Objective assessment of concert hall acoustics

Proceedings of the Institute of Acoustics

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OBJECTIVE ACOUSTICS
Mike Barron

ASSESSMENT

OF

CONCERT

HALL

Department of Architecture and Civil Engineering, University of Bath, Bath BA2 7AY

Presentation: www.akutek.info/Presentations/MB_Objective_Assessment_Pres.pdf1

INTRODUCTION

With the introduction of objective measures relating to subjective characteristics for listening to classical music in ISO 33821, most new auditoria are now tested in some sort of model, either computer simulation model or scale model. An alternative is to test by auralisation, an approach more valued by some than others! For work using objective measures, criteria areneeded to assess the numerical values, the most common of which is to compare measured or predicted values with an optimum range. If a value of an objective measure falls outside the optimum range it can often not be obvious why this has occurred, what aspect of the geometrical design is responsible? The revised theory of sound level in rooms offers a technique for assessing acoustic behaviour whichcomplements approaches that are already in use. The following discusses the rationale behind and the use of ‘temporal energy analysis’ for assessing concert spaces.

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SUBJECTIVE CONSIDERATIONS

Though the acoustic character of a concert hall is often discussed as an overall characteristic, this is to ignore the fact that listeners differ in their preferences. This was first demonstrated in astudy conducted in Berlin in the 1970s, reviewed by Cremer and Müller2, and apparent in this author’s subjective study of British halls3. At least three groups have been identified: those that like reverberance (sense of reverberation), those that like acoustic intimacy and those that above all prize high clarity. If one wishes to buy a good bottle of red wine, does one ask advice from someonewho always drinks white wine? Fortunately this metaphor does not appear to entirely apply to concert hall listening. For the trained ear it seems that all important subjective characteristics can be appreciated and assessed, even though individual preference varies. But one does need to question how suitable it is for one consultant/listener to impose their own preferences on a concert hall design?In addition, though the subjective acoustic character of a hall as a whole is often considered, there will generally be significant subjective variations between different seating areas. When interpreting the results of objective measurements, just working with average values of quantities which vary throughout the auditorium is inappropriate. Reverberation time is the exception here since itusually varies little throughout the space and single hall values are acceptable.

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3.1

OBJECTIVE MEASURES
General considerations

Vol. 28. Pt.2. 2006
Page 70

Proceedings of the Institute of Acoustics

A set of objective measures are now recommended and generally accepted for use in music auditoria1. It is important never to lose sight of the fact that current objective measures arenot perfect; they are not perfectly correlated with the subjective impressions to which they are linked. Nor do current objective measures cover all subjective aspects of sound in halls. In the case of measurements in full-size halls, objective measurements are generally conducted without an audience present. The most obvious change between no audience and with audience is that the reverberationtime falls. The corresponding changes for other objective measures are that early decay time (EDT) decreases, the early-to-late sound index C80 increases and total sound level, G, decreases. For valid comparisons between halls, correction for the effect of audience is essential. Several correction techniques for reverberation time (RT) have been proposed4; for modest RT changes they are all...