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468 Transactions of 8JLP.E., Vol. XIIL No. 38, 1929
contrast between the two portions would be increased and the faults proportionally emphasized.
It can easily be shown that a screen will reflect a much better picture before being perforated than after it has been so treated, even though the perforated screen be given more than enough extra light to compensate for the light which passes through the perforations.
The great objection to increased amperage or light is the excessive damage to the film and also the. extra fire hazard.
A method of screen construction has been evolved however, and is now being perfected, which will permit free passage of sound through the screen and yet inhibit the j^assage of light, so that there is not only an improvement in the sound effects but in the picture as well. In this construction there are no pores or perforations having axis normal to the screen surface, and consequently no light from the projector passes through the screen, unless, of course, i'£m projected from a severely oblique angle, and since there are no open spaces or passages discernable to the eye, it follows that the black spotted effect will not be present and consequently there will be no smudge or blurred effect in the screen, and the pictures will be equal in every respect to what they were before sound pictures and permeable screens were introduced.
The construction of this screen is such that the openings are oblique to the screen surface and is based on the well known fact that most sounds readily pass around objects and corners while light (except under certain conditions) will not turn corners; as it only travels in straight lines.
This method makes it possible to have unobstructed passage for sound equalling 45% to 80% of the screen area and yet retain a 100% opaque light reflecting surface.
Several methods of construction have been tried out, but the best results have been obtained by assembling very narrow strips of thin opaque light reflecting material somewhat in the form of a louver.
■ This gives the necessary depth to the sound openings to inhibit the passage of light and still permits the use of thin materials, so that the absorption or damping factor is kept at a minimum.
The directional effect, that such a construction might be expected to have on sound, has been found to be negligible if apparent at all.