Active cancellation of noise in a liquid‐filled pipe using an adaptive filter

An experimental study of active attenuation of sound in a liquid‐filled pipe is reported. The pipe was connected to a ‘‘noise’’ source at one end and opened into a large liquid reservoir at the other. A sound source for active cancellation purposes was located midway between the two extremities. A cancellation signal to drive the active source was generated by a digital, adaptive filter from hydrophones located in the duct and reservoir. The reduction in noise level was measured at the exit of the pipe into the reservoir and at selected locations in the reservoir. Sound attenuations in the 20‐dB range were observed.