Sound Power & Intensity

LO4by: Azarnoush

Just a simple example…Our vocal chord is a source that produces sound. this sound wave carries power and energy. Production of sound energy is due to vibration of the chords in which converts the mechanical energy into sound energy.

The greater the waves amplitude the more energy the wave carries.

This wave energy can change over time known as power: P= E/t

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NOW… the question is where does this sound power go to?! …well EVERYWHERE..!!! it spreads out in all the directions. IF we are at a certain distance from a source of sound, for example someone talking to us, we will hear the same loudness sound independent of where we are standing: either in front of the person or behind him it wouldn’t matter. loudness of a voice depends on how far we are from that sound source.

** Loudness is a physical property associated with intensity.

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. Intensity of any wave is the rate of power of that wave per area. Also for area the only geometric shape that has all points equal distance away from a source is a sphere (4pi.r^2).

I = ⟨P⟩/A

All points within this area get the same intensity( loudness).

. For sound power we have this formula:

P= (1/2) MV(w^2)(A^2)and so

I = (1/2)(p)(v)(w^2)(A^2) **p as in mass density

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we are used to measure sound we hear in loudness. For example the sound of your friend is loud when she is yelling at you and on the other hand her sound is not loud when she is whispering to you.As we said before Intensity is the amount of energy a sound has over an area; based on the upper example a) when we shout, the sound power produced is higher and so it carries more energy with itself and so the INTENSITY is higher. b) when we whisper the sound power produced is low and so it carries less energy with itself and so the INTENSITY is lower.

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let’s combine our knowledge and solve this question

Q: Determine the amplitude of sound wave if the wave travels at a frequency of 1000 Hz in air of density 2 kg.m^ -

3 at 400 ms^-1 with an intensity of 10 Wm^-2 ??

Thank you