Volume Compressor Noise Sound Power Level Measurement - Simplified Method
Introduction
Numerous machines and equipment emit noise as part of their normal operation. In many cases, the level of that noise is regulated, and the ability to accurately measure the sound power level is essential. This article will address the GB7022-86 standard which describes measurements of sound power produced by volume compressors.
Methodology
The GB7022-86 standard describes a simplified method for measuring sound power level emitted by volume compressors. A test rig is created consisting of the compressor under test and microphone. The microphone is mounted at a distance from the compressor in accordance with the standard, such that the sound pressure level reaches a steady state. The test rig is then placed in a double integral baffle, which minimizes reflected sound and allows for accurate measurement of sound emitted from the source.
Once the test rig is placed in the baffle, the spectral response is determined by measuring sound pressure levels at multiple octave frequencies. The sound pressure levels at each frequency band are then converted to the equivalent level at a source pressure level of 1µPa. These are then converted to sound power levels using the directivity index for the source under test.
Once the sound power level at each frequency is determined, the overall sound power level of the compressor can be determined by summation of the frequency values weighted by the A-weighted response.
Results & Discussion
The sound power level of the volume compressor is then determined at each frequency by summing the octave band contributions, weighted by the A-weighted response. The total sound power level is then determined by summing the individual octave band values. The results are then compared to the applicable standard.
Conclusion
The GB7022-86 standard provides a simplified method for measuring sound power level emitted by volume compressors. This method involves the use of microphones, baffles and frequency weighting to obtain an accurate measurement. The standard also provides guidance on how to use the results to compare against applicable standards. This method is generally easier to use than direct methods, and therefore provides a desirable way to quickly and accurately measure sound power levels.
