Evaluation of the global attenuation noise coefficient of an active control system in a open space

Ester Naves Machado Borges1
Eduardo Bauzer Medeiros2
1-Coordenação de Ciências, CEFET-MG
2-Dept. de Engenharia Mecânica da UFMG, Av.Antonio Carlos 6627, 31270-901 Belo Horizonte, MG
tels:+ (31)34995247/4995140 FAX: +(31)3443-3783, email: flugzbau@dedalus.lcc.ufmg.br

SUMMARY

In many applications of active noise control it is important to evaluate the efficiency of the system by means of the attenuation coefficient PR. However, an incorrect estimation of the value of PR can lead to a false evaluation of the performance of the proposed system, so it is important to determine the relationship between local reductions and the global value in the far-field. This work develops a method for the determination of the global attenuation coefficient, considering the relationship between the values obtained at the error sensors and the estimated values at the far-field. A system composed of a set of irradiating flat plates, the sound source, emitting in an open field, in the range of low frequencies is analyzed. The control is achieved by means of a system of loudspeakers, the secondary sources. A typical application of such a system is the control of the noise emitted by electrical transformers in substations. The value of the global attenuation coefficient is evaluated for some practical situations. The analysis of some situations shows that a wrong evaluation of the relationship between local and global attenuation coefficients can lead to an improper estimation of the performance of a system.

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