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An Introduction to Virtual Phased Arrays for Beamforming Applications

Comesaña D. F., Holland K. R., Escribano D. G., de Bree H. E.

Archives of Acoustics

2014

Vol. 39, No. 1

81--88

Sound localization problems are usually tackled by the acquisition of data from phased microphone arrays and the application of acoustic holography or beamforming algorithms. However, the number of sensors required to achieve reliable results is often prohibitive, particularly if the frequency range of interest is wide. It is shown that the number of sensors required can be reduced dramatically providing the sound field is time stationary. The use of scanning techniques such as “Scan & Paint” allows for the gathering of data across a sound field in a fast and efficient way, using a single sensor and webcam only. It is also possible to characterize the relative phase field by including an additional static microphone during the acquisition process. This paper presents the theoretical and experimental basis of the proposed method to localise sound sources using only one fixed microphone and one moving acoustic sensor. The accuracy and resolution of the method have been proven to be comparable to large microphone arrays, thus constituting the so called “virtual phased arrays”.

Anechoic measurements of particle-velocity probes compared to pressure gradient and pressure microphones

Woszczyk W., Iwaki M., Sugimoto T., Ono K., de Bree H. E.

Archives of Acoustics

2007

Vol. 32, No. 3

643--658

The Microflown is an acoustic particle velocity sensor invented at the University of Twente in Holland in 1994 and commercialized in 1997 [1, 9]. The sensor directly measures particle velocity rather than pressure-gradient as do most unidirectional and bidirectional microphones. The sensor has several interesting operational characteristics however few measurements of the Microflown have been published until now making it difficult for a potential user to assess the merits of this transducer in comparison to high quality condenser microphones commonly used in music and speech recording. This paper offers some insight by presenting anechoic measurements of particle velocity probes compared to the measurements of pressuregradient and pressure microphones (of condenser type) made under identical acoustical conditions at varying distances from a point source having a wide frequency range. Detailed frequency response measurements show how the characteristics of these transducer types are dependent on their distance to the source, and highlight the need of transducer calibration with respect to distance. Very few microphone manufacturers publish frequency response data for more than one reference distance to the source although distance is often used to modify the applied response of the microphone. An additional goal for making these measurements is to establish the relationship between particle velocity and pressure gradient values using the same acoustical conditions. The measurements were made in the large anechoic chamber of the NHK Science and Technical Research Laboratories (STRL) in Tokyo during the April-May of 2006.