Theatre Design & Technology - Fall 2020 - 39

spaces with only one or two seating levels. This resulted in large, impersonal auditoriums lacking warmth and intimacy.
Moving balcony rows forward to give better sightlines would create considerable
depth and place a significant number of
audience members under the balcony,
where poor acoustic conditions would
result from the deep overhang. The distance to the stage would also be longer.
Maekawa developed the concept of
the auditorium with seats spread in a fan
shape at the rear sides of the lower level
and stacking a series of narrow balconies
above. The balcony seats are on the three
sides, facing the stage and down the side
walls. They are shifted by half a floor-level
so that the gaps between the balconies
are tightened to fill out the entire wall
surfaces with the seats. In this way, the
total of 2,340 seats are stacked in a tight
footprint.
The side and rear walls of the auditorium are inclined outward by 6.5 degrees
to improve the sharp downward line of
sight from the audience to the stage and
reduce the difference in levels between
the seats. Owing to these ingenious arrangements, the maximum distance of
a seat from the stage is kept within 38
meters even with more than 2,300 seats,
and good sightlines are provided. It also
helps the performers on the stage to feel
as if they were embraced by the audience. The balcony fronts, then, have a
curved face. The shape was designed to
optimize the acoustics of the auditorium,
but also to reinforce the significance of
the room as a public place where people
meet. The interior shapes also suggest
the shape of the big eaves on the periphery of the building.

Acoustical Innovations

A major design issue was acoustics so
an acoustical design team was involved
from the earliest conceptual design
phase. The team was from NHK Science
& Technology Research, and the contract
was directly with the client.
The site is close to a railway station,
which is convenient for visitors, but vibration and the noise of whistles from freight
cars using Ueno station was a challenge.
The team measured the levels of noise
and vibration to obtain data to identify
and solve this problem. A first step was
to locate the stage of the large hall as far
from the railway track as possible. This

House interior as seen from the stage. | Photo by Shozo Motosugi.

resulted in the small hall, originally conceived as a conference hall, being located
close to the railway track. To reduce vibration, it was lifted to the second-floor level
and the sound insulation of the surrounding windows and walls was enhanced.
Repeated sound measurements led
to design and construction solutions to
minimize the disturbing effects of noise
and vibration carried through the air and
ground from the railway track. Floating
isolating layers were conceived and arranged on the sidewalls of the stage and
the roof of the audience seats. Noise
and vibration from the heating, ventilation, and air conditioning systems was
reduced by mounting fans and pumps
and using silencers and other measures
on the ducts and chambers to reduce airborne noise to achieve a Noise Criterion
rating of NC-20.
Detailed acoustic knowledge was
limited, and the design process was iterative for this early post-war building.
The only acoustic information available
was the experimental results of Haas
related to the reflected sound up to 50
milliseconds, which was obtained from
literature. Considerable effort went
into tracking reflected sound based on
the hexagonal plan, sloped walls, and
the shaped balconies. The goal was to
identify the optimum routes by which
sound from the stage could be reflected
and delivered to each spectator equally, and what kinds of room shape and

finishing are required to optimize the
room acoustics.
The shape of the downward ballooned ceiling of the auditorium was
generated through the above process. It
was designed to play an important role
in delivering the early reflected sound effectively to the entire audience. The ballooned part was made with 50-millimeter
thick lightweight cast in situ concrete. It
is believed that this structure has contributed to " the warm tone " of the hall.
Diffusers or sound-absorbing surfaces are attached to the walls to affect
reflected sounds of 50 milliseconds or
higher. The sculpture-like wooden acoustic diffusers attached on the side walls of
the auditorium close to the stage and the
big white curved ceiling over the orchestra pit are typical examples. It is said that
TBK was one of the first halls to adopt
the irregular widths and spacing of ribs
used on the sound-absorbing surfaces.
The experience and acoustic experiments in designing and building TBK
caused a great step forward in acoustical design in the country and were used
in the acoustical design of subsequent
multi-purpose halls in Japan. Minoru
Nagata, the founder of Nagata Acoustic
Inc. and now one of the most acclaimed
acoustic consultants, was a member
of the TBK acoustical design team. His
three key expressions " silence, good
sound, and good tone " are based on the
experience he gained in this team.
FALL 2020 | THEATRE DESIGN & TECHNOLOGY

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Theatre Design & Technology - Fall 2020

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