Jonathan Andrew Hargreaves

Jonathan Andrew Hargreaves
University of Salford · School of Computing, Science and Engineering

MEng, PhD

About

39
Publications
8,381
Reads
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169
Citations
Introduction
My research expertise lies on the interface between the mathematical, notably boundary integral methods, and real-world acoustical applications and measurements. I am particularly interested in Galerkin BEM with oscillatory basis functions, since I feel that this provides a means of bridging the 'mid-frequency gap' in acoustics between conventional BEM/FEM/FDTD and Geometrical Acoustics methods. I am also active in studying low frequency room acoustics effects and equalization, and am very interested in microphone and loudspeaker array techniques, being a physical manifestation of the mathematical methods above. Finally I have recently begun seriously investigating improved material characterization techniques, since I realize this is a factor limiting accuracy in room acoustic simulation.
Additional affiliations
January 2007 - September 2016
University of Salford
Position
  • Researcher
Education
April 2003 - July 2007
University of Salford
Field of study
  • Acoustics
September 1996 - June 2000
University of Oxford
Field of study
  • Engineering and Computing Science

Publications

Publications (39)
Conference Paper
Full-text available
Room modes are known to be problematic in small critical listening environments. They degrade the acoustic quality at low frequencies, producing peaks and nulls in the frequency domain and ringing in the time domain. The Finite Element Method (FEM) is currently the easiest way to predict such resonances for arbitrarily shaped rooms. This solves for...
Conference Paper
Full-text available
Raytracing is an established method for computing the late-time part of room impulse responses. But it has the drawback that only very crude Monte Carlo models of boundary scattering and diffraction are possible to include without losing its attractive computational cost scaling. This happens because higher-resolution models of these processes outp...
Poster
Full-text available
It is well known that acoustic cavities have frequencies at which certain free-response ‘modes’ of propagation respond especially strongly. In the absence of significant damping, these cause peaks of high SPL in the frequency response as well as spatial non-uniformity and temporal ringing. The spatial non-uniformity is especially problematic since...
Conference Paper
Full-text available
The Transfer Matrix Method (TMM) is an established way of computing reflections from porous absorbers in the frequency domain. Recently there has been increasing interest in time domain simulation e.g. so that auralisation can be performed. Often this models materials by fitting a digital filter to the surface impedance. Here a different approach i...
Article
No PDF available ABSTRACT The Finite Element Method (FEM) and Boundary Element Method (BEM) are established numerical simulation techniques that are widely used in Engineering, including in Acoustics. This tutorial lecture will give a brief tour of both methods, some discussion of their pros and cons—including when to choose which, or when to use a...
Conference Paper
Full-text available
In small room acoustics, the range from the first resonant frequency up to the Schroeder frequency is dominated by modal resonances and the Speaker-Boundary Interference Response (SBIR). Both are very sensitive to the positioning of sources, receivers and room geometry. The source locations determine which modes are excited , and the listener locat...
Article
No PDF available ABSTRACT Salford is one of the UK's leading centers for research and teaching in acoustics and audio. The courses are delivered by a research-active academic team at the very pinnacle of the profession, with an attractive staff to student ratio. Our taught courses are well-established and well-respected—we have offered postgraduate...
Conference Paper
Full-text available
It is well known that material absorption and scattering is dependent on incidence and observation angle. Despite this, the corresponding standardised coefficients, which are used to represent these mechanisms within computational acoustic models, aggregate all such dependency into single random-incidence parameters. This limits the accuracy that c...
Article
Full-text available
The Boundary Element Method (BEM) is a proven numerical prediction tool for computation of room acoustic transfer functions, as are required for auralization of a virtual space. In this paper, it is validated against case studies drawn from the “Ground Truth for Room Acoustical Simulation” database within a framework that includes source and receiv...
Article
Full-text available
It was found that the formulation presented in this article contains a sign error that has been carried forwards into several of the outcomes of the paper. This error originates because the Wronskian relationship on page 915 was written with incorrect sign. This error has propagated forward through the paper, in particular affecting the results in...
Article
Full-text available
In this paper, a new Boundary Integral Equation (BIE) is proposed for solution of the scalar Helmholtz equation. Applications include acoustic scattering problems, as occur in room acoustics and outdoor and underwater sound propagation. It draws together ideas from the study of time-harmonic and transient BIEs and spatial audio sensing and renderin...
Presentation
It is well known that acoustic sources, such as musical instruments or loudspeakers, exhibit angle dependent variation in the acoustic intensity they radiate termed their ‘directivity’. This property can be included in a numerical model by including a mesh of the source; however it is often more convenient to work with measured datasets, which are...
Presentation
Auralization of a space requires measured or simulated data covering the full audible frequency spectrum. For numerical simulation, this is extremely challenging, since that bandwidth covers many octaves in which the wavelength changes from being large with respect to features of the space to being comparatively much smaller. Hence, the most effici...
Article
This work continues a series of studies on the link between the microstructure of multiscale materials and their acoustical properties [1]-[3]. Granular activated carbons are excellent low frequency sound absorbers. Two factors contribute to this. (i) They have three scales of heterogeneities: millimetric grains and micrometric and nanometric inner...
Article
Full-text available
We propose a method for efficient evaluation of surface integrals arising in boundary element methods for three-dimensional Helmholtz problems (with real positive wavenumber k), modelling wave scattering and/or radiation in homogeneous media. To reduce the number of degrees of freedom required when k is large, a common approach is to include in the...
Conference Paper
Full-text available
Acoustic energy density and acoustic intensity are quantities which are well established and widely applied. When these are applied to pressure and particle-velocity fields which are the linear superposition of more than one wave they naturally separate into multiple terms; some of these involve only one of the constituent waves and others involve...
Conference Paper
Full-text available
The Boundary Element Method (BEM) is a powerful method for simulating scattering of acoustic waves which has many advantages, particularly when the problem concerns an object in an unbounded medium. Its applications are however limited in practice because standard schemes have a computational cost which grows extremely quickly as size and frequency...
Article
Full-text available
Most spatial audio reproduction systems have the constraint that all loudspeakers must be equidistant from the listener, a property which is difficult to achieve in real rooms. In traditional Ambisonics this arises because the spherical harmonic functions, which are used to encode the spatial sound-field, are orthonormal over a sphere and because l...
Conference Paper
Full-text available
Prediction models are at the heart of modern acoustic engineering and are used in a diverse range of applications from refining the acoustic design of classrooms and concert halls to predicting how noise exposure varies through an urban environment. They also allow Auralisation to be performed for buildings and spaces before they are built or long...
Article
Full-text available
This paper describes a numerical method for simulating far-field scattering from small regions of inhomogeneous temperature fluctuations. Such scattering is of interest since it is the mechanism by which acoustic wind velocity profiling devices (Doppler SODAR) receive backscatter. The method may therefore be used to better understand the scattering...
Article
Full-text available
Prediction models are at the heart of modern acoustic engineering. Current commercial room acoustic simulation software almost exclusively approximates the propagation of sound geometrically as rays or beams. These assumptions yield efficient algorithms, but the maximum accuracy they can achieve is limited by how well the geometric assumption repre...
Article
Full-text available
Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining the resonant frequencies of Helmholtz resonators with...
Conference Paper
Full-text available
This paper presents an algorithm which couples the time domain Boundary Element Method (BEM) with a digital filter surface model. This aims to achieve the same extent of applicability and accuracy for transient sounds as is available for time-harmonic excitation with the established approach of substituting locally-reacting surface impedance direct...
Conference Paper
Full-text available
In recent years various sound reproduction systems have been proposed which attempt to use multiple transducers to tame the modal behaviour often prominent in rooms at low frequencies. Of particular interest is the Controlled Acoustic Bass System (CABS) proposed by Celestinos and Nielsen, and it was decided to install a permanent system in our ITC...
Article
Full-text available
Is noise from large wind turbines more annoying than noise from small wind turbines? The listening test results of this study find no evidence for a significant difference in annoyance between small and large wind turbines as long as total noise levels and tonal characteristics are taken into account in the assessment.
Conference Paper
Full-text available
The Boundary Element Method (BEM) can be used to predict the scattering of sound in rooms. It reduces the problem of modelling the volume of air to one involving only the surfaces; hence the number of unknowns scales more favourably with problem size and frequency than it does for volumetric methods such as FEM and FDTD. The time domain BEM predict...
Article
Full-text available
Room modes are well known to cause unwanted effects in the correct reproduction of low frequencies in critical listening rooms. Methods to control these problems range from simple loudspeaker/listener positioning to quite complex digital signal processing. Nonetheless, the subjective importance and impact of these methods has rarely been quantified...
Article
Full-text available
Boundary Element Methods (BEMs) may be used to predict the scattering of sound by obstacles, which has accelerated the prototyping of new room acoustic treatments such as diffusers. Unlike the more popular frequency domain method, the time domain BEM is usually solved in an iterative manner which means it can exhibit instability, a crucial impedime...
Article
Full-text available
Room acoustic diffusers can be used to treat critical listening environments to improve sound quality. One popular class is Schroeder diffusers, which comprise wells of varying depth separated by thin fins. This paper concerns a new approach to enable the modeling of these complex surfaces in the time domain. Mostly, diffuser scattering is predicte...
Article
Full-text available
The best way of representing compliant surfaces in time domain prediction models, such as the transient Boundary Element Method (BEM), is currently unresolved. This is not true of frequency-domain, time-invariant models, where the common practice is to represent the characteristics of a material by its surface impedance. A BEM may be used to predic...
Article
Full-text available
Boundary element methods (BEM) may be used to model scattering from hard rigid surfaces such as diffusers. They have the advantage over volumetric methods that only the surface need be meshed and the surface velocity potential found. Unlike the more widely used single frequency methodology, transient BEM discretizes integral equations to produce an...
Article
Full-text available
Being able to accurately predict acoustics is important to built environment design. Currently prediction models that can deal with whole rooms are based on geometric or statistical methods, and are only partially successful. Wave based models should be more accurate, but computational time and storage limitations restrict their usefulness. One cla...

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