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