EAW Three-way Loudspeakers Guida di riferimento rapido
The Laws of Physics /The Art of Listening
CINEXPO WHITEPAPER
Three-wayLoudspeakers
fortheDigitalAge
INTRODUCTION
Theprimaryrequirementofleft/center/rightmainchannel
cinemaloudspeakersisthattheyfaithfullyreproducethe
entireaudiospectrumfrom20Hzto20 kHz. While crisp,
naturalreproductionofthevocalrange(300 Hz - 2 kHz) has
always beencriticaltogoodcinemasound,veryhighand
verylowfrequencies(above 4 kHz and below200Hz)
demandparticularattentionintheageofdigitalcinema
audio.Theadventofdigitaltechnologyhasbroughtsound
effectstotheveryextremesofhearing,fillingtheseranges
withsonicmaterialwhichtodaydefinesthedigitalage
cinemaexperience.
Traditionaltwo-way cinema loudspeaker design (a large
conewooferandahorn-loadedhighfrequencycompression
driver)suffersfromanunfortunate500 Hz crossoverplace-
mentthatrobsdialogofmuchofitswarmth.Byrequiring
thehighfrequencycompressiondrivertocover frequencies
aslowas500 Hz, two-waydesignintroducessubstantial,
audibledistortioninthevocalregion,leaving voices sound-
ingharshandhollow.
Similarly, a 500Hzcrossovercompromisesaloudspeak-
er’sreproductionofextremehighandlow frequencies.
Transducers(coneorcompressiondrivers) haveoptimal
rangesinwhichtheyaremost“comfortable” and reproduce
soundmosteasily. When a driverisaskedtogobeyondits
“comfortzone,” distortion and/or inadequate response
result.Whileitispossibleforatwo-way design to employ
driversthatcoverextremehighsandlowsadequately, it
wouldrequiresacrificingresponseinotherfrequencyranges
–notablythevocalrange.
Finally, for a traditional two-waycinemaloudspeakerto
achieveadequatepatterncontrolfrom500Hzto20kHz,
thehorn’sthroatmustbeofsuchasizethatcancellations
withinthethroataddyetmoredistortion,typicallyinthe
700 Hz range.
Thispaperwillendeavor to show that bydedicatinga
subsystemtothevocalregion,three-wayloudspeakersare
betterabletohandlethenewdemandsofdigitallyedited,
mixedandencodedsoundtracks.Comparedtotwo-way
designs,three-wayloudspeakersimprove vocalclarityand
warmth,reducedistortionfrombothhorn-throatcancella-
tionanddriverexcursion,increasetheloudspeaker’s power
handlingcapability, and improvesperformanceacrossthe
audiospectrumincludingextremehighsandlows.
DIVIDING THE AUDIO SPECTRUM
Theaudiblespectrumspansjustunder10octaves ranging
from20Hzto20kHz(20,000Hz).Frequencyismeasured
accordingtoalogarithmicscale;foreachoctaveascended,
frequencydoubles.Ifmiddle“C”is300Hz,thenthe“C”
aboveitwouldbe600Hzandthe“C”below, 150Hz.
Sinceasingletransducercanonlyeffectivelycoverso
muchofthisrange,two-wayandthree-wayloudspeakersys-
temsdividetherangeintohigh/low-andhigh/mid/low-fre-
quencysections,respectively.
Ourresearchandexperiencehaveshownthatasingle
transducer’scomfortzoneusuallyspansnomorethanthree
andahalfoctaves.Yettraditional500Hzcrossoverdesign
requiresthehighfrequencycompressiondrivertocover well
inexcessoffiveoctaves.
Whilecompressiondriversreproducefrequenciesabove
1kHzquitewell,muchhigherdistortionresultbelow that
pointduetoexcessivedriverexcursion.Criticalvocalmateri-
alinthecompressiondriver’slowest octave(500-1000Hz)
fallsoutsidethedriver’scomfortzone. The resulting distor-
tiongivesvoicesaharsh,unnaturaledgesometimesrender-
ingthemunintelligible.Onecannotoveremphasize the
importancethisholdsforcinemasound;withoutintelligi-
bledialog,thecinematicexperienceismeaningless.
Bydedicatingasubsystemtothemidfrequencyrange,
three-wayloudspeakerseffectivelyeliminatetheseprob-
lems.EAW’sthree-waydesignsuselargeconewoofers,cone
drivenmidrangesubsystems and horn-loaded high frequen-
cycompressiondrivers.Weplacecrossoverpointsatspecific
frequenciesselectedtooptimizetheperformanceofeach
particularloudspeakersystem.Ingeneral,thelow/mid
crossoverissetaround350Hzandthemid/highcrossover
around2kHz.
Simplyaddinganotherhorn-loadedcompressiondriver
tocoverthemidfrequencyrangedoesnoteliminatedistor-
tionfromthevocalrange;infact,itaggravates the problem.
Ifexcessivedriverexcursionat500Hzcausesacompression
drivertointroducesignificantdistortion,distortionat300
Hzwillbeevengreater. To eliminate distortion from the
20 100 1000 10000 20000
dB SPL
Frequency (Hz)
Traditional 2-way loudspeaker design
vocal range
woofer compression driver
20 100 1000 10000 20000
dB SPL
Frequency (Hz)
EAW 3-way loudspeaker design
vocal range
woofer compression drivermidrange cone
vocalregionandgive dialog exceptional warmth and clarity,
EAW always employsconedriversforitsmidfrequency
subsystems.
Sincethree-waydesigndividestheaudiospectrum
betweenthreesubsystems, each only needs to coveralittle
overthreeoctaves – a range overwhicheachdrivercanbe
trulyoptimized.Thehighfrequencycompressiondriver
nowoperatesonlyinthetruehighfrequencyrange, mean-
ingbetterperformanceintheveryhighfrequencyrange.
Similarly, optimized wooferscanbetterhandlethelowfre-
quencysoundeffectsthatgivefilmsthat“digitalsound.”
THREE-WAY IMPROVES OUTPUT
Themaximumvolume(peakoutput)thataloudspeakersys-
temcangenerateisrelatedtotwofactors:sensitivity(output
generatedby1Watt of powerasmeasuredat1meter)and
powerhandling(theamountofpower a loudspeaker can
bearbeforefailure).
Horn-loadedcompressiondriversenjoyexcellentsensi-
tivitycharacteristicsbuthandlerelativelylow amounts of
amplifierpower,particularlywhendrivenatverylowfre-
quencies(i.e.500Hz).Bycomparison,ahorn-loaded,
heavy-dutyconedriver is somewhat less sensitive but han-
dlessubstantiallymorepower.Thecalculatedpeakoutputof
theconedrivensubsystemwillbe6-10dBhigherthanthat
ofanequivalentcompressiondriven subsystem.Higher
peakoutputgivesloudspeakersagreaterdynamicrange
throughouttheaudiospectrum,whichparticularly
improvesreproductionoffullrangemusicalscoresand
soundeffects.Italsopermitsagreaterdegreeofpassive fil-
teringtosmooththetotalsystem’s frequency response with-
outsacrificingpeakoutput.
ACCURATE WIDEBAND DIRECTIVITY
Theabilitytoputsoundwhereitisneededandkeepsound
away fromwhereitisnotwanteddistinguisheswell-
designedloudspeakers.Whenaloudspeakerwithpoor
directivitycharacteristicssendssomefrequenciesatwide
anglesandothersatnarrowangles, listeners at the edges of
itscoverageareawillhearsomefrequenciesandnotothers.
Furthermore,uncontrolledsoundwavesreflectingoffwalls
andceilingscancreateunacceptablereverberationsthat
degradethesoundqualityintheentirevenue.
Thedirectivitycharacteristicsofaloudspeakercanvary
widelydependingonthefrequencyandthesizeofthe
soundproducingdevice.Theruleofthumbgoesasfollows:
asthelengthofasoundwave decreases (with rising frequen-
cy)toapproachthesizeofthedriverconeorhornmouth,
directivitynarrows;asthesoundwavebecomessmallerthan
thesizeofthedriverorhornmouth,directivitybecomestoo
narrowformostapplicationsincludingcinema.Thelower
thefrequency, the more difficult it is to confine to a narrow
angle;thehigherthefrequency, the more difficult it is to dis-
perseatawideangle.
Traditionaltwo-way cinema loudspeaker design uses an
exceptionallylargehighfrequencyhorntoprovidepattern
controlat500Hz(whichitdoesadmirably).Butmaking
veryhighfrequencysoundwaves“fillthebell”ofthehorn
requiresanexceptionallylonghornthroat.Solong,infact,
thatcancellationeffectswithinthehornthroatcausesignifi-
cant,audibledistortioninthe700 Hz region. Smaller for-
mathighfrequencyhornsoneencountersforsmallercine-
masproducemuchlessdistortion,butlackthenecessary
patterncontrolat500Hz.
Byaskingeachsubsystem to coverasmallerrangethan
two-waydesigns, three-wayloudspeakerscancontrolboth
midandhighfrequencieswithoutintroducingdistortion.
EAW’slargerthree-waycinemadesigns–CB223and
MC4972–employsmallerformathighfrequencyhorns
withveryshortthroats.Sincetheydon’tneedtocontrol
soundsinthe500Hzrange, their size is quite manageable.
Thesehornsdispersethehighestfrequenciesacrossawide
areawithoutnoticeabledistortion.Oursmallestthree-way
cinemasystem,CB150,loadsacompressiondriver on our
shallow,throatlessWaveGuidePlate™givinghighfrequen-
ciesanexceptionallysmoothcharacter.
EAW’sproprietarymanufacturingtechniquesallowsusto
producethemostmathematicallyaccuratemidfrequency
hornsintheindustry. Automatedsaws and routers cut
groovesintheenclosurethatacceptaflexiblehardwood
veneershellwhichactsasaformforstructuralfoamwhich
weinjectintotheenclosure. The foam/veneerhornprovides
muchgreaterrigiditythanfiberglasshorns,allowingitto
controlmidfrequencysoundwaves with greater ease.
20 100 1000 10000 20000
dB SPL
Frequency (Hz)
2-way w/ compression driven high frequency
distortion comfort
20 100 1000 10000 20000
Frequency (Hz)
3-way w/ compression driven midrange
distortion comfort
dB SPL
continued
One Main Street, Whitinsville, MA 01588 tel··800 992 5013··508 234 6158 fax··508 234 8251 web··http://www.eaw.com
EAW INTERNATIONAL LTD., The Old Coach House, Amersham Hill, High Wycombe, Buckinghamshire, England HP13 6NQ tel··+44 1494 539090 fax··+44 1494 539091
The Laws of Physics /The Art of Listening
1447 / June 1997
CONCLUSION
Thedigitalageofcinemaaudiodemandsmorefromloud-
speakersthaneverbeforeandthesystems designed for cine-
mausemustkeeppace. Sound effects at the extremes of the
audiblespectrumhave come to define the digital age cinema
experienceandrequireupdatedloudspeakerstoaccurately
reproducethem.
Three-wayloudspeakersallowdrivers to operate in more
narrow,optimizedranges,eliminatingthedistortionthat
resultsfromexcessivedriverexcursion.Theseoptimizeddri-
verscanthencovertheirintendedfrequencyrangesmore
effectively,withoutsacrificingresponseatextremefrequen-
cies.Sincethree-waydesigndoesnotaskasinglehornto
controldirectivityfrom500Hzto20 kHz, pattern control
canbeoptimizedwithoutintroducingdistortion.EAW
three-wayloudspeakersemployonlyconedrivers for their
midfrequencysections,providingbetterpower handling
and,whennecessary, greater peak output than two-wayor
three-waysystems using horn-loaded compression drivers
forthemidrange.EAW’sconedriver, selected for their opti-
malmidfrequencyresponse,reproducedialogwithexcep-
tionalclarityandwarmth.
Bymovingtoacceptthree-way loudspeaker design as the
newstandardfordigitalagecinemasound,forward-think-
ingexhibitorscanofferaudiencesthefulladvantagesofdigi-
tallyrecorded,mixed andeditedsoundtrackswhich,until
now,haveonlybeenenjoyed in production studios’ private
screeningrooms.
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