Strong lateral low‐frequency components reflection from canopy complex comprising triangle plates in concert halls

Abstract

By using the line integration along the edge of thin rigid plates, which is derived from the integral theorem of Helmholtz‐Kirchhoff by Maggi‐Rubinowicz transformation, the impulse response of triangle canopy panels of various shapes was calculated. The transfer function (TF) in the frequency domain is obtained by its fast Fourier transformation. Numerical calculations of TF showed that the optimum inner angle of the equilateral triangle, which gave a flat response extending to lower frequencies, was in the range of 95° to 115°. It is interesting to note that the canopy in Tanglewood Music Shed satisfies this optimum inner angle. The TF of small‐sized triangle panels installed above the stage in FUJITA HALL 2000, a concert hall designed and constructed by our group, clearly indicates the strong lateral low‐frequency components of reflections for the audience. The higher‐frequency components of the reflection, however, are from the triangle panel complex suspended in front of the top of the proscenium arch. In this hall it was thus realized that both the lower‐and higher‐frequency components by reflection made the IACC values at the audio‐frequency range low and uniformed expansion of the sound field better.