Wk10--The Attenuation of Sound Abbreviations:
Sunday, December 6, 2020 9:48 PM b/w = between
w/ = with
INC = increase
DEC = decrease
• Sound waves propagate in air as pressure. -> The amplitude of a sound wave is
measured by the amount of INC or DEC in pre above or below the ambient pressure.
• Transmitted wave: the new sound wave transmitted when a sound wave hits a solid
and the solid pushes on the air behind it.
○ Pt: amplitude of the transmitted wave. Depends on the mass per unit area of the
wall σ and the frequency of the wave v:
○
𝑝𝑡/𝑝𝑖 = sqrt[1 / (1+(𝜋𝑣𝜎/𝜌𝑣)2)] Eqn 10.1, approximation
○ where pi is the amplitude of the incident wave and ρ is the density of
air(velocity on bottom). Ratio pt/pi is the transmission coefficient. -> What
fraction of the wave is being transmitted?
○ Eqn 10.1 is only an approximation due to diffraction and reflections off the
attenuator/other surfaces that could lead to deviations.
• Velocity of the sound waves u: u = vl, where l is wavelength. Constant at 344m/s in
air at 20C.
• You will place various attenuators between the two speakers and measure how much
they affect the amplitude of the sound waves received by the second speaker.
Sunday, December 6, 2020 9:48 PM b/w = between
w/ = with
INC = increase
DEC = decrease
• Sound waves propagate in air as pressure. -> The amplitude of a sound wave is
measured by the amount of INC or DEC in pre above or below the ambient pressure.
• Transmitted wave: the new sound wave transmitted when a sound wave hits a solid
and the solid pushes on the air behind it.
○ Pt: amplitude of the transmitted wave. Depends on the mass per unit area of the
wall σ and the frequency of the wave v:
○
𝑝𝑡/𝑝𝑖 = sqrt[1 / (1+(𝜋𝑣𝜎/𝜌𝑣)2)] Eqn 10.1, approximation
○ where pi is the amplitude of the incident wave and ρ is the density of
air(velocity on bottom). Ratio pt/pi is the transmission coefficient. -> What
fraction of the wave is being transmitted?
○ Eqn 10.1 is only an approximation due to diffraction and reflections off the
attenuator/other surfaces that could lead to deviations.
• Velocity of the sound waves u: u = vl, where l is wavelength. Constant at 344m/s in
air at 20C.
• You will place various attenuators between the two speakers and measure how much
they affect the amplitude of the sound waves received by the second speaker.
