在多音源之自由音場以音壓測定評估音源貢獻度

Evaluation of Noise Contribution in Multi-Source Field with Sound Pressure Measurement – A Free Field Approach

基於保護現場作業勞工聽力，減少勞工因暴露於噪音作業環境以致聽力受損，作業場所之噪音工程控制可由下列兩方向進行：1.降低噪音源之噪音，2.阻絕噪音傳播途徑，以達減少作業人員之噪音暴露劑量。無論以上任一方式進行工程改善，如能針對影響最大之噪音源，則可發揮最大改善效果。在一個多噪音源場所每一音源對各個位置均有不同之貢獻量，經由噪音源在各位置的貢獻量的計算，將可把各噪音源在場所內的貢獻度大小依序排列出來，如此將有助於工程控制改善順序之擬定。本研究提出一種方法，使現場工程師在多個音源同時作用下的音場環境，定量地辨別何者為最大噪音源。首先，採用自由音場的聲學理論公式作為音場環境的數學模式，透過幾個位置的音壓級測定，以電腦程式計算音源的貢獻度，最後可得到一組代表音源聲功率的解答。一旦知道各音源的聲功率後，音源被放置在其他位置或場所時，工程人員亦可評估噪音分布情況。

In order to conserve labor’s hearing and reduce noise induced hearing loss, there are two measures to implement engineering control on noise source: eliminating noise generated at the source and obstructing the transmission path. No matter which one of the mentioned measures is chosen, it is more efficient to work on the dominant source. The sound pressure at every location inside a multi-source acoustic field has different contribution from each source. By sorting the noise sources based on their contribution at each location, a source order-ranking list can be generated. From the list the most effective candidates for noise control can be assessed. This study proposes an approach, which enables the engineers to pinpoint quantitatively the most significant source with the machines operating simultaneously. Initially, a set of acoustical equations was adopted to formulate the problem. By measuring sound pressure levels at a couple of locations in a factory, a computer code is designed to calculate the source contribution. Finally, a set of solutions, which represent sound powers of noise sources, can be found. With the help of sound power obtained, the engineers would be able to evaluate the noise distribution of a workplace with different layouts in the future.