Accuracy requirements for ear-positioning in active noise control headrests for automobile road noise with different secondary source configurations

This paper investigates the impact of head movement on the performance in reducing road noise inside a vehicle cabin using active noise control headrests. Based on the rigid sphere scattering model in free space, a performance analysis model for active noise control headrests is established. Numerical simulations are conducted to compare the noise reduction losses caused by the translation and rotation of the rigid sphere when using headrest speakers or seat speakers as secondary sources. Additionally, an empirical formula is developed to predict the noise reduction losses due to head movement, and the accuracy requirements for ear-positioning are discussed. Finally, road test results in an electric car running at a constant speed of 50 km/h validate the simulation findings. The experiment analyzes the noise reduction at the ears due to head translation and rotation and provides accuracy requirements for an in-vehicle ear-positioning system. The results show that head deviation from the initial position leads to a decrease in noise reduction, with greater losses observed at higher frequencies, larger relative distance changes to the secondary sources, and higher initial noise reduction levels. When using headrest speakers as secondary sources, the accuracy requirements for ear-positioning are higher. If the initial noise reduction is 9.3 dBA and the allowable noise reduction loss is within 3.0 dBA, the ear-positioning system should maintain a translational accuracy better than 1.6 cm and a rotational accuracy better than 5.9°.