The Control of the Interference Pattern From a Double Exhaust Tailpipe During a Motorcycle Pass-by Test: An Additional Free Muffler

A double tailpipe from the same muffler acts as two point sources in phase: this produces a characteristic interference pattern with high-energy and low-energy lobes oriented in the space. This interference pattern has been analyzed in detail by means of a computational code, to check how the double tailpipe design parameters (mainly the tips distance) affect the interference phenomena during a pass-by noise test, in order to reduce the noise levels at the microphones. Being the simulation promising, a prototype muffler with two movable tips has been realized and tested with a motorcycle on the road: the data analysis, in different frequencies, showed a good agreement with the model. A methodology has been developed and validated to exploit the interference phenomena in order to reduce the noise radiated from the tailpipe to the roadside, exploiting the free field as an additional silencer.