The Effects of the Directivity of Sound Source for Chamber Music Acoustics

• Main Authors: LEE JOW-YEH, 李宙燁
• Other Authors: Chiang Weihwa
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/22768559571656751653

碩士 === 國立臺灣科技大學 === 建築系 === 91 === Effects of directional source on room acoustics of rectangular chamber music halls were evaluated based on acoustical simulations using Odeon 5.0 software and field measurements. For computer simulation, all surfaces were plane and relatively large. Controlling variables included size, proportion, stage layout, side-wall layouts, seating layouts, directivity of the source, and aiming direction of the sound sources. Acoustical measure clarity (C80) and early strength (G80) was used. In a 365-seat hall and an 831-seat hall, the field study examined the effects of room width, detached side reflectors, and aiming directions. A dodecahedron speaker source was compared to a speaker having the directivity similar to a trumpet, which was aiming to the front, the left, the right, and the top (30° tilting towards the front). Based on computer simulation, it has been found that the effects of source directivity significantly increased with increasing room width and slightly increased with the increasing overall size. Inside a 5000-m3 hall with nearly 1:2 width-to-length ratio, turning a trumpet sound source between +45° and -45° making 2.5dB~3dB difference on both C80 and G80. The effect became significantly large when the room width was increased from 17 m to 21 m. Lateral reflectors were useful for enhancing high frequency G80 for seats that located opposite to the aiming direction but splayed front side-walls were useless because the reflections were directed towards the end of the hall instead of crossing to the other side of the hall. Subdividing the hall with a lower centerpiece and higher perimeters was effective in reducing the difference due to turning aiming directions. The field measurement agreed with the computer modeling regarding the importance of room width. The larger and wider hall (27-m wide) caused a much higher directional difference than the smaller and narrower hall (17-m wide). Detached side reflectors (6 m apart from each other) were effective in enhancing G80 measured in right side audience when the source was aiming to the left of the hall. The top-aiming source caused very little difference from the front-aiming source. This can be attributed to the low ceiling in the smaller hall and the low proscenium arch as well as suspended ceiling in the larger hall.