An experimental evaluation of regular polyhedron loudspeakers as omnidirectional sources of sound

Abstract

Multiple-driver dodecahedron loudspeakers are commonly used in room acoustics measurements as omnidirectional sources of sound. Yet they and other regular polyhedron loudspeakers become "multidirectional" above their omnidirectional cutoff frequencies ͑often near 1 kHz͒. 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 3382:1997͑E͒ 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 4 kHz bandwidth, even though it exhibits the lowest cutoff frequency.

Investigation of Auditory Objects Caused by Directional Sound Sources in Rooms

“…[4][5][6][7]. More recently, spherical arrays with independently controlled transducers were used as sources featuring adjustable directivity [8][9][10][11][12].…”

Laser-induced acoustic point source for accurate impulse response measurements within the audible bandwidth

“…In contrast, with the spherical loudspeaker (upper box, solid line), the floor reflection in the deconvolved response is hard to detect due to interference with reflections produced by the different driver elements in the array. 1 Furthermore the amplitude of the ceiling reflection is reduced due to ceiling absorption when compared to the floor reflection amplitude in the LIB room response. The reflection produced by the loudspeaker above the LIB position is also noticeable (ceiling LS in Fig.…”

“…For instance, spherical loudspeakers are typically assumed to be point-like, although they are directional at high frequencies and have considerable size. 1,2 Electrical sparks are small, but they are not repeatable and feature directional radiation patterns. 3 A potential candidate for an omnidirectional and repeatable acoustic point source with sufficient sound pressure is the laser-induced air breakdown, LIB.…”

Room acoustic modelling of textile materials hung freely in space: from the reverberation chamber to ancient churches

“…A tetrahedron sound source with three small loudspeakers (one on each side except in the base which lay on the floor) was used as an approximation of an omnidirectional source. In fact, as demonstrated by Leishman, Rollins, and Smith (2006), despite this regular polyhedron having a low cutoff frequency, which according to the physical dimensions is 166 Hz (full scale), it shows the most uniform radiation above that limit. Measurements along the horizontal plane in free field conditions showed that small variations (within ±1.5 dB) in the level appeared at 250 and 500 Hz octaves (full scale), while at 125 Hz and 1 kHz, variations were greater (within ±3.5 dB).…”