University of Puget SoundSound Ideas

Summer Research

Summer 2016

The Acoustics of Harmon MutesZachary T. Armstrongzarmstrong@pugetsound.edu

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This Article is brought to you for free and open access by Sound Ideas. It has been accepted for inclusion in Summer Research by an authorizedadministrator of Sound Ideas. For more information, please contact soundideas@pugetsound.edu.

Recommended CitationArmstrong, Zachary T., "The Acoustics of Harmon Mutes" (2016). Summer Research. Paper 265.http://soundideas.pugetsound.edu/summer_research/265

TheAcous*csofHarmonMutesZachArmstrong,RandWorland

DepartmentofPhysics,UniversityofPugetSound,Tacoma,WA

Introduc)onHarmonmutesareusedbytrumpetplayerstoaCainadifferentsoundthanisnormallyproducedbytheinstrumentbyinser*ngtheHarmonmuteintothebelloftheinstrument.ThesoundisoFendescribedasasoFersoundwithadis*nc*vebuzztoit.MilesDaviswasapopularemployeroftheHarmonmute.Althoughtrumpetsthemselveshavebeenthoroughlystudied,theacous*csoftrumpetmutesremaintobefullyunderstood.Somejazzmusiciansbelievethatden*ngHarmonmutescanleadtoanimprovementinsoundandintona*on.Theacous*csofden*ngHarmonmuteswasinves*gatedusingimpedanceandsoundspectrummeasurementsinthehopesofdeterminingthespecificacous*ceffectsofden*ngmutes.

Figure1.AHarmonmuteinthebellofatrumpetreadyforperformance.

Figure2.TwoHarmonmutes.Onedentedandoneundented.

MethodsAcous*cimpedancemeasurementsgivespecificinforma*onaboutalltheresonancesoftheinstrument.Smallchangestoaninstrumentoramutecanbedetectedwithchangestotheimpedancespectrum.TheBIASsystemisastateoftheartimpedanceheadthatcanbeusedfortakingimpedancemeasurementsofbrassinstruments.TheBIASsystemhastheadvantagethatitdoesnotrequireactualplayingoftheinstrument,soresultsare100%reproduciblewithdifferentusers.Becausethisinves*ga*onisfocusedonhowthesoundofHarmonmuteschanges,soundspectrawerecollectedtohelpquan*fyanychangesthatmightbedetectedwiththeear.Soundspectraweretakenbyplayingintoamicrophoneconnectedtoapreampwhichoutputsthesignaltoaspectrumanalyzer.Soundspectraaredependentontheplayerandonthenotebeingplayedandthusarenotasversa*leasBIASmeasurements.Modifica*onstotheHarmonmuteswereeitherdentsorholesplacedsequen*allywithdatabeingtakenaFereachfurthermodifica*on.Dentsweremadewithahammerandholesweremadewithadrillpress.

Figure3.TheBIASsysteminplaceformeasurementoftheimpedancespectrumofatrumpet.

AcknowledgementsIwouldliketothanktheMcCormickfamilyforprovidingthefundstopursuethisresearch.IwouldalsoliketothankGregEllioCandBobPeasleefortheirhelponthisproject.

Figure4.ImpedancespectrumofatrumpetandHarmonmute(redcurve)overlaidonaspectrumofanormaltrumpet(bluecurve).

Themoststrikingdifferencesbetweenthespectrumofthenormaltrumpetandistheseriesofraisedpeaksabove1400Hzwherethepeaksinthetrumpetspectrumfadeaway.Thislossofhighfrequencyresonancesisassociatedwiththeshapeofthebellofthetrumpet.Itseemsini*allythatthemutereturnsthesewavesbacktotheinstrumentsincethepeakshavealsoreturned.Itwasfoundthatothertrumpetmuteshadasimilareffectofraisingmorehighfrequencypeaks.Apreliminaryden*ngexperimentwasconductedtodeterminethebasicac*onofthesemodifica*onsontheimpedancespectrum.

Figure5.Overlaidimpedancespectrafromtheini*alden*ngexperimentshowingwherethemajorityofthechangeshappened.

Figure6.Overlaidimpedancespectrafromtheini*aldrillingexperimentshowingwherethemajorityofthechangeshappened.

Results

Figure7.ImpedancespectraoftheHarmonmuteaFervariousamountsofden*ngordrillingshowingdifferentchangestothespectrumfordifferenttechniques.

Figure8.Soundspectrafromthethirddrillingexperimentshowingthelossofhighfrequencypeakscausedbythemutepeakapproachingthefundamental.GraphsontheleFarenormalsoundspectraandgraphsontherightaresoundspectrafromwhenthosenotesceasetosoundgood.

Asseenabovethemajorityofthechangestotheimpedancespectrumaretothelowerfrequencypartofthespectrumwiththehigherpeakslargelyunaffected.Thiswasunexpected,astheraisingofthosepeaksareduetothemutebeingused.Apreliminarydrillingexperimentwasconductedtoseeifchangestothehighfrequencypartofthespectrumcouldbeobtained.Smallaperturesareknowntocauseabuzz,whichisnotonlyassociatedwithHarmonmutesbutisalsoassociatedwiththepresenceofhighfrequencyharmonics.

PuZngholesinthemutehadanalmostiden*caleffectontheimpedancespectrum.Therewerechangesinasimilarfrequencyrangeasbefore,withthehighfrequencypeaksbeinglargelyunaffected.

Thechangestotheimpedancespectrainthepreliminaryden*ngexperimentswerelargelyduetotheshiFingofthesmallresonanceassociatedwiththemuteitself.Thissmallpeakisnormallyabsentfromspectraoftrumpetswithanopenbellandwasfoundtomovetoahigherfrequencywhenholesordentswereplacedinthemute.Anothersetofden*nganddrillingexperimentswereconductedwithimpedancedatatakenofthemuteitself,withoutthetrumpet.

Asseenabove,den*nganddrillingaffectdifferentresonancesofthemute.Giventhatthelargemuteresonancesdonotshowupintheimpedancespectrumofthetrumpetandthemute,liCleisknownabouttheireffectontheimpedancespectrum.However,den*nganddrillingwerefoundtohaveasimilareffectonthesoundoftheinstrument.Beyondacertainpoint,thesoundbecameweakanddifficulttoplayintune.Thiswascharacterizedinthesoundspectrabyalossofhighfrequencypeaks.Inanotherdrillingexperimentmanyholeswereplacedinthemute,causingthemutepeaktoshiFupaconsiderableamount.Itwasnotedthatthe*meapar*cularnotebegantosoundweakorbadwasaroundthe*methemuteresonancewasclosetothetrumpetresonancecorrespondingtothatnote.

ConclusionsPlacingdentsandholesinHarmonmuteswerefoundlargelytodegradethesoundoftheinstrument.Thisisbecausechangestotheresonanceofthemuteaffectstheresonancesofthetrumpet.Itwasfoundthatsmallamountsofden*ngcouldchangethetoneinaposi*vewayandevenmakethemutelouder.Perhapsdentedmuteswouldbesuitedforsec*onworkinjazzorchestrasandundentedmutesarebeCerforsolosandsmallformatgroups.Thedis*nc*vesoundoftheHarmonprobablycomesfromtheraisedsetofpeaksaround3000Hzseeninthesoundspectra.Thissoundandthesepeaksgoawaywhenthemuteismodifiedtoomuch.FurtherworkshouldincludeamorecarefulstudyofhowtheotherpeaksintheimpedancespectrumofjusttheHarmonmutecometoinfluencethesoundoftheinstrument.Itwouldalsobeinteres*ngtorepeatthedrillingexperimentswithsmallersizedholestotrackmorepreciselythechangesinthesoundandacous*csofthemuteandinstrument.

Normal

Dented

Drilled