Graduate Students: David Dick and Matthew Neal
A custom omni-directional sound source was built for accurate room impulse response measurements. This source enables a high bandwidth of omni-drectional performance, allowing for accurate calculation of room acoustic metrics over a much wider range of frequencies that is typically available with commercial sound sources. Most commercially available sources become directional at mid to high frequencies, around 1 or 2 kHz, and cannot achieve accurate signal-to-noise ratios due to lack of low frequency performance. To design as repeatable and robust a source as possible, a three-way source was created. A three-way design allows for an adequate signal-to-noise ratio at low frequencies to be achieved, while still allowing for an extended high-frequency omni-directional performance. During measurements, each source is positioned at the same location, and three separate measurements are taken, which are then processed into one final omni-directional room impulse response.
The low frequency sub-woofer consists of two 10″ sub drivers in a sealed box, which can provide adequate signal-to-noise ratio down past 20 Hz, the lower limit of the audible range of human hearing. The medium sized dodecahedron loudspeaker consists of 12 four inch drivers, operating omni-directionally up to 2 kHz. The final high-frequency dodecahedron , or the ‘Baby’ Dodec, consists of 12 half-inch tweeters, which can achieve omni-directional behavior up to the 5000 Hz third-octave band. This medium dodecahedron and the small dodecahedron are 11 inches and 3.25 inches in diameter, respectively. This source extends our usable frequency range of room acoustic measurements quite drastically, improving the repeatability of our measurement results.
- Dick, D.A., Neal, M.T., Tadros, C.S., and Vigeant, M.C. (2015). “Evaluation of a three-way omnidirectional sound source for room impulse response measurements (A).” J. Acoust. Soc. Am. 137:2394 [Best Student Paper Award]