Papers by Keith Attenborough
The Journal of the Acoustical Society of America
The Reflections series takes a look back on historical articles from The Journal of the Acoustica... more The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.
A rough surface formed by regularly spaced acoustically hard parallel strips or grooves gives ris... more A rough surface formed by regularly spaced acoustically hard parallel strips or grooves gives rise to non-specular diffracted modes and surface waves. Surface waves result in values greater than +6 dB in spectra of the sound field relative to the direct field (excess attenuation). As well as surface wave generation, measurements of excess attenuation over regularly spaced parallel strips show effects of the finite array dimensions. Numerical predictions of pressure contours at the frequency of main surface wave energy show that the surface waves are created by overlapping, interacting, quarter wavelength resonances in the gaps between roughness elements or within grooves. Additional peaks in EA spectra result from interference between surface waves and diffracted components travelling towards the source. Surface waves are reduced if roughness elements resonate at surface wave frequencies. Predictions over periodic rectangular grooves with the same width but depths varied to create a phase change of 2π over each period show non-specular behaviour associated with surface wave generation and diversion of energy into diffracted modes. Useful traffic noise insertion loss due to a periodic surface consisting of rectangular grooves with different depths is predicted.
Academia Engineering, Aug 24, 2023
Greening the environment can improve soundscapes by reducing unwanted sounds and introducing soun... more Greening the environment can improve soundscapes by reducing unwanted sounds and introducing sounds that are generally considered more desirable. This review concentrates on the physics by which increasing the area of natural ground cover and vegetation can reduce sound levels. Most naturally occurring ground surfaces are porous. If a source of sound and a listener are close to a porous ground surface, the sound reflected from the surface combines with sound traveling directly to the listener such that the phase difference due to the path length difference adds to the phase change during reflection at the surface. At the listener, the two components will partly cancel each other; in other words, the direct and reflected waves interfere destructively, and there is a reduction in the total sound level over a range of frequencies. Also, viscous drag and heat exchange at leaf surfaces adds to sound attenuation. Measurements and predictions show that the viscous and thermal processes and 'soft' ground effect are the most important contributors to sound attenuation through crops and densely planted trees and contribute to the acoustical influences of roof top gardens and vegetated façades. Although widely used schemes for predicting outdoor noise allow for a porous ground effect and for attenuation through foliage, they are not sufficiently accurate either to explore the potential of 'greening' for noise reduction or to be useful in devising plans to exploit it. Improved prediction schemes are key to realizing the potential of greening for noise reduction.
Journal of the Acoustical Society of America, May 1, 2022
PUBLISHED BY IMPERIAL COLLEGE PRESS AND DISTRIBUTED BY WORLD SCIENTIFIC PUBLISHING CO. eBooks, Dec 1, 2004
Springer eBooks, 2007
... The pressure at the receiver is the sum of four terms that correspond to the sound paths SgER... more ... The pressure at the receiver is the sum of four terms that correspond to the sound paths SgERg, Si ERg, SgERi, and SiERi. ... For example, the diffracted wave along the path SgERg would be given by P1 = Att1ei[k(r0+rr )+π/4] (20) ...
HAL (Le Centre pour la Communication Scientifique Directe), 2008
Journal of the Acoustical Society of America, 2008
In a study of hooded crow communication over open fields an excellent correspondence is found bet... more In a study of hooded crow communication over open fields an excellent correspondence is found between the attenuation spectra predicted by a “turbulence-modified ground effect plus atmospheric absorption” model, and crow call attenuation data. Sound propagation predictions and background noise measurements are used to predict an optimal frequency range for communication (“sound communication window”) from an average of crow call spectra predicted for every possible combination of the sender/receiver separations 300, 600, 900, and 1200m and heights 3,6,9m thereby creating a matrix assumed relevant to crow interterritorial communication. These predictions indicate an optimal frequency range for sound communication between 500Hz and 2kHz. Since this corresponds to the frequency range in which crow calls have their main energy and crow hearing in noise is particularly sensitive, it suggests a specific adaptation to the ground effect. Sound propagation predictions, together with background noise measurements and hearing data, are used to estimate the radius of the hooded crow active space. This is found to be roughly 1km in moderately windy conditions. It is concluded that the propagation modeling of the sort introduced here could be used for assessing the impact of human noise on animal communication.
Designs with uniformly distributed slits normal or inclined to the incident surface exhibit a gre... more Designs with uniformly distributed slits normal or inclined to the incident surface exhibit a great potential because of their simplicity and good acoustical performance. However, production of materials of this sort is challenging as the required fabrication precision is very high. This paper deals with additive manufacturing, modeling, and impedance tube testing of a few slitted geometries and their variations, including cases where the dividing walls between slits are perforated. They were designed to be producible with current 3D printing technology and provide reliable measurements using standardized equipment. The normal incidence sound absorption curves predicted analytically and numerically were verified experimentally. It is observed that such simple configurations may lead to absorption properties comparable to porous acoustic treatments with more complex microstructure. The good agreement between the predictions and measurements supports the validity of the multi-scale modeling employed
한국소음진동공학회 국제학술발표논문집, Aug 1, 2003
Scattering Theory for fibrous media23 Single scatterer theory Multiple scattering theory Exp~rime... more Scattering Theory for fibrous media23 Single scatterer theory Multiple scattering theory Exp~rimenta1 results Discussion and conclusions Waves in fluids Waves in solids Scattering coefficients Expressions for computer program Energy dissipation calculations .. Constants, basic expansions, List of samples Viscoelastic absorber~ scattering coefficients Spherical scatterer-solid stress components Photographs
Journal of Sound and Vibration, Jul 1, 1989
As part of their studies of a second level course T234 Environmental Control and Public Health, a... more As part of their studies of a second level course T234 Environmental Control and Public Health, approximately 600 students of the Open University per year make noise measurements in and around their homes or other local study venues. These measurements are made with integrating sound level meters issued as part of their Home Experiment Kit for the course. Methods are described by which the accuracy and calibration of these meters has been ensured. Such methods, together with other checks on meter and student performance which are also outlined, have established the reliability of the student data in surveying external noise levels, internal noise levels and domestic appliance noise levels in the U.K. Some preliminary results of these surveys are presented in order to illustrate the range of noise data which the students have been able to obtain.
Applied Acoustics, 1993
The acoustic field due to a point source above a low-density elastic foam has been measured. The ... more The acoustic field due to a point source above a low-density elastic foam has been measured. The field has been predicted using both elastic-porous and rigid-porous models for the foam and appropriate propagation models. The pore-related and elastic parameters of the foam were either measured directly or deduced using non-acoustic methods. The calculations were compared to the measured field and it was found that, within the restricted frequency range permitted by the laboratory environment and the elasticity data, the predictions using the numerical propagation code FFLAGS that allows for the elastic-porous model were much closer to the measurements than those using the standard analytic approximation (and hence the rigid-porous model). The differences between the two sets of predictions were large enough to suggest the need for an elastic-rather than rigid-porous model for the foam when calculating oblique-incidence fields.
Springer eBooks, 1985
Studies of outdoor sound propagation, particularly at near grazing-incidence and of the phenomeno... more Studies of outdoor sound propagation, particularly at near grazing-incidence and of the phenomenon of acoustic-to-seismic coupling have motivated a search for suitable models for the acoustical characteristics of outdoor ground surfaces. In many instances of outdoor propagation, it has been found possible to obtain sufficient accuracy by assuming both that the ground is locally-reacting, so that it may be described by its normal surface impedance (Zs), and, by calculating Zs from empirical power law relationships for the characteristic impedance of fibrous absorbents1. These relationships introduce a single parameter, the flow resistivity of the surface. The range of validity of these empirical relationships was stated by their authors to be 0.01 < (fΩo/Rs) < 1; where f is the frequency in Hz, Ωo is the equilibrium density or air in Kg m -3 and Rs is the flow resistivity in N s m-4. Moreover the relationships were derived from data for dry fibrous materials with porosities near unity and flow resistivities ranging from 5000 to 80000 N s m-3. Despite this, the relationships have been used successfully in combination with well-established theory for propagation from a point source above an impedance boundary to describe excess attenuation, up to 1000 Hz, over short ranges encompassing a wide variety of ground surfaces outdoors 2. The single parameter that, consequently, describes the acoustical behaviour of the ground has been called the effective flow resistivity (Rse).
Journal of Soil Science, 1992
SUMMARYTwo acoustic techniques for determining the air‐filled porosity and air permeability of so... more SUMMARYTwo acoustic techniques for determining the air‐filled porosity and air permeability of soil surfaces, and the near‐surface variation of these properties with depth, have been applied to several soils in situ. The techniques depend upon an inversion process using data on sound propagation near to the soil surface and through the soil surface. The measured difference in acoustic spectra received by two vertically separated microphones above the ground surface and by probe microphones beneath the surface were matched theoretically to deduce the porosity of air‐filled connected pores and an effective air permeability which depends on pore shape and size distribution. This modified permeability parameter and the acoustically deduced porosity varied realistically with surface sealing and compaction. The acoustically deduced porosities were within 10% of those obtained conventionally. Changes in acoustically deduced parameters occurred with changes in moisture content both in soil ...
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Papers by Keith Attenborough