锥形渐变截面驻波管及其极高纯净驻波场的实验研究

锥形渐变截面驻波管是用锥形管代替突变截面驻波管突变截面部分的驻波管。为对比研究锥形渐变截面驻波管与突变截面驻波管的声学及其极高纯净驻波场性质,首先借助传递矩阵,对锥形渐变截面驻波管的声学性质进行了实验研究。研究表明,与突变截面驻波管一样,锥形渐变截面驻波管也属于失谐驻波管。利用其失谐性,在一阶共振频率激励下,锥形渐变截面驻波管获得了181dB的极高纯净驻波场。在对锥形渐变截面驻波管和等长的突变截面驻波管的驻波饱和性质进行对比实验研究后发现,在一阶共振频率下,锥形渐变截面驻波管不仅能很好地抑制管内驻波场高次谐波的增长,而且能有效地降低管内驻波场的能量损耗,在相同扬声器激励电压下获得声压级更高的大振幅纯净驻波场。实验研究还发现,在三阶共振频率激励下,锥形渐变截面驻波管的大振幅驻波场三次谐波频率接近声压级传递函数谷值对应的声源端七阶阻抗共振频率,三次谐波随基波快速增长并表现出趋于二次谐波的饱和性质。

Experimental study on the standing-wave tube with tapered section and its extremely nonlinear standing-wave field

A standing-wave tube with tapered section (STTS) is evolved from a standing-wave tube with abrupt section (STAS) whose abrupt section is replaced with tapered section. The research is intended to compare the acoustic properties and the extremely nonlinear pure standing waves of STTS and STAS. The acoustic properties of the STTS are studied with the help of transfer matrix. It is proved, like the STAS, that the STTS is dissonant standing-wave tube. With its dissonant property, the 181 dB extremely nonlinear pure standing wave is obtained in the STTS excited at its first resonance frequency. Then the comparative experimental studies on the saturation properties of the extremely nonlinear standing waves are carried out in the STTS and the STAS with the same length. It is found that the STTS can suppress the harmonics and meanwhile reduce energy loss of the standing wave more effectively. Compared with the STAS, under the same voltage of the loudspeaker, the STTS obtains a higher extremely nonlinear pure standing wave. Moreover, it is found that under the third resonance frequency, the frequency of the third harmonic in the STTS is close to the seventh resonance frequency of sound source impedance, to which the valley value of the sound pressure level transfer function corresponds, and that the third harmonic increases rapidly with the increase of fundamental wave and it tends to saturate.