Dr. Kim & Dr. Cadieux
Module 11.3 – Audition (The Stimulus – Sound Waves)
Sound waves are vibrations in air particles.
o Like light, sound travels in waves
o Unlike light, sound waves travel much slower and require some medium to travel
Sound waves are initiated by either a vibrating object (vocal cords or a guitar string), a
sudden burst of air (clapping), or by forcing air past a small cavity (pipe organ)
o This causes the air molecules surrounding the source of the sound to move,
causing a chain reaction of moving air particles.
Responding to Changes in Air Pressure
Condensed bands of air particles ripple away from the sound source.
The eardrum responds to air pressure changes -- bands of air molecules push the eardrum
inwards and outwards.
o Compressed air particles push it inwards
o Less dense air particles move it outwards
Pressure changes in sound waves can be graphed as a sine wave.
o In audition, the three physical characteristics of a wave ( amplitude, wavelength,
and purity) translate into the three psychological properties of loudness, pitch,
1. A wave's amplitude (height of a sound wave) affects the perception of loudness. o Since waves of greater amplitude correspond to vibrations of greater intensity,
higher waves correspond to louder sounds
o Humans are very sensitive to a very wide range of different sound amplitudes --
as such, loudness is measured using a logarithmic scale of decibels (