Bel One Bel log I 1I 0 where

Bel One Bel = log (I 1/I 0), where I 1 is the absolute measured power, and I 0 is a reference power. Reference used is usually the least sound level that can be detected.

Normal human hearing in terms of bels l Least amount of sound power that can be detected: 0 bel l Sounds that are damaging to the ear: 14 bels

Decibel (d. B) One Decibel = one-tenth of a Bel, i. e. 1 Bel = 10 Decibels Therefore d. B = 10 log (I 1/I 0)

Normal human hearing in terms of decibels l Least amount of sound power that can be detected: 0 d. B l Sounds that are damaging to the ear: 140 d. B

INTENSITY LEVEL l Intensity expressed in terms of power with a reference power of 10 -12 W/m 2 or 10 -16 W/cm 2 is called INTENSITY LEVEL (d. B IL)

Pressure and Intensity l Pressure Square root of Intensity P I OR P 2 I

Normal human hearing in terms of pressure l Least amount of sound pressure that can be detected: 0. 0002 dynes/cm 2, or 20µPa (20 x 10 -6 Pa) l Sounds that are damaging to the ear: 2 x 108µPa

Decibel: Expressed in terms of pressure Decibel = 20 log (p 1/p 0) where p 1 is the absolute pressure of sound p 0 is the reference pressure

SOUND PRESSURE LEVEL Intensity expressed in terms of pressure with a reference pressure of 20 micropascals (20 µPa) or 0. 0002 dynes/cm 2 is called SOUND PRESSURE LEVEL (d. B SPL) One µPa = 10 -6 pascals

Absolute Power Absolute Pressure Bel Decibel Minimum detectable sound levels 10 -12 w/m 2 20µPa 0 0 Whisper at 1 meter 10 -10 w/m 2 2 x 102 µPa 2 20 Normal conversation at 1 meter 10 -6 w/m 2 2 x 104 µPa 6 60 Heavy traffic 10 -4 w/m 2 2 x 105 µPa 8 80 Damaging sound levels 102 w/m 2 2 x 108 µPa 14 140

Decibel questions l Two types of questions: 1. What is the intensity in d. B IL or d. B SPL of a sound with an absolute power of X w/m 2 or absolute pressure of X µPa? 2. What is the absolute power or pressure of a sound with an intensity of X d. B IL or X d. B SPL?