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Studies in modal density – its effect at low frequencies

Wankling, Matthew and Fazenda, Bruno (2009) Studies in modal density – its effect at low frequencies. In: Proceedings of the Institute of Acoustics. 25th Reproduced Sound Conference 2009: REPRODUCED SOUND 25: The Audio Explosion, 31 . Instute of Acoustics, Brighton, UK, pp. 62-73. ISBN 978-1-61567-685-9

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The ability to objectively measure the reproduction quality of a small room at low frequencies has long been desired. Over many years, there have been attempts to produce recommendations, metrics, and criteria by which to define a particular room. These have often concentrated on some aspect of the modal distribution, such as spacing or density. Other attempts have focused upon the deviation from a desired frequency response. Whilst the subjective validity of objective measures such as these has often been questioned, the notion that a transitional region between a modal and diffuse sound fields exists, dependant on the room volume and reverberation time continues to permeate much thinking. The calculation of this transitional frequency relies on the calculation of a desired modal density. In the case of the most well known definition, the Schroeder Frequency1, the transitional frequency is that point where the density becomes sufficient that three modes lie within one bandwidth. Although this idea may well be useful in some instances, such as defining points for the use of statistical sound field analysis, recent thought has cast some doubt over its relevance as a subjective frequency above which we may ignore modal issues2. This paper highlights a number of studies along with a new listening test, which help us to better understand the role of modal density upon subjective perception of modal soundfields.

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Item Type: Book Chapter
Uncontrolled Keywords: room modes, low frequency, modal density
Subjects: T Technology > T Technology (General)
Schools: School of Computing and Engineering
School of Computing and Engineering > Music Technology and Production Research Group
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References: M. Schroeder, Statistical parameters of the frequency response curves of large rooms, J. Audio Eng. Soc., vol. 35 (5), 1987, pp. 299-305 B. Fazenda and M. Wankling, Optimal Modal Spacing and Density for Critical Listening, Proc. 125th AES Convention. San Francisco (2008) R.H. Bolt, Normal Modes of Vibration in Room Acoustics: Angular Distribution Theory, J. Acoust. Soc. Am., vol. 11, 1939, pp. 74-79. M. M. Louden, Dimension-Ratios of Rectangular Rooms with Good Distribution of Eigentones, Acustica, vol. 24 (5), 1971, pp. 101-104 O. J. Bonello, A New Criterion for the Distribution of Normal Room Modes, J. Audio Eng. Soc, vol. 19, pp. 597-606 R. H. Bolt, Note on Normal Frequency Statistics for Rectangular Rooms, J. Acoust. Soc. Am., vol. 18 (1), 1946, pp. 130-133 M.M. Taylor and C.D. Creelman, PEST: Efficient Estimates on Probability Functions, J. Acoust. Soc. Am., vol. 41, 1967, pp. 782-787. M.M. Taylor, S.M. Forbes, and C.D. Creelman, PEST reduces bias in forced choice psychophysics, J. Acoust. Soc. Am., vol. 74, 1983, p.1367-1374 B. Fazenda, M.R. Avis, and W.J. Davies, Perception of Modal Distribution Metrics in Critical Listening Spaces-Dependence on Room Aspect Ratios, J. Audio Eng. Soc., vol. 53 (12), 2005, pp. 1128-1141. M. Avis, B.M. Fazenda, and W.J. Davies, Thresholds of detection for changes to the Q factor of low-frequency modes in listening environments, J. Audio Eng. Soc., vol. 55 (7-8), 2007, pp. 611-622. Y. Huang et al. Pair-Wise Comparison Experiment on Subjective Annoyance Rating of Noise Samples With Different Frequency Spectrums but Same A-Weighted Level, Applied Acoustics, vol. 69 (12), 2008, pp. 1205-1211
Depositing User: Matthew Stephenson
Date Deposited: 25 Jul 2013 10:26
Last Modified: 28 Aug 2021 19:50


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