9 拡散体を取り付けた壁面からのエコーの分布に関する超音波を利用した模型実験

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タイトル別名
  • (9) MEASUREMENTS OF ECHO DISTRIBUTION BY MODEL
  • 拡散体を取り付けた壁面からのエコーの分布に関する超音波を利用した模型実験
  • カクサンタイ オ トリツケタ ヘキメン カラ ノ エコー ノ ブンプ ニ カンスル チョウオンパ オ リヨウ シタ モケイ ジッケン

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抄録

The distribution of echo from wall on which many kinds of diffusers were fitted were measured by scale models to find out the suitable shape of diffusers. The scale of the wall model is 1/10 and its size is 180cm in width and 30cm in height. The shape of wall models are flat and curved surface of 5m in radius. The shape of diffuser which are fitted on these walls are polytriangular and polycylindrical, and their width and depth is 18cm and 2.7cm. The sound used in these experiments is 1/3 octave band noise and their mean frequency is 2.5kc, 5kc, 10kc and 20kc. The cone type tweeter is used as the sound source forthe lower frequency and the condenser speaker for the higher frequency. The microphone is condenser type for all frequency range. At the first stage of these experiments, the distribution of echo from flat wall on which there no diffuser was measured. This case is very simple, so the theoretical calculation of the echo distribution is easy. From the comparison of the results of experiment and calculation, it was found that the accuracy of this experiment is ±1.5dB. At the second stage of these experiments, the distribution of echo of more complex cases were measured. In these cases theoretical calculation is difficult. The results of these experiments are as follows. 1. Tne pifference of echo intensity level between front and side area of the wall is much more when the diffuser is triangular than it is polycylindrical. 2. When the triangular diffuser is fitted, loud echo is observed at the side area of the wall at the higher frequency (10kc and 20kc). 3. The echo distribution is more uniform when the polycylindrical diffuser is used. 4. The reason of these phenomena is that the plane surface of every triangular diffuser reflects sound regularly at the higher frequency, so the neflacted sound separate into two groups which travel towards left and right, so reflected sound towards the front of the wall is weak, but the polycylindrical diffuser reflects sound towards wide direction.

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