leads to an appropriate source of electrical power to be hereinafter described additional apertures not shown in mandrel 74 may be provided if necessary for routing end leads of coils 90 and 92 in like manner acoustic reflector 76 will similarly to base 64 include an upper o ring retainer groove 116 which carries an upper o ring 118 for sealing engagement between the outer cylindrical periphery of reflector 76 and the inner surface of housing 60 in this manner it will be understood that an inner volume 124 shown in fig3 will thus be provided which is sealed off from the outside of housing 60 and from areas above and below reflector 76 and base 64 respectively volume 124 will preferably be filled with a fluid such as oil or the like for acoustical impedance matching with fluid 14 referring now to fig3 and 4 in greater detail it will be recalled that these figures are respectively elevational and plan views of the acoustic source 26 of fig2 showing additional detail thereof first it will be noted that internally and longitudinally of middle mandrel 74 reflector 76 and upper mandrel 78 along central axis 28 respective coaxially aligned passages 98 100 and 102 are disposed passage 98 communicates with apertures 94 and 96 thereby providing means for routing end leads of coils 86 92 through apertures 94 and 96 and through passages 98 102 to an appropriate source of electrical energy still referring to fig3 and 4 threaded recesses 104 and 106 are provided in base 64 and threaded recesses 108 and 110 in reflector 76 for threadably receiving matingly threaded end portions.