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Effect of Microphone Number and Positioning on the Average of Frequency Responses in Cinema Calibration

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When measuring the response of a loudspeaker by averaging multiple points in a room, the results typically vary according to the number of microphones employed and their positions. This report focuses on the application to cinema calibration, where one critical goal is to achieve consistent perceived loudness and frequency response between dubbing stages, where content is produced, and the various theaters where it is exhibited. It is shown that averaging converges to a compromise response over the relevant listening area at a rate inverse to the square root of the number of microphones employed. Experimental results confirm the predicted scaling of the deviations, and quantify their magnitude in typical rooms.

JAES Volume 63 Issue 10 pp. 777-785; October 2015
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Raimonds Skuruls

Comment posted November 17, 2015 @ 17:41:51 UTC (Comment permalink)

How unfortunate that authors do not see that their „the Average” is Sound Power Frequency Response. And proposed method (a math described in p. 778 as (1) ) is used for decades for evaluation of SPFR of loudspeakers in reverberation chamber and the choice of averaging in energy (power) domain is described as free choice here.

Same time, the problem to know how measurement error depends on number of measurement points would be actual if every measurement point is costly. Authors do not see the solution offered about 10 years ago, showed in 3 AES conventions, ready for practical and commercial use and is taking 0.3 sec for one measurement point and making the problem mentioned negligible. Even Mr. Ray Dolby honored that project by his visit.

Yang and Ellison evaluated the dependence of accuracy of SPFR on number of measurement points in their work – S.J. Yang, A.J. Ellison, “Machinery noise measurement”, Clanerdon Press, Oxford, 1985, p. 58.

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