REPORT 039
LEFT: Acoustic refl ector at the Marlowe Theatre in Canterbury increases the frontal refl ections. © Helen Binet
Introduced by Ian Stickland, a Senior Consultant for Charcoalblue, who specialises in project management and audiovisual systems for the performing arts.
ship to other areas and the personal experiences of the listener. This concept of a complete aural experience has long been understood in architectural acoustics, and much work was carried out in the 20th Century to provide a set of criteria with which concert halls can be compared. While the work of Beranek and others was initially intended to assess the quality of a room for music performance, the descriptors used form a very useful basis for the analysis of most spaces, and both unamplifi ed and reproduced sound. The criteria that Leo Beranek of BBN Technologies used to compare concert halls include terms such as spaciousness, envelopment, clarity and loudness. These criteria were developed following conversations with musicians and educated listeners, and therefore relate to how the hall is perceived acoustically. When designing a space it can be problematic to rely on these perceptions and is often more useful to assess the sound arriving at a listener using four of its own measurable and predictable aspects: time, level, frequency and direction. It is import- ant to note that each of these can be applied not to just the direct sound but also the indirect sound and the relationships between each of the refl ections and the initial source. Each of the criteria used for assessing and comparing halls is derived from one or more of the four properties of the sound. For example clarity is a combination
of level and time, and spaciousness combines time and direction. Considering the time, level, frequency and direction of the sound at the desired listener’s position therefore provides a very clear way of informing the selection and positioning of loudspeakers.
TIME
In 1925 the American theatre impresario Roxy Rathafel proclaimed: “Acoustics no longer present a problem, since the amplifi cation system, with which we are now experimenting, will carry the voice and will send it perfectly almost any distance with- in reason, and certainly a distance greater than could be found in any theatre.” Of course we now know this to be untrue as level alone does not produce a satisfactory audio system and when poorly deployed in highly reverberant spaces, can actually exacerbate the problem. Rathafel does though highlight an important point - that the developments in audio technology have changed the expectations of the aural land- scape. It is easy to hypothesise that the increased availability of high quality sound reproduction in domestic and professional circumstances has increased expectations, but in order to meaningfully explore this it is useful to consider the change of
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