Vibro-Acoustic Sources in Lightweight Buildings
The work reported in this thesis addresses the problem of structure-borne sound transmission in buildings. Vibrating sources, such as services plant and domestic appliances, transmit vibro-acoustic power, causing noise complaints by occupants in rooms removed from the source room. There is not yet an accepted practical method of predicting the installed power into floors or supporting walls, and thence the resultant sound pressure in rooms. This study concentrates on the prediction of the installed power from mechanical installations in lightweight buildings composed of framed and ribbed plates. To identify the characteristics of such receiver elements, a field survey has been undertaken, which involved measurement of the point and transfer mobilities of common wall and floor structures. It is shown that the range of measured values of receiver point mobility is surprisingly small and that the constructions investigated often displayed thin plate-like characteristics, with relatively small spatial variations in point mobility. These field measurements give support to the notion of averaging over contacts. This single equivalent receiver mobility has been assembled both from measured data and from the approximate method and then used in combination with single equivalent source data, to yield an approximate prediction of the installed power. The agreement obtained between the exact and approximate values allowed consideration of a practical implementation of the approximate prediction method, based on a reception plate method which yields the activity and mobility of the tested machine as single equivalent values.
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accelerometer angular velocity Applied Acoustics building elements Chapter components of excitation considered contact points coupling function dynamic behaviour effective mobility effective point mobility equivalent receiver mobility estimates exact power fan unit four contacts free velocity frequency range Gibbs B. M. heavyweight buildings high mobility source infinite plate installed power joist chipboard floor lightweight building structures loss factor low frequencies low mobility source measured point mobility medium size fan Moorhouse A. T. Normalised power obtained Petersson B. A. T. phase assumption point and transfer Proc random phase approximation reactive forces receiver structures reception plate method shown in Figure single equivalent receiver single equivalent source Sound and Vibration sound pressure levels source and receiver source characterisation source data source descriptor sources in buildings spatial variation Statistical Energy Analysis structure-borne sound power structure-borne sound sources timber joist chipboard timber joist floor transfer mobilities University of Liverpool wavelength whirlpool bath