Reverberation time recommendations for noisy industrial workshops.

Industrial workshops or any other industrial premises where noisy machines are operated should be as acoustically absorbent as possible. On the other hand, acoustic treatments are expensive (especially when correcting existing premises), messy, and not always compatible with the implemented production processes. Therefore, there is a need for acoustic specifications to find the best compromise between cost and efficiency. In France, for noisy industrial workshops to be compliant, the regulation requires the rate of decay of sound per distance doubling (DL2) to exceed compulsory limit values, unless this does not have a significant impact on workers' exposure to noise. However, that rate of decay is difficult and time consuming to evaluate. The purpose of this paper is to provide recommendations based on reverberation time (RT), which is not only easier to measure but is also widely used. The D2L values are conventionally measured in industrial workshops together with RT values and thus a database compiling both RT and DL2 values was available. It has been used to draw up reference limits for RT values consistent with the DL2 regulation limits. These reference limits were validated by comparison with the literature and with a new set of data collected specially for the purposes of performing that comparison. The final limits are divided into four categories: compliant/non-compliant, for furnished/empty industrial workshops, using a 95/99% confidence interval. They are intended to enable the acoustic treatment of a workshop to be evaluated using a simple metric, either at the design stage or for monitoring or occupational inspection purposes.

Sound transmission loss of rectangular and slit-shaped apertures: experimental results and correlation with a modal model.

Among noise control techniques, enclosures are widely used. It is known that enclosure acoustic efficiency is strongly influenced by the presence of openings or leaks. Modeling of diffuse field sound transmission loss (TL) of apertures and slits is therefore critical when the enclosure acoustic performance characteristics need to be predicted with confidence either for design or for modifying existing enclosures. Recently, a general model for diffuse field sound TL of rectangular and circular apertures has been developed and validated with respect to existing analytical or numerical models. This paper presents an experimental validation of this new model. The aim was to develop a simple, reliable tool for predicting enclosure insertion loss using statistical energy analysis. Twelve out of the 15 test configurations were found to be reliable and were compared with theoretical models, which in fact correlate closely (without adjustment) with the experimental work.