Perceptual relevance of location of reverberation in a concert hall.

Abstract

Standard reference texts as well as the International Organization for Standardization (ISO) standard on room acoustic quality (see, e.g., Beranek, 2004; Barron, 2010; and ISO3382-1:2009) focus on temporal distribution of energy [e.g., reverberation time T, G, and C80] and binaural aspects [lateral energy]. Kahle (2013) suggested that this description is insufficient when working with concert halls and that spatial aspects of sound fields need to be taken into consideration beyond binaural aspects. Furthermore, spatial aspects should be considered independently and separately for the (source presence) and the (room presence; see, e.g., Kahle, 1995, for details on source presence and room presence). For source presence, lateral reflections have different effects than ceiling reflections; this difference is taken into account by the objective criterion of lateral energy and the subjective factor of apparent source width. For room presence, listeners prefer to be fully enveloped by room sound; when talking to musicians and experienced listeners it is clear that this must not be limited to the frontal hemisphere and the question of lateral energy. All of the room around the listener should be active and this includes the parts of the room above us and behind us. Finally, when accepting the concept of segregation into a foreground source stream and a background room stream, a generalization of the cocktail party effect suggests that segregation is facilitated when the center of gravity (or direction of arrival) of the source is spatially separated from the center of gravity (or direction of arrival) of the room stream. Room reverberation should hence ideally be spatially homogeneous or come from a different direction than the source stream. In this paper, case studies are examined that show how spatial aspects of late sound can influence the perception of early sound and how frontal noise can influence the perception of both source presence and room presence. This suggests that spatial direction of arrival can strongly influence the perception of room acoustic quality.Case Study: Electro Acoustic Enhancement System Stockholm Concert HallThe Stockholm Concert Hall (Konserthuset, see Figure 1 for a photo of the hall) had been plagued with acoustic problems for decades (Dahlstedt, 1974) and has undergone several renovations. During the 1972 renovation, an electro-acoustic enhancement system was installed the hall, but apparently decommissioned after few months of use (Dahlstedt, 1974). The reasons for the decommissioning of the system are unknown, but probably the increase of natural reverberation during the renovation was at the time considered as being sufficient. Further renovations 2000 and 2005 decreased reverberation time and as a consequence the audibility of the late room response was significantly below optimum after 2005.As already indicated, it was found that one of the main reasons for the insufficient reverberance (what musicians described as lack of bloom) was the presence of a semitransparent technical ceiling installed under the lighting bridges for practical and esthetic reasons. The semitransparent expanded-metal ceiling (which can be seen at the top of Figure 1; Figure 2 shows a more detailed side view) created a slight transmission loss both on the way in for sound into the volume under the roof and on the way out. As a consequence, no reverberation could be heard coming from the top of the room and the ceiling was felt as being acoustically absent.First as a tryout and then as a final solution, an electro acoustic enhancement system based on the multiple channel amplification of reverberation (MCR) principle (de Koning, 1983-1984; Mulder, 2001) was installed the volume above the semitransparent ceiling, with microphones picking up the sound under the stretched-metal ceiling and loudspeakers enhancing the sound above the stretched metal ceiling. …