Theatre Design & Technology - Oct 1970 - 7

reduction systems and compressors that are
used in the system. High frequency boostin
recording systems compensates in part for
the cut in reproduction. As a result, reproduced sound in a motion picture theatre
is essentially flat, in the case of 35mm
prints to about 7 kilihertz, and in the case
of 16mm to about 5.5. It may sound restricted to you. It is, but the quality can still
be there.
Those sounds in real life that I think are
worth hearing fall within a dynamic range of
about 70db. In recording for motion pictu res we have to reduce this dynamic range
to about 55db in order to match signal to
noise ratio of the 35mm optical sound track.
In the theatre, where this track is played
back, there is a sustained noise level of
30-40db, and this constitutes a threshold
for reproduced sound which is added on to
the noise base. As a result, the audience
will experience program maximum listening
levels of 85-95db. Average levels of film
tracks are a bit lower but mostly above the
median, and we know therefore that a high
percentage of movie audio will be reproduced at levels substantially above those of
real-I ife sound. Where system distortion is
low, frequency response of the system is
within
specifications, and the powerhandling ability of the ampl ifier and speaker
are adequate, the audience will acceptthese
high levels and appear to enjoy the heightened sense of realism that they provide. If
technical qual ity is poor, the listening quality
is dreadful.
Unnatural conditions exist to some extent in every motion picture theatre, and
they must be minimized so that the movie
sound can be reproduced with maximum effective realism. Low distortion and faithful
treatment of the dramatic responsibilities,
(the music, the dialogue, and the effect)
are important, and voices of course must
be recogr,izable. This can be more readily
achieved in the future because of the new
techniques for objective measurement and
relatively simple electrical correction. Complex tools and processes are used in the
preparation of motion picture sound tracks,
bu t if they are properly used and the characteristics of the room in which they are
played back are good, they will not intrude
themselves upon the audience even though
a dozen or more original tracks have been
combined.
I do not know whether criteria for motior. picture applications are suitable for
multi-media theatre, but there is enough in
common to suggest that motion picture experience has relevance, and that the characteristics essential to good cinema are also
essential to the exciting field of new theatre.
At the very least we both aim for a good
show and that is a good and worthwhile
objective.

@ITO THEATER DESIGN AND TECHNOLOGY

INSTALLING PERMANENT
ELECTRO-ACOUSTIC
SYSTEMS
T. Richard Fitzgerald
Sound Associates, Inc., New York

he design of an acoustic reinforcement
must incorporate components which will
produce maximum acoustic gain with minimum distortion. In order to use acoustic
gain we must design systems with sufficient power-handling capabilities to produce
at least 110db four feet away from one
lot. At 100 feet your sound pressure level
is down to 82 db from that lot, and if we
want to maintain a program level of 90db
we would have to incorporate an amplifier
of 60 watts if we figure 10db peaking
margin.

The logical goal of a sound system is
the duplication at the most remote seat of
a sound pressure level equal to sitting at
the microphone. When we're dealing with
average distances in the theatre of approximately ten feet from a footlight microphone
and even with detailed equalization, we
cannot expect (before feedback) the system
gain to exceed more than 20db. We certainly can't expect a director to employ his
actors within 12 inches of the microphones.
It is our desire to design a system where
the theatre's last row can be relatively
moved a great deal closer to the stage.
There are a few variations a scene designer can come up with to affect sound
system design. One thing he can do which
can hamper our design is move the orchestra from the pit onto the stage. In doing
this, we have the advantage of being able
to mike the orchestra as though it were in
a recording machine, but we have the severe
disadvantage of an echo-type effect between
the live sound of the orchestra and the reproduced sound coming from wherever our
speakers are placed. We must baffle the
orchestra correctly and mike it properly,
using close-in miking so that we can contro I th e echo effect.
Electronic instruments can be bridged into
the system. Miking with baffles can be used,
so that each particular section of the orchestra can be balanced throughout. If we do
not baffle or mike, by the time we get our
stage microphones up to the level we need
to get the dialogue over the music numbers,
we have brought the music up so high that
we cannot understand anything that is going
on.
Approaching the stage area where the
actors are playing is a very, very serious

OCTOBER,1970

matter. However, in this area we cannot use
close-in miking. I always try to design a
sound system all eviating the use of radio
microphone devices. They are a nuisance to
wear, and they make it impossible to balance all the dialogue, voices, and music.
A reinforcement system is not a public address system. If it is designed properly, no
one should be aware that it exists. Wireless
microphones do have their place in the industry, but I think that they should only be
used where another solution is impractical.
We are left with a multiple of source devices including dynamic condenser and ribbon microphones with interference tubes that
cover the stage area. Once again we find
that we are limited in our choices by the
scene designer. If there is no place to hang
a microphone on stage, we have to cover
it with tormentors or from the footlights. If
the orchestra happens to be on stage, we
could conceivably cover the whole downstage area with seven or ei ght microphones
and the footli ghts. If the orchestra is in the
pit we should make some arrangements to
mike it from a little closer in, because some
actors will yet far upstage. Under normal
conditions a Broadway musical in an existing theatre in New York could be miked
with ten microphones; seven in the foots
and three extraneous microphones either
hanging or somewhere on the set.
Speaker placement in the legitimate theatre is probably the biggest thorn in the designer's side.
Most theatres were built years ago when
sound reinforcement was unheard of, so we
have problems like those of the Colonial
theatre in Boston. The walls there are covered with silk fabric and expensive bronze
sconces hung throughout. To design any
thing hanging on the walls would not be acceptable to the theatre owners.
Of all speaker arrangements, a configuration of the single source cluster, which
hangs above the stage apron, offers the most
advantageous placement for two reasons.
The first is balance control throughout the
house. This can be more readily achieved
with a single source cluster than with a
combination high-low level system. Second,
we can determine more precisely the critical distance in a reverberant area. By using
a sound pressure meter we can find in a
reverberant area a distance (from the radiated source) beyond which there is no decay
in level. This distance is the critical distance and is necessary for calculating the
type and number of horns required in an
existing structure.
Let us assume that the critical distance
of a particular loudspeaker in a particular
environment is 35 feet. Beyond this distance the reflected sound becomes greater
than the direct radiated sound. As the dis-

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