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Enclosures are commonly used to reduce the sound exposure of workers to the noise radiated by machinery. Some acoustic predictive tools ranging from simple analytical tools to sophisticated numerical deterministic models are available to estimate the enclosure acoustical performance. However, simple analytical models are usually valid in limited frequency ranges because of underlying assumptions whereas numerical models are commonly limited to low frequencies. This paper presents a general and simple model for predicting the acoustic performance of large free-standing enclosures which is capable of taking into account the complexity of the enclosure configuration and covering a large frequency range. It is based on the statistical energy analysis (SEA) framework. The sound field inside the enclosure is calculated using the method of image sources. Sound transmission across the various elements of the enclosure is considered in the SEA formalism. The model is evaluated by comparison with existing methods and experimental results. The effect of several parameters such as enclosure geometry, panel materials, presence of noise control treatments, location of the source inside the enclosure, and presence of an opening has been investigated. The comparisons between the model and the experimental results show a good agreement for most of the tested configurations.

Acoustics 08 Paris 5545Enclosures are a classical solution to reduce the sound exposure of workers to the noise radiated by machinery. Their acoustic design can be achieved with the help of predictive tools based on simple analytical tools or sophisticated numerical deterministic models. However, there is no simple and fast tool allowing to account for the complexity of the enclosure configuration, capable of better simulating the non-diffuse nature of the field inside the enclosure and covering the typical frequency range [100Hz; 5000Hz]. This paper presents the development of such a tool for the prediction of the acoustic performance of enclosures. It is based on a hybrid model: the statistical energy analysis (SEA) for the sound transmission across the various elements of the enclosure and the method of image sources for the sound field inside the enclosure. The approach is validated by comparing calculation and experimental results carried out in a semi-anechoic room on rectangular and L-shape enclosures for several inner source locations. The effect of an opening is also investigated. The comparisons between the models and the experimental results show a good agreement for most of the tested configurations.

A pressure pulp screen is a machine used in the pulp and paper industry to remove and class cellulose fibres in paper pulp. It involves an inner perforated cylindrical basket which receives the pulp under pressure, an inner rotor with profiled blades used to clear the holes or slits of the basket, and an outer cylindrical shell. The noise radiated by the outer shell is characterized by discrete frequencies in mid- and high frequency (1–4 kHz). A preliminary study has shown that the radiated noise is due to the vibration of the perforated basket under the moving load of the rotor. This vibration is transmitted to the outer shell through various paths which were analyzed and classified. An analytical model of the vibroacoustic behavior of a cylindrical shell under a circumferentially moving load was used to establish various rotating speed regimes with respect to the vibration and sound radiation of the shell. It was shown that a circumferential modulation of the load (corresponding to the effect of holes or slits on the inner basket) leads to theoretical noise spectra similar to measured data. On the practical front, the model was used to identify significant design parameters with respect to the noise of the machine. The paths of energy transmission from the basket to the outer shell were studied and various noise reduction approaches have been investigated.