When tires with circumferential grooves are in contact with pavement, tubes are formed that are open at the leading and trailing edge of the contact patch. In the simplest case of straight ribs, and no other tread pattern, these tubes or "organ pipes" can radiate sound efficiently at their resonant frequencies. Radiation from the open ends is either in phase or out of phase depending on whether the tube harmonic is odd or even. This creates a complex sound field to the side of tire featuring local maxima and minima as measured near the tire. For more complex tread designs, identification of the effects of tube resonance can be accomplished by detail source mapping near the tire sidewall, by measurement of the tire at different operating speeds, by operating on porous pavement, or by filling the grooves with open cell foam. Using these means, tube resonance has been identified on truck and light vehicle tires of different design. Tube resonance effects have also been identified for longitudinally grooved pavement. These results are discussed in this paper along with a brief discussion of the underlying theory.
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