equipment of the Dynamic Monitor and of the monitor transducer, 

 Only one model of the Dynamic Monitor was constructed and no 

 effort v;as spent in refining the design so that the apparatus 

 could serve as a production prototype o 



Submarine Noise Reduction. 



The submarine noise reduction program required sound meas- 

 urement apparatus in order to determine standards of accept- 

 ably quiet performance which would be calibrated in absolute 

 terms and so permit comparison amon^ the results obtained at 

 different bases and on tests with different ships The New 

 London engineers undertook to assist in the development of a 

 device to meet this problem,, The result was the design of 

 Model OAY Sound Measuring eouipment which provided readings 

 of sound pressure level over a frequency range from 100 to 

 20,000 cycles per second directly referred to o 0002 dyne per 

 square centimeter and over a dynamic range of 110 decibels „ 

 The gear was most useful for overside measurements of submarine 

 sounds, particularly for detecting abnormally noisy auxiliary 

 machinery units during the course of construction,, The equip- 

 ment was made up as a rugged portable unit and was sufficiently 

 flexible in its applications to permit various types of sound 

 measurements on shore, on shipboard, or from small boats „ 



Hot only could noisy auxiliary machinery units be detected 

 and the trouble remedied before the ship left the yard, but 

 overside measurements could also be made on submarines in com- 

 mission or when they were at dock, secured to buoys , or 

 anchored or drifting,, The OAY equipment was customarily 

 located aboard the surfaced submarine with the hydrophone hung 

 overside at a standardized location as near as possible to the 

 noisy part of the auxiliary machinery to be measured,, Noise 

 level readings thus obtained in absolute units could be com- 

 pared with the standard values for acceptable performance, as 

 previously determined. The OAY had a response that was flat 

 for 100 to 10,000 cycles per second and was good to 20^,000 

 cycles per secondo 



Many OAY units were put into use at submarine bases 

 throughout the world and the equipment found application in 

 other types of sound tests where a rugged portable instru- 

 ment with a wide flat frequency response was needed . 



86 



