PHYS1006 Lecture Notes - Lecture 14: Inverse-Square Law, Logarithm, Sound Intensity
5 Jul 2018
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Chapter 12 Intensity of Sound
Learning outcomes:
The characteristics of sound
Sound intensity and sound waves
Sound intensity level
Sources of Sound
A sound can be produced by any vibrating object, eg. strings, vocal chords, air columns in
pipes.
Frequency Ranges
F < 20Hz Infrasonic, eg. whales and elephants
F = 20Hz 20kHz Audible range
F > 20kHz Ultrasonic, eg. dogs, bats and dolphins
Human perception of sound
How the human ear perceives sound is determined by two characteristics – pitch and
loudness.
1. Pitch
Whether a sound is high or low pitched is determined by the frequency of the sound.
2. Loudness
Loudness is determined by the intensity of sound, where high intensity equates to a
louder sound.
Intensity of Sound
Intensity is determined by the amount of energy transported by a wave per second across a
unit area held perpendicular to the energy flow.
Intensity Level
Loudness (sound level) is measured by the intensity level.
The unit is called bel (B), named after Alexander Graham Bell, the inventor of the
telephone..
Intensity level (in decibels):
= Intensity of sound
= Intensity of reference sound
Threshold of hearing
Sources of sound Intensity J m-2s-1 Intensity level (dB)
Ear drum ruptures 160
Jet plane at 30m 140
Threshold of pain 1 120
Rock band 1 120
Thunder 110
Subway 100
Heavy traffic 90
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Document Summary
A sound can be produced by any vibrating object, eg. strings, vocal chords, air columns in pipes. F < 20hz infrasonic, eg. whales and elephants. F = 20hz 20khz audible range. F > 20khz ultrasonic, eg. dogs, bats and dolphins. How the human ear perceives sound is determined by two characteristics pitch and loudness: pitch. Whether a sound is high or low pitched is determined by the frequency of the sound: loudness. Loudness is determined by the intensity of sound, where high intensity equates to a louder sound. Intensity is determined by the amount of energy transported by a wave per second across a unit area held perpendicular to the energy flow. Loudness (sound level) is measured by the intensity level. The unit is called bel (b), named after alexander graham bell, the inventor of the telephone What is the intensity level of a sound whose intensity is 2. 0 10-6 w/m2 at a distance of 2. 0m from the source? db.
