspeaker cone andoptimizepower
handling capacity.Onlythefinestcompressedwoods,
furniture hardwoodsandhardwoodveneersareused—
carefully selected, skillfully preparedandhandrubbedtoa
rich, lustrous finish enhancingthenaturalbeautyof
individual grainstructureandcolor.Detail work isobvious:
joints areexpertlyclosed; scratches, dents,gluelinesand
other defects arenon-existent.Acousticdampingmaterialis
applied tosideand'backpanelstoeliminatestandingwaves
within theenclosure.Toachievemaximumstrengthand
resistancetovibration,allpanelsareconstructedof3/4-or
1-inchstock;andalljointsarehand fitted, lockmiteredand
wood welded.
The L100enclosureisfinishedinhand-rubbedoiled
walnut. Occasionaldusting with a clean,softcloth will
maintain theoriginalbeautyofthe finish. Thegrillecanbe
easilycleanedbygentlydustingit with a householdvacuum
cleaner. Since moisturecannotpenetratetheoiledsurface,
most householdstainscanberemoved with a dampcloth.
The surfaceshouldbetreatedonly with waxspecifically
formulated foruseonoiledfinishes.Conventional furniture
waxes,polishesor cleaners arenotrecommended.
14

Astheoilpenetrates deeper and deeper intothewalnut,
thefinishmay appear tobedryingout.Manyowners find it
desirabletore-oiltheenclosuresurface from timetotime.
With each application,thebeautyofthefinish will become
moreapparentanda warm,richpatina will eventuallybe
obtained.
To re-oila JBLfinish,useanyoneoftheseveral clear oil
finishing preparationsavailablethroughfurnitureor
hardwareoutlets.Applya liberalamountofthepreparation
overtheentirefinishedsurfaceoftheenclosure.Intento
fifteen minuteswipeofftheremainingoil with a soft,clean,
dry cloth.Smallsurface scratches canusuallyberemoved
bygentlyrubbingthemout with veryfinesteelwool(4/0
grade)andapplyingoiltotheentirepanel.Whenusingsteel
wool, applylightpressureandrubonlyinthedirectionof
thegrain.Very deep scratches, dentsorotherserious
damage shouldberepairedonlybya qualifiedfurniture
refinisher.
A JBLloudspeakersystemresponds with verbatim
accuracy tothesignalsuppliedbytheaudiopowersource;
itwill thereforereproduceextraneous noises justas
accuratelyasitreproducesdesiredprogrammaterial.Noise
seldomoriginatesintheloudspeakersystem.Its presence
usuallyindicatesthatoneoftheothercomponentsofthe
musicsystem,ortheprogrammaterialitself,isfaulty.In
rare instances whensomething does gowrong with the
loudspeakersystem,oneormoreofthecomponent
loudspeakers will stopworkingaltogetherora distinct
rattling orscrapingsound(indicatinga rubbingvoicecoil)
will beheardwheneverthesystemisoperating.
If onechannelofa stereoinstallationisnotoperating,
examinetheloudspeaker wiring and check the balance
control. If wiring instructionswerefollowedcorrectly,ifthe
connectionsarecleanandtight,andifcenteringthe balance
control does notremedythesituation,reversetherightand
left loudspeakerconnectionsattheamplifier,taking care to
turn theamplifieroffbefore each connectionor
disconnection.Ifthepreviouslynon-functionalloudspeaker
systemoperates,theamplifieroroneofthecomponent
program sources (tuner,phono,tape deck, etc.)is
malfunctioning. Intheeventthatthe suspect loudspeaker
systemis still inoperative,itisprobablydefective.
To determinewhetherthe defect liesintheamplifierorin
oneofthecomponentprogram sources (afterverifyingthat
theloudspeakersystemsarenotdefective)reversetheright
andleft cables from theprogram source attheamplifier.If
theoriginalchannelis still inoperative,theamplifieris
defective;ifthepreviouslyinoperativechannelfunctions,
15

theprogramsourceisdefective.Iftheamplifierisnot
faulty, alternately check each programsource until the
defective unit hasbeenisolated.Itisunlikelythatmore
than oneprogramsource will befaultyatanygiventime.
Extraneousinterferencesuchasstaticorradio broadcast
signalscanbepickedupbythecomponentdevices.When
this occurs,thetroublesome unit canbeidentifiedby
disconnectinginputs from thereceiveroramplifier until the
interferencestops.Again,iftheinterferencepersists with
noneoftheinputdevicesoperatingthroughthepower
source,thereceiveroramplifieritselfisprobablydefective.
Shorting plugs,available from yourJBLAudioSpecialist,
should beinsertedinunusedphonoinputstohelpeliminate
strayhumorsignalpickup.
Fuzzy orindistincthighpitchedsoundscanusuallybe
"tracedtotherecordingitself,a defectivecartridge,a worn
stylusorinsufficienttrackingforce.Problems with low
frequencyreproductionareusuallytheresultofroom
acoustics orplacementofthe speaker system.Excessive
bass boostorincorrectloudnesscompensationtendtogive
amuddyor"boomy"qualitytoreproducedmusic.The
musicsystemcanbe checked forturntablerumbleorother
extraneouslowfrequencysignalsbyremovingthe
loudspeakergrilleassemblyandobservingthemotionofthe
low frequency cone whilethesystemisplayingathigh
volume. Ifthe cone continuallymovesinandoutmorethan
V2inchorso, excessive lowfrequencypowerisbeingfedto
theloudspeakersystem.
Hum maybe caused bylocatinga turntableortape
recorderdirectlyoverorunderneaththeamplifieror
receiver.Thefarthertheaudiopowersourceislocated from
thephonographcartridgeortapeheads,the less chance
there will beofpickinguphum.TheACleadsandshielded
cables shouldbeaswidelyseparatedaspossible;AClines
should never cross cables or speaker wiring. Powerline
interferencecanbefurtherattenuatedbyusinga heavy
duty lineinterferencefilterbetweentheaudiopowersource
andtheAC wall outlet.
Acoustic feedback istheresultofmechanicalvibrations
producedby excessive bass atveryhighvolumelevels.The
loudspeakersystemcanproduceenoughenergytovibrate
other objects intheroom—includingtherecordplayerand,
bydirectmechanicaltransmission,thestylusitself.These
vibrations areamplifiedagainandagain,producingvery
loud "rumble''orevena sustained howl that increases in
intensity asthevolumeor bass controlisturnedup.
Possiblesolutions:1)locatethe speaker cabinets asfaras
possible from theturntable,2)adjustorreplacethe
turntable shockmountings,3) place theturntableona
rubberorspongemattofurtherabsorbvibrations.Ifthe
low frequencytoneis still audible,itisprobablytheresult
ofinherentturntablerumbleratherthanacoustic feedback.
16

Should yourJBLloudspeakersystemrequireservice,
return ittotheJBLdealer from whom itwaspurchased.Ifit
is notpossibletocontacta dealer, write directlytotheJBL
ServiceDepartmentdescribingthe difficulty as fully as
possible.Productsreturnedtothefactorymustbesent
prepaid and will notbe accepted unless written
authorization has first beenobtained.Thewarrantyis
recognizedonlywhenthe unit isrepairedbyJBLoran
authorized JBLServiceAgencyandiftheserialnumberof
the unit hasnotbeendefacedorremoved.
In additiontotheestablishedfive-yearwarranty,JBL
will, atitsoption,repairthespeakersfreeofchargeduring
their entirenormal life iffactoryinspectiondisclosesan
original manufacturingdefect.Toestablishthewarranty, fill
out and mail thewarrantycard within tendaysofpurchase.
The L100Centuryepitomizes JBL's reputationfor
leadershipinacousticandvisualdesign.Itestablishesa
pinnacleofqualityformusicreproductioninthehome,just
asithasintherecordingstudio.Itisoursincerebeliefthat
the L100Century —like allJBLproducts —will provide
undiminished listeningpleasureformanyyearstocome.
If youhave difficulty inachievingthefineperformanceof
which yourJBLloudspeakersystemiscapable,consultthe
JBL Audio Specialist from whom thesystemwaspurchased.
He isequipped with theknowledgerequiredtoprovide
expertadviceand assistance. IfforsomereasontheJBL
dealerisunabletoassistyou, write directlytotheJBL
TechnicalInformationDepartmentexplainingthe difficulty
in detail.
17
SUMMARY

James B.LansingSound,Inc., 3249 Casitas Avenue,LosAngeles,California 90039.
50625OM100A/74PrintedinU.S.A.