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An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.

To estimate the structure-borne sound power of vibrational active machines or components two source quantities, corresponding to the source activity and mobility, and one receiver quantity, the mobility, are usually required. A practical, laboratory-based measurement procedure for the characterisation of mechanical installations has recently been proposed, which yields single equivalent values of source strength and source mobility. In order to predict the power in the installed condition, an estimate of the receiver mobility also is required, again, for practical reasons, in the form of a single equivalent value. This paper considers the single equivalent receiver mobilities for lightweight building structures - timber joist floors. The value obtained is in the form of the average magnitude of the effective mobilities over the contact points. A simple prediction method is proposed for point- and transfer mobilities (both are required to yield the effective mobility at each contact) based on infinite beam and infinite plate behaviour. Estimates for point-, transfer- and single equivalent receiver mobilities are discussed and compared with measured data.

The total structure-borne sound power of an installed machine is a function of the source activity and mobility, and the receiver mobility, at each contact and for each component of excitation. The data and computational requirements for prediction therefore are large. Manufacturers view their products as single entities and desire corresponding single values of source strength. A laboratory reception plate measurement procedure has been proposed which yields single equivalent values of source strength and source mobility. The source data, in combination with an estimate of the single equivalent value of receiver mobility, yields the approximate total installed power. The accuracy of the estimate is dependent on the spatial variation in contact conditions over the connections. In addition, phase information has been lost in the simplification. Case studies are described for multiple contact sources on a non-homogeneous plate (a timber-joist floor) where the approximate estimates of structure-borne power are compared with exact values obtained from full mobility formulations.

A practical method is proposed for predicting the total structure-borne sound transmission from machines installed in lightweight buildings. The total structure-borne sound power is a function of the source activity and mobility, and the receiver mobility, at each contact and for each component of excitation. The data and computational requirements for prediction normally are large and are required to be in complex form for the cases where source mobility and receiver mobility are of the same magnitude. This can occur in lightweight framed buildings. However, manufacturers view their products as single entities and desire corresponding single values of source strength. They also desire simple measurement methods
and the data obtained to be in octave or one-third octaves. A laboratory reception plate measurement procedure has been proposed which yields single equivalent values of source strength and source mobility. The source data, in combination with an estimate of the single equivalent value of receiver mobility, yields a simple prediction of the total installed power. The accuracy of the simple prediction depends on the spatial variation in contact conditions. For example, the receiver mobility over a joist is likely to be significantly lower than for positions between joists. Case studies are described for multiple contact sources on a timber-joist floor where the simple predictions are compared with exact values obtained from a full mobility formulation.

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.

Single equivalent excitation for the structure-borne power from machines on ribbed-plate structures
(2009)

Machines impart structure-borne power into connected and supporting structures through all contact points and by up to six components of excitation. It is recognised that considering all transmission paths for prediction purposes generally is not a practical approach, due to the large data and computational requirements. Reduced data sets and less computationally demanding procedures are sought which give the total power to the accuracy appropriate for the particular engineering design requirement. In this paper, single equivalent source and receiver values are considered for machines on ribbed-plate structures. In this case, large variations in the structural dynamics at the contact positions can be expected, and spatial averaging will lead to loss of accuracy. Single equivalent values have been assembled from measured source and receiver data. Case studies are described, for a fan unit and a whirlpool bath, on a timber-joist floor, which is a complicated periodic point-connected plate-rib structure. Approximate estimates of structure-borne power are compared with exact values obtained from full mobility matrix formulations. The case studies presented indicate the loss of accuracy of the prediction, which, in many situations, may be sufficiently small to allow such simplifications.