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he microphone is now in position to balance piano and orchestra. The recording engineer in the booth (left rear window) controls s position between selections. Photos by Orville Coldner.
1(1 the rable in the box winds mo the drum.
F wo suggestions here for anyhuilding such a unit: first, the ^cs of the drum are much 1 than necessary, and, second, le drum shown could be made of .inch h'ghter material. These modirations would reduce the inertia 1 the drum and lighten the load n the motor.
The motor is a war-surplus Bell nd Howell projector mechanism, ripped of all parts except the mo3r and gearing. Any reversing mo)r of adequate power could be sed. A gear was silver soldered on
sprocket wheel shaft, and another ear in appropriate ratio was lountcd on the shaft attached to :ie drum. Chain appropriate for he sprockets drives the drum.
In the control room of the Conert Hall a wall panel contains a onlocking spdt switch, a spst witch, and a jack. The spdt witch controls a 24-volt relay 'hich starts the motor for either •p or down movement of the mijrophone. The jack permits plug, ,ing in a remote switch on an
extension cord for use at the console 6 feet away. The spst switch provides off-on control for a relay provided to activate a power supply in the attic for certain types of microphones when required. All power switching, therefore, is done by relays in the control box in the attic over the stage; low-voltage wire, multiple conductor and rubber-covered, conducts control current to the relays from the control room; no conduit lor this circuit was required. If, however, conduit had been available, a 120-volt switching circuit would have eliminated the relay system and simplified installation.
The relays — also surplus — have 120 volt contacts and coils operate on 21 volts A.C. These are wired appropriately to energize the re\'ersing and off-on switch of the projector motor. The imit is fused. On the top of the electrical component box control switches are du]jlicated to facilitate servicing and adjusting the unit.
Especially important is the limitswitch system. A surplus geared radio dial unit was attached to the
shaft of the drum; to it, two mercury switches, such as are used in furnace controls, were mounted in fuse clips on a piece of brass strap. ,\s the gear is turned by the drum, the switches are tilted. One is in the forward circuit, one in the reverse. When the motor runs forward — microphone down — the forward circuit is broken when the microphone reaches its lowest level; the reverse circuit mercury switch is in the "on" position where it remains until the microphone is raised to its top limit, when this switch breaks the "up" circuit Incidentally, gear drag in the mechanism is sufficient to eliminate need for a brake system, and since a motor line filter is used there is no pick-up of noise from the motor, relays, or switches.
So, in our Concert Hall the microphone can be set at any elevation appropriate for each ninnber in a program: the console operator just touches the switch. Further, alter performances, the microphone is withdrawn into the attic, out of sight, and in a relatively clean storage place, a round tube.
fcdScreen & AV Guide — January, 1959
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