Sound power levels of hydraulic pumps using sound intensity techniques: towards more accurate values?

The determination of airborne noise levels is extremely important for the component selection in hydraulic fluid power systems. In the past, for pumps and motors, the only standardized procedures assuring the highest grade of accuracy were based on sound pressure measurements and required strictly controlled conditions such as hemi-anechoic or reverberant chambers (ISO 4412). In the last years, the publication of the ISO 16902 Standard for the determination of sound power levels based on sound intensity measurements, has fostered a hope of getting the same results in less strict conditions. This paper describes a series of experiments carried out in order to determine the sound power spectrum of a hydraulic fluid power pump, according to the ISO 16902 test code, based on ISO 9614-1 (sound intensity measurements at discrete points). The intent of this investigation is to verify the suitability of this procedure when it is applied to these components and to confirm or reject the expectation, reported in the Introduction of the Standard, saying that for these sources just an "engineering" or "survey" grade of accuracy can be achieved.