Sound propagation in a street

The propagation of sound in a street has previously been treated almost exclusively by the use of ray-tracing techniques. As a result, the effects of scattering from objects and protrusions in the street have not been taken adequately into account. In this paper, the sound field is analysed in terms of its propagating modes. The use of this technique allows the effect of scattering to be calculated, assuming a rather simplified model of a scattering surface. Although a number of important assumptions are made, the predicted attenuations at points down a street are in good agreement with results obtained from model studies. These attenuation curves are also similar in form to ihose obtained in full-scale tests.     

微晶玻璃中的声传播

本文把悬浮液中的声学处理方法应用到微晶玻璃中,导出了微晶玻璃中声速和声衰减系数随结晶度变化的表达式,并通过实验进行了证实。     

The effect of a twin tunnel on the propagation of ground-borne vibration from an underground railway

Accurate predictions of ground-borne vibration levels in the vicinity of an underground railway are greatly sought after in modern urban centres. Yet the complexity involved in simulating the underground environment means that it is necessary to make simplifying assumptions about this system. One such commonly made assumption is to ignore the effects of neighbouring tunnels, despite the fact that many underground railway lines consist of twin-bored tunnels, one for the outbound direction and one for the inbound direction.This paper presents a unique model for two tunnels embedded in a homogeneous, elastic fullspace. Each of these tunnels is subject to both known, dynamic train forces and dynamic cavity forces. The net forces acting on the tunnels are written as the sum of those tractions acting on the invert of a single tunnel, and those tractions that represent the motion induced by the neighbouring tunnel. By apportioning the tractions in this way, the vibration response of a two-tunnel system is written as a linear combination of displacement fields produced by a single-tunnel system. Using Fourier decomposition, forces are partitioned into symmetric and antisymmetric modenumber components to minimise computation times.The significance of the interactions between two tunnels is quantified by calculating the insertion gains, in both the vertical and horizontal directions, that result from the existence of a second tunnel. The insertion-gain results are shown to be localised and highly dependent on frequency, tunnel orientation and tunnel thickness. At some locations, the magnitude of these insertion gains is greater than 20 dB. This demonstrates that a high degree of inaccuracy exists in any surface vibration prediction model that includes only one of the two tunnels. This novel two-tunnel solution represents a significant contribution to the existing body of research into vibration from underground railways, as it shows that the second tunnel has a significant influence on the accuracy of vibration predictions for underground railways.     

Sound and light propagation in a weakly inhomogeneous atmosphere

Small-scale inhomogeneities caused by atmospheric turbulence have a considerable effect on sound and light propagation, producing the fluctuations of these wave fields. V A Krasilnikov [1, 2] performed experiments on phase and amplitude variations of a sound wave propagating through the atmosphere. Fluctuations of light-wave parameters occur, for example, in the well known phenomenon of star scintillation, apparently strongly connected with turbulent irregularities of the atmospheric temperature field [3, 4]‡.

Some calculations of phase (arrival angle) and amplitude fluctuations for a wave propagating through a turbulent medium are described by Krasilnikov [1, 3, 8]. All these and similar calculations are based on the geometrical optics (acoustics) approximation, which may be the reason for disagreement between calculation and experimental data in some cases. Thus, for example, amplitude fluctuations in the geometrical approximation turn out to be proportional to the distance of propagation through a turbulent medium to the power of 3/2. However, observations usually show much slower fluctuation growth.

This paper represents an attempt to consider the problem of amplitude and phase variations for a scalar wave field in terms of more general equations including some diffraction effects. Incidentally, the range of validity of geometrical optics theory becomes clear.     

Sound propagation and radiation through a vaneless diffuser

A simple analysis has been carried out to examine acoustic effects of attaching to the termination of an annular duct a vaneless diffuser through which incident plane waves propagate and radiate out circumferentially. The results are shown in the form of a reflection coefficient which expresses the ration of the incident and reflected waves at the diffuser inlet.     

Sound wave propagation in a vertically inhomogeneous ocean

Propagation of sound waves generated by a time dependent acoustic source in a vertically inhomogeneous ocean is considered. The effect of the solid bottom is included so that both the longitudinal and shear waves can be excited inside the bottom. The possibility of exciting a lateral shear wave by the acoustic source is also discussed. Although the results presented here are formal and general, physical interpretations have been offered whenever possible.     

Sound propagation and energy relations in churches

The results of an acoustic survey carried out in a group of Italian churches differing in style, typology, and location were used in order to study how the acoustic energy varies inside this kind of space. The effect of different architectural elements on sound propagation was investigated by means of three-dimensional impulse responses measured using a B-format microphone with sweep signals. Side chapels, columns, and trussed roofs appeared to scatter the reflections, so that the purely diffuse exponential sound decay begins after a time interval which grows with the source-receiver distance and with the complexity of the church. The results of the measurements were then compared with predictions given by existing theoretical models to check their accuracy. In particular a model previously proposed by the authors for a specific type of Romanesque churches was further refined taking into account the new findings and making some simplifications. Its application to the wider sample of churches under analysis showed that strength, clarity, and center time can be predicted with reasonable accuracy.     

Sound propagation in fluids and neutron spectra

Using a model kinetic equation the properties of very short wavelength sound modes in fluids are studied over a wide range of wavenumbers and densities. The main features, in particular propagation gaps at high densities, agree with those found in real fluids and molecular dynamics simulations.     

复杂厂房噪声传播

本文导出一个工业厂房噪声传播数学模型.这模型适用于任意形状、任意边界条件和有任意障碍物的厂房.发展这个模型的目的是为了电厂噪声预测.电厂厂房噪声传播测量结果表明,模型有很高精度和对各类复杂厂房的适应性。     

Sound propagation in the North Sea

Results of an experimental study of shallow-water sound fields are presented. The experiment is carried out in the frequency range 112–3200 Hz on a 150-km-long propagation track. A comparative analysis of experimental and calculated data is performed. Estimates are obtained for the loss coefficient associated with sound attenuation in the bottom, as well as for the parameters of the bottom, which is modeled as a homogeneous liquid absorbing half-space. The vertical interference structure of the sound field formed at a frequency of 112 Hz in the vicinity of the source is considered.     

Sound propagation in soundproofing casement windows

Casement windows consisted of two wooden frames that can be opened and closed at various angles are widely used in developing countries with tropical climates. However, an annual increase in a number of motorcycles and automobiles and traffic noise level these countries have rendered these windows to be useless. In this paper, we present a model for manufacturing windows which are suitable for the developing tropical countries. These windows are capable of ventilating, regulating sunlight, protecting against coldness, and reducing traffic noise and fumes from motor vehicles. The ventilation and soundproofing unit hold an importance place in the design of the windows and are calculated using the wave equation and observations of higher-order mode waves. In order to maximize the soundproofing ability, the selection of size and placement of input and output openings in such a way that would minimize the effects of higher-order mode waves are considered in details.     

Sound propagation in complicated industrial enclosures

I.IntroductionInordcrtocfficlcntlyprcdictandcontro1thenoiseinindustria1enclosurcs,manypeoplehavestudicdmathmodclsforsoundpropagationinindustria1enclosurcs.Butsofar,thereisnosatisfactoryrcsult.Inthepast,a1mostal1studieswcrercstrictedtoidealemptyindustrialcnc1osurcs,andonlyafewofthcm['-']concerncdtheinfluenceofobstac1cswithinthemodel.Thcscmodc1strcattheobstac1eeffcctsbythemethod-ofimagesandcanonIybeusedtoregu-larhexahcdronroomswhcreobstaclcsareassumedtobedistributesuniformIy.Ondet'sartic1el'],…     

Sound propagation in railway line cuttings

Sound propagation in and around railway line cuttings is in many cases dominated by multiple reflections between train body and cutting wall or between the cutting walls. Typical situations were examined by a large number of scale model experiments. Based on these results a simple empirical calculation scheme was deduced to estimate sound fields in the surroundings of railway line cuttings. The basic idea is to compose the sound field from three parts: the direct sound from the wheels, first order specular reflections and a diffuse sound portion that is emitted from the upper edges of the train body. The scheme can easily be incorporated into existing railway noise models.     

Experimental comparison between speech transmission index, rapid speech transmission index, and speech intelligibility index

During the acoustical design of, e.g., auditoria or open-plan offices, it is important to know how speech can be perceived in various parts of the room. Different objective methods have been developed to measure and predict speech intelligibility, and these have been extensively used in various spaces. In this study, two such methods were compared, the speech transmission index (STI) and the speech intelligibility index (SII). Also the simplification of the STI, the room acoustics speech transmission index (RASTI), was considered. These quantities are all based on determining an apparent speech-to-noise ratio on selected frequency bands and summing them using a specific weighting. For comparison, some data were needed on the possible differences of these methods resulting from the calculation scheme and also measuring equipment. Their prediction accuracy was also of interest. Measurements were made in a laboratory having adjustable noise level and absorption, and in a real auditorium. It was found that the measurement equipment, especially the selection of the loudspeaker, can greatly affect the accuracy of the results. The prediction accuracy of the RASTI was found acceptable, if the input values for the prediction are accurately known, even though the studied space was not ideally diffuse.