Projection engineering (Jan 1932-Mar 1933)

JANUARY, 1932 Page 21 half that for the consonants (Ac). Likewise, the lower dotted curve contains all the points in which the vowel absorption is twice that for the consonant. In brief, the area above the middle dotted line represents unbalanced absorption of the usual kind while the area below represents a reversed absorption unbalance which is most unusual. Many interesting deductions can be made from this chart. Perhaps the most interesting thing to note is that the condition of unbalanced absorption causes the vowels to rise far above the normal level for initial speech which is bound to decrease the articulation. On the other hand, the reversed unbalance causes the vowels to be much lower in level and in some cases to be below the normal level. Further experiment will show that the articulation will be improved in a corresponding way. The effect of the size of the room is strikingly shown when the same calculations are made for a room with a volume of 410,000 cubic feet. Here there is less opportunity to keep the level of the vowels at or below the normal level of initial speech. However, the reversed absorption condition is far superior to even the balanced condition. In the application of acoustical treatment, one must not lose sight of the fact that coefficients of absorption which are available, are painfully limited. Practically all the materials on the market 256 511 ..OTA Frequency, C.P S TfiAb 4,096 Fig. 11. Coefficients of, absorption curves of well known materials for different frequencies, also one material of special design to correct unbalanced absorption in acoustic treatment. have absorption curves similar to those which are shown in Fig. 11. The slopes of these curves are of special interest in view of the data given in the chart presented. The absorption at high frequencies which controls the consonants is between twice and three times that at low frequencies which controls the vowels. These curves have the usual unbalance which results in the vowels being intensified in excess of the consonants. The net effect is to lower the articulation. The new acoustic treatment which is indicated by the curve "X" in this figure is designed to aid in the correction of the unbalanced condition. The cost of treatment which will give the extreme slope of one-fifth is considerably more than a modified treatment on the same principle which has a slope of one-half. Referring again to Fig. 10, the smaller room gave an articulation of 79 per cent when the reverberation was adjusted to a period of 1.2 seconds for a sensation level of 72 db. (J. C. Steinberg, J. A. S.., Oct., 1929). In this room (whose dimensions were 20 x 30 x 15 feet), the coefficients Av and Ac were approximately equal to 0.12. Reading the chart, it will be noted that the vowels are about 3 decibels above the normal, or a total of 18 db. above the consonants. If this room were treated with the new material with a reversed absorption curve, the average coefficient for the vowels Av could be adjusted to 0.30 keeping the A c at 0.12. The result would be to bring the vowel level completely down to the normal for initial speech, thereby enhancing the intelligibility. In conclusion, the method of acoustic treatment of auditoriums which employ a new material with maximum absorption at low frequencies has unusual possibilities for improving the articulation of speech. That there is a sound scientific basis for such a conclusion in addition to experimental confirmation is most reassuring to the engineer who desires to determine the specifications of acoustic treatment to give a certain percentage of articulation at a prescribed acoustic intensitv level. AAA WUNDER LEAVES ACADEMY AT a meeting of the Board of Directors of the Academy of Motion Picture Arts and Sciences on Nov. 11, Dr. Clinton Wunder resigned as executive vicepresident. He announced that he had accepted the invitation of the Institute of Religious Science and Philosophy of Los Angeles, to share the leadership of the Institute with Ernest Holmes, its founder, and to become editor of the magazine, "The Science of Mind," beginning his new duties December 1. M. C. Levee, president of the Academy, made the following statement : "The resignation of Dr. Wunder was accepted with regret as in the two years that he has been executive head of the Academy he has gained the thorough confidence of the board of directors and of our membership. His qualities of leadership, distinguished standing as a student of public affairs and his ability as a speaker have exercised a genuinely helpful influence throughout the motion picture industry." Previous to his association with the MORE TECHNICAL QUESTIONS Continuing the series of examination questions introduced in the October issue of Projection Engineering, herewith are presented questions No. 26 to 32. The correct answers will be published in the February issue. 26. State what is meant by self-induction. 27. What percentage of light is lost between the arc and the screen and where is this percentage lost? 28. What precautions must be taken in mounting lamps for mazda projection? 29. Can you use a prismatic condenser for projection stero slides? 30. Give four reasons for low volume from horns when using sound-on-film. 31. Give three reasons for low volume from horns when using soundon-disc. 32. Give a full description of the input and voltage amplifier panels Type "B" as used by R.C.A. What type tubes are used on this panel ? Academy, Dr. Wunder was for ten years minister of the Baptist Temple of Rochester, New York, one of the largest churches in the Protestant denomination. In this position he established a national reputation as a liberal in religion and philosophy. For the past fifteen years he has lectured in all parts of the United States on the social and educational aspects of the motion picture. Through the Academy, Dr. Wunder has had opportunity to extend his study of the relation of the motion picture to religious and secular instruction. He plans to continue his interest in this field and in the public relations program of the industry. A BOOK REVIEW "TALKING PICTURES," by Bernard Rroiv-n. 305 pp. Isaac Pitman & Sons. 2 West 45 St., New York, 1931. Mr. Brown has succeeded in producing a thoroughly practical and popular account of the principles of construction and operation of the apparatus used in producing and showing sound pictures. The price of the book is $3.00.