The Acoustics of Harmon Mutes - Sound Ideas
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University of Puget SoundSound Ideas
Summer Research
Summer 2016
The Acoustics of Harmon MutesZachary T. Armstrongzarmstrong@pugetsound.edu
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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
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