In this paper, two basic improvements on the prediction method of road traffic noise have been made for the well-known equally spaced vehicles model in a free sound field. One is based on the standard model of typical city environment with skyscrapers which has an exponential type propagation characteristics of the pseudo-diffuse sound field, since we considered that it is essentially unreasonable to apply the above well-known model in a free sound field to urban road traffic noise. The other is based on a traffic flow model in which a grouping effect of vehicles has been taken into consideration on the standard traffic flow of equally spaced vehicles model, under two typically idealized sound propagation fields corresponding to rural distincts and urban areas. Through the above improvements based on newly introduced ideal models of the sound propagation fields and the grouping pattern in traffic flow, we have been able to get a more precise information on the predicted fluctuation pattern of road traffic noise though it still amounts to no more than a fundamental viewpoint for the actual road traffic noise.
System function of an acoustic transmission system including an audio apparatus shows a complicated aspect in general. This paper describes the methods and the means for compensating these system function, a concrete example being shown. In the first place, the procedure for obtaining the transfer function of a compensation circuit is described. For realizing this transfer function, a statespace realization without integrators is used, which is constructed using systems theories. As an example of compensating system function, a loudspeaker system in free field is adopted and the procedure for constructing the compensation circuit is described in detail. After the utilization of the compensation circuit is confirmed, the problem on compensating system function is considered. According to circumstances, the frequency response of the compensation circuit is wanted to make variable. Thereupon, the compensation circuit which makes parameters in a transfer function variable is investigated. As the result, new original circuits are thought out from state-space realization without integrators.
Possible location of a context-dependent perceptual mechanism in the human auditory system is investigated through experiments on dichotic fusion. As an experimental hypothesis, peripheral/central dichotomy of the perceptual mechanism has been assumed by taking a model of dichotic fusion into account. Two types of dynamic vowels, one the form[u-Vowel-u]and the other the form[e-Vowel-e], were synthesized to form a pair of the dichotic stimuli. A stimulus of one type was presented to one ear and the counterpart of the other type to the opposite ear simultaneously. Two experimental conditions, condition #1 and #2, were set up for the pairs of stimuli. In condition #1, formant frequencies of the middle vowels in each pair of stimuli were the same or very close to each other but differed in phonetic quality, while in condition #2, formant frequencies of them were different but the same in phonetic quality. Listeners were asked to make judgment of fusion for the middle vowels of each dichotic pair. It has been found that the fusion occurs for stimuli in it condition #1 but does not in #2, that is, when the formant frequencies of the two vowels are very close irrespective of their phonetic quality. This suggests that the context-dependent mechanism dose not take place in the peripheral auditory system but is likely to be a function of the central processes.
The uniform asymptotic solution derived by Kouyoumjian and Pathak for a spherical sound diffraction by a wedge of arbitrary angle and the two asymptotic solutions derived by Pierce are quantitatively compared with the rigorous integral solution developed by Wiegrefe, Macdonald, and Carslaw. Level difference between Kouyoumjian & Pathak's asymptotic solution and the rigorous solution is less than 0. 5dB for the wedge of arbitrary exterior angle νπ only if kr_sr/L≧0. 25π, here r_s and r are respectively the distances from the edge of the wedge to the source and the observating point and L is the shortest distance to the observating point from the source in stepping over the edge. On the other hand the approximation error of Pierce's first and second asymptotic solutions become greater as ν→1. However Pierce's second solution has less approximation error than Kouyoumjian & Pathak's solution for ν≦1. 4. For ν=2;namely a half plane the above three asymtotic solutions become a same expression which level difference from the rigorous solution is less than 0. 5dB only if kL≧0. 21π. The above mentioned is confirmed also by the experimental results.
This paper presents a new method for the field measurement of short-range sound propagation. It is based on the correlation method, and uses a coherency recovering means which detects fluctuation in the propagation time and synchronizes a transmitted signal to a received one with the aid of a pilot signal. The pilot signal is radiated together with the test signal, and at a receiving spot, it is extracted from the received signal. Then, it is converted to a clock pulse train by which a new signal similar to the test signal is generated. Since this signal contains the same fluctuation as the received one, it becomes possible to take cross-correlation between them coherently, and the measured correlation function represents sound propagation characteristics. This paper also presents an inverse-filtering method for compensating frequency responses of acoustic instruments used in the measurement. Theoretical considerations for the properties of the system which has a statistically fluctuating response are also made. A device utilizing the methods said above is made with a micro-computer, and the experimental results show the effectiveness of the methods.
A generalized description of community noises is studied to estimate its equivalent continuous sound pressure level L_<eq> on the basis of Weibull distribution. The goodness-of-fit is verified on the Weibull probability paper by the linearity of values of L_α which are exceeded α% of the time, and L_<eq> of a specified community noise is easily obtained through the parameter m and η of Weibull distribution. Differences between estimated and measured values of L_<eq> are found to be small and below 1. 0dB at most case of community noises, while parameters m and η exist within range of 1. 0<m<2. 5 and 5. 0<η<15. 0 respectively.
Patterns of time series of sound levels observed every one second successively at the site near the traffic flow, can be represented by evaluation of probability density function and the transition probability density function of sound levels. A method of predicting these function from traffic volume, vehicle speed, percentage of heavy vehicles and the distance between traffic road and observation point, is discussed under following assumptions:1. Sound levels are observed at an equal time interval successively and are read in discrete integers. 2. Vehicle speed is constant during observation period. 3. Traffic is mono, lane, and consists of heavy and light vehicles. 4. Road is flat, and there are no buildings which prevent the sound propagations from the road to the observation point. 5. There is no branch extending over enough length on the road, and traffic is steady flow. 6. The ratio of the distance between traffic flow and observation point l to average vehicle spaces d is the 0. 46<l/d<1. 60. The parameters which need evaluating in the probability density functions, are the average relative sound level(The reference 0dB is the minimum sound level during the observation period. ), the relative maximum sound level, the probabilities in which the sound level decreases and increases by one dB respectively during two successive observations. The comparison between the measured values and the calculated ones shows good agreement.