Alexander Southern

Room Impulse Response Synthesis and Validation Using a Hybrid Acoustic Model

Synthesizing the room impulse response (RIR) of an arbitrary enclosure may be performed using a number of alternative acoustic modeling methods, each with their own particular advantages and limitations. This article is concerned with obtaining a hybrid RIR derived from both wave and geometric-acoustics based methods, optimized for use across different regions of time or frequency. Consideration is given to how such RIRs can be matched across modeling domains in terms of both amplitude and boundary behavior and the approach is verified using a number of standardised case studies.

Acoustics of Epidaurus - Studies With Room Acoustics Modelling Methods

The 3D model of Epidaurus is simulated with two room acoustics modelling methods. The low frequencies up to 1000 Hz are simulated with a 3D FDTD method able to predict the wave-based phenomena such as diffraction and interference. The high frequencies are predicted with a beam tracing method. The early parts of the computed impulse responses are analyzed to explain the well-known acoustics for speech in the ancient theatres. The prediction results are compared to real measurements and visualized with various methods both in the time domain and in the frequency domain. The results suggest that when an actor was on the stage (which does not exist anymore) his direct sound was supported by several early reflections from the ground, from the stage, and from the staircases of the audience area. All this early energy is assumed to fuse well with the direct sound resulting in a strong voice being perceived at every seat in the audience.

Finite-difference time domain method source calibration for hybrid acoustics modeling

Finite-difference time domain methods are commonly used for acoustics modeling of enclosed geometries. For large spaces and high frequencies, the computational requirements become prohibitive in practical use. Thus, geometric acoustics algorithms are used in those cases. The results of these two classes of algorithm can be combined to model the full acoustic response. To allow direct mixing of the results, the source strengths should be calibrated. This paper derives calibration factors for various finite-difference time domain methods. It is shown that the modelled acoustics responses can then be easily combined to synthesise wide-band hybrid responses.

A hybrid acoustic model for room impulse response synthesis

The prediction and synthesis of room impulse responses (RIR) has wide application from computer gaming to architectural acoustics. When a level of physical accuracy is important, a single acoustic modeling technique is usually limited by its computational load. Hybrid acoustic models target different time/frequency regions of the RIR with different modeling techniques. This paper introduces a hybrid acoustic model consisting of a physical FDTD model for low-mid frequencies, beam-tracing, and the acoustic radiance transfer method in the early part and late parts at high frequencies respectively. In this work, attention is given to establishing the equivalence of the boundary characteristics in each modeling domain. Good agreement is demonstrated indicating that mixing the separate model responses leads to an energetically consistent RIR.