On the use of single equivalent excitation to estimate the structure-borne sound power from machines on timber joist floors

  • Vibrational active sources introduce structure-borne sound power to the supporting structure through all contact points and by up to six components of excitation. The total structure-borne sound power is a function of source activity, source mobility and receiver mobility and receiver mobility is expected to vary significantly with source position on lightweight structures such as timber joist floors. A case study is presented, in which the spatial variation in structure-borne sound power is examined for a fan unit mounted on a timber joist floor. The exact structure-borne power is obtained from measured source free velocity, and measured source and receiver mobility, where forces are assumed the dominant excitation mechanism. The exact calculations are computationally intensive and require large data sets, and this is generally not a practical approach for prediction purposes. In addition, manufacturers view their products as single entities and desire corresponding single values of source strength. A laboratory reception plate measurement procedure has recently been proposed which yields single equivalent values of source strength and source mobility. This paper investigates if this collapsed data format appropriately describes the dynamic behaviour of the source and especially inhomogeneous receiver structures, to obtain estimates of total structure-borne sound power within acceptable accuracy. Since measured receiver data is usually not available, an approximate method is described, of estimating the point and transfer mobility, based on infinite beam and infinite plate behaviour. The single equivalent receiver mobility then is easily obtained and, when used in combination with single equivalent source data, yields an approximate prediction of the total installed power. Single equivalent estimates of structure-borne sound power are compared with exact values obtained from full mobility formulations. Results indicate that the accuracy of the approximate prediction may be sufficient for such installations.

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Author:Andreas R. Mayr, Barry Gibbs
Parent Title (English):16th International Congress on Sound and Vibration, ISCV16, Krakòw, Poland, July 2009.
Document Type:Conference Proceeding
Publication Year:2009
Tag:Structure-born sound power; Timber joist floors; single equivalent exitation
faculties / departments:Fakultät für Angewandte Natur- und Geisteswissenschaften
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 53 Physik