Enhanced Acoustic Modelling for Auralisation using Hybrid Boundary Integral Methods

This project will develop a new acoustic modelling method, ideally suited for simulation of rooms and city squares, which will outperform existing methods either in its accuracy or computational efficiency. Developing such an algorithm is a particular concern for practitioners who use auralisation as a consultation tool in acoustic design of built spaces. In this process the data from the simulation model is rendered as sound by a loudspeaker system allowing a client or stakeholder, who is unlikely to be an expert in acoustics, to form a judgement on whether the acoustic design fits their needs. This process is of course only valid if the acoustic model delivers accurate prediction of how sound behaves in the space, and current commercial software does not always succeed in this task because the high-frequency geometric propagation assumption on which it is based breaks down at low frequencies and in spaces where diffraction effects are significant. Although alternate numerical methods exist they are typically limited to modelling only low frequencies since their computational cost becomes impractical as frequency or time-resolution is increased. In response to these shortcomings, this project will develop a new hybrid method which combines the best features of geometric methods and fully numerical boundary element method (BEM) solvers to provide a scheme that inherits desirable characteristics from both approaches; i.e. fully error controllable schemes, more accurate than geometric methods for low to mid range frequencies, but with reduced computational cost at higher frequencies compared to standard BEM, all achieved within a single unified framework. Such a model would potentially include all wave terms, geometric and diffracted, but lower energy reflections would only be included where necessary to achieve a given accuracy criterion (e.g. an SPL threshold or a function of the ear's perceptible difference limen) hence computational efficiency would be maximised.

Introducing an element of interactivity to the auralisation process, where a user would be able to explore the space and/or make dynamic changes to the sources and building geometry or materials, would be desirable from a consultation-productivity perspective but place extremely high demands on the acoustic model. Not only must the model dynamically update to reflect the modifications made by the user, but the requirement for accuracy is even more pressing since any feature the client chooses to introduce must be accurately rendered, even if it has a strong acoustic effect (e.g. concave focussing surfaces, room resonances, unusual echo patterns), and there will be little or no opportunity for an expert to check that the sound is realistic. The new algorithm we propose will address these needs since, as well as having improved accuracy, it also has the desirable characteristic that only a small easily identified subset of the acoustic interaction data needs to be re-computed when a change in building geometry or source location occurs; incorporating support for modelling time variant and interactive scenarios would hence be relatively straightforward. Towards this goal the project will also develop a new auralisation orientated audio platform which will represent acoustic interactions by a network of digital filters and output sound direct to audio hardware, and the simulation algorithm will be geared towards outputting reduced acoustic models in this format. Pilot studies will investigate how interactivity might be supported, as dynamic modifications of scenario objects and corresponding filter network elements, and how standard lumped parameter sound insulation and stochastic reverberation models may be incorporated. The project will conclude with a work package dedicated to modelling some real-world scenarios which would cause difficulties for current acoustic modelling software.

This project has been specifically designed to address a knowledge gap in acoustic simulation. In particular we believe that this is limiting the impact of auralisation technology as a consultation tool to aid design of urban environments, so the project contains features specifically targeted at this application. Such tools are typically used to support improvements in acoustics to grant better quality of life (e.g. less intrusive background noise, more intelligible speech) hence this project also has ambition of significant societal and economic impact.

Using auralisation technology for planning consultation improves information delivery and informs choice, engaging stakeholders and enabling them to understand and evaluate changes planned in their communities, thereby minimising decisions which would have negative effects. This research therefore aligns directly with the Sustainable Society sub-theme of the Digital Economy theme, and will benefit both the general public and the public and commercial sectors, who will get a tool which can test public opinion to acoustic concerns in a direct way. In the short term acoustic consultancy firms will benefit by having an improved tool both for engaging, informing and selling concepts to clients and for providing accurate predictions so that designs may be refined in advance. This latter point also benefits the clients and end users of the spaces since it allows superior acoustic specifications, or similar specifications at a cheaper cost or with more sustainable methods and materials, and reduces the chances of poor designs being realised. These new technologies will almost certainly first be applied to high value projects where acoustics or noise are of particular concern, hence the immediate groups to gain these benefits will likely be users and patrons of arts and music facilities or stakeholders in planning situations where noise may be a problem (e.g. the use of Arup's SoundLab to gather evidence on noise attitudes regarding the planned High Speed 2 rail link). As the use of auralisation technology becomes more commonplace these benefits will spread to other areas, for example: schools (where poor acoustics has been shown to harm learning); hospitals (creating a more tranquil environment for recovery); urban cityscapes and transport interchanges; and homes and dwellings. In the longer term it has the potential to be a disruptive technology in urban and rural planning and is expected to drive increased consideration of "soundscape" concepts in these applications.

Much of the impact above is also education of non-specialists to consider and better understand their acoustic environment. As such the project outcomes will also offer new opportunities in public engagement into the understanding of science, acoustics, and human perception of sound.

With the increasing use of spatial audio in gaming, tele-collaboration and broadcast there is a demand for tools which assist sound designers in the realistic placement of sources within a 3D virtual environment. This project will directly inform such tools and the involvement of the BBC through the Audio Research Partnership at Salford will help steer the project towards impactful outcomes in this area and permit further work to re-package the new algorithms for use by broadcast professionals. Beneficiaries will be the UK broadcast and gaming industries and the end users of their products.

Although the project is focused on acoustics, the wave propagation model and computational framework developed in this project will also apply to other wave phenomena, notably electromagnetics. Dissemination into this academic field will influence the telecoms and defence industries in particular, which in turn have wide societal/economic impact through improved communications and national security.