CONCERT SOUND REINFORCEMENT - fulcrum …

1 LOUDSPEAKERMANIFORLDSFORHIGH-LEVEL2387(D -ii)CONCERTSOUNDREINFORCEMENTD avidCarlsonDavidGunnessElectro-Voice, ,MichiganPresentedatAUDIOthe81stConventi on1986 November12-16 LosAngeles,CaliforniaTh/spreprinthasbeen reproducedfromtheauthor'sadvancemanuscri pt,withoutediting, ,60 East42ndStreet,NewYork, ,oranyportionthereof, ,midbass,andhigh-frequencydevicesaredisc ussed,eachofwhicheffectivelysumstheoutpu toffourloudspeakers, ,reducedpolarresponselobtng,small-fronta lareaarrays,smalltransportableenclosures , , ,amanifold, ,small-frontal-areaarrays.

2 Smalltransportableenclosures,greatlyredu ceddirectiveresponseanomalies, ' , ! (driverswith4gmmexitsintoaspecialhorn),w hichrevealswhymanywhohaveexperimentedwit hY-throatsdescribethemas"dull-sounding". (whicharecapahleofpistonicmotionthrought hepassband),greaterpower-handling(therma l-limit)persquarecentimeterofdiaphragm, ,Henricksen[1]hasshownthatgivencurrently knownmaterials, ,agivensystemrequirementmaycallforacompr essiondriverthatisnotphysicallyrealizabl e, , "like"driversvaryfromoneanother,asallrea ldriverswill?

3 Atlowfrequencies,thatisfrequenciesatwhic hthereismutualcouplingbetweendriver_, ,thetypeofvariationsthatoccurgenerallysu mmathematically(andacoustically) ,compressiondriversmayshowsignificantuni t-to-unitvariations, ,asusedhereintsdefinedasthedifferencebet weenthe1/3-octavesmoothedresponseofahorn -drivercombinationandthe1 ,asunit-to-unitvariationsbecomesignifica ntathigherfrequencies,directivebehavtor( raypropogation) "rays",aswellassoundwaves, , ,theconcepthasbeenfoundtobeequallyvaluab leatlowerfrequencies, , , , , (likespokesofawheel).

4 ,arelativelyseverebendmustoccurwithinthe manifold(a90-degreebendfortheclosestexit spacing).Andsecond,convex-drivecompressi ondriversareinherentlybettersuitedtothis typeofdesignthanequivalentconcave-drive, through-the-pole-piecedrivers,sincetheco nvex-drivemagnetsarebehindthediaphragms, ,aright-anglereflectivebendwasmodelledan dfoundtoworkverywell, ,whenseveralofthesereflectorsarebroughtt ogetherinamanifold,thepathofeachwavefron tleavingttsreflectorisnotconstrainedhyat ube, ,aspresentedinKinslerandFrey[2], :p=A ( )(1).

5 A=theradiusofthepiston(usetwicetheradius ofthetube),t-theangleofthebend,k=thewave number(w/c),A=theunperturbedresponse(sam esourcewithoutbend),Ol(x)= , ,ifthefunctiontsplottedforvariousangles, ,themanifolddesignwasrefinedonestepfurth erbytiltingtwoofthedrivers45degrees, ( ) , (1),theirsummationwouldbesimilartoeither contributionsingly(thesumofequation[1]fo rtwodifferentanglesisanotherfunctionrepr esentablebyequation[1]).Fortunately,thou gh, ,thetwocharacteristicsdohaveageneralsmoo thingeffect, , , ; :otheexcessivediameterofthethroat(ifthet hroatistoolarge,theinitialdispersionisna rrowerthanthecoverageangleofthehorn, , "attempt" (asopposedtothecenter),thewavefrontacqui resanintensitycomponentthatisdirectedacr ossthedesiredpropagationpath, , ,graphically, ,accurately, , , , ,andreflectingsurfaceswereusedtoachieveg oodsummation,Beforetheproblemsofmanifold ingcouldbetackled, , ,25cmcone-typeloudspeakerwaschosenastheb asicdriveunit, ,buttosummarize.)

6 , ,thephaseplughasarectangularexit, ,astngledrivermountedonamid-basshorn( )wascomparedwithtwodriversmanifoldedonas imilarhorn( ). , ,at1200wattscontinuouspowerhandlingcapab ility,candeliver138dBSPL(144dBpeaks) ,sincephasecancellationsanddestructivein terferencetypicallyarenotproblemsatlowfr equencies(becauseofthelongwavelengthsinv olved);however, ,twobasicloudspeakerdesignshaveprolifera tedintheconcertsoundindustryforthereinfo rcementandreproductionoflowfrequencies; , ,however, [3] , , , (top,bottom,andrear)sothattheloud-speake rsradiatedintoacommonchamber(themanifold chamber)withasingleexit,andtheportswerer elocatedtothenewfrontofthecabinets(outsi dethemanifoldchamber).

7 ,thereareseveraldifferencesthatarereadil yapparent;below70 Hzthemanifoldedsystemhassubstantiallymor eoutputthanthedirect-radiatingsystem;abo ve100 Hzthemanifoldhasslightlylessoutput; ' ,Pritchard[4]pointsoutthattheresistiveco mponentisabsolutelyconvergentforallvalue sofa(theradiusofthepistons)andd(thecente r-to-centerdistancebetweenthetwopistons) , ,ct-radiatingandmanifoldedsystems, ,andadditionally, , , , (lessthan200Hz), ,conversely, ,ALL-MANIFOLDEDSYSTEMA nexampleofthisnewmanifoldtechnologyisthe MT-4,afour-way-active, ( )

8 , ,Thelowerbox,theMTL-4,isavented-boxdesig nthatcontainsfour46cmwoofers, ,thewoofersaremounted"magnets-out" ,themanifolddesignisnearlytwiceasefficie ntastypicalborn-loadedsystemsofequivalen tsize.[tssensitivityof101dB(IW/lm)and160 0wattcontinuouspowerhandlingcapabi)ityen ableittoproduce133dBSPL(13gdBpeaks) ,ofcourse, ,theMTH-4,isathree-waymid-bass/midrange/ high-frequencysystem, , ,1600Hz, , (mid-bassthroughhighfrequencies),increas edefficiency(lowfrequencies),andextremel yhighpower-to-enclosure-volumeratios(all ranges).]

9 Applicationssuchasconcertsoundreinforcem ent,whichrequireextremelyhighacousticpow eroutput, ,mostnotablyRayNewman,ChiefEngineer-Loud -speakers, ,toKetthWalkerforprototyptngandsettingup numerous"1/2-tonlisteningtests",andtoShe ldonCrapo, [1] ,"SoundSystemDesignsUsingMech-anicalSpec ificationsofDrivers",S_naudconTechTopics , , (1983).[2] ,FundamentalsofAcoustics,Wiley,1966.[3] ,"AnEfficiencyConstantComparisonBetweenL ow-FrequencyHornsandOtrectRadiators" , ,-1_1976.[4] ,"MutualAcousttcImpedanceBetweenRadiator sInanInftniteBaffle", , , , (June1950).

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