Sound radiation from thin metal plates has consistently been recognized as a severe noise problem. One of the most popular approaches to suppressing this noise is applying viscoelastic layers, also called free layer damping (FLD), on the plate surface, which can damp the structural motion and minimize the radiated sound. The thickness of the FLD is an important parameter. It needs to be optimized for the target acoustic limits through numerical simulations, as the total mass and the costs may rise unnecessarily. This paper investigates the sound radiation from thin metals of particular sizes with different thickness values of FLD. A unique test setup was established to measure vibration and sound for three different sized plates, with each one having three different FLD thicknesses, namely, 0.5 mm, 0.75 mm, and 1 mm. In parallel, vibro-acoustic analyses were performed for the same configurations using the finite element method. The damping of the FLD was defined using the Rayleigh damping model, of which coefficients were obtained through a prediction formula developed earlier by the authors. After validating the model with the test, the effect of FLD on the extended acoustic parameters (radiated sound power, directivity) was also analyzed.

薄金属板发出的声音一直被认为是严重的噪音问题。抑制这种噪声的最流行方法之一是在板表面上应用粘弹性层（也称为自由层阻尼（FLD）），该粘弹性层可以阻尼结构运动并使辐射声最小化。FLD的厚度是重要的参数。由于总质量和成本可能会不必要地增加，因此需要通过数值模拟针对目标声学极限进行优化。本文研究了具有不同FLD厚度值的特定尺寸的薄金属的声辐射。建立了一套独特的测试装置来测量三种不同尺寸的板的振动和声音，每块板具有三种不同的FLD厚度，即0.5 mm，0.75 mm和1 mm。在平行下，使用有限元方法对相同的配置进行了振动声学分析。FLD的阻尼是使用瑞利阻尼模型定义的，其系数是通过作者先前开发的预测公式获得的。在通过测试验证模型后，还分析了FLD对扩展声学参数（辐射声功率，方向性）的影响。