A new method for the calculation of room acoustical impulse responses is described, which is based on two well-known computer algorithms, the ray-tracing and the image-source models. With the new method, the procedure of sieving the ‘‘visible’’ image sources out of the enormous quantity of possible sources is carried out by examination of the histories of sound particles. From the obtained list of visible image sources, the impulse response of the enclosure is easily constructed. The new method combines the advantages of the ray-tracing process, namely, the relatively slow increase of computation time with the length of the impulse response, with the accuracy inherent to the image-source model, which is even sufficient to calculate the Fourier transform, i.e., the steady-state transmission function of the room, or to convolve the impulse response with sound signals.

Using a novel variant of dichotic selective listening, we examined the control of auditory selective attention. In our task, subjects had to respond selectively to one of two simultaneously presented auditory stimuli (number words), always spoken by a female and a male speaker, by performing a numerical size categorization. The gender of the task-relevant speaker could change, as indicated by a visual cue prior to auditory stimulus onset. Three experiments show clear performance costs with instructed attention switches. Experiment 2 varied the cuing interval to examine advance preparation for an attention switch. Experiment 3 additionally isolated auditory switch costs from visual cue priming by using two cues for each gender, so that gender repetition could be indicated by a changed cue. Experiment 2 showed that switch costs decreased with prolonged cuing intervals, but Experiment 3 revealed that preparation did not affect auditory switch costs but only visual cue priming. Moreover, incongruent numerical categories in competing auditory stimuli produced interference and substantially increased error rates, suggesting continued processing of task-relevant information that often leads to responding to the incorrect auditory source. Together, the data show clear limitations in advance preparation of auditory attention switches and suggest a considerable degree of inertia in intentional control of auditory selection criteria.

Noise abatement in office environments often focuses on the reduction of background speech intelligibility and noise level, as attainable with frequency-specific insulation. However, only limited empirical evidence exists regarding the effects of reducing speech intelligibility on cognitive performance and subjectively perceived disturbance. Three experiments tested the impact of low background speech (35 dB(A)) of both good and poor intelligibility, in comparison to silence and highly intelligible speech not lowered in level (55 dB(A)). The disturbance impact of the latter speech condition on verbal short-term memory (n=20) and mental arithmetic (n=24) was significantly reduced during soft and poorly intelligible speech, but not during soft and highly intelligible speech. No effect of background speech on verbal-logical reasoning performance (n=28) was found. Subjective disturbance ratings, however, were consistent over all three experiments with, for example, soft and poorly intelligible speech rated as the least disturbing speech condition but still disturbing in comparison to silence. It is concluded, therefore, that a combination of objective performance tests and subjective ratings is desirable for the comprehensive evaluation of acoustic office environments and their alterations.

Geometrical acoustics are used as a standard model for room acoustic design and consulting. Research on room acoustic simulation focuses on a more accurate modeling of propagation effects such as diffraction and other wave effects in rooms, and on scattering. Much progress was made in this field so that wave models also (for example, the boundary element method and the finite differences in time domain) can now be used for higher frequencies. The concepts and implementations of room simulation methods are briefly reviewed. After all, simulations in architectural acoustics are indeed powerful tools, but their reliability depends on the skills of the operator who has to create an adequate polygon model and has to choose the correct input data of boundary conditions such as absorption and scattering. Very little is known about the uncertainty of this input data. With the theory of error propagation of uncertainties it can be shown that prediction of reverberation times with accuracy better than the just noticeable difference requires input data in a quality which is not available from reverberation room measurements.

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A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, “real-world” spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large extent can be traced back to the simplified use of random incidence absorption and scattering coefficients and shortcomings in the simulation of early reflections due to the missing or insufficient modeling of diffraction.

A real-time audio rendering system is introduced which combines a full room-specific simulation, dynamic crosstalk cancellation, and multitrack binaural synthesis for virtual acoustical imaging. The system is applicable for any room shape (normal, long, flat, coupled), independent of the a priori assumption of a diffuse sound field. This provides the possibility of simulating indoor or outdoor spatially distributed, freely movable sources and a moving listener in virtual environments. In addition to that, near-tohead sources can be simulated by using measured near-field HRTFs. The reproduction component consists of a headphone-free reproduction by dynamic crosstalk cancellation. The focus of the project is mainly on the integration and interaction of all involved subsystems. It is demonstrated that the system is capable of real-time room simulation and reproduction and, thus, can be used as a reliable platform for further research on VR applications.