Theatre Design & Technology - Feb 1974 - 22

articulating shell volume of 66,000 cubic feet. The
combination shell design is similar to the articulating shell
in the music pavilion/amphitheatre. The advantages of a
combination shell in a mUlti-purpose theatre with full
stagehouse are higher sound pressure levels throughout the
time frame and the possibility of storing curtains and
scenery in thee upper portion of the stagehouse, without
acoustical impairment of concert conditions.

II. Mid-and High-Frequency Diffusion and Distribution
Patterns
To balance the various sections of the orchestra in both
end room and articulating shells and distribute sound
evenly throughout the listening area, one must provide
sufficient change of slope in diffusion surfaces under ten
feet, for each section of the orchestra, so as to permit
optimum distribution of mid- and high-frequency sounds
from front to rear of a pavilion/amphitheatre and from
orchestra to balconies in a multi-purpose concert
hall/theatre design.
In a combination shell design, this applies solely to the
inner articulating diffusers. The outer box-like
construction of the reverberant chamber within the
stagehouse does not have to meet any special shaping
criteria in terms of distribution, although focusing
surfaces should be avoided.

V.

On-Stage Sound Distribution

A designer enables the musicians to hear themselves
and other sections of the orchestra by providing mid- and
high-frequency stage return from the diffusing surfaces.
This can be developed as micro-diffusion surfaces within
the overall esthetic design of the shell.
Cross-stage diffusion patterns are helpfu I in th is
instance, and should be incorporated in the final design
pattern. The side walls of the shell are important in terms
of improving the musicians' hearing capabilities, and it is
essential that the percentage of side wall opening be kept
between 5% and 10%.

VI. Orchestral Balance Techniques
In a contained shell we should usually provide some
sort of absorption near the brass and timpany section.
This can be developed in the form of panel absorption,
boundary surface absorption, or suspended absorption
using -acoustical absorptive materials. Sometimes it is
possible to rearrange and reseat the orchestra in such a
way that the bodies of the musicians act as suspended
absorbers and help improve balance problems.
In an articulating shell it is usually not necessary to
incorporate these techniques. The design of the shell
allows the escape of energy near the brass and timpany
sections.

III. Low-Frequency Diffusion Patterns and Acoustic

VII. Materials of Construction and Maximum Percentage

Coupling Techniques
In a contained shell, the shell ceiling should have the
proper slopes in its reflecting surfaces over ten feet to
allow a major portion of low frequency energy to reach
the upper portion of the listening area.
In an articulating design this is not critical since the
open ceiling allows low frequency components to decay in
the upper reverberant field of the stagehouse, the rear of
the pavilion or the stagehouse box, providing the familiar
bass-rich reverberant field representative of the best
concert hall designs.
A 30% opening in the ceiling pattern of an articulating
shell is the maximum that should be considered, since we
do not wish to lose the early reflected mid- and
high-frequency harmonic structure so important to the
development of instrumental timbre and tonal quality. In
this connection, it is desirable to design the articulating
ceilings so that their attitude as well as height from the
stage floor can be readily changed. Once the building is
completed and the shell installed, it should be possible to
tune the ceilings while the orchestra is actually
performing.

IV. Seating Risers
It is important not to exaggerate tier risers for the brass
section, which includes the highest energy directional
instruments of the orchestra. Over-dominant brass is one
of the most frequent complaints regarding concert halls.

22

~

Openings
In a contained shell it is essential to utilize material
weighing at least 2 Ibs.lsquare foot in the shell design and
keep openings in the shell to a minimum, not above 2%.
As mentioned above, it is important to shape the ceiling
so that a certain portion of low frequency energy can
reach the reverberant upper portion of the listening area.
In an articulating shell, since the stagehouse of a
multi-purpose concert hall/theatre or the ceiling and wall
areas of a pavilion/amphitheatre structure are the actual
containment devices, the shell itself does not have to
weigh more than 11,-1 Y.. Ibs.lsquare foot. In th is instance,
side wall openings should be limited to 5-10% and ceiling
openings to 15-30%, depending on height; for example,
the lower the ceiling, the higher the percentage.
In the combination shell, criteria for the stagehouse
box would be similar to those of the contained shell,
while the criteria for the inner shell would be similar to
those of the articulating shell.
There is a recent classification of a "no-shell" shell,
which is placed in front of the proscenium in a
mUlti-purpose concert hall/theatre. This design is made
possible by a double system of stage lifts and movable
seats forty feet forward of the proscenium arch. The
acoustical isolation of the stagehouse is accomplished by
lowering the fire curtain and thus using it as the rear wall

THEATRE DESIGN AND TECHNOLOGY

FEBRUARY, 1974
Table of Contents for the Digital Edition of Theatre Design & Technology - Feb 1974
