ACOUSTICS
106 AUDITORIA 2019 VOLUME ONE
between each terrace are vertically inclined to
direct early reflections down to the audience.
Particular to the Fuzhou concert hall, the outer
walls are also vertically inclined to generate
additional reflections.
The size of those large outer petals is
acoustically advantageous, but they also had
to be designed carefully, to avoid undesirable
echoes. A special acoustic algorithm was
developed, to determine which zones of the
acoustic petals were efficient in providing
early reflections and which could potentially
generate undesirable reflections.
Based on the output of that algorithm, a
non-homogeneous surface texture was designed
and applied exclusively to those zones that do
not provide useful early reflections. This surface
texture was obtained by integrating embossed
artisanal ceramic tiles of varying shape and
pseudo-random arrangement into the smooth
curve of the petal.
“Unlike in some recent concert halls,
a generalization of this diffusing acoustic
treatment to the entire reflector was not allowed,
in order to keep the crucial contribution of
reflections from these surfaces to the acoustic
quality fully intact,” says Eckhard Kahle, founder
and managing director at Kahle Acoustics.
Balancing act
The symphony hall has 1,000 seats,
including the choir seating behind the
orchestra, which can also be used to
expand the audience. This relatively small
seat count may seem at odds with the
large stage platform for a full symphony
orchestra of more than 100 musicians and
the full concert organ; thus, to avoid the
sound becoming overly loud, the acoustic
volume was increased much further than the
traditionally advised ratio of 10m3 (353ft3) per
audience member. The final volume is 17,000m3
analysis directly within the architectural 3D
computer model, the curved sculpture was
acoustically optimized. The entire surface
was analyzed to identify areas of acoustically
positive focusing and those areas that
generated focusing problems for certain
combinations of stage/pit sources and
audience zones. After quantifying the
strength of the focusing, the shape was
optimized either by reorienting the
surface or by ‘ironing out’ and ‘inflating’
certain areas until optimized reflection
coverage was obtained.
The acoustic analysis employed a nonuniform
rational basis spline-based simulation
technique, which enabled both highly timeefficient
calculation of the acoustic reflections
and a continuous collaboration and exchange
by both architects and acousticians throughout
the whole process.
To soften the highest frequencies and avoid
harshness of tone, the large-scale freeform
shape was lined with approximately 1.5 million
small ceramic tiles in 13 different shapes and
various shades of purple and gray. Crucially,
the amplitude of the fine-scale diffusion pattern
was limited to 10mm (0.4in), to retain coherent
reflections and maintain the acoustic signature
of the room. The opera hall is designed to
combine excellent clarity and presence
with a reverberation time exceeding
1.5 seconds – which can be extended
to 1.8 seconds when the orchestra shell
is installed in the stage house.
The symphony hall
In contrast to the freeform shape of the
opera hall, the interior of the symphony
hall is formed entirely of large segments of
spheres. All wall surfaces are convexly
curved in the shape of petals and, as in many
vineyard-type concert halls, the separating walls
Top: The symphony hall has
two levels of convexly curved
and inclined walls designed
to create early lateral and
enveloping reflections
Above: A non-homogenous
surface texture was applied
to zones that don’t provide
useful early reflections
In the
symphony hall,
specific zones are
treated with protruding
ceramic tiles while
smooth areas enhance
the coherence of
the reflections