Measuring Sweeping Echoes in Rectangular Cross-Section Reverberant Fields

We investigated a new acoustical phenomenon, which we call sweeping echoes, in a two-dimensional (2D) space. Sweeping echoes in a three-dimensional (3D) space have recently been reported. We first investigated the regularity of reflected sound in a 2D regularly shaped space based on number theory. The reflected pulse sound train has almost equal intervals between pulses on the squared-time axis as in a 3D space. This regularity of the arrival time of reflected pulse sounds generates sweeping echoes whose frequencies increase linearly with time. Computer simulation of room acoustics shows good agreement with the theoretical results. We first describe our investigation of a square cross-section based on number theory. Next, we describe rectangular cross-sections with various aspect ratios investigated based on the same theory as that for the square. We also discuss our measurements of sweeping echoes in a long hallway. We propose a method for extracting sweep rates of sweeping echoes by calculating their correlation with a time stretched pulse. We analyzed the sweeping echoes for a source and receiver at the center of a rectangular cross-section. These sweeping echoes were not only perceived at the exact center position but also around the center.