Noise exposure is not only related to the non-auditory effects that endanger worker safety, but is also related to hearing loss. Permanent hearing loss and its associated problems are clearly a critical and widespread consequence of excessive noise exposure. Thus, it is necessary for industrial engineers to evaluate quantitatively the dominant noise source while multiple machines are running. This paper presents an efficient method to determine sound power levels (PWLs) of the near noise sources generated by the simultaneous operation of multiple machines. PWLs, generally based on the point source and spherical radiation in a free field, are obtained from required data such as the measured sound pressure levels (SPLs), the locations in which the SPLs are measured, and the locations of the machines, using a harmony search (HS) algorithm. Relevance to industry The procedure for determining the PWL of an individual machine is a useful tool for industrial engineers to identify the dominant noise source in the workplace. With the proposed optimization technique, the manufacturing industry can evaluate the workplace noise levels emitted by multiple machines and determine whether industrial workers are exposed to a noise hazard due to the dominant noise source.