Gibbs B.

A practical structure-borne sound source characterisation is discussed for mechanical installations in buildings. The machines nearly always are installed in contact with plate structures such as heavyweight homogeneous structural floors and walls, or floating floor systems, or lightweight cavity constructions. Manufacturers require a laboratory-based measurement system which will yield single values of source strength in a form which is transferable to a prediction of the sound power generated in the installed condition, and thence the sound pressure in rooms removed from the source. A laboratory method is proposed which yields the source activity in the form of a free velocity, summed over the contact points. In addition, the source mobility is obtained separately, as the average of the effective mobility, also over the contact points. Both quantities are employed in estimating the installed power for a range of floors likely to be encountered in buildings. An approximate estimate is obtained by reference to a high source mobility condition, a low source mobility condition, or to a maximum value, the characteristic power.