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sories, it is important to obtain one specially matched to the projectors.
The change-over unit is electrically connected to both projectors and is provided with two or more switches which enable the operator to make the change-over without actually touching the controls of the projectors. A simple movement of one switch starts up the motor of the next machine to be used, whilst another will produce a smooth change-over of both picture and sound.
The use of a unit which can only produce a simultaneous change-over of picture, however, may not be completely satisfactory for projectors fitted with filament lamps and having no dowser control. A filament lamp may take a full second or more to produce full brightness on starting, and a unit which incorporates means of momentarily delaying the switching off of one lamp until the other has achieved full brightness may be a necessary adjunct for perfect dual projection.
On the other hand, such a delayed action would entail a momentarily double load on the supply circuit and before such a unit could be used precautions would have to be taken against the possibility of a fuse blowing. But when using any kind of change-over unit, similar precautions should be taken for the double load.
Apart from any such drawbacks, however, the change-over unit is often a necessary piece of equipment to the user of dual projectors, unless they are of the type which have no separate exciter. In that case, excitation originates from the projector lamp and can only occur when the lamp is switched on, thus enabling a change-over to be made for both picture and sound by using the lamp switch only.
Monitor Speakers
The monitor is a separate loudspeaker installed in the projection-room and its use permits the projectionist to gauge and control the sound in the auditorium which perhaps he cannot hear direct.
It is preferable to obtain one fitted with its own volume control, as this allows its sound to be in proportion to auditoriumsound. Blaring sound at auditoriumvolume is quite unnecessary and can easily cause the projectionist to develop a neurosis.
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