Abstract: Method and apparatus are disclosed for reducing breathing-wave induced no in a liquid-filled elongate hose housing a hydrophone array. The arrangement involves sensing radial strain induced in the hose wall by the breathing waves (created as the hose is drawn longitudinally through water) and subtracting a multiple of the sensed value thereof from the array hydrophone output. Arrangements for measuring the breathing-wave-induced wall strains include (1) relative phase shifts in light passing through the sensing arm of an optical fiber interferometer, and (2) signal currents generated from piezolectric polymer both of which are disposed inside the hose wall surrounding a hydrophone.

Abstract: An method and apparatus for active noise cancellation in a conduit carrying a liquid, employing a detector hydrophone, an acoustic canceler downstream of the detector hydrophone, an error hydrophone, and an adaptive filter. The outputs of the detector hydrophone, acoustic canceler, and error hydrophone are directed into the adaptive filter, which uses them to select the form of acoustic signal which the canceler directs into the liquid to cancel the noise. One embodiment of the invention employs two such cancellation circuits, and an additional adaptive filter which globally optimizes the cancellation of both circuits.