Sound
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
vibrations.

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
342m/s.
 The speed of sound varies with the
temperature and phase of matter it is traveling
through.

◦ 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
frequency
◦ Shorter waves produce high frequency

Pitch is a person’s perception of sounds
frequency. (Subjective)
◦ High pitch = high frequency
◦ Low pitch = low frequency
Ultrasound

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.