Application of Nearfield Acoustical Holography to Tire/Pavement Interation Noise Emissions

Tires are one of the dominate sources of exterior vehicle noise. In this study, Nearfield Acoustical Holography (NAH) is used to investigate the sources of noise generated by tire interaction with an outdoor road surface. One tire on a two wheel trailer is examined while towed by a vehicle at 56 km/hr (35 mph) along a smooth, consistent road surface. The complex pressure is measured at discrete points along a plane parallel to the side of the tire by scanning with an array of five microphones. Because of the incoherence of noise generated at the leading and trailing edges of the contact patch, and radiation from the side wall, three reference microphones are used. NAH is used to reconstruct the pressure on planes towards and away from the tire, thereby obtaining a three dimensional image of the acoustic pressure, particle velocity, and intensity for noise generated at the contact patch leading edge and trailing edge, and by the tire sidewall vibrations. The findings should identify sources on the tire, as well as provide a better understanding of tirelpavement interaction noise generating mechanisms.