对共鸣管测声速实验的改进

Improvement of measuring the sound velocity by using resonant pipe device

本实验是封闭奶茶吸管的一端,并对另一端吹气使其发声,用频谱分析软件确定此声信号的基频,进而得出空气中的声速.文中指出理论与实验事实不一致:理论上基频所对应的管长为四分之一个声波波长,只要知道基频与管长即可算出声速;事实上管的有效长度是实际管长加上管口校正量,管口校正量因管口厚薄、管体形状等因素而有所不同.在本实验中,对于直径约为1.1cm和0.6cm的吸管,分别采用0.5d和1d的校正量获得了比较理想的声速值.指出管的长度不宜过短,否则将无法获得较准确的基频值.

In order to make a sound, one end of the straw is sealed with blowing another end of the straw. Based on the software of spectral analysis, fundamental frequency of the acoustic signal is ascertained. The differ- ence between theory and experiment is pointed out. In theory, since the corresponding tube length of fundamental frequency is a quarter of the acoustic wavelength, the sound velocity can be calculated with fundamental frequency and tube length. But in fact, the effective tube length is the combination of the real tube length and the end correc- tion which is changed by the different thickness and shape of the tube. In experiment, for the straws with the diame- ter of 1.1cm and 0.6cm, better sound velocity is achieved with the application of the end correction of 0.5d and l d respectively. Besides, if the tube length is too short, it will be hard to acquire the accurate fundamental frequency.