Interactive auralization based on hybrid simulation methods and plane wave expansion

Abstract

The reconstruction and reproduction of sound fields have been extensively researched in the last decades leading to an intuitive approach to estimate and evaluate the acoustic properties of enclosures. Applications of auralization can be found in acoustic design, subjective tests, virtual reality and entertainment, among others. Different methodologies have been established to generate auralizations for room acoustics purposes, the most common of them, the use of geometrical acoustics and methods based on the numerical solution of the wave equation to synthesize the room impulse responses. The assumptions and limitations of each approach are well known, which in turn, restrict their application to specific frequency bands. If the aim is to reconstruct accurately the sound field in an extended range of frequencies, a combination of these methodologies has to be performed. Furthermore, recent advances in computational power have enabled the possibility to generate interactive atmospheres where the user is able to interact with the environment. This feature, although it expands the applications of the auralization technique, is nowadays mainly based on geometrical acoustics or interpolation methods.

The present research addresses the generation of interactive broadband auralizations of enclosures using a combination of the finite element method and geometrical acoustics. For this, modelling parameters for both simulation methods are discussed making emphasis on the assumptions made in each case. Then, the predicted room impulse responses are represented by means of a plane wave expansion, which in turn, enables interactive features such as translation and rotation of the acoustic fields. An analytical expression is derived for the translation in the plane wave domain. Furthermore, the transformation of the plane wave representation in terms of spherical harmonics is also explored allowing the acoustic fields to be rotated. The effects of assuming a plane wave propagation within small enclosures and the consequences of using a finite number of plane waves to synthesize the sound fields are discussed.

Finally, an implementation of an interactive auralization system is considered for different reference cases. This methodology enables reconstruction of the aural impression of enclosures in real-time with higher accuracy at low frequencies compared to only geometrical acoustics techniques. The plane wave expansion provides a convenient sound field representation in which the listener can interact with the acoustics of the enclosure. Furthermore, the sound reconstruction can be performed by implementing several sound reproduction techniques extending the versatility of the proposed approach.

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Identifiers

ORCID for Filippo Fazi: orcid.org/0000-0003-4129-1433

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