日本音響学会誌
Online ISSN : 2432-2040
Print ISSN : 0369-4232
短音減衰波形の物理量化と室内音響指標の検討
木村 翔関口 克明
著者情報
ジャーナル フリー

1973 年 29 巻 9 号 p. 517-526

詳細
抄録

Studies have been made by many investigators to seek for new acoustical criteria in room acoustics by converting echo oscillograms into physical quantities. In making an acoustical design of an auditorium, we obtain proper indices for the shape of the room by conducting an acoustic model experiment. We intend to use effective physical quantities out of the acoustic criteria obtained in the experiment for the actual design of the auditorium. This paper summarizes the results of our study and discussion regarding the relations between the physical quantities and the room shape, between various quantities themselves, and between the physical quantities and the subjective evaluations on the basis of the room distributions of various physical quantities obtained by converting the respective echo oscillograms into physical quantities regarding nine halls of different shapes of room (Fig. 5). We studied the numerical physical quantities regarding the D value (Definition) of the energy volume when the time axis is fixed, the time required for attenuation by 3 dB from the stationary state (T_<-3dB>, Rise Time) and the time required for attenuation by 10 dB (T_<-10dB>, Early Decay Time) as the value of the time when the energy attenuation is fixed, and the center time (ts). As a result, we found that the distributions of the physical quantities in the auditorium in correspondence to the variation in the hall dimensions and shapes tended to vary depending on what point of time of the initial attenuation the physical quantities were evaluated. In other words, the D value and the T_<-3dB> evaluated at a very early time tended to be influenced more by the delicate variation in the neighborhood of the measured point than by the difference in the basic shapes of the auditorium, whereas T_<-10dB> evaluated in a later point of time in the initial attenuation tended to show relatively more clearly the difference due to the basic shapes of the auditorium (Fig. 6). For this reason, it was considered better to use T_<-3dB> for observing the difference in the basic shapes of an actual auditorium, and that it would be more appropriate to evaluate the difference in detailed parts in the physical quantities at a shorter time point. Moreover, we observed that various physical quantities in the same echo oscillograms were often quantified in different directions even when evaluating the same type of subjective quantities (Fig. 7 and Fig. 8). Thus, considering these findings, we found that when the initial attenuation characteristic was represented by the bend b=T_<-10dB>/T_<-3dB> (b_0=3. 33 for exponential attenuation), this tendency appeared if b/b_0 was deviated greatly from 1, and that the respective physical quantities showed relatively constant relations when b/b_0 was used as the correction value (Fig. 10). Taking the foregoing into consideration, we performed a hearing test on the subjective reverberation which is one of the principal subjective quantities in room acoustics by the pair comparison method. As a result, we found that regarding the specimen sound sources of a wide range of reverberation time (RT=1. 1〜1. 6 seconds), such physical quantities requiring a relatively longer time for observation as the reverberation time, the time required for attenuation by 20 dB from the stationary state, and the center time were well correlated, and the subjective reverberation was basically evaluated by the length of the reverberation time. On the other hand, regarding the echo oscillograms having the same degree of reverberation time, we found that such physical quantities determined in the earlier initial period as the ratio of the energy up to 100 ms〜150 ms to the total energy and the center time ts were well correlated (Fig. 11). It is to be noted that the center time ts which in particular represented the time distribution of energy in all the echo

(View PDF for the rest of the abstract.)

著者関連情報
© 1973 一般社団法人 日本音響学会
前の記事 次の記事
feedback
Top