Theatre Design & Technology - Oct 1970 - 8

tance from the loud speaker is squared, the
direct radiated level is reduced 6db. So at
70 ft. the direct radiated level is 6db below the reflected level. At 140 ft. the direct Ievel is 12 db below the reflected leve. When the direct level falls more than 12
db below the reflected level, the sound becomes unintell igible. We can implement
one of three modifications to solve the
problem of unintelligibility beyond 140 feet
in this situation. We can increase the cue
of the speaker system. We can change the
area of the hall, or we can change the coefficient of absorption, which is changing
the material in the hall. Since the critical
distance is a product of the three changing
factors, anyone will affect the direct proportionate change beyond 140 feet.
Thus in the design of a system in an existing structure, our engineering statistics
enable us to choose equipment with the
necessary parameters, and also to select
the most efficient process for achieving the
desired results. For example, it might be
less expensive and more advantageous to
carpet a floor than to assume the cost of
increasing the cue of a system. Either
change will produce the same effect.
Unfortunately, in most cases a producer
or theatre owner will not allow a single
source array to be placed in the theatre.
Some of the reasons include the difficulty
in suspending such a device, the labor involved, and the undesirable honk of this
apparatus hanging above the orchestra and
the audience.

COM PLETE ELECTROACOUSTICAL SYSTEMS
David L. Klepper
Bolt, Beranek and Newman, Inc.
Downers Grove, III.

ost sound systems are based on the
fact that theatres have special requirements. For example, the first step in
designing theatre electro-acoustics is the
preparation of some kind of program. We
should decide what the system is supposed
to do. We might want sound reinforcement,
or we might want a playback of performance
sound effects, or preparation of sound effects. We might want playback of motion
picture sound, or recording, performance
monitoring, paging, intermission playback of
music in lobbies, or audience recall. We
might want production communications, rehearsal talk-back, telephone, simultaneous
translation, electronic sound and reverberation, acoustical envelope for on stage communication, or pick-up for broadcasting.
These are all potential problems that are
given the sound system designer, or electroacoustical designer. The sound system designer and the acoustical engineer have to
work closely with the theatre consultant in
establishing uses. This is not just an electroacoustical probl em, it is a theatre use problem too. At the same time, the electroacoustic designer is asked to place an es-

timate on each of his functions. The owner
and the architect who control the purse
strings can decide which functions are important enough to pay for, which should be
forgotten, and which might be provided for
by conduit and space, and added in the future. It is a tough problem to estimate the
cost of a sound system before you have designed it. Still, with experience in previous
theatre projects, access to manufacturers'
prices, and a good idea of the local labor
situation, ballpark estimates can be made.
We also have to know what the communications requirements will be. Who is going
to talk to whom? Obviously in a reinforcement situation, the actors are going to talk
to the audience. But in some shows the
audience is supposed to talk to the actors.
It is important to find this out as part of
the reinforcement package. Some are less
obvious. The acoustical envelope or Instage communications system may be required merely to furnish the singer's or
actor's own voice back to him. Maybe,
(and I would consider this an aspect of bad
acoustical design) it is necessary to pick up
pit and orchestra sound, and send it to the
stage. I prefer to do that nonelectronically.
Sometimes there are program monitoring
and paging system requirements. A box office may require continuous program monitoring. A dressing room may require a program monitor with paging override. Will this
paging override be on an individual basis or
an all call basis? Sometimes different rooms

Of all the reasons for not designing a
cluster, the theatre itself contributes most
substantially. Balcony overhang in the Shubert chain theatres prohibits coverage of
the rear of the orchestra from anywhere but
the rear of the orchestra.
Since acoustic gain and distribution are
irrevocably tied together, to achieve uniform coverage we. must use a number of directional devices in the same area. Since
we must maintain plus or minus 3db throughout, we need maximum dispersion coupled
with maximum flexibility. To cover half of
an orchestra floor from one side of the
stage, we should try to use at least three
individually focused sectoral devices.
When a system is properly installed,
the last phase of tuning is easy. Tuning
brings the system into uniform acoustical
response in its environment. Knowingwhich
frequencies the house reflects most efficienily allows us to compensate for those
frequencies in the system. Graphically, the
compensation would produce the final product; uniform or flat response to noise generated through octaves throughout the hearing spectrum. It must be remembered that
whether a system is permanent or portable,
the results must be the same. The means
of achieving these results must include extensive research, good equipment, practical
design, and innovative engineering

A sound reinforcement system using microphones placed across the stage with a
central loudspeaker cluster.

Iill!O THEATER DESIGN AND TECHNOLOGY

OCTOBER,1970

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