Lokki et al. have recently published an express letter in JASA proposes that large and flat surfaces surrounding the listeners are better than diffusing surfaces. It also suggests that reflecting surfaces above the listener and stage contribute to reduce the perceived sound quality. In concert halls early reflections are normally needed to raise the total perceived sound level. According to this paper, early reflections from directions outside the sagittal plane that have a frequency and phase response comparable to the direct sound are most effective for boosting loudness without leading to negative sound characteristics. This express letter is freely available and includes a video with auditory demonstrations.
This proposal support the findings from the research project presented in this website: that a narrow and high stage enclosure is more beneficial than a wide and low, and that the reflecting surfaces close to the orchestra at the sides can be made flat and non-diffusing to effectively compensate for low direct sound levels from strings.
David Griesinger has studied how early reflections and reflected sound in general affect our engagement as listeners. In a recent paper presented this year, available from his web site, he proposes a psycho-acoustic model that links aspects of perceived speech and music to the physical acoustic response from an enclosed space. The proposed model differ from the precedence effect, but implication of the model also agree with the conclusion that a high stage enclosure is beneficial for an orchestra.
Whereas the model of Lokki et al. favours early reflections from the sides, Griesinger’s model doesn’t. But they both demonstrate that the acoustic measure C80 has limited relevance for perceived clarity of the sound. The last word has definitely not been said regarding early reflections within performance spaces.