The city of Tsuyama is located about 100 kilometers west of Kobe. The fundamental shape of the plan and cross sections of the hall were designed by applying the theory of subjective preference [Ando, Architectural Acoustics (AIP Press/Springer-Verlag, New York, 1998)]. Special attempts made in the acoustic design of this hall are: (1) a number of columns distributed in front of the walls at the audience level and on the stage: This may keep a small value of the IACC and a certain initial time delay gap between the direct sound and the first reflection, making an increase of the subjective preference for both listeners and musicians; (2) a stage enclosure with the canopy of several triangular reflectors at adjustable height for musicians, to control the preferred delay time of the reflections in performing a certain type of music; and (3) the shape of the rear wall of the stage, to control the IACC for listeners.
Although a large number of studies have been made on a theory of scattering, no studies have been attempted to evaluate the scattered sound fields in a concert hall. This paper will show an evaluation method of sound fields that involve scattered reflection by a circular-columns array installed in front of both side walls. Measurements were performed by use of a 1/10 scale model of the concert hall. Here, scattered sound fields are evaluated by four acoustic factors (SPL, DT1, Tsub; IACC, and in addition WIACC and tauIACC). It is found that the IACC and Dt1 of the sound fields of the concert hall are improved with use of the circular columns array.
Convex tilted rear walls in a stage enclosure, an array of circular columns installed in front of walls, and triangular reflectors above the stage were newly adopted as scattering obstacles in an acoustic design of Tsuyama Music Cultural Hall, called “Bell Folêt Tsuyama.” The fundamental shape of the hall was designed using the theory of subjective preference. To calculate the effects of scattered reflections on a sound field in a real concert hall is extremely laborious. For this reason, the evaluation of effects of scattered reflections on the sound field in the hall was made experimentally by use of a 110 acoustical scale. After construction of the hall, therefore, sound fields of the hall, which involves scattered reflections caused by the tilted convex rear, by the array of circular columns, and by the triangular reflectors, were measured using four orthogonal physical factors (LL, Δt1, Tsub, IACC) described in the theory and the acoustical character of these scattering obstacles was clarified. Results clearly showed that these new attempts on scattered reflections substantially improved the quality of the sound field in the hall.
Thesis advisor: Yoichi Ando
Copies of this thesis written in English can be obtained from Yukio Suzumura. E-mail address: ysuzu11@lapis.plala.or.jp
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