This part of ISO/TS 7849 gives basic requirements for a reproducible method for the determination of the sound power level of the noise emitted by machinery or equipment by using surface vibration measurements, together with the knowledge of the machinery specific sound radiation factor in the frequency bands. The method is only applicable to noise which is emitted by vibrating surfaces of solid structures and not to noise generated aerodynamically.
This vibration measurement method is especially applicable in cases where accurate direct airborne noise measurements, e.g. as specified in ISO 3746, ISO 3747, and ISO 9614 (all parts), are not possible because of high background noise or other parasitic environmental interferences; or, if a distinction is required between the total radiated sound power and its structure vibration generated component.
NOTE 1 One of the applications of this part of ISO/TS 7849 is the distinction between the radiation of airborne sound power generated by structure vibration and the aerodynamic sound power components. Such a distinction is not feasible with ISO 3744, ISO 3745, ISO 3746 and ISO 9614 (all parts).
NOTE 2 Problems may occur if the noise is generated by small parts of machinery surfaces (sliding contacts, e.g. slip ring brush or the commutator and the brush in electrical machines).
The methods described in this part of ISO/TS 7849 apply mainly to processes that are stationary with respect to time.
Recommendations on the selection of frequency bands are given in Annex C.