ONE-DIMENSIONAL ACTIVE NOISE-CONTROL IN 2 DIRECTIONS

An experimental study of a duct with active noise cancellation both '' upstream'' and ''downstream'' of a primary sound source is presented; this is an extension of the common single-channel installations, where sometimes a detrimental sound radiation from the upstream end occurs. The two adaptive feedforward systems, controlled by the filtered-X LM S algorithm, operate almost independently of each other. The duct sect ion between the two secondary sources becomes an acoustical resonator with sound-soft reflection at both ends. Some passive absorption in th e duct is advisable to avoid resonance overload of the active componen ts.