An integrated acoustic–mechanical development method for off-road motorcycle silencers: from design to sound quality test

Vehicle noise is one of the main sources of complaints because it is widespread and active in almost all environments, from urban areas to rural context. The present work aims to describe a practical procedure to design silencers for off-road motorcycles so that, once produced, they are lightweight, do not affect the engine performances and cut noise emissions to a sustainable limit. The required noise reduction, usually around 35–40 dB, can be achieved only by carefully designing the exhaust system. The first part of the paper provides the theoretical background of noise propagation in ducts, describes the main attenuation devices as tools the designer can use in the development process and outlines the workflow. In the second part, a case study of silencer optimization is presented: the noise emitted by a real off-road motorcycle is characterized and, once the sound pressure level and the mass flow generated by the engine are known, a silencer fulfilling noise attenuation, size and pressure drop requirements is designed, 3D-modeled and rendered. The outcome of the acoustic design process can be used to perform virtual sound quality tests, which can be of interest for manufacturers to catch the attention of passionate users.