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

Abstract

Laser induced air breakdown is proposed as a sound source for accurate impulse response measurements. Within the audible bandwidth, the source is repeatable, broadband, and omnidirectional. The applicability of the source was evaluated by measuring the impulse response of a room. The proposed source provides a more accurate temporal and spatial representation of room reflections than conventional loudspeakers due to its omnidirectionality, negligible size and short pulse duration.

Review of Acoustic Sources Alternatives to a Dodecahedron Speaker

“…The maximum difference in energy level is less than 1 dB within the range from 0 • up to 90 • for all frequency bands. In a subsequent study by the author [138], the magnitude response of the pressure pulse measured along 0 • , 45 • and 90 • directions deviates by less than 0.5 dB at frequencies above 10 kHz, and no noticeable differences were found at frequencies less than 10 kHz. In a study by Hosoya et al [139], the point sound source was generated in an anechoic box were twelve microphones (30 • differences) were placed 80 mm from the sound source.…”

“…One of the many uses of pulsed lasers is to generate acoustic pulses in the air beside solid and liquid media [136,137] which can be used as a source for impulse response measurements within the audible bandwidth [138,139]. An acoustic point source can be generated by focusing a pulsed laser beam to rapidly heat the air at a focal point which produces a small expanding plasma ball.…”

“…Referring to research, in a study by Bolanos et al [138], the source was used for the measurement of the impulse response of a room. The accuracy of the results was assessed by comparison with impulse responses measured with a custom-made spherical loudspeaker and a directional loudspeaker.…”

Beamforming with a volumetric array of massless laser spark sources—Application in reflection tracking

“…4 These characteristics make it a potential source for virtual acoustic beamforming. The LIB is generated by focusing the beam of a pulsed laser into a sufficiently small spot to exceed the optical intensity threshold for plasma production.…”

“…8 However, the repeatability of LIB produced by a 5-8 ns and 200-1000 mJ neodymium-doped yttrium aluminum garnet (Nd:YAG) laser pulse suffices for acoustic applications. 4,7 Moreover, since most LIB applications would be off-line, averaging can be used to improve the signal-to-noise ratio (SNR).…”