Low Frequency Noise and Vibration Annoyance Due to Low Speed Rotating Machinery

Abstract

This paper presents the findings of an investigation into a low frequency noise/vibration problem caused to residential property by low speed (250 to 700 rpm) rotating machinery. A large rope-making machine was added at a site with a great number of existing but small machines and round the clock operations commenced. One resident, about 100 metres distant from the machine area, appeared to complain whenever the large machine was run. On the assumption that the newly introduced large machine was to blame, the factory management requested a low key survey of noise and an assessment as to whether the complaint was justified or not. The initial surveys found that the complaint was justified and that the situation was more complex. During a comprehensive programme of tests and measurements, it was found that the complaint occurred even when the new machine was stopped which was quite a surprise. Some thirteen machines were run individually to find their contribution to emissions. Part of the efforts were directed at finding whether airborne or groundborne effects or both were involved; groundborne vibrations in the range 8 to 13Hz proved to be the main effect. The data obtained was compared with levels reported in the literature to be audible and cause complaint. The levels of annoyance had to be related to the prospects of various options to control the effects at source. The solution to the problems emerged as relatively simple, all being connected with sensible maintenance of the machines. Improvements or reductions in vibration at source were achieved in the range 15 to 20dB which satisfied the complainant and improved the serviceability of the machines.