Improvement of the sound transmission loss of a finite plate by a parallel arrangement of a slit resonator

Abstract

In this paper, an improvement of the sound transmission loss (STL) of a finite plate realized by attaching a slit-type Helmholtz resonator or a slit resonator in a parallel arrangement is studied. The slit resonator is designed such that the poor STL at the dip corresponding to the first natural frequency of the plate can be enhanced by tuning the resonance frequency of the slit resonator to that of the plate. The STLs of the slit resonator, plate and the combined structure of the slit resonator and the plate are derived analytically. It is found that as the slit length or width increases, or the slit depth decreases, the resonant frequency increases with an increase in the peak amplitude. The effects of the slit geometry and the cavity size on the resonance frequency can be explained by assuming a Helmholtz resonator with an equivalent circular neck. The slit width is the most important parameter with regard to changes in the amplitude of the peak of the STL, as the slit width appearing in the complex density acts as a frequency-dependent damping term. Regarding the effect of the gap between the slit and the plate, it is found that as the gap increases, the STL decreases slightly beyond the peak. The predicted STLs of the plate, slit resonator and the combined structure of the slit resonator and the plate are compared with experimental results gained using an impedance tube to validate the proposed method, showing good agreement.