The goal of this work is to propose a new strategy for the attenuation of the traffic noise, which constitutes one of the main sources of acoustic pollution in urban and suburban areas. This strategy is based on the measurement of the noise radiated by each individual vehicle using an electro-acoustic system, composed of two microphones for the acquisition of the engine and of the rolling noise. These microphones have been situated inside the engine hood and close to the right back tire respectively. The signals have been recorded for diesel and petrol engines and through typical urban and suburban courses with different persons. Using this procedure, we aim to characterise the drivers responsible of the highest noise levels producing maximum annoyance.
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| The position of the microphones close to the engine (left) and close to the tyre (right) | |
The near-field measurements have been then extrapolated to far field positions using an analytical filter that takes into account absorbing properties of the propagation floor. For the internal signal it has been necessary to characterise the acoustic properties of the engine hood experimentally using an array of microphones surrounding the vehicle. The propagated noise is calculated considering the absorption due to the geometrical divergence, the absorption by the air, and the effect of the propagating surface. A comparison between measurements and prediction is performed with a simultaneous acquisition of the near-field and far-field levels situated at 7.5 m long and 1.2 m high from the vehicle when circulating at different velocities. The proposed formulation has been shown to be reliable for the extrapolation of the traffic noise in the medium and high frequencies. The signals extrapolated to the receiver position could be compared with the current normative to propose recommendations concerning noise control actions.
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| Power Spectrum of the experimental noise levels measured by the engine microphone (blue), by the rolling microphone (red), by the far-field microphone (green) and calculated with the analytical model (pink) for a velocity of 80 km/h | |
