有源吸声层理论研究

Generalized Engineering Analysis of Active Surface of Sound Absorption

提出一种可用于吸收低频斜入射声波的有源吸声结构。文中描述了吸声层的组成形式，然后建立理论模型，按近场方法推导了有源控制前后反射声功率的计算公式，而后按声反射功率最小化准则求得最优次级力源复强度。最后通过计算机仿真证明了该吸声层吸收低频声波的有效性，并研究了吸声效果与次级力源位置的关系。

In many applications, such as reduction of the reflected noise of highway traffic, active surface of sound absorption is highly useful. But research is still very limited, hampering its widespread use. In order to make theory more useful to engineers, we generalize it in two aspects: (1) the incident sound wave may be oblique, i.e., not limited to being normal to active surface; (2) our theory can be applied to different media (air, water, oil). Fig.1 shows a rectangular parallelepiped, where the top flexible plate is the active surface, and the other five rigid sides support the active surface and contain the medium. We excite the active surface with controllable secondary force sources. Eq.(7) gives the reflected acoustic power for the cavity structural coupling system. Minimizing eq.(7), I obtain the optimum reduction achievable with control. The calculated solid curve in Fig.3 shows the variation of reflected sound power with frequency before control and the calculated dotted curve, the variation after control. Fig.4 shows the calculated sound reductions for various locations of secondary exciting force source.