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Understanding the Doppler Effect and Its Impact on Sound Perception

This lecture covers the Doppler Effect, demonstrating its influence on sound waves, as well as the role of the human ear in sound amplification. Key concepts include the calculation of force and pressure on the eardrum, sound absorption, noise reduction, and the relationship between frequency, intensity, and pitch perception. It explores how both stationary and moving sound sources affect an observer while considering factors like mechanical advantage and acoustic impedance across various media.

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Understanding the Doppler Effect and Its Impact on Sound Perception

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  1. PHY238YLecture 13 The Doppler Effect References: Halliday, Resnick, Walker: Fundamentals of Physics, 6th ed., Wiley 2003, Chapter 18 (18.8) Hallett et al.: Physics for the life sciences, 4th ed., 2003, Ch.2 (2.7) Some of the pictures were taken from Hyper Physics: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/soucon.html#soucon Thanks to dr. Rod Nave for the permission to use the above resource

  2. PHY238YLecture 13 • Hearing: pressure in the cochlear liquid vs. pressure on the eardrum (does human ear really amplifies sound?) • Example (Ear amplifier) 1) Calculate the maximum net force on an eardrum due to a sound wave having a maximum pressure of 2* 10-3 N/m2, if the diameter of the eardrum is 0.0085m. 2) Assuming the mechanical advantage of the hammer, anvil and stirrup is 2, calculate the pressure created on the oval window (Ao = 0.03cm2) 3) Assuming the acoustic impedance of air Zair = 416 N*s/m3; and water Zwater = 1.48*106 N*s/m3, calculate the relative transmission of the oval window to sound waves (stransmitted/sincident).

  3. PHY238YLecture 13 • Absorption of sound: sound waves produce molecular motion in the material they propagate; • Friction reduces intensity by energy dissipation. • Inside a medium: • The attenuation length x0 depends strongly on: frequency and the type of medium involved.

  4. PHY238YLecture 13 Attenuation of sound waves in various media

  5. PHY238YLecture 13 • Noise; noise reduction • Decrease of sound intensity: where a is the characteristic dissipation coefficient for a given medium

  6. PHY238YLecture 13 Sound source is stationary, observer (detector) is moving “into the waves”

  7. PHY238YLecture 13 Doppler effect for a source at rest (a) and moving (b). Observer (detector) is at rest.

  8. PHY238YLecture 13 • Both detector (observer) and source move • Speed of sound is v • Speed of the observer is v0 • Speed of the source is vs

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  12. PHY238YLecture 13 • Is Doppler effect an illusion? J.G. Neuhoff, M.K. McBeath: Am. J. Phys., Vol.65(7), 1997 found out that: • Perceptual processing of frequency and intensity interact; • Judgments about magnitude and direction of pitch change are influenced by changes in loudness; • The intensity of a Doppler-shifted tone rises as the source approaches; loudness changes influence pitch change, so pitch is also perceived to rise ?

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