Loudness Power, intensity, intensity level,

Power and intensity Sound detector Energy: will accumulate in time Power: rate of energy transfer, stays the same Dependent on detector area Intensity: rate of energy transfer per area 1J=1Nm 1W=1J/s 1 W/m 2 =1J/sm 2

Inverse Square Law B A radius B = 2 radius A area B = 4 area A intensity B = 1/4 intensity A

Sound intensity level  Physiological response to loudness does not simply scale with intensity  Loudest possible sound waves: 1 Watt / square meter 1 Watt / square meter  Softest perceptible sound: Watt / square meter Watt / square meter Chosen as reference intensity Chosen as reference intensity

Sound intensity level  1 Decibel=1/10 bel (Alexander Graham Bell)  “1 bel” for a sound means: the ratio of its intensity to a reference is 10:1 the ratio of its intensity to a reference is 10:1 Decibel measure the relation between two sounds, not an amount of sound.

Chart of sound levels source L (dB) I (W/m 2 ) reaction inaudible Empty auditorium Library conversation Factory Amplified Rock Painful

Sound level and music  More than 50 dB (eliminates background)  Above 100 dB: damage to ears  ffff (95 dB) to ppp (50 dB)  More likely 60…85 dB for symphony concert  Determined by range of instruments (typically < 40dB) Wood-wind: only 10 dB dynamic range Wood-wind: only 10 dB dynamic range

Sound levels and multiple sources Violinist A I A =60 dB Violinist B I B =60 dB What is the resulting sound level L? W/m 2 2∙10 -6 W/m 2 (60+Log2) dB = 63 dB

Sound levels and multiple sources What is the resulting sound level L? W/m 2 10∙10 -6 W/m 2 70 dB W/m W/m 2