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Acoustical measurement in a concert hall 4
1/10 scale model experiment, effect of reflector panels

Now, the effect of the reflector panels on the ceiling of the stage area is analyzed. Calculation conditions are same as before. 

This is the calculation condition. Frequency band between 16 and 2000 Hz is analyzed. For a full scale measurement, the important frequency band is between 125 Hz and 8000 Hz. 

The picture shows the reflector panels on the ceiling. These panels are installed to improve the acoustical qualities around the stage area. 

The picture shows the audience area. Reflector panels on the ceiling and columns around the wall can be seen. 

Sound file: hall4.wav (48kHz / Stereo / 0.683s / 128KB)
Wave file can be loaded by RA. Click "Load" > "Wave File" on the impulse response measurement window. 

The impulse response for all frequency range is shown. It is zoomed up to x64. Green and red lines show the direct and the first reflective sound respectively. 

This is the impulse response for 500 Hz band. 

The graph below shows the reverberation time in six frequency bands for various absorption conditions. 

This is the impulse response for 2000 Hz band. The IACC value was decreased from 0.48 to 0.41 after the reflector panels were installed. It means that the acoustical quality has been improved. 

The figures show the IACC values in the condition with (right) and without (left) the reflector panels. As shown in the figures, the IACC value was improved in 2/3 of the audience area. The effect of the reflector panels was found especially around the stage area. Generally,  it is difficult to improve the acoustical quality around the stage area because the direct sound is too strong. But it has been confirmed that the reflector panels on the ceiling can improve the quality. This finding was recognized as an originality of the acoustic design of Tsuyama hall. This research has been published from Journal of Sound and Vibration. 

Below is a quotation from the article, M. SAKURAI, S. AIZAWA, Y. SUZUMURA, & Y. ANDO (2000). A DIAGNOSTIC SYSTEM MEASURING ORTHOGONAL FACTORS OF SOUND FIELDS IN A SCALE MODEL OF AUDITORIUM, Journal of Sound and Vibration, Vol. 232, No. 1, pp. 231-237.
(See also http://www.ymec.com/doc/study.paper/jsv/paper.htm .)

As mentioned above, in order to examine effects of reflectors' array on the IACC for the 2000 Hz range at 15 seating positions shown in FIGURE 6, measurements were performed with and without reflectors above the stage. As indicated in this figure, the location of the sound source is marked by a star, and triangular reflectors` arrays [10] are installed above the stage. FIGURE 7 shows the measured results of the IACC without reflectors, and FIGURE 6 shows those with reflectors` array. The IACC values of the 2 kHz-frequency band for a real room were measured at the 20 kHz frequency band in the 1/10 scale model.

As shown in these figures, the reflectors decrease results of the IACC at the 9 measuring points, so that acoustic quality is much improved. Especially, the decrement of IACC values was remarkable in the frontal area close to the stage in audience floor except for the center, due to the reflections from above the stage to the listeners.

June 2003 by Masatsugu Sakurai

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