1. The Didgeridoo and its Acoustic Properties:
Image from: didgeridoowebshop.com
The Didgeridoo and its Acoustic Properties:
Physical Variation and its Effect on Frequency and Amplitude
Yolnan Chen, Andrew Parker
Frontiers of Science Institute
University of Northern Colorado

2. 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 amplitude

3. Background Didgeridoo Originates from Australia
Tree branch or root hollowed out by termites
Decorated (painted, engraved or stained)
Simple instrument

4. Amplitude: ‘size of vibration’
Frequency: ‘speed of vibration’(Hz)
f = nv 4ƛ
f = frequency
ƛ = wavelength
n = resonant number
v = velocity
Oscillation: vibration of 2 sources against each other
1 Hertz = 1 oscillation per second

5. Higher Frequency
Pressure (Pa)
Time (msec)
Lower Frequency
Pressure (Pa)
Time (msec)

6. Pressure is measured in Pascals (Pa)
Pressure is directly related to amplitude
Less Dense
More Dense

7. Longitudinal Wave
particles temporarily displaced, return to original position
one particle transport energy to another (horizontally)
Standing Wave
2 waves, opposite direction, same frequency

8. Reflection
Can cause standing waves
Sound Wave Absorbing Materials
Hard→very reflective
Soft→less reflective

9. Acoustic Impedance: resistance of air to flow
Some energy transmitted
Some energy reflected

10. Fundamental Frequency -The lowest frequency of a periodic waveform
Harmonics
Amplitude (dB)
Other Terminology:
Fundamental Frequency
-The lowest frequency of a periodic waveform
Harmonics
-The following frequencies at intervals of 4 (harmony/chords/pitch/octave)
Frequency (Hz)

11. Methods
Play the PVC pipes simulating didgeridoos of various lengths and diameters
Human didgeridoo player
Sound insulated box reduce background noise
Snapshots of spectrogram & oscilloscope

12. Materials PVC pipes Particle Board Insulation foam USB microphone
Didjeridu
Funnel

13. Results (Length Changes)
Amplitude (dB)
Frequency (Hz)
Frequency (Hz)
Didgeridoo 1
length: 39.1in
diameter: 1.25in
Didgeridoo 2
length: 48.9in
diameter: 1.25in

14. Results (Diameter Changes)
Amplitude (dB)
Frequency (Hz)
Frequency (Hz)
Didgeridoo 6
length: 39.1in
diameter: 2in
Didgeridoo 7
length: 39.1in
diameter: 0.75in

15. Results (Bell vs No Bell)
Didgeridoo 8
(with bell attachment)
Amplitude (Pa)
Time (msec)
Didgeridoo 3
(without bell attachment)
Amplitude (Pa)
Time (msec)

16. Bell Effect Gradual change in diameter Decreasing impedance
Less reflection, more transmission
Pressure inside air cylinder different than pressure outside

17. Conclusion Hypothesis correct
Wish to add filling to inside of PVC pipe

18. Sources
Wolfe, J. (2005). Didgeridoo Acoustics/Yidaki Acoustics. University of New South Wales. Retrieved from
Sound Waves and Music. The physics classroom. Retrieved from
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

19. Acknowledgements Thanks 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)

20. Questions?
Image from: colourbox.com