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GENERAL TRENDS AND RECENT INVENTIONS 419
INCIDENT LIGHT BEAM
SPREAD OF IMAGE IN EMULSION
Fig. 174. — Image spreading by reflection.
When the control signal is between l/3rd and 1/2 strength a relay control automatically inserts two banks of additional speakers. These speakers may be placed at the most advantageous positions, either behind or at the side of the screen, to give the impression of a broad sound source. The volume from each bank of speakers will then be equal to that obtained from the normal speaker system. When the control signal increases in strength above the level this amplification of the entire system is raised and the impression of a broad source of even greater volume is thus obtained.
This system has the advantage that it is entirely automatic from the projectionists point of view; that the size and position of the control track scanning point is relatively unimportant; that projectors fitted with this refinement are still capable of handling normal films which do not contain a volume control track, and that films which do contain such a track may also be projected on machines which are not fitted with the attachments necessary to take advantage of its possibilities.
(c) Ultra-Violet Sound Recording and Printing. Another development in the field of sound recording and reproduction concerns the advantages gained by using light of a particular wave-length when original sounds are recorded or when copies are being printed. This system, the introduction of which is largely due to the R.C.A. Company, is known as 'The UltraViolet Sound Recording and Printing Technique'. If a narrow pencil of light of known dimensions is directed onto a photographic film (as will occur in any sound recording process), it is essential that the dimensions of the resultant silver image are as near as possible to those of the original light beam. Obviously, if any image spreading occurs, it is conceivable that, at the high frequencies, this spreading might become so serious as to fill in the separations between individual wave forms and so lower the upper frequency response of the system. That this actually occurs when normal tungsten fight is employed will be appreciated from Figure 174. The desired width of the light beam is indicated at *A-A' but, as the beam penetrates the emulsion (which must