IZUMIYAMA MASAMI

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IZUMIYAMA, MASAMI

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Studies on Influences of Train Noise uponSchoolchildren: II. On Speech Articulation著者 IZUMIYAMA MASAMIjournal orpublication titleTohoku psychologica foliavolume 23number 1-2page range 3-7year 1966-01-10URL http://hdl.handle.net/10097/00123701STUDIES ON INFLUENCES OF TRAIN NOISE UPON SCHOOLCHILDREN: II. ON SPEECH ARTICULATION By MASAMI IZ UMIY AMA UJ'<W9=t::::.) (Miyagi Gakuin Women's College, Sendai) An articulation measurement was carried out under a sound condition of train noise on recording. The result showed that the efficiency of speech communication presented by the articulation index was seriously lowered by the noise level of 74 phons and the level which exerted no influence upon listening registered 50 phons. However, it is clear that the level of 50 phons as an allowable limit is not fitted to the real condition of ordinary schools in cities. The writer proposed to place the allowable limit at 60 phons for the reason that 70% of the articulation index was equivalent to 90% of the intelligibility index and no lowering of efficiency of listening to speech appeared in usual communications which have some contexts, on the noise level at that time. One of the great troubles to school children when trains pass hard by the school by a new plan of the National Raillway is a lowering of efficiency in hearing in the class room owing to the train noise. It is a serious problem if the lowering exceeds the limit at school. The object of this investigation is to observe the situation of speech commnication under a condition of train noise and to settle an allowable limit in the school. References to effects of noise on word articulation are found in fields of psychology, physiology and acoustic engineering and these observations were made under simple sound conditions, pure tones and other regular complex sounds like as white noise or band noise, but no investigations by means of real train noise have been made. As train noise is very specific in the characteristics of sound pressure and frequency, it may be necessary to observe by using real train noise as inserted stimulus in these kinds of the experiments. So, the noise previously recorded at a certain place similar to the place in question was used. Two channel recording and playing back system were adopted to produce the effect of reality and feeling of the moving train. We used the method of syllable articulation measurement and compared its result with that under the general condition of other school. There are two main methods to measure efficiencies of speech communication, that is, intelligibility and word articulation. The latter was chosen because the technique was so easy to use and available for application that many reseachers have been using in measurement of efficiency of telephons, and estimation of the sound condition of the interior of a room and etc. 4 Masami lzumiyama METHODS Recording of train noise: A large quantity of the noise made by the passing train to be used as inserted stimulus in the following experiments (II-V) had previously been recorded at a certain place similar to the school in the sound condition, and the place was chosen by clarks of the National Railway on the basis of geographical feature and was located at 40m distance from the railway line. The recording material of train noise contained some combinations of almost every kinds of trains, namely, up trains or down trains, electric or steam locomotives, freight or passenger trains. The stimuli were arranged as follows; the passing of a train for about 25 seconds and the silence interval for 15 seconds. During the experiment the stimuli were presented continouusly. As the apparatuses of recording were used two channel tape recorder (type Ampex 310), condenser microphones (type Sony C 37-A) and the monitor system. Subjects and procedure: The subjects consisted of 8 university students- 4 men and 4 women. They had all normal auditory acuity. The arrangement for playing back the sounds is shown in Figure 1. The sounds were presented in a sound-proof experimental room of the Psychological Laboratory in Tohoku University. The subjects sat down on a chair at a table and were tested as a group. In front of them, a speaker for voice of articulation measurement was set and on either side a speaker for train noise was set. The task required of them was to listen to the voice of test and train noise through these speakers and write down what they heard on recording sheets. tape players and 0 0 0 0 I subjects 1 produced system speaker for voice ~~ & ~ ~speakers for train noise Fig. I. Plane view of the experimental room depicting the player system and speakers. Produced levels of voice and noise were varied systematically from 40 dB (SPL) to 80 dB and 40 phons to 80 phons at 5 dB (phon) step. The materials of articulation test which consisted of Japanese syllables in random order were previously recorded in tape by trained announcers. It took about 4 minutes to read and record one material. As this test was carried out continously for an hour, 15 materials were prepared. The train took 25 seconds, to pass, so we inserted the noise of two up and down trains within a minute. Studies on Influences of Train Noise upon Schoolchildren: II. 5 RESULTS Table 1 shows the results obtained in articulation test by combining levels of voice and train noise. Table l. Articulation index in this experiment. ---~evel of voice I I I level of noi~e -~~ ------~-------~T--4-0--~-45--~-5-0--~--55 ______ 60--+--6-5--~-7-0~---75--~8-0(_d_B_) 0 40 45 50 55 60 65 70 75 80 (Phon) 50 40 30 20 10 82.4 78.4 75.0 68.8 60.2 55.4 51.0 42.6 32.4 24.3 88.3 80.7 80.1 75.6 70.3 65.4 56.4 47.4 33.8 20.6 88.6 82.3 82.1 79.0 72.3 70.5 6.7 50.0 43.2 30.4 90.1 86.2 84.0 75.0 72.8 69.5 68.6 50.9 43.0 35.3 92.7 83.4 82.6 76.5 74.6 72.4 67.2 60.6 48.5 36.7 93.6 88.5 84.0 76.3 75.1 74.1 65.3 62.7 56.3 40.5 93.5 90.3 84.7 80.6 75.8 70.6 62.3 63.5 50.3 45.6 Fig. 2. The three dimensional plot of articulation index. 93.3 89.2 83.4 81.1 76.5 70.3 66.5 63.5 54.7 45.2 92.0 86.7 82.3 82.5 85.0 72.4 67.4 64.2 52.6 44.8 The school When no noise was heard, the articulation index (average percentage on responses to 100 syllables) was above 82.4%. In general, it is accepted to be desirable to keep above 80% as a situation of speech comminication, because 80% of articualtion index was equal to 100% of intelligiblity. But there are area few places with such a sound condition of educational environment in this area. We had measured the noise in some schools and knew that the noise level of one school even in quiet residental quarters was 50-60 phons and the level of other schools near busy streets or along the railway lines were 60-70 phons. 6 Masami Izumiyama The level of noise in this school presupposed by the method of accoustic calucula-tion was 74 phons and the level of teacher's voice was usually 65 phons in the middle of the class room. So, it was possible to locate this point (noise level; 75 phons, voice level; 65 phons) in a three dimensional plot and to indicate the articulation index in such a sound condition. According to the plot, the index of 56.3% is shown. It is obvious that the percentage is too low to keep a situation of speech communication. According to our experience, we are apt to raise our voice more as noise becomes more disturbing. The indexes of the same levels of voice and noise is shown in Figure 3. It is indicated that the articulation drops with the increase of levels. Futhermore, the standard deviation of subjects at that time increases also distinctly, that is, we can recognize difference in the influence of noise among individuals. articulation index 100 90 80 70 60 50 f( 5 10 5 0 ---1---~f----..,f----+---+-.:..:::naise (phon) 40 50 60 70 80 voice (dB l /X ~x---x X--X standard deviation Fig. 3. Thr articulation index and the standard deviation at the same levels of voice and noise. The results may be briefly summarized as follows. (1) According to the results of test, the articulation index under the condition of 74 phons presupposed was below 60%. It is clear that pupils are in a serious situation as an educational environment of the school. (2) On the assumption that the level of teacher's vocie is approximately 65 phons, the noise level for keeping 80% of a articulation percentage is below 50%. But there are few places under such a condition as school environment. Even if the lowering of 10% in intelligibility happens, it may generally be said it is possible to keep perfect recognition of usuall speech which has some context of sentences. Therefore, the writer Studies on Influences of Train Noise upon Schoolchildren: II. 7 can fix the articualtion index as the allowable limit, that is, 60 phons on the noise level. (3) When the noise and the voice rise on the same level, the articulation index is not always constant. The curve as shown in Figure 3 describes a parabola and the increase of standard deviation is shown. It is found that there are individual differen-ces in the effect of noise on the level of above 60 phons. From the view-point of the SD, it may be reasonable to fix 60 phons as the allowable limit. (Received Sept. 10, 1964) ZusAMMENFASSUNG Unter Benutzung von dem aufgenommenen Gerausche des voriiberfahrenden Zuges wurde die Silben-Deutlichkeitsmessung (syllable articulation measurement) der Stimme ausgefiihrt. Daraus folgt, dass der Deutlichkeitsindex als Verstehbarkeit der Sprache bei 50 Phon Gerausch nur ein wenig beeinflusst wird und dass er bei 74 Phon Gerausch sehr merklich abnimmt. 

Studies on Influences of Train Noise upon Schoolchildren: II. On Speech Articulation

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Studies on Influences of Train Noise upon Schoolchildren: II. On Speech Articulation

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