Projection engineering (Sept 1929-Nov 1930)

Page 56 Projection Engineering, September, 1929 core upon The new Best theatre pickup. perfectly. That is true of high and low frequencies. The idea of the Best engineers was to design a pick-up which would give the general public the benefit of a pick-up which would be in every way comparable with those now used in the theatres and which cost well over $200. The Best Theatre Pick-up has a response curve which is remarkably close to the high priced, oilfloated types it is claimed. Needle scratch is appreciably less end record life is thereby greatly increased. NEW GENERAL AMPLIFIERS The General Amplifier Company, 27 Commercial Avenue, Cambridge, Mass., has introduced three new power amplifiers : Models GA 10, GA 20 and GA 30. The GA 10 is a two-stage amplifier employing one 227-type tube, one 230 and a 281. It will deliver approximately 4 watts of undistorted energy to the speaker. The GA 10 amplifier lists for S88. The GA 20 is a three-stage amplifier employing two 250s, two 226s, two 281s and a 227. It will deliver approximately ■14 watts to the speaker. The GA 20 lists at $225. The GA 30 is a three-stage amplifier employing two 250s, two 281s and two 227s. It will deliver approximately 12 watts to the speaker. The price of the GA 30 is $175. All three amplifiers are designed for use with either a magnetic or a dynamic speaker. No output devices are required. Each amplifier employs filters in the plate and grid circuits of the tubes, thus isolating the signal voltage from the plate supply. The General Amplifier Company is in a position to manufacture amplifiers to meet special requirements. THORDARSON R-260 AUDIO TRANSFORMER The Thordarson Electric Manufacturing Co., of Chicago, are marketing a new type of audio transformer of small dimensions, known as the R-260. Though this transformer measures only 2 by 214 inches, it has excellent frequency characteristics. Its fine performance is partly attributable to the Thordarson "DX Metal" which the coils are wound. It is claimed that the R-260 transformer is entirely devoid of resonance peaks and provides excellent performance over the entire audible band. The list price of the R-260 transformer is $5. Thordarson R-260 Audio Transformer NEW AMPLION EQUIPMENT The Amplion Microphone is of an unusual design. The design was the result of the efforts of the engineers to produce a microphone that could be relied upon regardless of the weather or the nature of the usage. The result was a microphone that did not pack during operation and the granular hiss was reduced to a negligible quantity. No metal diaphragm is used in its construction. There are no carbon buttons. These items were eliminated by the engineers forming a narrow channel-way across the face of the microphone. This channel-way is formed with moulded bakelite. It is 3/16" deep, iy2" wide, and 2%" long. At each end of the channel-way is a carbon electrode and the rest of it is filled with a special granulated carbon obtainable only in Europe. These carbon granules are held in position by a very thin rubber membrane. All sound impinges on this membrane, creating a displacement of the carbon granules, said displacement producing a fluctuation of the electric current which flows through them from one carbon electrode to the other. This variation is in direct proportion to the volume of the sound impact and in absolute synchronism with its frequency. This microphone will not blast and will stand up under extremely rough usage. It requires approximately 25 volts d-c. for maximum operation, due to the fact that it has an internal resistance of 500 ohms. At this voltage, a current of 60 milliamperes flows through the microphone, making possible an extremely high sensitivity, wherein sounds produced at the average voice amplitude can be heard as far away as 60 feet. Should the sensitivity be too great, the operator has only to reduce the current flow to any value below 60 milliamperes and this sensitivity will drop in direct proportion. The Amplifier The Amplion Corporation of America has produced a microphone input amplifier that will operate in connection with this microphone. It supplies the energy necessary from 110-voIt 60-cycle current, eliminating all batteries. It has one stage of audio amplification, bringing the energy level of this microphone up to a value equal to a phonograph pickup. This amplifier has three controls. One control regulates the voltage so that it can be adjusted to the current value regardless of the fluctuations on the 110-volt supply. The second control regulates the amount of current that is to be put through the microphone, making it possible for the operator to adjust the microphone for any degree of sensitivity. The third control regulates the volume of the energy put out by the amplifier so that any adjustment of volume can be realized regardless of the sensitivity adjustment. This amplifier has a very unique circuit, which was necessary to obtain such flexibility. This circuit does not employ any of the conventional methods of grid biasing, making it possible to obtain a special patent on this new unique circuit. Due to the high voltage and the high resistance characteristic of this microphone, it is possible to locate said microphone as far as 1000 feet away from the microphone input amplifier without suffering any material loss in either quality or volume. The Horn The Amplion type M-10 Horn is a 10-foot exponential air-column horn, designed to operate in connection with the Amplion Giant Dynamic Horn Unit. This horn has a remarkable flat performance curve from 60 cycles to 6000. It is exceedingly light, weighing only 48 pounds, in view of its large size and sturdy construction. It is made of a wood fiber specially treated with a special type of paint which is necessary for protection against inclement weather and for the efficient projection of all audio frequencies. The Units The Giant Dynamic Unit which is used in connection with this horn is a remarkable invention. Its distinct and unique features lie in the fact that a double sound chamber is employed so that both the low. and the high frequencies are taken off the same diaphragm. This makes possible a much wider frequency range than ever before realized on a speaker unit. The result in its performance is that a remarkable tonal separation is immediately noticed. NEW AUTOMATIC DIMMER FLASHER A new type of Reco dimmer has been developed by the Reynolds Electric Company, Chicago. The company states that no longer is it necessary for a skilled operator to be in constant attendance, for the new type dimmer flasher affords perfect automatic control, and is capable of producing the stage's most difficult mobile color effects. This dimmer is also for use in producing dimming and color-blending effects in the theatre interior, fountains, etc. It gradually dims lights in 50 steps from bright to dark and back to bright. There is no limit to the number of colors that may be softly dimmed and dissolved into one another. NEW GARVER RECTIFIER A new rectifier for motion picture projectors has been placed on the market by the Garver Electric Company of Union City, Ind., manufacturers of National Mazda Regulators. It is claimed that the new rectifier will produce from alternating current, up to 30 amperes direct current of special adaptability to low intensity arc lamps. The rectifier, which is registered as the Garver Kurrent Changer, is said to feature beauty in design, quietness in operation, and aurability. NEW LENS FOR CLOSEUPS Harry Fischbeck, contract cameraman at the Paramount studios in Hollywood, has developed a new lens for closeups and portraits and according to reports this new lens gives a third dimension effect. As a tryout, this new lens is being used for all the closeups of Clara Bow and her supporting cast in "The Saturday Night Kid." Fischbeck claims that he is now working toward the perfection of his new lens where it will permit depth photography and medium and long distances. ACOUSTIC ROARD MADE OF WASTE FARM MATERIALS A new material for treatment of acoustical faults and preparation of desirable acoustical conditions, has been developed, being called Halezite. Use may be made of it in the construction of theatres, of studio stages and sets, and of furniture. It is a synthetic lumber, made out of cornstalks, chaff, wood shavings and other waste material. Working in a New York laboratory, two men have developed a chemical binder which, when sprayed over shredded cornstalks, woodchips and the like, and subjected to tremendous pressure, produces in fifteen minutes a synthetic lumber board in any shape or size desired. Fine veneers, as well as colored wallboard especially desirable for theatres and studios, are an important development of the process. It is said to be cheaper than natural wood. Its sound-proof qualities and fire-resisting qualities are more than ten times those of wood, and it has a high electrical resistance, thus making an excellent insulator. The New York Testing Laboratories, reported in part : "The composition was found to saw, plane and file easily without splitting or excessive tearing. The material has about the same holding power when nailed as the better class of wood, with no tendency to split. The density and hardness of Halezite composition fall within the range from that of soft to hard natural woods. It possesses tensile strength considerably in excess of pine or equal to red oak when taken across the grain. The water absorption tests show no disintegration whatsoever. In the boiling water tests, while the commercial ply wood joints all opened, there was no separation of Halezite veneer from the core, nor any blistering of the top plies on Halezite board. Nor was the cornstalk board affected to any extent by the continuous boiling. "In the fire tests, the board shows more than 200 per cent better fire-resistant qualities than pine wood. "We are particularly impressed with the sound-proof qualities of Halezite composition. Our tests show that the cornstalk lumber has about ten times the sound-proof value of pine lumber, an interesting factor to be considered for modern building construction."