Experimental investigation into the role of nonlinear suspension behaviour in limiting feedforward road noise cancellation

Abstract

Feedforward control of road noise in cars is limited by the difficulty of finding reference signals that have adequate coherence with the sound at the passenger head positions. The dynamics of car suspensions are known to be nonlinear and could therefore restrict the coherence between reference and error sensors and limit the performance of linear feedforward road noise control systems. This paper presents two sets of experiments that investigate nonlinear vibration transmission through a car suspension and its implications for road noise control. The first experiment was conducted on an electric car; an analysis of the maximum theoretical cancellation that can be achieved with different sets of reference signals is presented and the influence of ‘smooth’ and ‘rough’ road surfaces is investigated. In the second set of experiments, components from the car’s suspension systems are tested in a laboratory. The experiments show that the car’s hydraulic dampers are strongly nonlinear at low audio frequencies, and suggest that they limit the cancellation that can be achieved with a linear controller.