Page 36 - Spring 2019
P. 36

Art of Concert Hall Anoustix
Where do we go from here? It can be tempting to conclude the correlation between estimated surface diffusivity and
that all new concert halls should be shoebox shaped and that overall acoustical quality perceived by musicians playing in
the acoustics in more complex geometries remain an unsolv- 53 different halls. As a result of the high correlation that they
able mystery. But as long as architectural and public demand found, as well as design preferences of many acousticians and
for creative room shapes continues to grow, we must keep architects at the time, many halls built in the last two decades
pursuing answers. have a high degree of surface diffusivity Not all of these halls
Two Trendsfmm have been regarded as acoustically successful, particularly
Ream Research and Experience when the articulation has-all been at the same physical scale
The im ortance of lateral reflections for s atialim ression is (meaning than surfaces diffuse sound m a narrow range of

P P P . . .
well-understood (Barron, 1971; Barron and Marshall, 1981; frequémles) and when ‘he diffusion has weakenec! _1atem1
Lokki es al., 2011), but more recem research has shown that reflections that we now better understand to be critical to
these reflections are also critical to the perception of dynam- mumple Perceptual factors‘
ic responsiveness. Patynen et al. (2014) have recently shown The title of a recent presentation is particularly illustrative of
that lateral reflections increase the perceived dynamic range the growing opinion among acousticians who caution against
by emphasizing high-frequency sounds as the result of two the use of too much diffusion: “Halls without qualities — or
important factors: musical instruments radiate more high- the effect of acoustic diffusion” (Kahle, 2018). Although the
frequency harmonics as they are played louder and the hu- tide seems to be shifting away from high surface diffusiv-
man binaural hearing system is directional and more sensi- ity and there is more evidence to substantiate the need for
tive to high-frequency sound that arrives from the sides. If strong lateral reflections, there is still limited evidence from
lateral reflections are present, they will emphasize high-fre- research to explain exactly how diffusion impacts the listen-
quency sound radiated from instruments as they crescendo, ing experience.
and our ears, in turn, will emphasize these same frequencies.
If they are not present, then the perceived dynamic range will Haw Vin" Concert Hall Acoustical
be more li.rnited. Increased perception of dynamic range has Design changa in the Future-_:
also been shown to correlate with increased emotional re- in Parallel with applying lessons learned from exisiing ha]_is_
5P01159 (P31Y595 31151 14011111» 201511 the future of concert hall acoustical design will be trans-
Building on these deveioninei-,is_ Green and Kahie (2013) formed by the power of auralization. An auralization is an
have recently shown that the perception threshold for lateral 311131 15551511113 013 51-1511131511 13115535511511 511359: 51931511 by
reflections decreases with increasing sound level, meaning convolving 11'5P111-55 155P05555 W1111 355511015 3111110 1550151‘
that more lateral reflections will be perceived by the listener 1585» P13Y551 0V51' 1°11‘15P531‘515 01 1153‘1P11°1155 101 SP31131-1Y
as die n-iusio oi»eseendos_ further heighiening the sense of realistic listening. Auralizations have been used in research
dynai-nie i—esnonsiveness_ From an aoonsiieai design Pei». and limited design capacities for several years, but recent
spective, it is easier to provide strong lateral reflections for 15511501081531 351V3115e1'551115 35505131551 W1111 measurement,
a 1ai—gei- audience ai—ea in a shoebox ha1] by si_i-nniy ieaving simulation, and spatial audio have the potential to leverage
large areas of the lower side wall surfaces hard, massive, and 31113111311011 531' 111015 155351531111 3511 W1‘155P1e351 1155 111 1115
flat. In a vineyard hall, the design process is more difficult f1111119- 11015511311)’ 355W51'1-1'13 P15V10“51Y 1151'55°1V551 111155‘
because individual balcony fronts and side wall surfaces are 110115 3110111 50115911 11311 35011511531 P5155P1105 31151 111551351
smaller and less evenly impact the audience area. R31-1151' 11135 3V51'3S1-1'13 311111 15111151-1'13 1-15P11155 1'55P05555 10
The role of diffusion has been hotly debated in architectural single number Pafameters’ ““”h""‘.“_“ smve to Preserve all

. . . . _ the perceptually u-nportant complexities and allow acousti-
acoustics for a long time. A diffuse reflection is weaker than dam ‘O make side_by_side Comparisons with their best tool?
a specular reflection and scatters sound in all directions. their ears 1
Diffusion is helpful for avoiding problematic reflection pat- 1
terns (such as echoes or focusing effects) without adding un- Auralizing the design of an unbuilt space requires simu-
wanted sound absorption. It can also be helpful for creating lating its impulse response. Commercially available room
a more uniform late sound field (such as in the upper volume acoustics software currently relies on geometric simulation
of Boston Symphony Hall). Haan and Fricke (1997) studied methods that model sound waves as rays, which is a valid ap-
an 1 AI:uuII:l:I Tbday 1 Spring 2019

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