| Author: | Gao, Jianliang |
| Title: | Semi-analytical prediction of energy-based acoustical parameters in theatre auditoriums |
| Advisors: | Tang, Shiu-keung (BSE) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Theaters Acoustical engineering Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Building Services Engineering |
| Pages: | xviii, 120 pages : color illustrations |
| Language: | English |
| Abstract: | The prediction of objective acoustical parameters, especially those based on energy relations, in theatres is generally not an easy task. Although Barron and Lee proposed a revised acoustic energy model for concert auditoriums, which has proved to be the most reliable among the existing models for the prediction of acoustical energy parameters in this kind of spaces [M. Barron and L-J. Lee, J. Acoust. Soc. Am. 84, 618-628 (1988)], it is still left unaddressed whether this model is also valid for theatres or not. For this sake, the present study applies Barron's model to a typical modern opera house in China, and compares the predicted values and those measured in a 1:20 scale model of the hall for six energy-based parameters: clarity C80, definition D50, center time TS, sound strength G, early strength G80 and late strength GL. The results show that the former three parameters can be predicted with acceptable accuracy in general, while the latter three are overall considerably overestimated. In addition to Barron and Lee's "revised theory", different models to improve prediction of energy-based acoustic parameters in churches have also been proposed by different researchers. There are two models that were well developed and are generally considered reliable for acoustic energy prediction in churches [E. Cirillo and F. Martellotta, J. Acoust. Soc. Am. 118, 232-248 (2005); T. Zamarreño et al., J. Acoust. Soc. Am. 121, 234-250 (2007)], both of which suggested modifications to the revised theory. The present study compares these three models taking advantage of the measurements carried out in two theaters in Hong Kong and Mainland China. The objective of this work is to lay the foundation for the proposal of a specific acoustic energy model for theaters by means of analyzing and summarizing the merits and flaws of other models when used to predict acoustic energy relations in theaters. The results indicate that the revised theory and the model of Zamarreño et al. (μ model) are inapplicable to the energy relation prediction in theaters in the light of their significant overestimation for the early, late, and total sound energy. Even though the latter can predict the parameters related to subjective clarity (i.e., C80, D50, and TS) with acceptable accuracy, a further analysis on different temporal energy components demonstrates that is just a coincidence and unbelievable. By contrast, Cirillo and Martellotta's "modified theory" is regarded as having a potential for use in theaters only with two prerequisites: sufficient accessible geometrical and acoustical information of the space, and an improvement in prediction accuracy for the late sound energy provided by model revision. However, the intrinsic complications of this model constitute an important factor that may affect its application in theaters. On the basis of the above findings, it is recommended to propose a specific acoustic energy model for theater auditoriums. For this end, extensive mono-aural measurements have been conducted in unoccupied auditoriums of seven theatre cases (including site survey for five halls and scale model measurement for two cases of another hall) according to the standard ISO 3382-1: 2009. Acoustical parameters, that are reverberation time T, clarity C80, definition D50, center time TS, sound strength G, early strength G80 and late strength GL, in the frequency range from 125 Hz to 4000 Hz (octave band) have been estimated through analyzing the impulse responses measured in each hall. However, only the data in 500, 1000 and 2000 Hz octave bands are considered in this study according to the most accepted criteria for sound field analysis in performance halls. Based on the measured values of early and late strength in five cases (three full-size halls plus two scale models), a semi-analytical model is proposed. The rest two site-surveyed halls, which are located at different countries and differ in size, interior decoration style and measurement technique, are chosen for validation of the model where the predicted results of the above-mentioned six energy-based parameters (i.e., G80, GL, G, C80, D50 and TS) by the proposed model are compared with the experimental data and the predictions of the "revised theory". The results reveal that the proposed model has significant improvement in prediction accuracy than the revised theory. The good agreement between predicted values by the new model and those measured indicates that this model can be used for point-by-point predictions of the energy-based acoustical parameters in theatres with reasonable accuracy. |
| Rights: | All rights reserved |
| Access: | open access |
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