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How to Calculate Sound Power

The sound we hear is the result of waves moving through a medium. As sound moves away from its origin the waves spread out. The energy carried by the waves also distributes over an ever-increasing area, causing a reduction in the intensity of the sound wave. The human ear is sensitive to a large range of intensities, and to accommodate this sound intensity is often reported on a logarithmic scale using the decibel as a unit. Sound power, measured in watts, relates the intensity of the sound wave to the distance the wave has travelled from its source.

Instructions

    • 1

      Convert the intensity (I) of the sound from a measurement in decibels (dB) to the SI units of watts per square meter (W/m^2). Use the expression for intensity: I(in W/m^2) = 10^[{I(in dB)/10} -- 12] to convert the decibel intensity to W/m^2. For example, substituting a decibel sound intensity of 90 dB into this equation yields an intensity, or I = 1e-3 W/m^2.

    • 2

      Measure the distance (r) from the source of the sound to the point where the power of the sound is to be determined. Record this measurement in meters.

    • 3

      Calculate the average sound power (P) at the specified distance from the sound source using the relationship P = 12.57 x (I) x (r) x (r). Report the power with the unit of watts (W). Note that this relationship for average sound power assumes a spherical wave front.

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Be Self Taught
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