A series of measurements is made on a lawn field for sound propagation in two opposite directions. The average and the standard deviation are calculated from the field data in order to obtain the mean excess attenuation with nearly zero vector wind and the variation of sound level within a range of wind speed less than 3m/s. It is shown that the mean excess attenuation approximately agrees with a theoretically predicted value of ground attenuation, but by the effect of meteorological conditions the variation of sound level extremely increases with distance. The mean excess attenuation and the sound level variation are approximated by simple expressions with a parameter of a specific distance from which the attenuation and the variation start to increase. It is shown that the specific distance has a linear relation with a mean propagation height on a logarithmic scale. Numerical expression is given to the relation and an engineering model is obtained for the mean excess attenuation and the sound level variation. It is applicable to rough estimation of traffic noise propagation over absorptive ground like lawn.

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Sound attenuation characteristics of barrier for underwater sound propagation was investigated through a reduced scale cistern experiment. From the observed data for a thin barrier, it was found that the sound attenuation characteristics in underwater is almost the same as that in the air, which has been obtained in the noise control engineering field. Next, a useful functional form was derived for predicting the sound attenuation in underwater and it's effectiveness was confirmed experimentally by applying it to the data measured in an actual sea area. Furthermore, a possibility for the prediction of sound attenuation value in the case of a finite wide barrier was considered as well. As a result, sound attenuation characteristics for the wide barrier were understood by a double diffraction process.

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When ultrasonic pulse travels in homogeneous material, it shows deformation by diffraction. An important approach to analyze this effect is to compute retarded potential of ultrasonic field together with Fourier's analysis. Deformation of sound pressure pulse with diffraction and that of axial component of particle velocity pulse with it are dealt with a numerical method by Fourier's analysis. They are compared each other in the case that a pulse is transmitted from a circular flat transmitter into isotropic and non-absorptive medium. Analyzed transmitting pulses are assumed to have several envelopes of ramp followed by exponential decrease with sinusoidal carrier wave. Waveforms of receiving pulses through a few transmission systems with a circular flat transducer and a point one and those with a pair of coaxial circular flat ones are derived. Ratio of peak value of receiving pulse to that of transmitting one is obtained with a computing precision of 0.1%. It corresponds to apparent attenuation of pulsed ultrasonic wave by beam divergence when a pair of circular flat transducers are considered.

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The estimation of acoustic characteristics based on the one-dimensional model of fourpole parameters matrix for the complex acoustic system is not always in good agreement with the experimental results. The fundamental resonance frequencies are shifted by the effect on the presence of higher order modes of wave propagation. Because of the influence of frequency shift, the estimated acoustic characteristics are different largely from ones of measurement when many elements are connected in series. In this paper, a method to derive the four-pole parameters matrix of the elliptical cylindrical cavity including the characteristics of the connection part of elements is presented. Furthermore, the method is developed in the case of circular cylindrical cavity. The experimental results are compared with the estimated characteristics obtained by the proposed method and those by one-dimensional model is made.

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As one of evaluation methods for the room sound fluctuation, a new trial to predict the probability distribution of the response sound fluctuation in the room excited by arbitrary type environmental noise input is proposed by emphasizing its methodological viewpoint. The response sound intensity of the room can be naturally expressed as a total sum on intensity scale of each frequency response component and its modelling error caused by the quantized error and/or the observation noise. Owing to the non-Gaussian property of intensity variable and modelling error, the well-known system identification method is too difficult to be directly applied to the present case. So, in this paper, first by newly introducing some kind of information measure in a form of mutual entropy quantity between input and output and maximizing it, a new estimation algorithm of acoustic characteristic parameters of the room is derived by applying a stochastic approximation method to the above extremal condition with using a general expression form of the Gram-Charier series expansion type non-Gaussian probability distribution. In the room excited by an arbitrary environmental noise input fluctuating in non-Gaussian type probability distribution form, the probability distribution of response sound fluctuation for an overall frequency range and each frequency band component can be predicted by using the above identified system model. The proposed method is applied to the room simulating the actual living acoustic situation and its justification and usefulness is experimentally confirmed, too.

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This paper describes a new and simplified method for estimating exclusively objective acoustic signal levels where the observation of the signals with microphones is inevitably disturbed by wind-induced noise in the outdoor measurement of low-frequency sounds. The estimation method in the frequency domain is discussed using the information on wind speed observed in the vicinity of a microphone, mainly from an experimental viewpoint. Concretely, the power spectrum of the wind noise and that of the observed sound (composed of objective signal and wind noise) are first expressed in the form of probability distribution conditioned by the wind speed. Next, a simplified method is shown for estimating the objective signal through a spectrum estimation procedure employing the conditional means of these power spectra. The method is supported by the fundamental additive property of power spectra based on the statistical independence of the signal and the noise. The effectiveness of the proposed method is finally discussed and shown through the measurement of an objective signal of band noise with the wind speed under breezy conditions.

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This study was aimed at making sure usefulness of assumption of Weibull distribution or Rayleigh distribution for estimating L_eq of community noise and road traffic noise from noise levels in L₅, L₅₀ and L₉₅. The results showed that Weibull distribution was very useful to estimate L_eq except few cases like the exponential distribution of noise levels and that Rayleigh distribution was also useful with permitting errors of about 1.5 dB (A) except such cases as distributions of noise levels were largely skewed to lower levels or higher levels.

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