Measurement of field complex noise using a novel acoustic detection system

This paper represents our recent experimental measurement study of the complex noise in industrial fields, using a novel acoustic detection system and wavelet transform algorithms. Noise induced hearing loss (NIHL) continues to be one of the most prevalent occupational hazards in the United States. Number of research on NIHL showed a complex noise could produce more hearing loss than an energy-equivalent continuous or impulsive noise alone. Many workplaces in varied industries are subjected to the high level complex noise (i.e., high-level impulsive noise mixed with continuous Gaussian noise). The current noise measurement guidelines and devices (e.g., conventional sound level meters) are based on the equal energy hypothesis (EEH), which states that loss of hearing by exposure to noise is proportional to the total acoustic energy of the exposure. However, the EEH does not accurately rate the impulsive noise and the complex noise. Therefore, the conventional sound level meter may not be able to accurately assess the complex noise in industrial fields. In this project, a new waveform profile based noise measurement system has been developed for evaluation of the high level complex noise in industrial fields. The system consists of four ½" condenser microphones, and it can simultaneously detect and record four waveforms of the complex noise with high sampling rate (125 KHz). In addition, a wavelet transform based signal analysis algorithm has been modified and implemented to characterize the complex noise. Pilot field measurements have been conducted in selected local coal mining fields (e.g., wet coal preparation plant and dry coal handling plant) using the developed system. The preliminary results showed that the system successfully detected and recorded waveforms of complex noise in industrial fields. The modified algorithm can decomposed the complex noise signals and display the detailed features in the time-frequency joint domain. The key parameters of co- plex noise can be determined, and the hazardous complex noise in industrial fields can be identified. In addition, when measuring the equivalent A-weighted averaged sound pressure level, the developed system is comparable to a conventional sound level meter.