Volume 120, Issue 3, September 2006
Index of content:
- ARCHITECTURAL ACOUSTICS 
Analysis of Sabine and Eyring equations and their application to concert hall audience and chair absorption120(2006); http://dx.doi.org/10.1121/1.2221392View Description Hide Description
Historically, two equations have been used for predicting reverberation times, Sabine and Eyring. A precise means is presented for determining Eyring absorption coefficients when the Sabine coefficients are known, and vice versa. Thus, either formula can be used provided the absorption coefficients for the Sabine formula are allowed to exceed 1.0. The Sabine formula is not an approximation to the Eyring equation and is not a shortcoming. Given low reverberation times, the ratio of to may become greater than 2.0. It is vital that, for correct prediction of reverberation times, the absorption coefficients used in either formula must have been determined in spaces similar in size and shape, with similar locations of high absorption (audience) areas, and with similar reverberation times. For concert halls, it is found that, when the audience area (fully occupied) and midfrequency reverberation time are postulated, the hall volume is directly proportional to the audience absorption coefficient. Approximately 6% greater room volumes are needed when choosing nonrectangular versus classical-rectangular shaped halls and approximately 10% greater volumes when choosing heavily upholstered versus medium upholstered chairs. Determinations of audience sound absorption coefficients are presented, based on published acoustical and architectural data for 20 halls.
120(2006); http://dx.doi.org/10.1121/1.2221552View Description Hide Description
Multiple-driver dodecahedron loudspeakers are commonly used in room acousticsmeasurements as omnidirectional sources of sound. Yet they and other regular polyhedron loudspeakers become “multidirectional” above their omnidirectional cutoff frequencies (often near ). Because these cutoff frequencies normally fall within common measurement bandwidths, one might question whether anything is really extraordinary about the dodecahedron loudspeaker or whether another regular polyhedron geometry would actually produce better average omnidirectionality over these bandwidths. This paper explores these questions through measured data, analysis, and comparison of frequency-dependent directivities of several regular polyhedron loudspeaker prototypes. It provides insights into their radiation properties and introduces an alternative method of quantifying omnidirectionality: the area-weighted spatial standard deviation of radiated levels over a free-field measurement sphere. It compares this method to the ISO 3382:1997(E) standard method, revealing certain discrepancies between the two approaches. A dodecahedron loudspeaker is shown to produce a relatively high cutoff frequency and reasonable radiation uniformity over measurement bandwidths. However, it does not necessarily excel as a better omnidirectional source than other regular polyhedron loudspeakers. A tetrahedron loudspeaker with an equal midradius provides the best average radiation uniformity over a bandwidth, even though it exhibits the lowest cutoff frequency.