1,257,836. Subaqueous transducers. WESTINGHOUSE ELECTRIC CORP. 13 March, 1969 [13 March, 1968], No. 13256/69. Heading H4J. A pressure compensated transducer for subaqueous use at great depths comprises a piezoelectric transducer element 10 having its side and rear faces spaced by a distance d from an inertia loading mass 12, e.g. of aluminium, lead, brass or gold. A sound-absorbing material 14 such as butyl rubber in which is embedded aluminium powder or flake acts as a pressuretransmitting means. Its specific acoustic impedance approximately equals that of sea water. The distance d is n#/4 where n is an odd number and # is the wavelength of a wave in material 14 at the operating frequency or at a slightly different frequency. Inertia loading masses 20, 21 decouple unwanted radiation in the material 14 from the surrounding sea water. A cover 24 and transducer fluid 26 both have acoustic transmission characteristics similar to that of sea water. Preferably the inertia loading mass 12 is of aluminium one inch thick and the transducer operates at 60 kHz, whereby the impedance of the mass 12 is approximately twenty times that of sea water. In a second arrangement (Fig. 5, not shown) the inertia loading mass is of lead. A second outer inertia loading mass (42) is spaced a distance d<SP>1</SP> from the first, the intervening space being filled with further sound-absorbing material. In a further arrangement (Fig. 8, not shown) a single inertia loading mass is provided, but the intervening space is filled with silicone fluid, the transducer element being resiliently held by corrugated metal between the element and inertia loading mass. A disc-shaped transducer element is also envisaged. In all embodiments the transducers are operative at frequencies below 100 kHz and sound energy radiated from the rear and sides of the transducer element is substantially absorbed while a forward beam is obtained.