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A technique for the in situ phase calibration of in-duct microphone arrays

A technique for the in situ phase calibration of in-duct microphone arrays
A technique for the in situ phase calibration of in-duct microphone arrays
In aeroengine noise experiments in-duct microphone arrays are often used to make detailed measurements of the sound field transmitted along the duct. The individual microphones in the array must be calibrated with respect to magnitude, and often more critically with respect to phase. Calibration is difficult to perform in situ due to the presence of the duct. This paper presents a technique to allow in situ phase calibration of axial microphone arrays. It relies on the observation that the measured cross-spectral pressure matrix at the array has a Hermitian Töplitz form in the case where the propagating duct modes are mutually incoherent. Using this property a system of equations can be written which, when solved, allows the phase calibration factors to be obtained. The technique is verified experimentally using a no-flow laboratory rig by comparing the phase calibration factors obtained with those measured in free-field conditions. The accuracy of the phase calibration factors obtained by the technique is limited by the degree of deviation of the measured cross-spectral matrix from Töplitz behaviour. In the experimental results shown this is less than 15° at duct frequencies below ka=25. The technique is a robust and rapid method for calibrating in-duct axial microphone arrays.
0022-460X
4634-4642
Lowis, C.R.
051751e2-c67f-4cd5-bc27-2237f7b0a33e
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Sijtsma, P.
0655cb93-eda5-4a82-9ad4-9e9e550b3d49
Lowis, C.R.
051751e2-c67f-4cd5-bc27-2237f7b0a33e
Joseph, P.F.
9c30491e-8464-4c9a-8723-2abc62bdf75d
Sijtsma, P.
0655cb93-eda5-4a82-9ad4-9e9e550b3d49

Lowis, C.R., Joseph, P.F. and Sijtsma, P. (2010) A technique for the in situ phase calibration of in-duct microphone arrays. Journal of Sound and Vibration, 329 (22), 4634-4642. (doi:10.1016/j.jsv.2010.04.035).

Record type: Article

Abstract

In aeroengine noise experiments in-duct microphone arrays are often used to make detailed measurements of the sound field transmitted along the duct. The individual microphones in the array must be calibrated with respect to magnitude, and often more critically with respect to phase. Calibration is difficult to perform in situ due to the presence of the duct. This paper presents a technique to allow in situ phase calibration of axial microphone arrays. It relies on the observation that the measured cross-spectral pressure matrix at the array has a Hermitian Töplitz form in the case where the propagating duct modes are mutually incoherent. Using this property a system of equations can be written which, when solved, allows the phase calibration factors to be obtained. The technique is verified experimentally using a no-flow laboratory rig by comparing the phase calibration factors obtained with those measured in free-field conditions. The accuracy of the phase calibration factors obtained by the technique is limited by the degree of deviation of the measured cross-spectral matrix from Töplitz behaviour. In the experimental results shown this is less than 15° at duct frequencies below ka=25. The technique is a robust and rapid method for calibrating in-duct axial microphone arrays.

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Published date: 25 October 2010

Identifiers

Local EPrints ID: 172733
URI: http://eprints.soton.ac.uk/id/eprint/172733
ISSN: 0022-460X
PURE UUID: 11ef818e-4662-429e-966d-97cec63f58fa

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Date deposited: 28 Jan 2011 11:38
Last modified: 14 Mar 2024 02:29

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Contributors

Author: C.R. Lowis
Author: P.F. Joseph
Author: P. Sijtsma

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