Towards a future primary method for microphone calibration: Optical measurement of acoustic velocity in low seeding conditions

Koukoulas, Triantafillos; Theobald, Pete D.; Schlicke, Ted; Barham, Richard

doi:10.1016/j.optlaseng.2008.06.005

Cited by 12 publications

(8 citation statements)

References 10 publications

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“…In previous standing wave tube experiments, 11 the level of received photons was, on average (depending on the level and kind of tracers), in the vicinity of 5 Â 10 6 counts per second (5 Mcps). Also, the collecting optics were positioned quite close to the standing wave tube in order to reduce optical losses due to the inverse square law.…”

Section: Discussionmentioning

confidence: 96%

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Gated photon correlation spectroscopy for acoustical particle velocity measurements in free-field conditions

Koukoulas

Piper

Theobald

2013

The Journal of the Acoustical Society of America

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The measurement of acoustic pressure at a point in space using optical methods has been the subject of extensive research in airborne acoustics over the last four decades. The main driver is to reliably establish the acoustic pascal, thus allowing the calibration of microphones with standard and non-standard dimensions to be realized in an absolute and direct manner. However, the research work so far has mostly been limited to standing wave tubes. This Letter reports on the development of an optical system capable of measuring acoustic particle velocities in free-field conditions; agreement within less than 0.6 dB was obtained with standard microphone measurements during these initial experiments.

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Section: Discussionmentioning

confidence: 96%

“…PIV 8,9 illuminates a two-dimensional plane and by using a high speed camera, the motion of airborne particles are captured in sequence so that their velocity can be deduced. PCS 10,11 uses two laser beams, both a) Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

Gated photon correlation spectroscopy for acoustical particle velocity measurements in free-field conditions

Koukoulas

Piper

Theobald

2013

The Journal of the Acoustical Society of America

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“…Other imaging modalities have also been used to visualize acoustic waves and sound fields. In the National Physical Laboratory review of acousto-optical sound field visualization [15], schlieren imaging is mostly overlooked in favor of coherent light techniques such as laser doppler anemometry (LDA) [16,17,18,19], laser doppler velocimetry (LDV) [20,21], and photon correlation spectroscopy (PCS) [22,23]. LDA and LDV have proved especially promising, with both techniques having been applied to the calibration of pressure microphones.…”

Section: Other Imaging Modalities For Acoustic Wave Visualization Andmentioning

confidence: 99%

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Harvey

Smithson

Siviour

2018

Optics and Lasers in Engineering

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We present a high-speed single-mirror double-pass coincident schlieren system and corresponding algorithms for the visualization of acoustic waves and recovery of their associated audio signals. Schlieren systems are extensively used to visualize strong shockwaves, such as those from supersonic motion or explosions. Recently, they have also been used to visualize lower amplitude non-linear acoustic phenomena, such as the weak shockwaves arising from impact events including hand claps, belt snaps, and towel cracks. Time-invariant sounds produced by loudspeakers have also been imaged, in one case leading to frequency analysis, although these have been limited to high-frequency signals at very high sound pressure levels. The research presented here shifts the focus from sound-field visualization towards audio signal recovery. A comprehensive exploration of several parameters for imaging sound sources, including frequency, wave form, and amplitude, is presented. In addition, we address for the first time the recovery of phase information, which would be essential for speech intelligibility, and the more general case of non-contact sound field reconstruction. Through image and signal processing, it is shown that audio signals can be recovered from high-speed schlieren video whose acoustic waves appear to be below the limit of visibility, and were previously deemed unrecoverable by virtue of their frequency and sound pressure level. This includes sounds at frequencies and loudnesses relevant for human hearing, producing the first 'schlieren microphone'.

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“…In the simplied environment of standing wave tubes laser Doppler anemometry (LDA) [4,5] and velocimetry (LDV) [6], particle image velocimetry (PIV) [5] and PCS [7,8] have all been applied to measure acoustic particle velocity with varying degrees of success. It has been shown that PCS can be applied with minimal seeding [9] meaning that the acoustic properties of the measurement medium are not changed and that it is possible to adapt this technique for use in a free eld (anechoic) chamber [10,11].…”

Section: Photon Correlation Spectroscopy For Measuring Acoustic Partimentioning

confidence: 99%

Sensing Sound Pressure in an Anechoic Chamber Using Backscattered Laser Light

Piper

Koukoulas

2015

Acta Phys. Pol. A

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Current standards for the measurement of the SI derived unit of sound-in-air pressure, the pascal, are based upon microphone reciprocity calibration and are achieved indirectly through microphone sensitivity. These methods require microphones of specic geometry and performance characteristics, eectively artefacts, and are traceable through standards for electrical and dimensional units. Measurement of acousto-optic interactions can provide a direct approach to measuring sound pressure. One acousto-optic interaction is the periodic scattering of photons caused by particles moving in a sinusoidal manner due to propagating sound across interference fringes formed at the intersection of two coherent laser beams. The sequence of these scattered photons, which is collected using telescopic optics and generated by a single photon counting device, can be autocorrelated to yield the periodicity of the photon events. Through mathematical analysis of the autocorrelation function it has been shown that acoustic particle velocity is inversely proportional to the time of the rst minimum. This has eectively been shown for measurements in acoustic standing wave tubes and has been developed into a method which can be applied in an anechoic chamber. This paper describes the design and implementation of such a system which allows for a comparison of sound pressure measurements using optical and microphone based techniques.

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Towards a future primary method for microphone calibration: Optical measurement of acoustic velocity in low seeding conditions

Cited by 12 publications

References 10 publications

Gated photon correlation spectroscopy for acoustical particle velocity measurements in free-field conditions

Gated photon correlation spectroscopy for acoustical particle velocity measurements in free-field conditions

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Sensing Sound Pressure in an Anechoic Chamber Using Backscattered Laser Light

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