3. 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.

4. 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.ht m

5. TYPICAL SOUNDS

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