Tongan Wang

Sound transmission loss of honeycomb sandwich panels

Honeycomb sandwich panels used for commercial applications are typically stiff and lightweight. They are optimized for mechanical performance, but have poor acoustical performance. Transmission loss (TL) is one of the metrics used to assess the acoustical performance of honeycomb sandwich panels. Transmission loss for these panels shows inferior mass law performance above coincidence frequency for commercially available panels. For superior transmission loss performance, it is critical to delay (maximize) the coincidence frequency, which is determined by the dispersive panel bending waves. Panel bending waves are characterized by three frequency regimes - total panel bending, core shear, and individual skin bending. These regimes are controlled by panel geometry, panel mass and elastic properties of the core and the skins. The coincidence frequency can be increased by designing panels with core shear wave speeds that are subsonic. In the present study, the influence of different panel design parameters, such as core density, core material, cell size, and cell structure, on the transmission loss of honeycomb sandwich panels is analyzed. Moreover, TL results of panels in three classes of core shear wave speeds - subsonic, transonic, and supersonic - are presented. For panels with supersonic shear wave speed, core density influences TL above the coincidence frequency, but other parameters like cell size and skin type show negligible effects. Panels with subsonic and transonic core shear wave speeds show improved acoustic performance compared to their supersonic counterparts. The mechanical performance of subsonic and transonic panel designs is generally inferior but can be improved when accompanied by weight increase.

Predicting the Sound Transmission Loss of Sandwich Panels by Statistical Energy Analysis Approach

A statistical energy analysis (SEA) approach is used to predict the sound transmission loss (STL) of sandwich panels numerically. Unlike conventional SEA studies of the STL of sandwich panels, which consider only the antisymmetric (bending) motion of the sandwich panel, the present approach accounts for both antisymmetric and symmetric (dilatational) motions. Using the consistent higher-order sandwich plate theory, the wave numbers of the waves propagating in the sandwich panel were calculated. Using these wave numbers, the wave speed of the propagating waves, the modal density, and the radiation efficiency of the sandwich panels were determined. Finally, the sound transmission losses of two sandwich panels were calculated and compared with the experimentally measured values, as well as with conventional SEA predictions. The comparisons with the experimental data showed good agreement, and the superiority of the present approach relative to other approaches is discussed and analyzed.

Small-scale transmission loss facility for flat lightweight panels

The design, construction and qualification of a small-scale sound transmission loss (STL) facility are described. STL measurements were made using the sound intensity technique based on ASTM E 2249-02. The volume of the irregular-shaped reverberant source chamber was 15 m3, and the volume of the regular-shaped anechoic receiver chamber was 20 m3. The facility was tested between 315 Hz and 10 kHz. Good spatial diffusion, and good repeatability for same and repeat installations were demonstrated in the above frequency range. The results from the small-scale facility were compared to tests conducted at a full-scale facility. The STL values of flat, lightweight sandwich panels measured at the small-scale chamber were greater than those measured in the full-scale facility. However, the results from the small-scale facility showed trends that were consistent with the sandwich panel theory above 1 kHz. The results demonstrated that the small-scale STL facility could be successfully used for qualitative comparisons of lightweight, sandwich panels above 1 kHz

Transmission loss assessments of sandwich structures by using a combination of finite element and boundary element methods

In this work, formulation of a 2D fully‐coupled finite element method (FEM)/boundary element method (BEM) to simulate the measurements of sound transmission loss of sandwich panels is presented. Specifically, the structural behavior of the sandwich panels, based on a consistent higher‐order theory, is implemented using finite element method (FEM), and the reverberant/anechoic chambers are accessed by boundary element method (BEM). The coupling between the structure and the acoustic medium is achieved by assuming the continuity of the normal velocities at the interface. The absorption of the receiving anechoic chamber is calibrated by comparing the numerically‐predicted sound pressure level difference between the two chambers with the Sewell’s expression for the forced transmission. The obtained correction factors are then used without any modification to predict transmission loss of other sandwich panels with different dimensions and material properties. Numerical examples are presented to validate the nu...

Prediction of sound transmission loss of honeycomb sandwich panel by higher order approach

People have studied the sound transmission loss (STL) of sandwich panels since the 1970s. However, most of the existing prediction methods have been based on single‐layer dynamical models, neglecting the symmetric (dilatational) movements of the skins. Consequently, the symmetric coincident frequency of the sandwich panel cannot be predicted using those approaches. To account for this dilatational motion of the sandwich structures, different methods were utilized. However, most of them were based on one dimensional sandwich beams theories. The authors have also applied the consistent higher order beam approach to calculate the sound transmission loss of a unidirectional sandwich panel. Although the one dimensional approximation is good in predicting STL, the effects of some factors, such as the anisotropy and orientation of the principle axis of the panel, cannot be estimated. In the current work, the authors extended that one dimensional beam model into two dimensions, which allows us to calculate the ST...

Measurement of transmission loss trends for orthotropic sandwich panels at a subscale facility

Interior noise studies in airplanes have identified floors as one of the primary noise paths. The acoustic barrier properties of floor panels are typically quantified by sound transmission loss (STL) measurements. A subscale transmission loss suite consisting of a reverberant room and an anechoic room was constructed and qualified to study the relative transmission loss trends of orthotropic sandwich panels used in airplane floors. A host of material combinations accounting for a variety of mechanical properties were tested for their acoustic performance. The transmission loss measurements were based on a sound intensity technique (ASTM E 2249‐02) and a sound pressure technique (SAE J 1400‐90). The results from these two techniques were compared to results from a full‐scale accredited facility using the two‐reverberation room method (ASTM E 90‐02). The STL trends for orthotropic sandwich panels from the sub‐scale facility were comparable to trends from the full‐scale facility between 315 and 5000 Hz. The ...