Intensity of Sound

It is defined as "The Sound energy flowing per second through unit area place perpendicular to direction of sound waves is called intensity of sound". It is denoted by I and its S.I unit is Watt Per Square Meter

Mathematically

Intensity of Sound = E/A.t

Sound level or Intensity level

It is the difference in loudness of any two sounds where one is the faintest audible sound, thus it is defined as "The difference in (L) loudness of any unknown sound of intensity (Ix) and (L.) loudness of faintest audible sound of intensity (Iy) is called sound level or intensity level".

Mathematically is can be represented by L – L.

General formula: L – L. = log (Ix / Iy)

Weber Fechner Law

According to this experimental law, we came to know this ""The loudness (L) of a sound is directly proportional to the logarithm (Log) of intensity (Ix) of sound.

L ∝ log Ix

L = K log Ix ------ eq (1)

If (L.) is loudness of faintest audible sound of intensity (Iy) then

L. ∝ log Iy

L. = K log Iy ------ eq (2)

Here, K is the proportionally constant of weber Fechner law. Now subtracting eq1 from eq2. so, we get

L – L. = K log Ix – K log Iy

L – L. = K log Ix / Iy

In S.I, if the value of K is 1. so

L – L. = 1. log Ix / Iy

L – L. = log Ix / Iy

S.I unit of Sound level or intensity level

The S.I unit of sound level is bel and it is defined as "The sound level is said to be one bel if the intensity of loudness of any unknown sound is ten times greater than the intensity of faintest audible sound".

So, sound level can be written as

L – L. = log Ix / Iy (bel)

Bel is very big unit, smaller unit of bel is decibel. Where one bel is equal to ten decibel and most of the time. The sound level is measured in decibel. so, sound level can be written as

L – L. = 10 log Ix / Iy (decibel)

L – L. = 10 log Ix / Iy (dB)

Hence, proved. and form further help, contact us and give feedback to us on social media. Facebook, twitter and Google+

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5 January 2015