Advanced Controls and Displays @ NASA Ames

Data on auditory thresholds for acoustic reflections were obtained from 29 subjects as a function of both spatial position and time delay in a simulated 5.1 surround sound listening environment. Absolute thresholds (perception of any type of change) were measured at the 70.7% level using a one up-two down staircase algorithm, for both anechoic and reverberant speech stimuli conditions, from 18 subjects. Additional data were gathered from 11 subjects for tone burst stimuli. Reflection threshold data are useful in the context of building acoustics, since path length attenuation and absorption can make potential reflections inaudible. Audibility of reflections is desirable for 3-D sound headphone simulations that require sound source externalization. The information is also useful for determining engineering parameters for the real-time simulation of virtual acoustic environments, such as headmounted displays that include head tracking. For all types of stimuli, results indicate that a single early reflection should be inaudible when less than 21 dB below the direct sound at 3 ms, and less than 30 dB at 15- 30 ms.