抄録
For the purpose of getting a testing method of the acoustical characteristics of the lecture room, the test of sound articulation and sentence intelligibility in Japanese language was carried out twice in a large lecture room and once in a small class room. The dimension of the large lecture room was of 52ft(width)×69ft(length)×33ft(height). The reverberation time calculated by Eyring's formula was 5. 8sec in empty and 2. 2sec in two thirds audience. The speaker stood on the center of the platform and spoke the sounds very slowly and the sentences in usual speed of lecture. During the first test in the large room the audience were 450 middle school students. The consequence of this test was as follows. The sound articulation was about 90% in front seats and about 10% in rear seats. The sentence intelligibility was 100% in front seats and about 80% in rear seats. The relation between the sound articulation and sentence intelligibility was very complex. During the second test in the large room the audience were 650 and the other condition was the same as before. Both percentage articulation and intelligibility were better than the former. The third test was carrisd out in a small room of 25×9. 6×22 cu. ft. The audience were 37 middle school students(18 boys and 19 girls). In this test, in the first halves of sound and sentence tests the audience were looking at the lips of the speaker, and in the second halves of them they were not looking at the lips but were using the ears only. These teste were performed in quiet, lower than the noise level of 40 db, and in the noise, thyratron noise of 60 db distributed uniformly in the room. The results of these tests were as follow. The sound articulation and sentence intelligibility was 92% and 61% in quiet and when looking at the lips, 88% and 60% in noise and when looking at the lips, and 70% and 54% in noise and when not looking at the lips, The fluctuation of data was very small in sound but large in sentence. The consequence of these three tests was as follows. (1)For testing the acoustical characteristics of lecture rooms the sound articulation test is better than the sentence intelligibility test. (2)To look at the lips of the speaker is one of the most important factor in order to obtain the higher percentage articulation.
