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In this study, multi-planar Nearfield Acoustical Holography (NAH) is used to investigate noise radiated from the front, side and rear areas of single tires on a two-wheel trailer. Contributions to the radiated noise from the leading edge, trailing edge, and sidewall of the tire are identified. Two tires - an experimental monopitch tire and a production passenger car tire - are evaluated on a smooth asphalt pavement at 58 km/hr. From the measured complex pressure, acoustic intensity is reconstructed on three planes surrounding the tire using modified NAH procedures. Additionally, sound power levels are presented in tabulated and spectra forms. Tire noise generating mechanisms are inferred based on the results.

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.