Propagation of sound in a T-shaped and U-shaped long enclosures

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Propagation of sound in a T-shaped and U-shaped long enclosures

 

Author: So, Sai-tung
Title: Propagation of sound in a T-shaped and U-shaped long enclosures
Degree: Eng.D.
Year: 2009
Subject: Hong Kong Polytechnic University -- Dissertations.
Architectural acoustics.
Absorption of sound.
Sound -- Measurement.
Department: Dept. of Mechanical Engineering
Pages: viii, 371 p. : col. ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2276591
URI: http://theses.lib.polyu.edu.hk/handle/200/5028
Abstract: The classical room acoustic theory was developed in early 20th century. The theory has been applied to enclosed spaces where a sound source emits primary sound rays in all directions. These rays impact on the surfaces of the enclosures and reflect from them. Within a small duration, a reverberant sound field is established in the enclosure. In addition to the presence of the direct sound fields, the reverberation sound field plays a significant role in the overall noise levels in the enclosure. A diffuse field is generally established in the enclosure and the listener can hardly detect the direction of sound. In this case, classical room acoustic theory can be applied. The layouts for classic architecture are relatively simple. However, the modern architectures are changing day by day because of the cost of land and the need to provide effective building services in an an enclosed space. The design of modern rooms is much more complicated. The quantity of rooms increases while their sizes decrease. The corridors become more winding and irregular. Since the corridors are long spaces and the sound fields propagate along the direction of the passage, this is not a diffuse field and the classical acoustic theory is not applicable. Generally, the nature of corridors can be classified as straight, elbow (L-shaped), T-shaped and U-shaped. In order to investigate the sound fields of corridors, researchers should study the above-mentioned sections independently. Furthermore, there have been many prediction models for numerical analysis of the sound fields in these corridors of complicated shapes. An image source method has been chosen for this study because it is one of the simplest numerical methods and requires relatively least computational times. The image source model can also provide a coherent model so that the sound field can be predicted in a narrow frequency band. Based on the narrow-band frequency analysis, the results for the octave band and one-third-octave band frequencies can be obtained. In order to validate the accuracy of the numerical model, indoor experiments in an anechoic chamber and field measurements in an enclosed corridor are conducted. Predictions according to numerical analyses are then compared with the experimental data. Further verification of the image source method is also compared with published experimental data. By using the basic theory for the decay of sound energy, the reverberation time can be predicted by the image source method. The rapid speech transmission index can be determined and compared with the published experimental results.

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