PHYSICSOFSOUNDINFOSHEET
SOUNDWAVES:Soundwavesaregeneratedbyasoundsource.Oncethesourceis
activated,theenergycreatedbyitrepeatsoverandoveragain–intheformofwaves–asit
movesthroughamedium(suchasairorwater).(Thinkofdroppingapebbleinalake).As
theenergymovesthroughthemedium,itvibratestheparticlesinthemedium(thinkabout
howyoucanfeeltheboominglowbassofasonginyourbody).Insinging,soundwaves
arecreatedbythevocalcordvibrationsandtravelthroughtheair(aswellasanythingelse
intheroom).
FREQUENCY:Thefrequencyofapitch/soundreferstohowoftentheparticlesofthe
mediumvibratewhenawavepassesthroughthemedium.Putanotherway,thefrequency
ishowquicklythesoundwaverepeatsitselfoverandoveragaininthemedium.(Putyour
fingersonyournoseandhummahighnote,andyou’llfeelthevibrationsmovingfaster
throughyournosethanifyouhummedalownote).
Measurements:FrequencyismeasuredincyclesperunitoftimecalledHertz(Hz).1Hzis
equalto1cycles(repetitionofthewave)persecond).MiddleChasafrquencyofabout262
Hz.Thismeansthateachsecond,tomakeaMiddleC,yourcordsarevibrating262per
second,andeachoneofthosevibrationsiscreatingawaveofenergythatisthensentoutinto
theworldatthatspeed.Ingeneral,men'svocalfoldscanvibratefrom90-500Hz,andthey
averageabout115Hzinconversation.Women'svocalfoldscanvibratefrom150-1000Hz,
andtheyaverageabout200Hzinconversation.Hereisahandylistofpitchfrequencies:
http://www.phy.mtu.edu/~suits/notefreqs.html
INTENSITY:Besidesfrequency,intensityistheotherimportantaspectofasoundwave.
Intensityishowmuchenergyisbeingcarriedinthesoundwave.Thegreaterthe
amplitude(thelargeness)ofvibrationsoftheparticlesofthemedium,thegreatertherate
atwhichenergyistransportedthroughit,andthemoreintensethatthesoundwaveis.In
otherwords,iftheparticlesvibratealotwhenthesoundwavehitsthem,thentheintensity
ishigh;iftheyonlyvibratealittle,thentheintensityislow.
So,really,intensity(insound)canberoughlydefinedasvolume.Thehighertheintensity,
thelouderthenoteis.(Thisismostlytrue.Becauseofthehumanear'stendencytoamplify
higherrangefrequencies(1000Hzto5000Hz),highnoteswillseemloudertothehuman
earthanlownotes,evenifsungatthesameintensity.Also,itshouldbenotedthatthe
intensitygetslessthefartherthesoundwavetravels–forexample,yousoundquieterto
someonefaraway.)
Measurements:WhileofficiallywemeasureintensityinWatts/meter(howmuchenergyis
containedinthesoundwavepereverymeterittravels),decibels(dB)isthemostcommon
waytoratevolume/intensity.(Thethresholdofhearingisassignedasoundlevelof0dB;this
soundcorrespondstoanintensityof1*10-12W/m2.)Rustlingleavesareabout10db;very
loudmusicinheadphonesis100db,andyoureardrumwillpopat160dB.
THEDIFFERENCEBETWEENFREQUENCYANDINTENSITY:Frequencyishowoftenthe
soundwaverepeats;intensityishowmuchenergyiscontainedwithinthesoundwave.So
ifIsingMiddleCsoftly,thatsoundhasalowINTENSITY,butthesameFREQUENCYasifI
sangaMiddleCloudly.Conversely,IcouldsingaMiddleCoraMiddleGat30dB–their
INTENSITYwouldbethesame,thoughtheirfrequencywouldbedifferent.
HARMONICS:Whenthesoundwavesinteractswithamedium/object,themedium/object
hasitsowntendencies,andsowilltendtovibrateataparticularfrequencyorasetof
frequencies.Thefrequencyorfrequenciesatwhichanobjecttendstovibratewithwhen
hit,struck,plucked,strummedorsomehowdisturbedisknownasthenaturalfrequencyof
theobject.Harmonicsarecreatedbytheinteractionoffundamentalsoundwave(pitch)
withthenaturalfrequenciesoftheobjectitismovingthrough.Whenyousing,wehearthe
harmonicsthatarecreatedthroughtheinteractionofthesoundwavefrequencyandthe
naturalfrequenciesofyourresonancechambers.
Asillyexampleisthatifyousayasentence(asoundwavefrequency)toaniceperson
(object’snaturalfrequency),theywillhearitasakindstatement(resultingharmonics);but
ifyousaythesamesentence(asoundwavefrequency)toameanperson(adifferent
object’snaturalfrequency),theywillhearitasaninsultingstatement(differentresulting
harmonies).
Measurements:Ourlanguageondescribingthisisalittleconvoulted.Thepitch(frequency)
ofanoteissometimescalledthefundamental.The1stHarmonicofasoundisthe
fundamental(pitch).Therestoftheharmonicsgoupfromthere.The2ndharmonicis
usuallyanoctaveup,and3rdHarmonicsisamusicalfifthabovethat.Sometimestheword
overtoneisused.The1stOvertoneisthesameasthe2ndHarmonic–don’tgetconfused!
Visualoffirst8harmonics:
linktoexampleofwhatthefirst16overtones/harmonicssoundlike
https://en.wikipedia.org/wiki/Overtone
TIMBRE:Inmusic,timbre(tam-bər)isalsoknownastonecolorortonequality.Different
typesofsoundproduction,suchasdifferentpeople’svoicesordifferentinstrumentssound
differentevenwhensinging/playingthesamenote.Thisistimbre.Timbreistheresultof
harmonicsandintensity/volume(sometimestalkedabouttogetherthespectralenvelope.)
Youcouldstopthereandhaveagreatundertandingofthephysicsofsinging,butifyouwant
toseehowyourphysiologyrelatestothephysics,then,keepreading…
RESONANCE:Insinging,resonancereferstothesoundwavemovingthroughthespaces
inyourthroat,face,andheadasitmovesthroughyourbodyandoutintospace.Assingers,
wemodifythesizeandshapeofthoseresonatorstogetthebestsoundpossible.
Inphysics,resonanceisdefinedasthephenomenonthatoccurswhenavibratingsystem
(orexternalforce)drivesanothersystemtooscillatewithgreateramplitudeataspecific,
preferentialfrequency.
So,let’scombinethosedefinitionsforacleanstatementonwhathappensinthephysicsof
singing.Thevibratingsystem(thesoundwavecreatedbythevocalcords)isdirected
throughtheothersystem(theresonancechambers)tomakethatsystemoscillate(vibrate)
atspecificpreferentialfrequencies(theharmonicsthatcreateyourbestsound).
FORMANTS:
AsweknowfromtheHarmonicssection,whensoundwavesinteractwitha
medium/object,themedium/objecthasitsowntendencies,andsowilltendtovibrateata
particularfrequencyorasetoffrequencies–thiscreatestheharmonics.Withinthose
harmonicscreated,interestingly,thesoundwavefrequenciesthatmost‘jive”withthose
naturalfrequenciesoftheobjectwillincreaseinamplitude.Inotherwords,sincethesound
waveandtheobjectshareacertainfrequency,theamountofvibrationatthatfrequency
willbeamplified…andsoitwillbelouder.
So,asthesoundwavegoesthroughalltheparticularobjectsofyourresonancechambers
(throatandface),eachpartofyourresonancechamberswillhighlightacertainfrequency
orsetoffrequencies.Thefrequenciesthatarehighlightedbyyourresonancechambers
interactingwithsoundwavesarecalledformants.So,aformantisjustahighlighted
frequencycreatedbytheinteractionofaresonancechamberandasoundwave.
Sillyexample:Youmeetsomeoneandtheirloveofpetsreally“resonates”withyou–you
bothstronglysharethatlove.So,whenyouarehangingouttogether,thatloveofpets
becomesstronger(isamplified)–youhaveitincommon,soyoudostufftogetherthathas
todowithpets.Theloveyouhaveforpetsisthesoundwavefrequency.Theloveyour
friendhasforpetsinthenaturalfrequencyoftheresonatingchamber.Theincreasedlove
ofpetswhenyouaretogetheristheformant.
Therearelotsofformants,astherearelotsofpartsofyou,butthetherearefivethatget
talkedaboutthemostinsinging.
The1stformantishighlightedsoundresultingfromtheinteractionofthesoundwavewith
thepositioningofthejaw.Themoreyourjawisdropped,thehigherthehighlighted
frequencyisinthesoundspectrum.Thefirstformantisaround500Hz(+/-300).
Thisisimportantforsingingbecauseifthefundamental/pitchiswellbelowthe
formantrange,thequalityofthesoundisrich,butifthefundamentalisabovethe
formantregionsthesoundisthin.So,onhighnotes,wherethefundamentalis
alreadyhigh,weneedtoincreasethehighlightedfrequencyoftheformantstokeep
thetonesoundingrich.Wecandothisbyopeningourjawtoincreasethefirst
fundamentalhighlighedfrequency(sothatthepitchissafelybelowit).
The2ndformantisthehighlightedsoundresultingfromtheinteractionofthesoundwave
withthepositioningofthetongue.Ahigherarchedtonguecreatesahigherhighlighted
frequency.Thesecondformantisaround1500Hz(+/-800)
Remember,ourearshighlightfrequenciesbetween1000and5000Hz,byarching
ourtonguepositiion,wecanhighlightthesecondfundamentalonthelowestnotes
andkeepitinourears’happyplace.Thesecondformantiscrucialincreatingthe
musicaltheatresound.Soundspectrums(visualrepresentationsofsound)show
thestrongestpeaksatthe2ndformantwhensingingmusicaltheatre.So,archyour
tonguesinthisstyle!
The3rdformantisthehighlightedsoundresultingfomroundedlipsvsunroundedlipsand
thetipofthetongueposition.Thethirdformantisaround2500Hz.The4thand5th
formantsaredeterminedbyvocaltractlength,pharynxshape,andlarynxshape.
SINGER’SFORMANT
Singersdosomethingcoolwhilesingingwell–theyactuallycreateanotherformant–one
thatdoesn’texistinspeech.Itisrightaround3000-4000Hz,andcreatesthe“ring”that
peopleassociatewithgreatsinging.Bywideningthepharynxandloweringlarynx,singers
createanewlittleresonatorshapethathighlightsfrequenciesinthe3000-4000Hzrange–
whichisdelightfulbecauseitmatchesthefrequenciesthatourearsliketohighlight.The
resultisasparkly,shimmerysoundtohumans.
Theshapeisonlycreatedthroughthemanipulationofthepharynxandlarynx.Without
movingthem,thepharynxistheopeningtothelarynxandtheyfunctiontogetherasone
resonator.Bychangingtheshapeofthepharynxandmovingthelarynxdown,thayareno
longerpartofoneresonatingsystembecausetheyareeachnowindifferentshapes.Boom!
Extra,sparklyresonator!
FUNFACT:
Intervalsthatwehearaspleasingtotheearhavereally“clean”numericalrelationstoeach
other!That’sonereasonsingingexactlyonpitchiscrucial…
Interval
Octave
Third
Fourth
Fifth
FrequencyRatio
2:1
5:4
4:3
3:2
Examples
220Hzand440Hz
220Hzand277Hz
342Hzand256Hz
384Hzand256Hz