Mechanism and calculation of the niche effect in airborne sound transmission

Abstract

The goal is to interpret and calculate the "niche effect" for the airborne sound transmission through a specimen mounted inside an aperture in the wall between the source and receiving reverberation rooms. The low-frequency sound insulation is known to be worse for the specimen placed at the center than for the specimen mounted at either edge of the aperture. As shown, the aperture with a tested specimen can be simulated at low frequencies as a triple partition where the middle element is the specimen and the role of the edge leaves is played by the air masses entrained at the aperture edges. With a centrally located specimen, such a triple system is symmetric and has two main natural frequencies close together. In this case, the resonant transmission is higher than for the edge arrangement simulated as a double system with one natural frequency. Analogous resonant phenomena are known to reduce the low-frequency transmission loss for symmetric triple windows or solid walls with identical air gaps and lightweight boards on both sides. The theoretical results obtained for the mechanical and acoustical models are in a good agreement with the experimental data.

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

“…Regardless of the niche type, it is seen that negative differences become greater below 800 Hz as the niche depth increases, whereas positive and negative differences appear above 1 kHz in relation to the wavelength. The tendency at low frequencies is consistent with the previous experimental results and the theoretical explanations by Vinokur [11] and Kim et al [10]. Regarding the recessing niche, the variations of the STL difference reasonably well correspond with those for a larger glass pane in [12].…”

“…Below this frequency, negative effects become greatest at the normal incidence, as suggested in the three-layer model of Vinokur [11]. Above this frequency, negative effects become greater with increasing incidence angle, which may be related to tangential modes in the niches.…”

“…Firstly, Vinokur proposed an infinite three-layer model where a limp plate is sandwiched by two air layers with lumped mass and stiffness [11]. However, this model is only valid for a low-frequency range below c 0 =S, where c 0 is the speed of sound and S is the aperture area.…”

“…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.…”

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

“…(11) and the expansion ofp 1 (x, y, z) in Eq. (9), and multiplying the resulting equation by / R and integrating over surface R F leads tô…”