What is sound?
• Sound is produced when something vibrates, like the speaker in your stereo. When the speaker
pushes on the air, it compresses it.
• The vibrating speaker produces a series of pressure waves
• The waves travel to the ear causing the ear drum to vibrate.
• But notice that you did not hear the speaker vibrate, nor the sound waves move through the air.
It was only when the sound waves moved your ear drum and activity reached your cortex that
you perceived sound. How this occurs is the subject of this lecture.
• A loud sound is produced when the speaker produces a large vibration. The large vibration
produces large waves of compressed air. Soft sounds are produced by a small vibration.
• A high frequency sound is produced when the speaker vibrates rapidly. This produces a
closely spaced series of air pressure waves. Low frequency sounds are produced when the
speaker vibrates slowly.
• The normal range of frequencies audible to humans is 20 to 20,000 Hz (the number of
vibration per second). A range of 200 to 2000 Hz is required to understand speech.