The On-Board tire sound testing technique is a research tool characterized by a near field measurement and recording of tire sound generated at the rear of the tire footprint. The measuring microphone is located directly behind the tire within the envelope of the slip stream of air moving around the tire. The test allows the continuous coast-down through the complete operating speed range, excluding the Doppler effect characteristic of the coast-by test. By presenting the coast-down results in a three-dimensional (speed, frequency, sound level) graphical manner, the speed dependent tread sound and constant frequency resonant sound can be easily recognized.
