Communications in noisy environments. Final report on CEC Contract 7206/00/8/09

Investigations were carried out with the objectives of providing a means for improving the design of communication devices, providing guidelines for identifying potential and existing communication difficulties early in system design procedures, and minimising potential difficulties arising from the need to wear hearing protection. These objectives were achieved by producing methods for the evaluation of non-verbal and verbal communication tailored to mining requirements.A method for evaluating and designing non-verbal auditory signals in relation to their auditory environment and the hearing abilties of the workforce was developed and tested with reference to the mining industry. It incorporated allowances for the factors of audibility, attention gaining, recognition, startle, noise exposure, and interference; and their interactions. The method was shown to be of practical utility not only in identifying difficulties but in arriving at specifications for appropriate replacements and new devices.A modified version of the Articulation Index was produced, incorporating the hearing abilities of individual workers. It was found to provide improved prediction of speech intelligibility for a wide range of mining noise environments.The effects of hearing protectors upon auditory communication were examined both empirically and using the prediction methods developed during the project. There was a high degree of correspondence between the experimental results and theoretically based predictions. It was found that a small proportion of the population could have communication difficulties when wearing hearing protectors. These difficulties would arise most noticeably in circumstances where there was noise of predominantly low frequency in combination with a hearing protector which emphasised this predominance, by attenuating to a greater extent at high frequencies, and a listener characterised by a relatively wide auditory filter.It was found that difficulties due to the use of hearing protectors could be to some extent alleviated by designing non-verbal signals to have their major spectral compoments in the frequency range between 1 and 2 kHz. It was possible to go further, however, and produce general design guidelines for hearing protectors which would be suited to mining conditions. The best protector for mining conditions would appear to be a helmet mounted circumaural protector having a flat frequency response, the minimum attenuation necessary to achieve the protection target, small standard deviations in attenuation, the ability to be rapidly fitted and removed, a low profile when stored out of use, a low mass/pressure ratio, and a regular maintenance procedure.