微缝吸声体理论

Theory of microslit absorbers

窄缝可做为声学原件，这是已知的。窄缝的声阻抗严格公式以及低频近似公式都存在。本文发展了窄缝的基本理论，求得了其声阻抗的简单实用公式。由此可见，缝宽减小至丝米级，其阻抗比将超过一，因而微缝板加后腔形成的微缝吸声体可具有良好吸声性能，而不需任何多孔性或纤维性材料。文中提出微缝吸声体的概念和严格理论，并讨论其吸声性能。微缝吸声体的公式与微穿孔吸声体的完全相似，只是其声阻系数较小而声抗过大，一般说，如参数相同，其吸声特性将比微穿孔吸声体为差。改进措施可有效地补救。

It is well known that narrow slit may be used as acoustical element. The exact formulae of the acoustical impedance of a narrow slit and its low-frequency approximation are available. The theory of slit is extended and a simple and practical formula is derived for the single slit. It is found that the resistances-to-reactance ratio of the slit increases to larger than one when the slit width is decreased to submillimeter range, and a panel with extremely narrow slits plus a back cavity will make an absorber with good absorption in a wide frequency range, without any porous or fibrous material. A complete theory of the microslit absorber (MSA) is, thus, presented and its absorption characteristics are discussed. It is found that the MSA has essentially the same formulae as the microperforated absorber (MPA), except that the numerical coefficient of the resistance is smaller and the end correction for the mass reactance is larger for the MSA, resulting a performance inferior to that of MPA, ordinarily. Measures are proposed to compensate for these.