The Simulated Open Field Environment (SOFE), a loudspeaker setup in an anechoic chamber to render sound sources along with their simulated, spatialized reflections, has been used for more than two decades in free-field hearing research. In 2004, the concept was revised to incorporate room-acoustic simulation software that computes sound reflections in arbitrarily-shaped rooms and auralizes them via many loudspeakers—the principle of various systems used today (Hafter and Seeber, ICA 2004). For a complete redesign of the system, an anechoic chamber has been purpose-built at TUM and I will talk about its specifications. The anechoic chamber hosts the real-time SOFE (rtSOFE), a setup with 61 loudspeakers to create a spatial sound field in a 5 m x 5 m area along with 360° of visual 3D projection. New room-acoustic simulation software for interactive computation of reflections computes room impulse responses in sub-millisecond intervals and updates a convolution system capable of convolving seconds-long impulse responses for many independent loudspeaker channels with very short latency. I will present the general concept and capabilities of the new rtSOFE, give details about its implementation and first experimental results. The rtSOFE in the new anechoic chamber at TUM forms a cutting edge research facility for interactive psychoacoustic and audio-visual research in virtual acoustic space.
The most well-known acoustical parameters -including Reverberation Time, Early Decay Time, Clarity, and Lateral Fraction -are measured using data obtained from omnidirectional or figure-of-eight microphones, as specified in ISO 3382. Employing a multi-channel receiver in place of these conventional receivers can yield new spatial information about the acoustical qualities of rooms, as well as the potential for new parameters that could have greater predictive power in terms of listeners' subjective preferences. In this research, a spherical microphone array was used to measure the room impulse responses of a number of different concert and recital halls. The data was analyzed using spherical harmonic beamforming techniques, along with other direction of arrival estimation algorithms, to understand how the soundfield evolves spatially over time at different points in the room. The results were compared to geometrical acoustic simulations and used to differentiate between listener positions which exhibited similar values for the standard parameters. In addition, new parameters were examined, including soundfield homogeneity and other spatial ratios.
Binaural models have a long tradition in the instrumental analysis of acoustical spaces. Room acoustical parameters such as the Binaural Quality Index (BQI) are derived directly from the measured Binaural Room Impulse Response (BRIR) of a concert space. The BRIRs are measured using an artifical head with a fixed head position and consequently cannot show the effect of head movements, which are essential for human listening performance. Based on a novel model architecture that utilizes head movements [Braasch et al., 2011, J. Acoust. Soc. Am. 129, 2486 (A)] and psychoacoustic experiments, the effect of head movements on the perceptual judgment of room acoustical parameters will be discussed. In addition, BRIRs for different azimuth angles are calculated from higher-order ambisonic microphone data that were obtained in several concert halls in the Northeastern United States. [Clapp et al., 2011, J. Acoust. Soc. Am. 130, 2418 (A)]. It will be demonstrated how the standard acoustical parameters change with head orientation and how dynamic head-movement cues can be utilized to better predict the perceived quality of concert spaces.
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