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Sound Measurements -Part II- Sound Intensity Measurements

written by: kkaarthic • edited by: Lamar Stonecypher • updated: 9/30/2008

This article describes in detail sound measurement and its importance.

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    Sound Intensity Measurements

    Sound intensity is the measurement of flow of sound power through a unit area. The unit for sound intensity is hence Watt/Meter Square (W/m^2). This measurement is a vector quantity and hence has both magnitude and direction. Sound normally tends to flow in certain direction and not in other directions. This measurement tends to help one in determining the direction from which the noise tends to propagate.

    Well here you may have a question, on what aspects does the measurement of Sound Intensity help us?

    Say for example we have plenty of machines in the shop floor of the factory. Each machine tends to vibrate and produce noise. The ultimate effect due to the noise leads to fatigue in the workers due to the prolonged exposure. Having a sound intensity measurement using the sound level meter can show the sound pressure levels, but in order to reduce this sound level we have to identify the source. This is the point where sound intensity measurements come into help. Since Sound Intensity measurements is a vector quantity, it tends to provide us with data pertaining to the magnitude and direction of flow of sound from a particular machine. This will help us in identifying the culprit making the noise and take necessary precautions to reduce the sound level.

    After all this we come across another question, what kind of instrument do we use to measure the sound intensity?

    Well the sound intensity measuring instrument is basically a construction consisting of two phase matched microphones. When I say phase matched microscopes, it means that the measurements taken by both the microphones tend to be in tandem with each other. Something like two cars on the same road traveling in the same direction and the same speed. So for a person looking at them it seems like they are moving in a tandem manner to each other. Well here is a small picture to make you feel on how it looks like basically. Click here to see the sound intensity probe construction.

    The measurement of the sound intensity moreover forms a basis for the determination of sound power. Moreover this provides an edge over sound pressure measurements because of its capability to phase out steady background noises. This also has the advantage of measuring the noise intensity in the near field of the machines.

    We will look further into the other types of sound measurements in the forthcoming articles.