In this paper a description of the use of simplified numerical methodologies for determining the low cut-off frequency of anechoic and hemi-anechoic chambers will be presented. The anechoic chamber has been modeled as a cavity with proper surface impedance boundary conditions. Firstly, the surface impedance is determined by means of a finite element model of the wedges in a "virtual" impedance tube for a plane wave field. Successively, both analytical and numerical procedure are used for determining the complex reflection coefficient for spherical waves at oblique incidence. Finally, a complex image source approach is used for predicting the sound field within the chamber. The methodology will be applied to the new anechoic chamber of the University of Ferrara, having volumes of 650 m3and 800 m3in anechoic and hemi-anechoic configurations, respectively. Results will be compared in terms of sound decays along fixed directions and surfaces pressure distributions.
In this paper a description of the use of simplified numerical methodologies for determining the low cut-off frequency of anechoic and hemi-anechoic chambers will be presented. The anechoic chamber has been modeled as a cavity with proper surface impedance boundary conditions. Firstly, the surface impedance is determined by means of a finite element model of the wedges in a "virtual" impedance tube for a plane wave field. Successively, both analytical and numerical procedure are used for determining the complex reflection coefficient for spherical waves at oblique incidence. Finally, a complex image source approach is used for predicting the sound field within the chamber. The methodology will be applied to the new anechoic chamber of the University of Ferrara, having volumes of 650 m3 and 800 m3 in anechoic and hemi-anechoic configurations, respectively. Results will be compared in terms of sound decays along fixed directions and surfaces pressure distributions.
Numerical methodologies for predicting the low frequency behavior of anechoic chambers
POMPOLI, Francesco;PRODI, Nicola
2009
Abstract
In this paper a description of the use of simplified numerical methodologies for determining the low cut-off frequency of anechoic and hemi-anechoic chambers will be presented. The anechoic chamber has been modeled as a cavity with proper surface impedance boundary conditions. Firstly, the surface impedance is determined by means of a finite element model of the wedges in a "virtual" impedance tube for a plane wave field. Successively, both analytical and numerical procedure are used for determining the complex reflection coefficient for spherical waves at oblique incidence. Finally, a complex image source approach is used for predicting the sound field within the chamber. The methodology will be applied to the new anechoic chamber of the University of Ferrara, having volumes of 650 m3 and 800 m3 in anechoic and hemi-anechoic configurations, respectively. Results will be compared in terms of sound decays along fixed directions and surfaces pressure distributions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
