On acoustic natural frequencies of planar wave sound field connected two acoustic tubes with different cross sectional area and length (Theoretical consideration)

Ducts are widely used in an industry field. For example, air conditioning ducts, exhaust smoke elimination ducts and silencers have been various ducts. In general, the a flow vortices generated duct sometimes cause resonance phenomenon self-sustained tone. Once occurs, high level sound is suppression of this strongly quickly required. It necessary to know natural acoustic frequency for examination cause. The straight with uniform cross section can be easily obtained but that varying can’t immediately. Of arbitrary by using transfer matrix method, FEM BEM. our previous studies, many interesting findings were understandings not adequate. Then paper, range where plane waves hold, mode order independent ratio two sectional areas discussed table which makes obtaining presented. Furthermore, we will show how understand relation between length ratio.