Computerized room acoustics modeling has been practiced for almost 50 years up to date. These modeling techniques play an important role in room acoustic design nowadays, often including auralization, but can also help in the construction of virtual environments for such applications as computer games, cognitive research, and training. This overview describes the main principles, landmarks in the development, and state-of-the-art for techniques that are based on geometrical acoustics principles. A focus is given to their capabilities to model the different aspects of sound propagation: specular vs diffuse reflections, and diffraction.

A new impulse-response model for the edge diffraction from finite rigid or soft wedges is presented which is based on the exact Biot-Tolstoy solution. The new model is an extension of the work by Medwin et al. ͓H. Medwin et al., J. Acoust. Soc. Am. 72, 1005-1013 ͑1982͔͒, in that the concept of secondary edge sources is used. It is shown that analytical directivity functions for such edge sources can be derived and that they give the correct solution for the infinite wedge. These functions support the assumption for the first-order diffraction model suggested by Medwin et al. that the contributions to the impulse response from the two sides around the apex point are exactly identical. The analytical functions also indicate that Medwin's second-order diffraction model contains approximations which, however, might be of minor importance for most geometries. Access to analytical directivity functions makes it possible to derive explicit expressions for the first-and even second-order diffraction for certain geometries. An example of this is axisymmetric scattering from a thin circular rigid or soft disc, for which the new model gives first-order diffraction results within 0.20 dB of published reference frequency-domain results, and the second-order diffraction results also agree well with the reference results. Scattering from a rectangular plate is studied as well, and comparisons with published numerical results show that the new model gives accurate results. It is shown that the directivity functions can lead to efficient and accurate numerical implementations for first-and second-order diffraction.

Inaccuracies in computation and auralization of room impulse responses are related in part to inadequate modeling of edge diffraction, i.e., the scattering from edges of finite surfaces. A validated time-domain model (based on analytical extensions to the Biot-Tolstoy-Medwin technique) is thus employed here to compute early room impulse responses with edge diffraction. Furthermore, the computations are extended to include combinations of specular and diffracted paths in the example problem of a stage-house. These combinations constitute a significant component of the total nonspecular scattering and also help to identify edge diffraction in measured impulse responses. The computed impulse responses are then convolved with anechoic signals with a variety of time-frequency characteristics. Initial listening tests with varying orders and combinations of diffraction suggest that (1) depending on the input signal, the diffraction contributions can be clearly audible even in nonshadow zones for this conservative open geometry and (2) second-order diffraction to nonshadowed receivers can often be neglected. Finally, a practical implementation for binaural simulation is proposed, based on the singular behavior of edge diffraction along the least-time path for a given source-edge-receiver orientation. This study thus provides a first major step toward computing edge diffraction for more accurate room acoustics auralization.

No abstract

Some linear time-varying (LTV) components used to control feedback in sound systems were tested experimentally in real-time simulators and rooms with and without external reverberation. Gain before instability (GBI) was measured in single channels employing frequency shifting (FS), phase modulation (PM), and delay modulation (DM) implemented on a digital signal processor. FS performed according to the established theory. For PM GBI increased almost monotonically with modulation index β, except for cases with large loop gain irregularities which displayed a reduced GBI for values of β that corresponded to low carrier suppression. Also, GBI was practically independent of the modulation frequency fm already from 0.5 Hz even when this was much lower than the correlation distance of the loop gain transfer function. Rooms with different reverberation times gave different initial (time-invariant) GBI values but these differences decreased by the use of modulation. The GBI increase was larger for cases with external reverberation than for cases without due to increased loop gain irregularity, and the GBI results depended on fm. Since the possible GBI increase is determined by the initial GBI, LTV system performance should be measured in terms of GBI and not GBI increase alone. Robustness increased by equalizing the loop gain before employing LTV components. DM gave little protection for low frequencies but was efficient at high frequencies.

No abstract

This article presents the comparison analysis and results of an experiment designed with two presentation modes: real environments and stereoscopic images. The aim of this article is of a methodological nature, with a main objective of analyzing the usability of stereoscopic image presentation as a research tool to evaluate the daylight impact on the perceived architectural quality of small rooms. Twenty-six participants evaluated 12 different stimuli, divided in equal parts between real rooms and stereoscopic images. The stimuli were two similar rooms of different achromatic-colored surfaces (white and black) with three different daylight openings in each room. The participants assessed nine architectural quality attributes on a semantic differential scale. A pragmatic statistical approach (Bland-Altman Approach) for assessing agreement between two methods was used. Results suggest that stereoscopic image presentation is an accurate method to be used when evaluating all nine attributes in the white room and nearly all attributes in the black room.

No abstract