Sound Power Assessment, Noise Source Identification and Directivity Analysis of Compaction Machines

NVH has gained importance in the field of earth moving equipment due to the demand of quieter machines and stringent in-cab as well as exterior noise emission norms. Several parts of the world have adopted strict legislation on noise emission by earth moving equipment, but many countries have not adopted any regulations till date. The aim of this study is to help governing bodies as well as machine manufacturers in adopting simple yet accurate testing method for compactor machine. The study consists of directivity analysis, noise source identification, noise source ranking and 4-point microphone position sound power evaluation method applied to compactors with wide range of engine power ratings. All the tests in 4-point method and directivity analysis were performed under stationary as well as dynamic conditions. Currently, several countries and vehicle manufacturers have adopted sound power evaluation of compactor exterior noise emission by 6-point method (as per ISO 6393 and ISO 6395) which consists of six microphone positions. The 4-point method presented in this paper tries to reduce measurement positions from 6 to 4, thereby simplifying the testing method, reduce instrumentation cost and measurement time. Results shows that the maximum error between the two methods was 0.7% in stationary condition and 0.6 % in dynamic condition. Directivity analysis shows that the compactor is extremely directive at its rear side and emitted maximum sound power at 180°. However, it is observed that microphone positions mentioned in ISO standards are not suitable enough to capture this noise which results in underestimation of exterior sound power level. Major noise source such as engine, cooling fan, hydraulic pump, air intake system were also analyzed. Air intake system was found out to be source of maximum noise in compactors.