The Film Daily (1930)

THE 15 -.asg^ DAILV Sunday, January 12, 1930 Theater Equipment flj WILLIAM ORNSTBIN , Proper Functioning of Horns is Outlined by A. L Abrahams A. I. Abrahams, president of Racon Electric Co., Inc. and an authority on the proper uses of horns and speakers in itieaters herewith outhnes methods for obtaining the best results in sound reproduction in theaters. J. speaker is merely a sound projector. It serves as a connecting link between the aniplilier and the air, and is the means of con>erting the reproduced sound into natural sound. 'i o be successful in a theater, a speaker niu.-.t deliver sound into every portion of the auditorium in a perfectly natural way, without the slightest inclination to being "tinny," "muffled," or "boomy." It is not onb essential that the speaker have a com plei.; frequency response range which musl rep.oduce music with all its low frequencies, and with all its harmonics, and reproduce spe. ch, so that it can be understood, but il muit be reproduced so as to be heard com picicly throughout the theater. Ill the sa.es talks of the different com pan.es selling speakers of ditTerent kinds for theater use, we have offered to us frequency response curves showing how perfect ly the speaker responds to the different frequencies, but the buyer forgets to ask how are these results obtained. Was a microphone placed directly in front of the speaker? Was a microphone quite a distance away from the spe.iker and off to a side, or was this an avL age response, with the microphone placed in different parts of the theater, in order to tind out what response was obtained in the e different parts? 1 may say that as fai as the buyer is concerned, if frequency response curves are offered without having cun hrniation of the method used in taking these response curves, then these curves are value less. A wrist watch may have a perfect mechan ism in it to keep iierfect time, and yet, no one would ever think of hanging a wrist wa.ch from the Woolworth Tower to show the time to passersby. This is exactly the conditions of a speaker. A speaker may have a 1 erfect response, but yet may not be suitable for the purpose to which it is being use.l, as aside from the fact that its response must be right, it must have all the qualifications which are mentioned above, and that is be able to distribute sound completely through out the theater, uniformly. This is the difference between using the correct type of speaker and the improper speaker. In one case, when we sit in a certain position in a theater, we will gel beautiful results, but if we sit in anothei section of the theater, everything is in a jumble, nothing is understandable, music i; one complete mass of sound instead of being individual instruments playing in harmony. In the other case, everything is clear and distinct in every part of the theater. MOTION PICTURE APPARATUS of Every Type Consult Us and Save Money REPAIR SHOP with Experts on Professional Cameras Right on Premises uiiuoa^HBys .▼▼llO West S2''St,N««york.NLy** Phone Penna. 0330 Motion Picture Department U. S. and Canada Agents for Debrie There are two types of speakers which arc at present available for theater use. One is the electro-dynamic cone type and the other is the electro-dynamic unit with exponential horn. Aside from the fact that the electro-dyr.amic cone is about 25 per cent as etiicient electrically as the electro-dynamic unit with the exponential horn, and aside from the fact that the cone unit carries with it a good deal of booming, sizzling and crackling which IS due to the paper diaphragm resonating, we do not think the dynamic cone is a proper speaker to use in a theater, inasmuch as the high frequencies are released in a very narrow band from the center of the cone, whereas, the low frequencies come from the edge of the baffle, which is quite a distance from the center. Besides the response being slightly out of phase, if we step off this narlow band, we lose all of the highs entirely which predominate in speech. An electrodynamic horn unit with an exponential horn IS extremely directional, forcing all the sound directly in front of the speaker. The air in front of the speaker is moved practically as a solid mass, which fills the theater completely with sound. Where speech is being repro duced, it can be heard in every section of the theater; where music is reproduced, it can be heard as well. Both speech and music .ire distinct and individual instead of being inmbled. Witli reference to the exponential type of horn, this particular type is used in pref ereiice to the conical one because it has been shown experimentally that of all horns having a given size, a given length and a Kiven terminal area, the exponential horn projects sound most uniformly over the complete fi equency range. Just what is an exponential horn? It is a horn which expands exponentially, or to ■ lut it more simply, it is a horn whose areas double at equal intervals along its length. These intervals determine the low cut-off of the horn. If the intervals are short the cnt-off is high, if the intervals are long the cut-off is low. It is unnecessary in this artick to go into the exact design sliowing the ex pansion required for a given ctit-off, but we might mention that where a cut-off of 6-1 cycles is desired, it is customary to double the areas every 12 inches. Where a cut-off of 128 cycles is desired, the areas double every 6 inches, and etc. In addition to the cut-off being determined by the expansion late, in order to prevent resonance of the bell, the bell opening must be of the propei size to conform to the cut-off for which the liorn is designed. A horn with a cut-off of 64 cycles must have a bell opening approxi mating 2100 square inches. If this bell open ing is made considerably smaller, there wil' be a good deal of resonance at the bell, which will muffle the low response. Inasmuch as low cut-offs are necessary for horns built for theater use, these horns require extremely long air columns, from aliout 10 to IS feet. It is necessary, therefore, to coil these horns up in some way in order to save space. The bends that are made should be made at points where the sound path is very narrow, so that the inside travel and the outside travel of the wave front are equal. Inasmuch as a horn is a carrier and projects sound which is a complete whole in itself, having .all the harmonics and qualities of the individual instruments being reproduced through it, it is essential that it have no resonance of its own. For this reason, very many horns on the market are failures owing to the fact that the walls of the horn are extremely resonant. Paper, plaster, thin metal, thin wood, combinations of any of these, all make for extremely resonant horns. Of course, if these particular types of materials were made thick enough, resonance could be prevented, but this would result in horns which are commercially impractical on account of extreme weight and cost. Wood should be a minimum of 1" thick, paper about 2", plaster about 4" and metal at least Vs". From this can be seen that horns manufactured from anyone of these types ot materials become entirely too bulky and too expensive to produce. The Racon, for theater use, employs a material of cloth which is impregnated with a gelatine composition, baked in ovens at temperatures of over 350 degrees, where the moisture is driven off and the horn is baked hard. Owing to the fact that this horn is made over a metal form, which form is taken out after the horn is completed, the interioi of the horn is an unbroken surface from it initial opening to its bell. This method of manufacture is patented by this companj and gives an extremely light and extremely rigid horn, and one that is adapted for ai types of haid usage without fear of damage. It has practically no resonance owing to the fact that it is made out of cloth, and it is therefore an ideal sound projector. Since horns are only projectors of sound. It is necessary to have some device on the small end of the horn to create a sound and wave motion. This, for theater use should be an electro-dynamic type unit, and must be of very high quality, as the horn plus the unit, which is a speaker complete, must give projection of sound in a moving picture the ater that is as nearly perfect as it is pos sible to obtain, as otherwise it wi 1 be evident in the proceeds of the box office. A electro-dynamic horn unit manufactured by Racon for use with the horn has a marvelous frequency response, can withstand the complete undistorted output from the commercial amplifiers without rattling, and owing to the patented type diaphragm that it uses a cloth and metal combination, will stand u; under continuous use for an unlimited time without damage. Claims New Film Coating Process Stops Breakage Triple life can be given to prints at no more expense than ordinary processing by a new indestructible coating is claimed in a patent by Dr. Albert Fiedler of Weehawken, N. J., and used by Empire Laboratories of New York. The coating is incorporated in the gelatine over sprockets only and is a hard permanent lubricant that rides smoothly and silently through the projector, and does not wear off as in the case of waxing. Use of this coating is especially designed for the sound track to prevent breaking and smearing of pictures, thus reducing troubles to a minimum. New Contner-Ross Lens Installed Uniontown, Pa. — The State here has added the new Contner-Ross sound projection lens apparatus to their Western Electric equipment. It is a new invention designed to improve the talking cinema, it is claimed, and does away with the necessity of "masking in" one side of the screen giving the audience a full sized picture throughout the performance. No unsightly Perforations Clear, realistic pictures, freedom from eye-strain, and natural tone quality is necessary to win and hold your patronage. To insure projection as good as you had before Sound, to get the best reproduction from your sound outfit, you must have the right kind of a screen. Vocalite Sound Screen is proven best by scientific test. Many successful installations have proved it to be superior in light, definition, and tone quality. It is the only screen optically cmd chemically correct for the projection of Colored Pictures. Full information will be sent on request, cost no higher than any good screen. \r©caLlite SoTumd Screen The First Screen Scie,ilil,cally Perfected for >,,„„,/ Pirmre, Beaded Screen Corp. Roosevelt, New York Porous but not perforated Approved by Electrical Research Products, Western Electric Co., Inc., and other makers of Sound Equipment. Fire Proof Non Inflammable