调制气流声源的原理

利用气流调制以产生声音是一个比较有效的方法。人的发声器官、旋笛、电动气流扬声器以及一般哨子等都是根据这个原理。气流声源的特点是效率高,功率可以很大,有实用价值。关于气流声源的发声原理,过去已有一些讨论,但有的是过分简化,有的比较细致,但又过于繁复,不便计算。本文从气体动力学的基本原理出发,求得气流声源的气流-压力特性,并用图解法求得在给定气室压力和气流喷口面积比的条件下声辐射特性的方法,考虑到气流声源的气流特性和辐射关系都是非线性的,但是辐射声功率主要由基频决定,从而用近似理论求得了声功率、气流产额和气流效率的简单表达式,和严格理论的结果相比,误差不到1分贝。文中把结果画成图表以便计算,并讨论了最佳设计的问题。

THEORY OF MODULATED AIR STREAM SOUND SOURCES

Modulation of air stream is an efficient method of sound production. Man's speech organs, sirens, electro-pneumatic loudspeakers as well as common whistles are all based on this principle. The features of air stream sound sources are their high efficiency and possibility of high power outputs, which afford them practical value. The sound production by modulating air streams were discussed by previous authors and theories-given, but some were oversimplified and others too involved to allow practical computations. In this paper, air flow vs pressure characteristics of air stream sources are derived from the basic theory of gasdynamics and graphical method is presented for the estimation of sound radiation under given conditions of plenum pressure and nozzle-to-horn throat area ratio. It is established that although the air flow characteristics as well as the radiation relations are nonlinear, the radiated sound power is determined mainly by the radiation of the fundamental, and approximations give rise to simple expressions for the radiated sound power, the air stream yield and efficiency, with an error less than 1 dB from exact results. Charts are given to facilitate design and question of optimum condition is discussed.