Introduction to Acoustics

342 Part C Architectural Acoustics
Part C 9.7
“Vineyard terrasse”
hall (Cremer)
Narrow/tall shoe box with
reverberation chambers (Johnson)
Directed reflection
sequence hall (Marshall)
Fig. 9.51 Three concert hall concepts with the potential of combining high clarity with long reverberation. From left to
right: vineyard (plan), shoe box with coupled reverberation chambers (cross section), and directed reflection sequence
(cross section)
intimate, and the large reflecting surfaces provide a stunningly
clear, dynamic and almost too loud sound. Still,
the reverberation is long and rich because of the significant
volume without absorption above/behind the
reflectors.
This aim towards a combination of high clarity
and high reverberance, probably developed through our
extensive listening to recorded music, requires close reflecting
surfaces as well as a large volume. The natural
consequence of this demand is to separate the early reflecting
surfaces from the room boundaries. Both the
terrace fronts in the vineyard halls and the suspended
reflectors in the DRS halls offer this possibility. A third
way to achieve high clarity as well as high reverberance
is a narrow shoe box with added surrounding volume,
as found in a number of halls since about 1990. In these
halls the volume of the narrow tall shoe-box hall providing
the early reflections is quite moderate; but an extra
volume is coupled to the main hall through openings
that can be closed by heavy doors, so that the total volume
can be varied. However, in such halls one should
be careful to make the coupling area large enough for
the added volume to have any significant effect (unless
one sits close to one of the open doors), otherwise
it is hard to justify the enormous costs of the extra
volume and door system. With weak coupling, a doublesloped
decay curve with a knee point perhaps 20 dB
down is created, whereby the added, longer reverberation
becomes barely audible except during breaks in the
music.
A recent design of such a rectangular hall with
a coupled volume is shown in Fig. 9.50.
The sketches in Fig. 9.51 summarize the basic design
of the three types of halls mentioned. It is seen
that they all possess the possibility of separating the sur-
faces that generate the early reflections from the volume
boundaries that generate the reverberation.
9.7.4 Multipurpose Halls
Many modern halls built for cultural purposes often have
to accommodate a variety of different types of events,
from classical to pop/rock concerts, drama and musicals,
opera, conferences, banquets, exhibitions, cinema and
perhaps even sports events. From an acoustical point of
view, the first concern in these cases is whether a variable
reverberation time will be necessary. The answer is yes
in most cases where some functions primarily require
intelligibility of speech while others require a substantial
reverberation, such as for classical music.
A hall in which these demands have been met by
means of variable absorption is Dronningesalen, at the
Royal Library in Copenhagen (Fig. 9.52). For this hall
both chamber-music concerts and conferences with amplified
speech were given high priority. The variable
absorption is provided by means of moveable panels
on the side walls as well as by folded curtains and
roller blinds on the end walls. Combining these measures
in different ways, T values in the range from 1.1
to above 1.8 s can be obtained (in the empty hall) as seen
in Fig. 9.52.
In many cases, stage performances with extensive
scenery are also required. The most common way to
accomplish this is to design a stage house, mount an orchestra
shell on the stage and raise the pit to stage level
for concerts. If a hall is also to be used for banquets and
exhibitions requiring a flat floor, it is common to place
the stalls seats on a telescopic riser system on a flat floor
instead of having a fixed, sloped seating. When not in
use, this riser system is stored along the rear wall or un-