2pAAa1. Variance and invariants in room acoustics: A random walk through reverberant fields.

Session: Tuesday Afternoon, May 14

Time: 3:50

Author: David Lubman
Location: David Lubman & Assoc., 14301 Middletown Ln., Westminster, CA 92683


The understanding of room reverberation has advanced notably in recent decades owing to the merging of statistical communication theory with room acoustics. New invariants expressed as simple and robust statistical laws govern steady-state variation of reverberant sound pressure over time, frequency, and space. Much of statistical room acoustics (SRA) theory can be developed by applying random walk theory to classical room acoustics. Reverberation time (T[inf 60]) controls the variance of reverberant pressure with frequency at each room location. The ``reverberation time-bandwidth'' (BT[inf 60]) product controls spatial variance. SRA contradicts the conventional wisdom that ``hot spots'' and ``dead spots'' indicate poor diffusion, implying instead that spatial variations are inevitable even in a perfectly diffuse field. SRA facilitated new measurement standards for estimating pure tone sound power in reverberation rooms by providing objective guidance for optimization of spatial averaging and estimation of error bounds. SRA points to fundamental uncertainties in low-frequency room behavior and connects room acoustics to the kinetic theory of gases. Using statistical theory to solve deterministic problems of room reverberation may seem paradoxical if not heretical. Yet SRA continues to provide unexpected insights and discoveries impacting room acoustic thinking and practice. This paper recounts developments from a research participant's perspective.

from ASA 131st Meeting, Indianapolis, May 1996