Page 32 - Spring2019

Art of Concert Hall Acoustics
Figure 2. Measured impulse responses (IRs) from the Rachel Carson Music and Campus Center Recital Hall, Concord, MA. Both IRs were measured with an omnidirectional (dodecahedral) loudspeaker, band-pass filtered in a 1-kHz octave band, and color coded by temporal region. Left: IR, measured with an omnidirectional microphone, shows relative timing and level of reflections arriving from all directions. Right: IR, measured with a multichannel directional microphone, shows relative level and spatial distribution of reflections. Photo by Kelsey Hochgraf.
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Using Auditory Stream Segregation to Decode
a Musical Performance
One innovative approach is based on the principles of au- ditory stream segregation, building on Bregman’s (1990) model of auditory scene analysis. According to this model, the brain decomposes complex auditory scenes into separate streams to distinguish sound sources from each other and from the background noise. The “cocktail party effect” is a common example of auditory stream segregation, which de- scribes how a person can selectively focus on a single con- versation in a noisy room yet still subconsciously process auditory information from the noise (e.g., the listener will notice if someone across the room says their name). See the discussion of similar issues in classrooms in Leibold’s article in this issue of Acoustics Today.
In a concert hall, the listener’s brain is presented with a com- plex musical scene that needs to be organized in some way to extract meaning; otherwise, it would be perceived as noise. Supported by research studies at the Institute for Research and Coordination in Acoustics and Music in Paris, Kahle (2013) and others have suggested that the brain decomposes the au- ditory scene in a concert hall into distinct streams: the source and the room. If listeners can perceive the source separately from the room, then they can perceive clarity of the orches- tra while simultaneously experiencing reverberance from the room. Griesinger (1997) has suggested that this stream segre- gation is contingent on the listener’s ability to localize the di- rect sound from individual instruments separately from other
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instruments and from reflections in the room. Although the brain may perceive the auditory streams separately, the source and room responses are dependent on each other acoustically. Developing a better understanding of this relationship, both spatially and temporally, is critical to integrating the range of acoustical percepts more holistically in the future.
Setting Acoustical Goals for a New Concert Hall
Without one set of perceptual factors to guarantee acoustical excellence, who determines how a new concert hall should sound? In recent interviews between the author of this arti- cle and acousticians around the world, three typical answers emerged: the orchestra, the acoustician, or a combination of both. Scott Pfeiffer, Robert Wolff, and Alban Bassuet dis- cussed the early design process for new concert halls in the United States, which often includes visiting existing spaces so that the orchestra musicians, conductor, acoustician, and ar- chitect can listen to concerts together and discuss what they hear. Pfeiffer (personal communication, 2018) expressed the value of creating a “shared language with clients to allow them to steer the acoustic aesthetic.” Wolff (personal com- munication, 2018) mentioned that orchestra musicians often have strong acoustical preferences developed from playing with each other for many years and having frequent oppor- tunities to listen to each other from an audience perspective. Bassuet (personal communication, 2018) asserted that it is more the acoustician’s responsibility to “transpose into the musician’s head when designing the hall” and set the percep- tual goals accordingly.