The film daily year book of motion pictures (1930)

is being reproduced, it can be heard in every section of the theater; where music is reproduced, it can be heard as well. Both speech and music are distinct and individual instead of being fumbled. With reference to the exponental type of horn, this particular type is used in preference to the conical one because it has been shown experimentally that oi all horns having a given size, a given length and a given terminal area, the exponental horn projects sound most uniformly over the complete frequency range. Just what is an exponental horn? It is a horn which expands exponentally, or to put 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 cut-off is high, if the intervals are long the cut-off is low. It is unnecessary in this article to go into the exact design showing the expansion required for a given cut-off, but we might mention that where a cut-off of 64 cycles is desired, it is customary to double the areas every 12 inches. Where a cut-oft of 128 cycles is desired, the areas double every 6 inches, and etc. In addition to the cut-off being determined by the expansion rate, in order to prevent resonance of the bell, the bell opening would be of the proper size to conform to the cut-off for which the horn is designed. A horn with a cut-off of 64 cycles must have a bell opening approximating 2100 square inches. If this, bell opening is made considerably smaller, there will 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 about 10 to 15 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 harmonies 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 Y%" . From this can be seen that horns manufactured from anyone of these types of 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 interior of the horn is an unbroken surface from its initial opening to its bell. This method of manufacture is patented by this company and gives an extremely light and extremely .rigid horn, and one that is adapted for all types of hard 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 electrodynamic type unit, and must be of veryhigh quality, as the horn plus the unit, which is a speaker complete, must give projection of sound in a moving picture theater that is as nearly perfect as it is possible to obtain, as otherwise it will be evident in the proceeds of the box office. An 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 up under continuous use for an unlimited time without damage. Read The Film Daily For Foreign News 987