Journal of the Society of Motion Picture Engineers (1930-1949)

702 ABSTRACTS [j. S. M. p. E. to keep the sound level too high with a resulting over-lap in the sound successions which is unpleasant. In other words, there is an upper limit of reverberation time. A balance must be found between loudness and reverberation for each theater. A summary is presented of Knudson's work on the quality of articulation in auditoriums and his method of testing is described. The ideal decay curve of sound heard in an auditorium should be comparatively smooth, whereas most rooms have some flat walls and pockets which cause sharp breaks in this curve. More attention should be paid in the future to naturalness and quality of sound rather than to intelligibility alone. — Kodak Abstr. Bull. Glance at Cinema Inventions. Bioscope (Mod. Cinema Technique), 81, Dec. 18, 1929, p. 1. Of patents issued in 1928 and 1929, 52 are concerned with color, 57 with synchronism, 21 with stereoscopy, 8 with continuous motion, 10 with mechanisms to avoid fire, 9 with filming apparatus, 5 are mechanisms for preparing films, 30 are for perfecting projection, and 23 are sundry inventions in the technical and photographic field. There is a notable increase in stereoscopic patents as compared with a similar review in 1918 to 1919. Continuous motion and anti-fire devices are about the same in number, while there is a striking decrease in inventions for perfecting material for film manufacture, filming, projection and similar devices. — Kodak Abstr. Bull. Vibration Plus Amplification in Acoustical Treatment. D. Fox. Ex. Herald World, 97, Section 2, Dec. 21, 1929, p. 31. Sound motion pictures have greatly stimulated research on acoustical problems. Q. Q. Sabine of Harvard was the first to make a series of actual measurements of several theaters and halls. According to a recent estimate made on the acoustic properties of the motion picture theaters of the United States, 80 per cent have faulty acoustics. E. Berliner, in studying these problems, applied the basic principles of vibrating diaphragms. He found that agitation of an air body enclosed in hard walls caused vibrations which resounded as reverberations. When this air body, called a tympanum, was enclosed by vibratory walls, the sound was amplified and the reverberation eliminated. The tympanums consist of flat disks of wire netting covered on one side with heavy paper, and on the opposite side with an acoustic plaster composed of cement mixed with pumice, sawdust, asbestos, and several other materials. These disks are nailed over the wall leaving a half-inch space between the wall and the netting. Several public buildings have been finished with this type of acoustic lining with improved acoustic results. — Kodak Abstr. Bull. Reverberation Time in "Dead" Rooms. CARL F. EYRING. /. Acoustical Soc. Amer., I, No. 2, Pt. 1, January, 1930, p. 217. The well known Sabine formula T = 0.05 V/a for the time of reverberation was experimentally determined by experiments in rooms in which the total absorbing powers were relatively low and the reverberation times correspondingly high. Theoretically, it is based upon the assumption of a homogeneous distribution of intensity, interference effects being neglected, and a random direction of propagation. This in effect amounts to assuming that the absorption at the bounding surfaces of the room is a continuous process. That these assumptions are valid in the case of "live" rooms, that is, rooms in which a large number of reflections are necessary to reduce the intensity of the reverberant sound to l/i .000.000 of its initial intensity, is shown by the agreement between theory and experiments. Measurement of the reverberation