Showing papers in "Applied Acoustics in 1999"

TL;DR: In this paper, the authors investigated the acoustic characteristics of leak signals in plastic pipes, including the frequency content of sound or vibration signals as a function of leak type, flow rate, pipe pressure and season, the determination of the attenuation rate, and the variation of propagation velocity with frequency.

TL;DR: In this article, a just noticeable difference in C50 values was determined for speech sounds in simulated sound fields, and it was estimated that it is probably necessary to increase C50 by approximately 3dB to create a readily detectable improvement in everyday situations.

TL;DR: In this paper, the effect of reducing the overall absorption by applying an adhesive is increased in smaller grain sizes, although absorption is observed to increase in materials made up of larger grains.

TL;DR: In this paper, the effects of vegetation on the perception of sound using both real traffic sources and reproduced recorded traffic noise were investigated and it was shown that on average listeners were more sensitive to noise when the source was visually screened.

TL;DR: In this article, an integral equation formulation of the problem is solved using a boundary element approach and the performance of the inclusion in impeding wave transmissions at a number of receiver positions is studied and measured in terms of insertion loss analogous to the study of noise barrier designs in outdoor sound propagation.

TL;DR: In this paper, a semi-empirical prediction method for fibrous media is described, which not only yields physically reasonable predictions for the bulk properties at arbitrarily low frequencies, but also is in good agreement with measured data at higher frequencies.

TL;DR: Sound pressure levels (dBA) were measured at 10 s intervals in the vicinity of a busy road carrying vehicular traffic and the resultant time series is analyzed using autoregressive integrated moving averages (ARIMA) modelling technique.

TL;DR: In this paper, the effects on roadside noise levels of applying sound absorptive materials to the traffic face of noise barriers were investigated under carefully controlled measurement conditions, and it was found that there was an increase of noise of generally less than 1 dB when the barrier face was changed from sound absorbing to reflective.

TL;DR: In this article, a diffusion equation is used to predict the sound propagation in long rooms with diffusely reflecting boundaries, and the model is defined by two parameters, the coefficient of diffusion depending on the mean free path, and an exchange coefficient expressing wall absorption.

TL;DR: A road traffic noise prediction model has been developed for environmental impact assessment in Thailand as discussed by the authors, which is made under some assumptions; vehicles were classified into two groups and the average stationary noise level of each group was then determined from measurement of many vehicles.

TL;DR: In this article, the authors used boundary element method (BEM) to determine the extent to which the noise reducing benefits of porous asphalt could be added to the screening effects of noise barriers in order to obtain the overall reduction in noise levels.

TL;DR: In this paper, the effects of initial hoop tension and the centrifugal and Coriolis forces on the critical speed of a rotating cylindrical shell with constant axial loads were analyzed.

TL;DR: The use of rapid speech transmission index (RASTI) in churches is studied and the relationships with acoustical and architectural parameters identified using a major survey of Catholic churches in Portugal as discussed by the authors.

TL;DR: In this paper, an alternative method of predicting the reverberation time for enclosures, using artificial neural networks, has been investigated, and the results indicate that there is a good basis for using trained neural networks to predict the reverberations of enclosures but that 15 input variables are required to achieve accuracy of ±10%.

TL;DR: In this article, a dual integral formulation for the Helmholtz equation for use in solving the acoustic modes of a two-dimensional square cavity is derived, and a general dual boundary element method (BEM) program is developed.

TL;DR: In this article, a variational model is proposed for the case of a rectangular, baffled, simply supported multilayered plate immersed either in a light fluid or in a heavy fluid.

TL;DR: In this article, the authors present the study of the sound radiation from a large power transformer in a substation and show that both the vibration of a transformer tank wall and the radiated noise consist of a series of tonal components mainly at the first few harmonic frequencies of 100 Hz.

TL;DR: In this article, results from measurements of the sound reduction index of some double walls are presented, where the walls are made from gypsum boards and filled with sound absorbing material (rockwool) in the gap.

TL;DR: In this article, two kinds of ultrasonic cleaners have been considered and the optimal arrangement of each cleaner has been suggested in order to improve the quality of cleaning, based on the vibroacoustic characteristics obtained analytically and numerically.

TL;DR: In this article, the dynamic density and bulk modulus of air in the porous media are used to describe the viscous effects and the thermal effects in an air-saturated rigid frame porous material.

TL;DR: In this article, principal component analysis (PCA) and partial coherent output power (PCOP) analysis are applied to scan near field acoustic holography (NAH) in order to identify partial sources.

TL;DR: In this paper, a meteorological mesoscale model is used to simulate the time dependent distribution of temperature and the corresponding development of slope-wind systems in a narrow two-dimensional valley during the course of a cloud-free day.

TL;DR: In this paper, a simple, accurate and flexible general algorithm for the study of a great number of beams vibration problems is presented, based on the Rayleigh-Ritz method with characteristic orthogonal polynomial shape functions.

TL;DR: In this paper, a new sound-propagation-curve prediction model is proposed for predicting noise in empty and fitted industrial workrooms, which account for variable room dimension, variable absorption and variable fitting density, and an empirical model for calculating reverberation times is presented.

TL;DR: In this article, an explicit formula of the transfer matrix is derived for evaluating the acoustic performance of the curved expansion chamber including curved duct bends based on the derived transfer matrix, the reactive sound attenuation of the chamber can be easily calculated by using an empirical formula for estimating the normalized maximum radial pressure of the fundamental mode in the curved duct bend.

TL;DR: In this article, two cylindrical shell structures with and without visco-elastic material were studied and it was shown that the effect of the modal truncation of the cavity modal basis is critical for the convergence of the predicted pressure field.

TL;DR: The theory discussed in the present study enables us to predict the time-average sound level, LAT, when the distance between the stopping line and the receiver exceeds the road width, acceleration length, and the length of the vehicle’s queue.

TL;DR: In this paper, the authors proposed a limit of 88dB(A) Leq for 8h/day and 48h/week with halving rate of 3 dB(A).

TL;DR: In this paper, the Millington reverberation time formula is validated and the sound field in a concert hall is predicted using three types of computer models used in the investigation, and the accuracy of these models is compared and the effect of applying different absorption coeAcients to be studied.

TL;DR: In this paper, a finite element analysis was used to study the vibrational properties of wooden bars for musical instruments, including the Young modulus and shear moduli along the grain and the density.