Active control of cabin noise Cabin noise has been a concern for transport engineers since the time of horse-drawn carriages. A group of European organisations worked together to develop and test several prototypes employing Active Noise Control (ANC) techniques to combat cabin noise in automobiles and trains. Digital Economy © Photodisc Cabin noise is unwanted sound that occurs in the cabin of an automobile, train, airplane or other form of transport deriving from the engine, exhaust system, wheels and other components. Cabin noise is associated with increased levels of discomfort, stress and health problems. There are both active and passive methods that can be applied to reduce cabin noise. Passive methods rely upon sound dampening or absorbing materials, such as foam, which are heavy and add unwanted weight to the particular vehicle and are not effective against low-frequency noise. On the other hand, Active Noise Control (ANC) seeks to prevent noise by using cancellation techniques, also known as anti-sound. It works by producing a sound field that mirrors the sound field of the disturbing noise, which cancels out the noise when played back. ANC techniques are advantageous for the automobile and train environments due to the comparatively light weight of the components and their effectiveness against the entire frequency range. A group of European organisations, including several high profile automobile manufacturers (e.g. Fiat and Ford), participated in a European-funded project to advance passenger comfort through technology. The group created innovative actuators and sensors (which combine to form transducers) from electro-mechanically treated film (EMFi), resulting in an extremely light ANC system. EMFi can be mass-produced at relatively low cost. The EMFi transducers were installed in both automobile and train cabins and tested in a controlled laboratory environment. The automobile set-up was supplemented by two ordinary car loudspeakers. The results show that the EMFi transducers can reduce high level operation noise to the level of background noise. However, improvements are necessary at low frequencies (in the range 100-600Hz) in the car environment and at higher frequencies in the train environment where some noise amplification (rather than cancellation) occurs. The project partners seek continued support of their research in this increasingly important field.
