Active noise control in a tractor cabin: implementation challenges and experimental testing in driving conditions

Tractor drivers are often exposed to high levels of low-frequency noise for prolonged periods, leading to discomfort and, in some cases, hearing loss. A major contributor to the noise transmitted into the cabin is the tractor engine, which generates a series of harmonic components, predominantly in the low-frequency range (below 1000 Hz). Due to space limitations inside the tractor cabin and the necessity of transparent surfaces to ensure visibility, effective passive noise mitigation can hardly be implemented. Active noise control (ANC) represents a suitable and modern technique to attenuate unwanted noise. This paper presents an experimental evaluation of a multi-channel ANC system applied to a tractor cabin, aimed at reducing the driver's exposure to noise generated by a four-cylinder engine. The system implements the well-established filtered-X least mean squares (FXLMS) algorithm in a multi-channel feedforward configuration to generate control signals, employing an accelerometer mounted on the engine as a reference sensor. Initial tests were carried out under stationary conditions, by varying the engine's revolutions per minute. Subsequent tests were performed under different driving conditions on an asphalt ring track, varying gear, range, and crankshaft rotational speed. The results demonstrate the effectiveness of the ANC system in reducing engine-related noise components between 80 Hz and 500 Hz. The low-frequency limit is imposed by the frequency response of the control loudspeakers. To enhance algorithm efficiency, a digital low-pass filter is applied to prevent instability introduced by high frequencies.