The summarized results of measurements of city noise in Tokyo are reported. The first measurement was carried out from 25th to 28th Nov. 1952, at the most noisy area in Tokyo; from Hibiya to Tsukiji. Average values and distribution of noise levels at 48 places from 8 a. m. to 9 p. m. and at 5 places from morning to the next morning were obtained. About one hundred observers belonging to twenty-one government and civil organizations took part in the measurement. The second one which was about the same scale as the first, was held from 25th to 27th Feb. 1953, at seven typical areas; Marunouchi, Kanda, Shinjuku, Shibuya, Hongo, Ueno and Asakusa. The main results obtained are as follows: (a) Variations of noise level during 24 hours are shown in Fig. 6-10, (b) Noise levels during the day; Fig. 11-18, (c) Distribution of noise levels at different areas and different street conditions are summarized in Fig. 19-21, (d) Noise from vehicles and their horns; Fig. 22, 23 and 25.
We have had occasions to measure sound levels of street-, vehicle-, traffic-, loudspeaker-, aeroplane-noise, etc. , in Osaka-area. Readings of sound level meter in the main street in Osaka City ranged 69. 5-84. 7 phons, being 74. 9 phons in average during day-time, and 69. 0-74. 9 phons and 72. 3 phons in the evening. Noise levels of vehicles, etc. were as follows: Street car ranged 80-97 phons, being 87. 8 phons in average; Omni-bus, 75-90 phons, average 83. 6 phons; whistle of vehicles, 60-105 phons, average 86. 5 phons. In the vicinity of the air-port, the noise level in a room was 80 phons in average (maximum 105 phons), when the aeroplane was flying over-head.
At the busy streets and crowded open areas in Tokyo, the commercial address by the loud speakers is one of the most violent noise sources. Noise survey of them was carried out concerning to (a) average level of the street noise raised by the speakers, (b) statistical distribution of peak level of speech and (c) service areas. As they are generally masked by the traffic noise, we classify the cases as follows: (1) speech level exceeds the traffic noise level, (2) speech level is much lower than the traffic noise level and (3) the former is comparable with the latter. These differences are caused by the electric power of the speaker, traffic noise level and also the distance from the source. In every case the intelligibility of the speech is as follows: in the case (1) it is excellent, in (2) poor and in (3) good, and it seems fairly intelligible though the speech level is 3 or 5 db lower than the average level of the traffic noise.
Noise measurements have been performed in 46 areas selected out of six classes of Tokyo City district, namely, the exclusive residential areas, the residential areas, the business areas, the small factory areas, the semi-industrial areas, and the industrial areas. Several representative areas were selected out of each quarters. Each area was a circle 500〜1000m in diameter and a square mesh of points at 100m intervals were selected as points of measurements in each area. The mean value did not change more than 4 phons when the mesh was shifted in the same area. It was revealed that the main part of the city noise was traffic noise, because noise-meters indicated higher levels in streets with streetcars (mean 77 phons) and in streets with great traffics (mean 67 phons) than in the very neighbourhood of factories (mean 57 phons). It was remarkable that the business areas were more noisy than the factory areas except in the suburban areas. The most noisy areas were the amusement areas.
In our country, the public nuisance caused by the city-noise has become one of the most important social problems. To make clear the responese of neighbours to the noises caused by factories, we have performed the following investigations in Osaka City and Amagasaki City: (1) measurements of noise level inside and outside the factories and in the houses in the vicinity of them, number of factories and houses investigated being 33 and 136 respectively; (2) the relationship between the psychic and somatic injury on the dwellers and the noise level in their houses. More than 25% of dwellers were injured emotionally at level of 40-45 phons, in daily life at 45-50 phons, and physically at 50-55 phons. At levels above 60 phons, most of dwellers were injured. From this study it seems to us that the tolerable level of noise caused by factories should not exceed 60 phons. We have proposed a noise abatement regulation in city in consideration of the above mentioned results and social conditions.
In this paper we intend to treat the permissible values for the sound levels of loudspeaker for advertisements of street. The following researches have been performed: (1) measurements of attenuation of sound from a loudspeaker propagating in an open field and on a street; (2) the articulation of syllables produced by the loudspeaker; and (3) the decrease of the syllable articulation in the presence of the sound produced by the loudspeaker. Sound levels of loudspeaker in an open field and on a street were almost proportional to the reciprocal of the distance from it. The articulation of syllables produced by the loudspeaker was about 70% when the sound levels from it were 5-10db above the background noise level. In the presence of the loudspeaker-sound with a level of 80phons, conversations were masked and syllable articulation was decreased to about 70%. Our conclusions are followings: the permissible sound level of loudspeaker is fixed 80phons and has no need of exceeding 10phons above a background noise level at the place 10m distant from it. 10m corresponds to average value of distances between adjacent houses.
The sound pressure levels and the spectra of various noises, to which the employees were exposed in the ship-yard, iron works, mines and so on, were examined. The frequency analysis was mainly performed by the octave-band analyzer. Sometimes the unsteady noises were recorded on a magnetic recorder. From the octave-band spectrum obtained, the loudness was calculated by the procedure of Mintz and Tyzzer, and the degree of hearing damage risk was proposed in five steps; namely, harmless (-), doubtful (±), harmful (+), very harmful, and extremely harmful, according as the loudness of any octave band was below 50, 100, 200, and 400 and over 400 sones, respectively. The statistical relation between the sound pressure level and the calculated loudness level was found. The difference of the two levels was considerably varied according to the shape of the spectrum, especially at high sound pressure levels, e. g. , the calculated loudness levels of 100db noises were distributed from 110 to 115phons but those of 115db noises from 122 to 136phons.
The level selector was applied to the measurement of fluctuating noise, such as city noise. The signal which exceeds predetermined level is cripped and integrated values are recorded by the mechanical counter. From the numbers of counting the time rate of the noise above reference level is estimated. The counting rate of the instrument was adjusted as 2. 5 per second. This apparatus is convenient for obtaining the statistical distribution of noise level for short time interval as well as for long time interval. For practical use, the 6-channel type selector with 30db range was constructed.
The statistical method of measurement of fluctuating noise was already proposed by the author. Some numerical examinations were carried out using the data obtained by the Noise Abatement committee of Acoustical Society of Japan. The deviation of average levels due to different calculating methods and the frequency of occurence of last figures of level reading were discussed. Also the typical frequency curve of street noise level was obtained from the summarized data.
Sound treatment of an IBM(International Business Machine)room- 7. 4×7×3. 2m^3. - is reported. Distribution and sound spectrum of noises produced by key-punches and verifiers were measured before and after treatment. Design of the treatment was also mentioned. (The wall and ceiling of the room were covered by hemp cotton of 5cm thick and 5cm-10cm air gap was retained from the wall. ) Reduction of the noise was about 6db near the machine and 13db at the corner of the room, the average reduction was about 10db.