提高阻抗管测量频率上限的研究

提出了一种提高阻抗管测量频率上限的新方法.该方法针对表面阻抗均匀的材料,通过对管道内高次模式声波的分解和测量,拾取对应于法向的入射波与反射波的(0,0)模式,获得法向吸声系数和法向声阻抗率,从而使测量不再受管道截止频率的限制,大幅度提高管道内测量的频率上限.介绍了利用单传声器轴向传动获取信号,在同济大学直立式阻抗管内进行的材料声学特性的测量.结果表明,阻抗管原有的截止频率为280Hz,采用提出的测试方法,可使测量频率上限提高到2 000Hz及以上.

Extended Frequency Range of Impedance Tube Measurement

The paper presents a new method for extending the frequency range of impedance tube measurement. The method is based on decomposing and measuring higher order mode waves in ducts and picking up (0, 0) mode of the incident and reflected wave for the material of uniform surface impedance. Therefore the normal incidence absorption coefficient and the acoustic impedance can be determined. Compared with previous research, the limit of cut off frequency in the tube can be avoided and the frequency range of measurement can be increased greatly. Finally, the verification test with the proposed method is carried out by adopting the single microphone axial transmission system in a large vertical impedance tube. From the test results, the upper limit frequency of the tube is extended from 280 Hz to 2 000 Hz or higher.