The intensity of sound is defined as the quantity of energy propagating through a unit area per unit time, the direction of propagation being perpendicular to the area. The amount of power transmitted is measured in Watt/m². A convenient unit is microwatts/m².
According to Weber Fechner law in psychology, the loudness of a sound as judged by the ear is proportional to the logarithm of the intensity. If I1 and I0 represent the intensities ot two sounds of a particular frequency and L1 and L0 the corresponding measure of loudness then L1 = KlogI1 and L0=KlogI0. The difference in loudness technically known as intensity Level, L between them is given by
L = L1 – L2 =K[logI1 – logI0]
L = K log( I1 / I0 )
Where K is a constant that depends on the units and I0 is some standard reference intensity arbitrarily takes as 10
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