Application of Phased Array Technology for Identification of Low Frequency Noise Sources

摘要

Noise Induced Hearing Loss (NIHL) is the most common occupational diseasenin the U.S. with devastating consequences particularly in the mining industry. Anstudy conducted by the National Institute for Occupational Safety and Healthn(NIOSH) revealed that 90% of coal miners have hearing impairment by age 50,ncompared to only 10% of those not exposed to occupational noise. According tonthe Mine Safety and Health Administration (MSHA), Continuous MiningnMachine (CM) operators account for 30% of workers exposed to noise dosesnexceeding the Permissible Exposure Level (PEL). This number becomes morendramatic considering that 49% of the total national underground coal productionnis extracted using these machines. In this context, NIOSH is conductingnresearch to identify and control dominant noise sources in CMs. Previous noisensource identification was performed using a Brüel &Kjær (B&K) 1.92-mndiameter, 42-microphone phased array. These measurements revealed that thenimpacts from the conveyor chain onto the tail roller, and the impacts from thenconveyor chain onto the upper deck are the dominant noise sources at the tail-nsection of the CM. The objectives of the work presented in this paper were: 1)nTo rank the noise radiated by the different sections of the conveyor, and 2) tondetermine the effect of a urethane-coated tail roller on the noise radiated by thentail-section. This test was conducted using an Acoustical and VibrationsnEngineering Consultants (AVEC) 3.5-m diameter, 121-microphone phasednarray. The results from this new test show that a urethane-coated tail rollernyields reductions in the tail-section of 2 to 8 dB in Sound Pressure Level in thenfrequency range of 1 kHz to 5 kHz. However, integration of the acoustic mapsnshows that the front-section and mid-section of the conveyor also containndominant noise sources. Therefore, a urethane-coated tail roller in combinationnwith a chain with urethane-coated flights that reduces the noise sources in thenfront and mid sections of the conveyor is required to yield a significant noisenreduction on the CM operator’s overall exposure. These results show thenapplicability of phased array technology for low frequency noise sourcenidentification.