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Evaluation and optimization of acoustical environments in eating establishments Razavi, Zohreh

Abstract

The acoustical environment (noise and reverberation) in eating establishments (EEs) is one of the most commonly overlooked design factors; and yet one of the most important. It can cause problems with verbal communication, especially for the hearing-impaired and second-language people. In extreme cases, too much noise can affect the health and safety of EE employees. Thus, to investigate acoustical environments in EEs, this research study was initiated. The objective was to evaluate the acoustical conditions to which customers and workers are exposed. It was to investigate how to optimize acoustical environments in EEs by way of room-acoustical design, acoustical treatment and noise control. Three EEs of three different types (restaurants, bistros and cafeterias) on and off the UBC campus were studied. To include hard-of-hearing people, two seniors’ homes were also included. To evaluate the acoustical environment of each establishment, Reverberation Time and of noise levels in the unoccupied and occupied EEs were measured. RTs were longer than optimal in unoccupied and occupied EEs due to low absorption. Noise levels varied from 42.5 to 61.5 dBA in unoccupied situations, and from 55.3 to 74.5 dBA when occupied. The noise exposure of employees was also measured. Employees’ daily noise exposure, on average, varied from 59.7 to 83.7 dBA, in compliance with the BC Worksafe regulations. Customer and employee questionnaires asking about the effect of the acoustical environment and factors that affect it, were developed, administered and analyzed. According to the responses, people visiting EEs tend to fall into two groups - one which visits for eating/drinking, talking and relaxing, the other for working/studying, business, celebration and relaxing - with different expectations of eating out. On average, they prefer to dine in a quiet environment with an appropriately low level of music. Sources of noise, such as people talking, moving, kitchen activities and equipment caused employees to suffer from fatigue, headache and tinnitus. Further analysis of measured occupied noise levels showed that customers used Casual to Raised voice levels for conversation, increasing their voice levels with increasing noise level (the Lombard Effect) at a rate of 0.7 dB/dB. Signal-to-noise level difference varied from -12 to 10 dBA. Predicted voice levels with an existing "Lombard prediction" model which developed in parallel with this work was use to predict speech intelligibility and speech privacy at a typical seating position in an EE. Predictions were made of Speech Transmission Index and its components, Early Decay Time and A-weighted Speech to Noise level difference in one of the studied EEs using the CATT-Acoustic software. Different acoustical treatments (e.g. adding absorption, barriers, lowering the density and decreasing the receiver to talker distance) were evaluated. It was found that the most effective treatment was inserting absorptive barriers with the addition of absorptive ceilings, which led to good Speech Intelligibility and normal voice level. Reducing the distance between talkers and receivers is another solution, but this may not always be feasible. Table size, receive-talker relationship and the number of the people in groups limit this solution.

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