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Sound Measurement - Noise Level / Source Mapping

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

This article deals with another methodology in sound level measurements – Noise Level/Source Mapping. This is an important method used to know the source of sound in any operating machinery.

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    Sound or Noise control initially begins with the methodology to identify the source of the sound or noise. Sound Intensity plays a very vital role in doing this because of the following reasons

    • The measurements can be carried out in site and does not need a special environment.
    • Sound intensity is a vector quantity and hence can define both magnitude and direction of the sound energy.
    • The best advantage of all is that it has the capability to handle data’s from multiple sources.

     

    We may ask, why do we need such a measure to identify the source of the noise? Well this is needed in order to optimize a certain device for trouble free use by an user, without the noise causing much trouble to him or her. Take for example, we need to determine the noise producing source in a motorcycle. We need to clearly pin point the location in order to attack the problem

     

    For this case the following things are done.

     

    A grid is constructed with the object in the real object in the background. The grid constructed could be made up of strings with equal sized grid boxes. The grid is basically made to define a surface where we are required to take measurements and sound intensity requires a known area in order to determine the sound energy flowing through it. Click here to see how the grid looks like.

    Sound intensity measurements are made normal to the surface in all the grid points available. This provides us with data for each grid which is stored. Click here to see how sound intensity measurements are made in each grid.

     

    These points can then be fed into the computer to give the detailed outline on hoe the noise intensity levels in the grid look like. The computer is made to generate a graph generated by joining lines through grid points having equal intensity. This is also called as sound intensity mapping. Click here to see how a sound intensity map looks like.

    What do we interpret from this map? This map gives us a basic understanding of from where the noise originates from in the vehicle. The map here shows the areas to be the engine and gearbox area in the motor cycle.

    Making a 3-Dimensional grid, acquiring the data and feeding this to a post-processing software would help us to visualize the sound field generated by the source as three dimensional plots.

     

    We will deal with further Sound Measurement techniques in the forthcoming articles of Sound Measurements.

     

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