Sound-power flow

To understand sound-intensity measurement, it should be realized that sound intensity is sound-power flow per unit area in the direction of sound propagation. Sound intensity can be measured in fluids such as air or water. Generally measurements cannot be made inside a solid. However there may be ways of measuring sound intensity in a solid, if the solid is transparent. Also sound intensity can be computed in a solid and then measured in a surrounding fluid to collate with the calculated results. In general the measurement of sound-intensity is relatively new. It can be measured either as a vector in three or two dimensions or as a single vector component. These features are discussed, together with some examples of sound-intensity measurement. An important use of a single component of sound intensity is the measurement of the sound power of a noise source. Another use is locating the primary sources of noise in operating machinery. The full sound-intensity vector can determine the direction of a noise source. Two vectors can determine the location of the source in space.