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Diffraction of Sound Waves
By: Adams Daramy
Diffraction
• Beam of light spread out=>passes through medium
-Accompanied by interference between the wave forms produced
• Wave bends when it passes around an edge/through a slit
• Change in the direction of waves as they encounter opening/barrier in their
way
• More pronounced with longer wavelengths:
Sound Wave
• Wave of compression/rarefaction
• Speed of Sound Wave (c)=wavelength/period of time
-measured in meters per second
• Can be heard around corners and barriers
• -due to diffraction and reflection of sound
Reflection of Sound Waves
• Leads to either an echo or reverberation
• Reverberation-Prolongation of sound; resonance
• Law of Reflection: angle of incidence equals angle of reflection
Sound Radiation in Woodwind Instruments
-Effects of Diffraction
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Standing waves in a tube, compressions/rarefactions, are longitudinal
From closed tube end, waves will be reflected > due to diffraction
Amount of diffraction depends on ratio of wavelength to bore diameter
Waves pass through large opening with minimal disturbance
-large proportion of sound energy reflected from open end
Acoustic Impedance
• Ratio of pressure fluctuation to particle velocity:
Z=p/v
• Volume Velocity/Discharge-the particle velocity times the
tube area A.
Z=z/A=p/U
• When waves meet at open end, encounter sudden change in
impedance