In order to optimise the performance of an Active Noise Control (ANC) system that reduces low frequency noise inside a van, an exhaustive analysis of its acoustical properties has been carried out. An acoustical characterisation of an ANC system is done in order to determined the best way to captured the necessary input signals related to the primary noise source and the position of the secondary sources that are considered fixed because of space considerations. An analysis of the spectral distribution of the primary noise reveals that every revolution regime is defined by a fundamental frequency. All the predominant components are an integer multiple of this value. When the reference is taken with a mechanical sensor, all these components show similar magnitudes except for the tower ones. An acoustical reference reveals which of these frequencies are emphasised by the vehicle structure. Higher harmonics can present high amplitudes hut not in a stationary way. So these components are more difficult to cancel. The coherence between the primary noise at the reference and error positions is greater at points where the causality principle is not achieved. But it is not a problem when the primary noise is strictly periodic. The coherence is greater for the spectral components with more energy, twice and four times the fundamental frequency of the engine. The coherence for the predominant components of the primary noise, can be considered acceptably high at all the positions tested. The analysis of the secondary paths is necessary to detect frequencies potentially no controllable. The measurements reveals that only frequencies out of the frequency response of the secondary sources can present problems. Finally a power sound map distribution simulation has been done for arbitrary signals ejected by the four secondary sources. This calculation shows that if low frequencies are considered a multiple-channel ANC system should be implemented. When the distribution is A-weighted, a single-channel system can be implemented.
Acoustical analysis aimed at the characterisation of an active noise control system inside a van and the improvement of its performance
Akustische Analyse bezüglich der Charakterisierung eines aktiven Geräuschregelungssystems in einem Lieferwagen und seine Leistungsverbesserung
2002
12 Seiten, 11 Bilder, 4 Tabellen, 4 Quellen
Aufsatz (Konferenz)
Englisch
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