A new technique to measure the ground to ground noise propagation was developed. The test sound of a band limited noise is emitted from a loudspeaker intermittently. A several second burst of the noise and the following pause of the same length are repeated. At a receiving spot, the sound intensity is integrated alternatively by two digital counters. One counter integrates the intensity of the test sound plus the background noise at that spot in the period for which the test sound is present. The other integrates the intensity of the background noise in the absent period of the test sound. Each of the devices at the source and receiving spots has a precise crystal oscillator as the clock. Once the synchronization of the two devices is made before a measurement, the relative phase of the operations of the devices is kept constant during the time of the measurement without any connection. After the completion of a predetermined number of integrations, the difference of the accumulated numbers in the two counters is read, which gives the intensity of the test sound at the receiving spot. Experiments using a 5-Watt loudspeaker showed that the noise attenuations of the distance of 170m can be measured with the statistical error less than 0. 5dB.
The purpose of the study is to gain a knowledge of the relation between the amount of personal exposure and his reaction to noise in his daily life. In this paper we discuss the details of noise exposure of 216 people who live in Sendai. The equivalent sound level L_eq is recorded every ten minutes over 24 hours and L_<eq(24)> is measured, too. Some of the findings from analysis of those data are as follows: 1)There is no difference in L_<eq(24)> among areas of residence, though the difference is seen among their daily activities. Especially for workers, the amount of L_<eq(24)> is dependent on the kinds of their work and their means of commutation. 2)Average difference in value between L_<eq> during some activities when the respondent felt annoyed and his L_<eq(24)> is found to be about 4dB. No significant difference is seen in this average value between Noisy Group (L_<eq> during working ≥ 80dB(A)) and Non-noisy Group (L_<eq> during working<80dB(A)). This fact suggests that there might exist hazard of insidious adaptation to noise in our daily life.
Experiments were carried out to measure the noise propagation over the ground when varying the combination of heights os an artificial noise source and several receiving points. Results on excess attenuation caused when the noise propagates over the ground are mainly described. Results obtained from our experiments are as follows;1)Excess attenuation due to the noise propagation over the soft ground is rather larger in low frequencies than we expected and also influenced by the wind. 2)Excess attenuation observed is, as a whole, larger in summer than in winter. From field experiments, the empirical equation predicting excess attenuation is introduced, using non-dimensional distance coefficient as a parameter. Further we apply our empirical equation to the data measured by other researchers and show that our equation is significantly effective to predict excess attenuation caused when the noise propagates over the ground.
The multi-blade fan is widely used for the reference sound source. Since the sound generated aerodynamically by it is considered to be caused by many dipole sources, behavior of the sound power and directivities of the sound effected by a reflecting plane is different from that of a monopole or a dipole source. For example, the sound power of the fan with the reflecting plane parrallel to the wheel shaft is within +1. 6, -1. 0dB as compared with that without the reflecting plane. In this paper, influence of the reflecting plane on the sound power and directivity characteristics of multi-blade fan is made clear by measurements on ILG181-12ZA and by calculation. The calculation is made on the assumption that the multi-blade fan consists of many dipole sources distributed randomly on the wheel and axes of these dipoles being normal to the wheel shaft. The results of measurements and calculations are in good agreement except for the case in the direction of the wheel shaft.
The distribution of houses plays an important role in the noise propagation in a city area. The tendency of road traffic noise propagation into the city area is made clear by means of scale model and field measurements. In these scale model experiments, an incoherent line source(jet noise type)is used as road traffic noise. Houses are assumed to be only one or two-story houses and are distributed in random order. In this scale model of the residential area, the spatial distribution of sound pressure levels at a specified distance from a road is observed. From the experimental results, we can derive an empirical equation which gives the excess attenuation caused by houses as a correction term. This correction is given as a function of the density of houses, the source height and the distance from the road. Predicted sound level obtained by using the correction term agrees well with the result of the field measurements.
A new algorithm for retrieving aircraft noise exposure forecast contours to minimize cost of the computation is proposed. The iterative technique of this algorithm distinguished from others is to seek for the contour point along circuler arcs on which dummy points for computation are settled with discrete radii and directions. Computational tolerance ⊿L is preferable to be set as 0. 05dB<⊿L<0. 1dB, besides the initial values γ_0 of retrieving radius should be 250m. As a result, it has been proved that CPU time to retrieve a contour is reduced by a large margin with small computational errors less than 0. 5% in comparison with the reference noise impact area.