Experimental Tests of a Multichannel Active Noise Control System for the Cancellation of Engine Noise Applied to the Cabin of a Tractor

Active noise control represents a valid solution whenever it is necessary to attenuate a disturbing noise in the low-frequency range. One example of application is the case of tractors, in which the agricultural operators are exposed for several hours per day to loud low-frequency noise, mainly associated with the harmonic components of the engine noise. In a previous work, a multichannel feedforward active noise control system with filtered-X least mean squares (FXLMS) algorithm was successfully tested on a tractor cabin in a hemi-anechoic chamber, to attenuate the simulated noise generated by a dodecahedron placed outside the cabin. In this article, the same active noise control system is applied to a motionless tractor and used to cancel the first orders of the engine noise, propagating from the engine into the cabin, at the driver’s head position. A comparison between the use of different reference signals is proposed. These signals were measured with a microphone near the cooling fan, an accelerometer on the outlet of the turbocharger and an accelerometer on the compressor of the braking system. It can be observed that the reference signal measured with the accelerometer on the turbocharger is the most coherent with the signals of the two error microphones and produces a more stable behavior with respect to the other positions. The results for different stationary values of rounds per minute show that the system is able to act on the first orders of the engine noise up to the third-octave band of 630 Hz.