Enhanced Acoustic Modelling for Auralisation using Hybrid Boundary Integral Methods

该项目将开发一种新的声学建模方法，非常适合于房间和城市广场的模拟，无论是在精度还是计算效率上都将优于现有的方法。对于将可听化作为建筑空间声学设计咨询工具的从业者来说，开发这样的算法是一个特别令人担忧的问题。在这一过程中，来自模拟模型的数据由扬声器系统呈现为声音，允许不太可能是声学专家的客户或利益相关者对声学设计是否适合他们的需求做出判断。当然，只有当声学模型准确预测声音在空间中的行为时，这个过程才是有效的，而当前的商业软件在这项任务中并不总是成功的，因为它所基于的高频几何传播假设在低频和衍射效应显著的空间中失效。尽管存在替代的数值方法，但它们通常仅限于对低频进行建模，因为随着频率或时间分辨率的提高，它们的计算成本变得不切实际。针对这些缺点，本项目将开发一种新的混合方法，它结合了几何方法和完全数值边界元方法(BEM)求解器的最佳特性，以提供一种继承了这两种方法的理想特性的方案；即完全误差可控的格式，对于中低频率比几何方法更准确，但在较高频率时与标准边界元方法相比计算成本更低，所有这些都在一个统一的框架内实现。这样的模型可能包括所有几何和绕射的波项，但较低的能量反射仅在达到给定精度标准(例如SPL阈值或耳朵的可感知差异阈值的函数)所必需的情况下才被包括在内，因此计算效率将被最大化。在可听化过程中引入交互元素，其中用户将能够探索空间和/或对源和建筑几何或材料进行动态改变，从咨询生产率的角度来看，这是可取的，但对声学模型提出了极高的要求。模型不仅必须动态更新以反映用户所做的修改，而且对精度的要求甚至更加迫切，因为客户选择引入的任何特征都必须被准确地呈现，即使它具有很强的声学效果(例如，凹面对焦表面、房间共鸣、不寻常的回声图案)，并且专家将很少或根本没有机会检查声音是否真实。我们提出的新算法将满足这些需求，因为它除了具有更高的精度外，还具有一个理想的特征，即当建筑物几何形状或震源位置发生变化时，只需重新计算一小部分易于识别的声学相互作用数据；因此，纳入对时变和交互场景建模的支持将相对简单。为了实现这一目标，该项目还将开发一种新的面向可听化的音频平台，该平台将通过数字滤波器网络来表示声学交互，并将声音直接输出到音频硬件，模拟算法将用于以这种格式输出简化的声学模型。试点研究将调查如何支持互动性，如场景对象和相应过滤网络元素的动态修改，以及如何结合标准的集中参数隔音和随机混响模型。该项目将以一个工作包结束，该工作包致力于对一些真实世界的场景进行建模，这将给目前的声学建模软件带来困难。

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.