Active noise cancellation: air conditioner and transformer case study

Two cases of active noise cancellation technique are discussed in the paper. A feedforward control systems for both cases were used. FxLMS (Filtered Least Mean Square) algorithm for noise reduction of air conditioner is implemented whilst sub band LMS utilized in transformer case. To provide a good quality of the reference signal the special method of flow isolation for reference and error microphones is proposed. The noise reduction efficiency of 15 and 10 decibels at frequencies 90 and 240 Hz is provided using proposed configuration of the system. Three tonal components 120, 240 and 360 Hz are dominated in transformer noise spectrum. Implementation of sub band FxLMS algorithm for transformer case has shown the high efficiency of proposed technique within local area for tonal component 120 and 340 Hz. The most wide silent zone at frequency 240 Hz is revealed during study.