### ASA 127th Meeting M.I.T. 1994 June 6-10

## 5pSA4. Calculation of the structure-borne sound power emission from
machines.

**A. T. Moorhouse
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B. M. Gibbs
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*Acoust. Res. Unit, School of Architecture and Bldg. Eng., Univ. of
Liverpool, P. O. Box 147, Liverpool L69 3BX, England
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The structure-borne sound power emission from vibration sources is the
closest analogue to airborne sound power and has tremendous potential benefit
in prediction of sound levels in buildings and machines. However, the concept
has yet to find wide application because the large number of terms needed to
calculate power makes practical implementation difficult. In the paper, some
simplifying assumptions are investigated, aiming to reduce the number of terms
while maintaining acceptable accuracy. In general, the power through one
contact point between a machine and its foundation depends on the velocity
contributions from other points. The phase angles of these coupling
contributions are investigated by measurement of free velocities and the
mobility matrix at the seven mount points of a large, resiliently mounted fan.
The assumption is that any phase angle is equally likely and this is shown to
be reasonable at the frequencies considered. It is shown that a simplified
calculation of sound power, using just seven terms causes little loss in
accuracy compared with the full 28-term formulation.