Properties of Sound
Sound waves are longitudinal!
 Sound can be explained by understanding:
◦ Speed
◦ Intensity and loudness
◦ Frequency and pitch
Most people hear sound between the
frequency of 20Hz and 20,000Hz.
Anatomy of Sound
External Ear:
◦ Focus the sound into
the ear canal.
Middle Ear:
◦ Amplifies the
Inner Ear:
◦ Senses the vibrations
and signals the brain.
Anatomy of Sound
The Middle Ear is made up of 3 tiny bones
known as the hammer (malleus), anvil
(incus) and stirrup (stapes).
A. Speed
The speed of sound (in dry air at 20°C) is
 The speed of sound varies with the
temperature and phase of matter it is traveling
◦ Most fast is solids
◦ slowest in gases
B. Intensity and Loudness
Intensity refers to the rate at which sound
waves travel in a given area.
◦ Depends upon the amplitude of the sound waves
and the distance from the source.
Loudness is a subjective term. It is the physical
response to sound intensity. Depends upon a
person’s health, age, etc.
B. Intensity and Loudness
Intensity is measured in
Bels (decibels, dB). The
scale is more logarithmic
◦ 0dB can barely be heard.
◦ 20dB is 100 times more
power than 0dB.
C. Frequency and Pitch
Sound frequency depends upon how fast
the source of the sound is vibrating.
◦ Longer waves produce lower sounds
◦ Shorter waves produce high frequency
Pitch is a person’s perception of sounds
frequency. (Subjective)
◦ High pitch = high frequency
◦ Low pitch = low frequency
Ultrasound waves are used in medicine and
sonar techniques.
Ultrasound can be used to construct images
of internal structures.
D. The Doppler Effect
The Doppler Effect explains
how the pitch of a sound can
change as it passes a person
or point.
It is the change in sounds
frequency caused by motion
of the sounds source, motion
of the listener, or both.
As a sound source approaches the frequency
increases. As the source moves away the
frequency drops.