the didgeridoo and its acoustic properties:
DESCRIPTION
Hypotheses We predict that when the physical attributes of an air cylinder that is closed at one end are altered, the frequency and amplitude of the energy produced are altered as well. Increase length→decrease frequency Increase diameter→increase amplitudeTRANSCRIPT
The Didgeridoo and its Acoustic Properties:
Physical Variation and its Effect on Frequency and AmplitudeYolnan Chen, Andrew ParkerFrontiers of Science InstituteUniversity of Northern Colorado
Image from: didgeridoowebshop.com
Hypotheses
We predict that when the physical attributes of an air cylinder that is closed at one end are altered, the frequency and amplitude of the energy produced are altered as well.
Increase length→decrease frequencyIncrease diameter→increase amplitude
BackgroundDidgeridoo● Originates from Australia● Tree branch or root
hollowed out by termites● Decorated (painted,
engraved or stained)● Simple instrument
Amplitude: ‘size of vibration’Frequency: ‘speed of vibration’(Hz)f = f = frequencyƛ = wavelengthn = resonant numberv = velocityOscillation: vibration of 2 sources against each other1 Hertz = 1 oscillation per second
Pre
ssur
e (P
a)P
ress
ure
(Pa)
Time (msec)
Higher Frequency
Lower Frequency
Time (msec)
Pressure is measured in Pascals (Pa)
Pressure is directly related to amplitude
More Dense
Less Dense
Longitudinal Wave● particles temporarily displaced, return to original position● one particle transport energy to another (horizontally)
Standing Wave● 2 waves, opposite direction, same frequency
Reflection● Can cause standing waves
Sound Wave Absorbing Materials● Hard→very reflective● Soft→less reflective
Acoustic Impedance: resistance of air to flow ● Some energy transmitted● Some energy reflected
Other Terminology:● Fundamental Frequency
-The lowest frequency of a periodic waveform● Harmonics
-The following frequencies at intervals of 4 (harmony/chords/pitch/octave)
Fundamental Frequency
Harmonics
Am
plitu
de (d
B)
Frequency (Hz)
MethodsPlay the PVC pipes simulating didgeridoos of various lengths and diametersHuman didgeridoo playerSound insulated box reduce background noiseSnapshots of spectrogram & oscilloscope
Materials● PVC pipes● Particle Board● Insulation foam● USB microphone● Didjeridu● Funnel
Results (Length Changes)
Didgeridoo 1length: 39.1indiameter: 1.25in
Didgeridoo 2length: 48.9indiameter: 1.25in
Am
plitu
de (d
B)
Frequency (Hz) Frequency (Hz)
Results (Diameter Changes)
Didgeridoo 6length: 39.1indiameter: 2in
Didgeridoo 7length: 39.1indiameter: 0.75in
Am
plitu
de (d
B)
Frequency (Hz)Frequency (Hz)
Results (Bell vs No Bell)
Didgeridoo 8(with bell attachment)
Didgeridoo 3 (without bell attachment)
Am
plitu
de (P
a)
Time (msec)
Am
plitu
de (P
a)
Time (msec)
Bell Effect● Gradual change in
diameter● Decreasing impedance● Less reflection, more
transmission● Pressure inside air
cylinder different than pressure outside
Conclusion● Hypothesis correct
● Wish to add filling to inside of PVC pipe
Sources ● Wolfe, J. (2005). Didgeridoo Acoustics/Yidaki Acoustics. University of
New South Wales. Retrieved from http://newt.phys.unsw.edu.au/jw/didjeridu.html
● Sound Waves and Music. The physics classroom. Retrieved from http://www.physicsclassroom.com/class/sound
● Heller, E. J. (2013) . Why You Hear What You Hear. Princeton, NJ:
Princeton University Press.
● Serway, R. A., & Jewett, J. W. (2010). Physics for Scientists and
Engineers (8th ed.). Boston, MA:Cengage Learning
AcknowledgementsThanks to...● Christopher Courrejou (mentor)● Rebecca Kipf (Advisor)● Dr. Semak (Physics Department Professor)● Dr. Galovich (Physics Department Chair)● Christopher Krause, Sofia Simina (Residential Advisors)● Noble Energy (Sponsor)● Rollie R. Kelley Family Fund at the Denver Foundation (Sponsor)● The Edward Madigan Foundation (Sponsor)● University of Northern Colorado● Steve Anderson (Head of MAST)● Lori Ball (Head of FSI)
Image from: colourbox.com
Questions?