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Signaling With a Multi-Unit Electric Air Oscillator oscillator was designed to meet demand for a powerful air signal which would be efficient and have low maintenance and repair costs. The construction and method of operation of the multiunit air oscillator differ fundamentally from those of other sound producers. It consists of two electric air oscillator units mounted one above the other and so spaced with relation to each other that the maximum efficiency of the combina- tion results. The axis of the horns of one unit is at right angles with the axis of the horns of the other unit. The construction of each. air oscil- lator unit comprising the multiunit air oscillator is similar to that of a telephone receiver. It consists of a powerful electromagnet so arranged that, when it is energized by alternat- ing current, it causes an armature rigidly fastened to each diaphragm to oscillate at a definite frequency. A cone shaped horn or trumpet and a re- sonating chamber are placed in front of each diaphragm and so proportion- ed that the maximum sound is emit- ted. The width of each oscillator unit is 42 inches and the overall height of the two combined units is 63 inches. The total weight is 2100 pounds. Te Multi-unit type electric air Signal Intensity and Distance Numerous experiments with fog signals have shown that the signal intensity at a distance bears very little relation to the signal strength near the source. The major portion of the sound produced by the average steam or air whistle is dissipated in overtones in the vicinity of the whistle. The comparatively pure low-pitched fundamental or master tone which is heard at a distance from such a steam or air whistle comprises what is left, after absorption by the atmosphere, of that small portion of the total energy which originally existed in the signal at that tone. Through the perfection of a design whereby perfect resonance is affected combined with the correct adjustment and accurate control of the frequency of the alternating current used to energize the multiunit air oscillator, the Submarine Signal Co. produced a fog signal with a pure tone of great carrying power. The aim in the design of fog signals should be to concentrate all of the sound energy into the mas- ter tone. Another advantage in the use of a pure signal developed electrically, is This article was prepared by a mem- ber of the staff of the engineering de- partment of the Submarine Signal Co., 160 State street, Boston. the feasibility of increasing the amount of sound energy developed at any point by increasing the number of units. By utilizing two units, for instance, as is done in the case of the multiunit air oscillator and sounding them in synchronism the sound out- puts from the two units are additive and, consequently, the intensity of the Signal is increased. This increase can be made as great as is desired by in- creasing the number of units. Creating Sound in One Plane This ability of the air oscillator units to, operate together makes it pos- sible to concentrate the sound in a horizontal plane. By mounting elec- tric air oscillator units one above the other and in the proper relation to each other, the sound can be transmit- ted horizontally where it is desired. Comparative tests made between one of the units used to make up the multiunit air oscillator and a 12 inch steam chime whistle show that the single unit will give a signal which is audible at substantially the same dis- tances} as is the 12 inch steam chime whistle. Therefore, if the multiunit air oscillator is installed on a light- vessel and through some mischance one of the units becomes inoperative the other unit can still be used effec- tively as a first-class fog signal. The necessity for furnishing a standby fog signal is eliminated. The development of a full power sound signal is practically instan- taneous. There is no delay between the closing of the key and the produc- tion of full power by the signal, as sometimes occurs with either steam or air operated whistles. The installation of the multiunit air oscillator near the power plant is unnecessary since the power is trans- mitted electrically. By the use of sea or shore cable this oscillator can be installed at remote places. Performance Tests Show Range A statement of ranges obtainable with air signaling devices may be mis- leading since, if the maximum ranges at which the signal had been heard under favorable conditions were given, one might expect better ranges than would ordinarily be obtained, while, on the contrary, if minimum ranges were given the device would be put at a disadvantage. To overcome this difficulty the Submarine Signal Co., decided to show ranges obtained with the multiunit air oscillator in com- parison with existing fog signals. The multi-unit air oscillator was compared for range of audibility with a 12 inch steam chime whistle oper- MARINE REvIEw—June, 1932 ated at 60 to 65 pounds pressure. From a test where the multiunit air oscillator was compared with a 6-inch steam siren and a 12 inch steam whistle the following results: With listening vessel underway maximum range of siren 23/5 miles; maximum range of whistle 4% miles; maximum range of multiunit oscilla- tor; not determined but every blast could be heard 7% miles. With listening vessel stopped; siren could not be heard at 3.7 miles, heard whistle 74% miles but missed many of the blasts; heard every blast of multi- unit oscillator plainly 7% miles and much louder than whistle. The siren and steam whistle used in the. tests were operated at 60-65 pounds pressure. The efficiency of the multiunit air oscillator is obvious, since the power consumption of this unit during the blast is approximately 6600 watts, whereas the input of the steam whistle is many times greater. The multiunit air oscillator has no moving parts that require lubrication. The only parts of the air oscillator that move are the ones that vibrate. Hence, there is no need for lubrica- tion because of the absence of friction. The multiunit air oscillator re- quires no _ periodical inspection of parts and no adjustments. Its opera- tion is simple; all that is necessary to put it into operation is the closing of a switch. The entire maintenance and repair of the installation are confined prac- tically to the power unit inasmuch as the expense involved in painting the fog signal itself is slight. The only cost, therefore, which should be con- sidered in arriving at the cost of oper- ation is that of the electricity which is used. U. S. Navigation Laws Arthur J. Tyrer, commissioner of the bureau of navigation, recently announced that a new volume of nay- igation laws now in force has been issued and is ready for distribution. The title is The Navigation Laws for 1931 and it contains a compilation mainly of those laws now in force from the first one passed in 1789 and signed by President Washington for the collection of tonnage taxes, to the latest. An effort has been made to confine this volume, which is a book of about 460 pages, to the laws actually in force with which owners, masters and agents of vessels should be acquainted. The new book is divided into ma- jor sections covering laws on meas- urement, load lines, documents, of- ficers of merchant vessels, merchant seamen, seaworthiness, inspection of steam vessels, discrimination and re- taliation, entry and clearance, cus- tom laws directly relating to ves- sels, and many other interseting sub- jects. 31