Prediction of the niche effect for single flat panels with or without attached sound absorbing materials

Abstract

The sound transmission loss (STL) of a test sample measured in sound transmission facilities is affected by the opening in which it is located. This is called the niche effect. This paper uses a modal approach to study the STL of a rectangular plate with or without an attached porous material located inside a box-shaped niche. The porous material is modeled as a limp equivalent fluid. The proposed model is validated by comparison with finite element/boundary element computations. Using a condensation of the pressure fields in the niche, the niche effect is interpreted in terms of a modification of the modal blocked pressure fields acting on the panel induced by the front cavity and by a modification of the radiation efficiency of the panel modes due to the presence of the back cavity. The modal approach is then used to investigate the impact of (1) the presence of a porous material attached to the panel on the niche effect and (2) the niche effect on the assessment of the porous material insertion loss. A simplified model for the porous material based on a transfer matrix approach is also proposed to predict the STL of the system and its validity is discussed.

Numerical examination of niche effect on sound transmission loss of glass panes

“…Some decades ago, several experimental studies demonstrated the niche effect [5][6][7][8][9], which was later investigated in theoretical and numerical studies [10][11][12][13]. So far, the following general findings on the niche effect have been obtained: 1) the effect is significant below the critical coincidence frequency; 2) the effect depends on the position of the specimen in the niche; 3) the lowest STL is obtained when the sample is located in the middle of the niche; 4) the highest STL is obtained when the sample is mounted flush at one of the edges of the niche; 5) the effect depends on the sectional shape of the niche around the specimen.…”