SOUNDPart 3

SOUND

SOUND ENERGY, INTENSITY AND POWER

The acoustic power of a sound source is the amount of sound energy produced by a source per second. Acoustic power is measured in Watts.

Sound intensity [ I, Wm-2 ] is the rate at which sound energy passes through an area of 1 square metre.

The intensity of a sound varies inversely as the square of the distance from the source inverse square law.

SOUND INTENSITY LEVELS

Humans can respond to sound intensities ranging from 1x10-12 Wm-2 [threshold of hearing] to 1.0 Wm-2 [threshold of pain].

This huge range in sound intensities is impractical for use in comparing the “loudness” of sounds, so a logarithmic scale was developed … the Bel scale

The sound intensity level is a comparison of the intensity of a sound to a reference intensity [threshold of hearing], measured in decibels (dB)

http://www.animations.physics.unsw.edu.au/jw/dB.htm

TYPICAL SOUNDS

HUMAN HEARING

http://www.youtube.com/watch?v=GGqfRvCkt-w&feature=related