Hypothesis: Alternating loud and soft sounds can be heard at a distance in front of two loudspeakers playing the same sound. The distance between the loud and soft sounds decreases if the frequency of the audio signal generator is increased. Aim: To investigate sound wave interference and how it varies with frequency.

1. Hypothesis: Alternatingloudandsoftsoundscanbe heardat a distance infrontof two loudspeakers
playingthe same sound.The distance betweenthe loudandsoftsoundsdecreasesif the
frequencyof the audiosignal generatorisincreased.
Aim: To investigate soundwaveinterference andhow itvarieswithfrequency.
Apparatus: Audiosignal generator,2loudspeakers,connectingwires,meterrule,chalk
Diagrams:
Procedure:
1. Two speakerswere connectedtoanaudiosignal generator.
2. The signal generatorwasstartedand adjustedtoemitidentical loudsoundsfromboth
speakers.
3. A student,blockingone earwasallowedtostandinthe centerof the speakersata certain
distance fromthem.
4. The studentwalkedparalleltothe speakersuntil the loudestsoundwasheard.Hisdistance
away fromthe centerwas recorded.
5. The studentreturnedtothe centerand walkedinthe opposite directionuntil the loudest
soundwasheard.The distance awayfromthe centerwas recorded.
6. Steps3-5 were repeated 4timesbuteach time the studentwalkedfurtherthanthe distance
before until the maximumsoundwasheard.
7. Steps3-6 were repeatedbutnotingareasof the softestsoundinstead.
8. The frequencyof the generatorwasincreasedandsteps3-8 were repeatedwithout
recordingthe distances.

2. Results:
Constructive Interference – Regions of Maxima
Distance Away From Center (cm) Average (cm)
21 19 20
42 38 40
58 62 60
80 80 80
99 97 98
Destructive Interference – Regions of Minima
Distance Away From Center (cm) Average (cm)
10 10 10
29 31 30
48 52 50
68 72 70
88 94 91
Whenthe frequencywasincreasedthe areasof maximumandminimumsoundcorrespondingtothose
recordedbefore were closertothe centerand closertoeach other.There were alsomore areas of
maximumandminimumsoundalongthe same distance walkedasbefore.
Analysis:
Soundwavesare longitudinalandtravel bya seriesof compressionsandrarefactions.
The speakersconvertedelectrical signalintovibrationscausingcompressionsandrarefactionsof air
moleculesthusallowingsoundtotravel tothe student’sear.Byblockinganear the studentwasable to
concentrate andallowthe soundto be heardfrom onlyone ear.
The studentnotedvariousareasof loudand softsounds.Thisindicatesthatinterference
was takingplace. The areasof maximumsound(maxima) were where constructive interference took
place and the areasof minimumsound(minima) were wheredestructive interference tookplace.
Constructive interference occurswhentwowavesthatare inphase combine toproduce a wave twice
the amplitude of the original waves.Thiswaswhere compressionsoverlappedeachotherand
rarefactionsoverlappedeachother.Destructive interference occurswhentwowavesthatare out phase
cancel out eachother.Thiswas where compressionsoverlappedrarefactionandrarefactions
overlappedcompressions.

3. The distance betweenthe areasof maximaandminimadecreasedwhenthe frequency
was increased.Frequencyisthe numberof wavesproducedpersecond.Since more wavesare produced
persecondthe wavesinterfere more frequently,thusproducingcloserareasof maximaandminima.
The wavelengthof soundcouldbe calculatedfromthisexperiment.Usingone areaof
constructive of destructive interference,itsdistance awayfromthe center(m),the angle the pathof
maxima/minimamakeswiththe center(pheta) andthe distance betweenthe twospeakers(d),itis
possible tocalculate the wavelength(lamda)usingthe followingformula: