Effective noise control through identification and ranking of incoherent noise sources

Industrial facilities often contain several simultaneously-operating noise sources that can cause the sound level in neighboring residential areas to exceed established limits, especially during nighttime hours. This paper describes an analytical procedure that may be used in conjunction with measurements of sound pressure levels near the individual sources and in a neighboring residential area to rank order the contribution of the various sources to the total sound level at a sensitive location in the community. The sources are assumed to be incoherent and not too close together. The procedure was applied to the sound from a coal-fired electricity-generating station that also provided steam heat for the community. A loudspeaker placed near a noise source produced an increment in near-field sound level along with the simultaneously-measured increment in total sound level in the neighboring residential area. Of 200 noise sources associated with the facility, 16 were shown to be the main contributors to the sound from the power station. Application of noise-control procedures reduced the sound level in the neighboring community by up to 15 dB. The uncertainty of the measurements was shown to be the least when the sound level changes were largest, and vice versa.