6561 



HYDROGRAPHIC MANUAL 



Page 614 



(d) The sensitivity of hydrophones of the same design must be uniform throughout the useful 

 frequency spectrum. This is especially important in hydrophones used on sono-radio buoys, as 

 nonuniform hydrophone characteristics would require a redetermination and readjustment of the 

 audio-amplifier gain each time the hydrophone of a sono-radio buoy was changed. Where all hydro- 

 phones of a type have uniform characteristics the sono-radio buoys and hydrophones are interchange- 

 able. 



(e) The hydrophone should be designed to minimize noises created bj- water currents or caused 

 by the motion of the hydroplioiie through the water. 



(/) The hydrophone must be portable for easy handling and light so that elaborate and bulky- 

 supports are not necessary. 



(g) The hydrophone must be strong and watertight, to withstand the hydrostatic pressure at 

 the depth where the hydrophone is normally suspended and all the shocks to which it may be sub- 

 jected during the handling of the sono-radio buoy. » 



During the development of R.A.R. many experimental types of hydrophones were 

 tested and a number of different designs have been used. Most of these were intended 

 for use with shore stations and need not be described, since sono-radio buoys are now 

 used almost exclusively. 



Two principal types of hydrophones are now used by the Coast and Geodetic 

 Survey: (1) The Dorsey hydrophone — used almost everywhere on the Atlantic and Gulf 

 Coasts and, since 1940, more and more in Alaska waters; and (2) the Vincent hydro- 

 phones — in the past used mostly on the Pacific Coast and in Alaska waters. 



6561. Dorsey Hydrophone 



The Dorsey hydrophone is a pressure-operated device with a thin hard-rolled brass- 

 diaphragm attached to a massive body which is little influenced by the sound wave. 

 As the diameter of the diaphragm is small compared to the wave length of the bomb 

 sound, this unit has little or no directivity. 



The assembled hydrophone is illustrated in figure 137. A flange near the edge of the diaphragm 

 fits loosely into a circular groove cut in the heavy brass base, a circular gasket of square cross-section 



SCALE IN INCHES 



Figure 137.— Dorsey hydrophone. 



fitting in the groove. The diaphragm and base are bolted together with 16 }^-28 brass bolts. A 

 cylindrical section of brass tube is secvired by watertight soldering in a recessed part of the back of 

 the base plate. The back end of the cylindrical section is closed by a rubber plug. The plug is a disk 



