残響室法吸音率の測定精度に関する研究(II) : 残響時間測定方法の検討と第4回協同比較試験

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In order to investigate the fluctuations of absorption coefficient related to the reverberation time measurement, experiments were conducted in the following ways. (1) Reference decay curves were recorded in two reverberation rooms with and without test materials. Copies of these decay curves were sent to 13 research laboratories and were read by 25 persons. Absorption coefficients calculated from these data are shown in Fig. 2. Deviations of coefficients are fairly large. Statistical analysis showed a significant difference among readers or decay curves. Fig. 1 illustrates the typical decay curves which cause relatively large deviations. From these results, it would be reasonable to think that the personal difference in reading the decay curves plays an important role in the precision of absorption coefficient measurement. (2) The absorption coefficient of identical test materials was measured by using the same instruments in 11 reverberation rooms. From the recorded decay curves the reverberation time was read by a single person. The absorption coefficients thus obtained are shown in Fig. 5. Compared with the results of the 3rd round robin test, deviation of absorption coefficients measured in different rooms are relatively small, i. e. , within ±10% in most frequencies. (3) To check the effect of dynamic characteristics of a high speed level recorder, decay curves were recorded by each level recorder in respective laboratories. These records were read at first by a single person and then by the respective persons in each reserch laboratories. The absorption coefficients thus obtained are shown in Figs. 6 and 7. From these results, it was concluded that the dynamic characteristics are sometimes connected with errors in absorption coefficients. Following this, the 4th round robin tests were conducted using the same test materials as in the 3rd round robin, but the specifications of measurement were supplemented by referring to the above investigations. Major items are as follows: adjustment of writing speed and linearity of a high speed level recorder, proper setting of writing speed and paper speed, determination of adequate number of decay curves for each frequency and exclusion of unfit curves. Results of this round robin showed fairly small deviations among different laboratories (Fig. 10). Fig. 11 shows the maximum deviations of absorption coefficients obtained in the successive steps of this investigation. Corresponding results of the European round robin tests are also shown in this figure. In conclusion, the accuracy of measurement is sufficient for usual purposes, as long as the deviation is kept within the range of this 4th round robin test. This is expected from the application of the specification of measurement derived from this investigation.
社団法人日本音響学会の論文
1968-11-30

残響室法吸音率の測定精度に関する研究(II) : 残響時間測定方法の検討と第4回協同比較試験

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