Motion Picture Herald (Apr-Jun 1931)

40 MOTION PICTURE HERALD May 2 3, 1 9 3 1 NEW ERPI MICROPHONE CUTS STUDIO TROUBLE New Erpi Microphone Bell Developmeni Ready; W. E. Says It Is Less Affected by Moisture and Barometric Pressure A new Western Electric microphone operating on a principle similar to that of the first telephone transmitter used by Alexander Graham Bell will be marketed by Electrical Research Products for use in recording talking pictures. The microphone, already in use in a number of studios for testing, and known as the Western Electric electrodynamic transmitter, possesses many improvements over the condenser type microphone generally used in recording until now. The new transmitter is a development of Bell Laboratories. Less Affected by Moisture Its use is said to eliminate several recording problems ; one of which has been the difficulty in hiding the microphone from the view of the camera. The new microphone is smaller and its associated amplifier may be located as far as 200 feet from the microphone, making it much easier to hide from the view of the camera. The amplifier for the condenser microphone was built as an integral part of the microphone housing and made it extremely difficult to camouflage in many sets. Other advantages claimed are that it is less affected by dust and moisture and need not be kept in a desiccator. It is unaffected by changes in temperature and barometric pressure. It is a further contribution in noiseless recording since its associated amplifier is quieter in operation. The transmission characteristics of the transmitter are superior and distortion caused by cavity resonance has been practically eliminated thus increasing quality and reality in recording. Increased volume is obtained since the transmitter and associated amplifier give from 10 to 15 decibels more overall gain than the condenser transmitter and amplifier. The principle on which the transmitter operates is the inverse of that employed in the Western Electric 555-W receiver used in the Western Electric sound system. In this receiver or any dynamic loud speaker the magnet system is so constructed as to produce a circular air gap, across which extends a radial magnetic field, between the inner pole and the surrounding outer pole. In this air gap is situated a thin circular coil which is attached to the diaphragm. If a sound current is passed through this coil, the electrodvnamic reaction between the current and the field will cause the coil to execute axial vibrations corresponding to the modulations of the sound current. Permanent Magnet Used Through the medium uf the diaphragm and horn, or baffle, these vibrations reproduce the original sound. This action can be readily reversed; if a sound falls on the diaphragm, causing the diaphragm and coil to vibrate, there will be generated in the coil a small alternat The new Western Electric electrodynamic transmitter mounted on a stand as used in studios. On the left is a closeup of the device, unnnounted. ing voltage which corresponds to the impinging sound waves. This is the way in which the electro-dynamic transmitter operates and indicates the origin of its name. The construction of the new transmitter is very similar to that of the 555-W receiver, except that instead of an electromagnet a permanent magnet of cobalt steel is used. There is, of course, no horn or baffle. The diaphragm if of thin duralumin. The coil is of edgewound aluminum ribbon. The diaphragm is protected by means of a disc of perforated sheet metal mounted in front of it and this in turn is covered by a thin piece of black silk. So far as is known this is the first time that the electro-dynamic principle has been used commercially in a transmitter. PREDDEY REFLECTOR LAMPS ON ATTRACTIVE TERMS CAN YOU AFFORD TO DISREGARD THEIR MANY ADVANTAGES ON SUCH EASY TERMS? Here is your chance TftlM IfiQlCaTOff ARC Ar-JU5TME.N. 5CR€\ TAHES 12' CARBOnS IN fRONT A BACH flAifi FCCO KMOe PRICE $250. EACH PAYABLE $12.50 Down and $12.50 MONTHLY No Interest or Other Charges Get Our Bulletin THOUSANDS IN USE TRY THEM FOR 30 DAYS AND NOTE THE BIG IMPROVEMENT IN PROJECTION AND SAVING ON BOTH CURRENT AND CARBONS 138 Golden Gate Avenue SAN FRANCISCO Every Theatre Needs These as a part of its Equipment RICHARDSON'S MOTION PICTURE HANDBOOKS Vols. 1 and 2 $ 6.20 Vol. 3 (on sound only) $ 5.10 Combination price (the 3 volumes) $10.20 Building Theatre Patronage $ 5.10 (By Barry & Sargent) We Are Handling Them for the Convenience of the Trade Motion Picture Herald Bookshop 1790 Broadway New York, N. Y.