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quiet, resilient floor covering material is recommended. This should not be restricted to the gangways, but should also be used on the floor in the seating area.
Where tip-up seats are used, it is necessary that the stops be well rubbered, and that the chair be so designed as to be as quiet as possible when the seat is being either raised or lowered.
Another common source of noise originating within the auditorium is the use of ill-designed lighting fittings which resonate or rattle.
The Screen
The kinema screen performs two functions : firstly to be opaque to and a good reflector of light, and secondly to transmit sound from the speakers, for which purpose the screen is perforated. The transmission of sound, particularly that of the higher frequency range, is considerably affected by the presence of the screen and the area of its perforations, which comprise only 8 per cent, of the total area when the screen is new.
When a screen is resurfaced the thickness of the screen is invariably increased and the area of the perforations reduced, with a consequential adverse effect upon the sound transmitted, which cannot be corrected by the frequency response characteristics of the reproducer equipment. It is therefore recommended that resurfacing treatment should not be resorted to more than twice, after which the screen should be renewed. Indeed, where a high standard is required the screen should be replaced after its first resurfacing.
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1
SEPTUM G C&PO.CITV
Watts output in relation to Seating Capacity.
2. POWER REQUIREMENTS
The acoustical energy necessary for satisfactory sound reproduction varies with the F'g [0. volume of the auditorium. This energy can be determined only empirically, and its value is most conveniently expressed in terms of electrical watts of amplifier output.
The curve shown in Fig. 10 is the mean of several that have been prepared by various authorities, and it is the opinion of the authors that adherence to this curve will provide adequate volume of sound reproduction for speech, music or for special sound effects. The curve is based upon the assumption that a modern two-way speaker system is installed.
3. OPTIMUM ACOUSTICAL DESIGN
For the purpose of the following proposals it is assumed that the reproducer equipment to be installed is free from intermodulation, that it has a satisfactory frequency response, that it possesses the ability to reproduce transients, and that it is capable of providing adequate sound volume throughout the whole of the seating area. A consideration in connection with the reproducer design, however, which has a fundamental bearing upon the design of the ideal auditorium is the maximum angle of satisfactory distribution for which the modern speaker system can be designed. In the paper presented to this