Theatre Design & Technology - Fall 1979 - 24

Background

Design

This console is an amalgamation of reasonably well established criteria tempered by the practical needs of the theatre
world. The most significant aspect confronting the designer of
such a unit is that there has been no established precedent in
commercial equipment. Therefore the need to establish a very
basic, universal design was foremost in this case.
Several authors have previously outlined very elaborate criteria for theatre sound systems, all of which have been extremely useful in making design decisions and are providing
new standards for the theatre industry. The primary contributors to this field have been Klepper, Dugan, and most recently Sanford.'·3 Dugan,' Scales," and Wicks s have also described actual systems currently in operation as well as
explaining the concepts behind their design.
In addition, our experience as a theatrical sound designer
has contributed the following needs:
1. Simple foolproof operation in which no specific combination of control positions is either forbidden or required for correct operation.
2. Use of layman's terms or theatrical terms rather than
technical ones for operation by stagehands.
3. The ability to repeat any control arrangement with the
use of cue sheets.
4. Flexibility which is derived from the expansion of a few
basic concepts rather than an increase in operational complexity.
5. The ability to preset arrangements as much as possible.
6. The need to reduce operator inconsistencies, primarily in
volume and timing.
7. The need to reduce operating time in slow volume
changes and crossfades.
Finally, the theatre industry has imposed its own set of
practical rules on the design of theatre sound equipment. 6
1. Minimal cost; very few theatre companies have a sound
budget as high as $1000 per year for equipment.
2. Portability.
3. Dependability; use for live performances demands maximum reliability.

Out of these requirements comes a stock theatrical sound
console. It is intended as an interfacing unit for all audio
equipment used in the reproduction of sound for a live theatrical performance, having a total of eight inputs which can be
matrixed in unlimited combination to sixteen outputs.
The block diagram of Fig. 1 shows that this is accomplished
with two different types of matrices, one for presetting and the
other for selection of presets. The output preset matrix comprises eight signal channels with sixteen slide potentiometers
in each channel, controlling the volume levels sent to sixteen
output channels. Six of these preset channels derive their signal sources from a switch matrix and the other two are permanently connected to individual input channels.
The second matrix comprises push-button switches, selecting combinations of six input channels to be distributed to six
output presets. This matrix is an active combining network
producing minimal noise by switching at ground potential with
low gain. 7
Concentrating on the input section, we see that auxiliary inputs seven and eight are conventional, passing through input
attenuators, microphone preamplifiers, volume controls,
equalization, and then into their individual output presets. Stereo input group C is also conventional, with both line inputs
passing through individual gain stages, volume controls, and
then a switch bank selecting output presets.
Stereo input groups A and B have unusual facilities. Each
of the four channels are fed to duplicate voltage-controlled
gain stages, each with its own switch bank. Four pairs of voltage-controlled amplifiers are assembled from this, and two
gain-controlling circuits act on the A group and B group independently.
This control circuit allows semiautomatic crossfades between two groups of voltage-controlled amplifiers, producing
no change in gain during crossfades when the outputs are
summed algebraically. In this way transitions from one set of
characteristics to another may be accomplished smoothly and
easily.

4. Permanence; embodiment of a basic design which will
not be outdated, as well as rugged construction and permanent labeling.
5. Insensitivity to electrical interference; as much as several hundred thousand watts of unfiltered electronic dimmers
may be sitting next to the unit.
6. It must be relatively insensitive to a cup of coffee spilled
over it.

Crossfading Circuit
Referring to the block diagram of the control circuit (Fig. 2),
a primary control voltage VA goes to the first pair of voltagecontrolled amplifiers. The control circuit then inverts this voltage and sends the inverse voltage VB to the duplicate pair.
The primary control element of the circuit is embodied in element 22.
This control element is detailed in the schematic diagram of

Fig. 1 Block diagram of sound console.

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Theatre Design & Technotogy

USITT /Fall, 1979

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