{"title":"Theoretical Analysis of Damping Due to Air Viscosity in Narrow Acoustic Tubes","authors":"M. Watanabe, T. Yamaguchi, M. Sasajima, Y. Kurosawa, Y. Koike","country":null,"institution":"","volume":78,"journal":"International Journal of Electronics and Communication Engineering","pagesStart":679,"pagesEnd":684,"ISSN":"1307-6892","URL":"https:\/\/publications.waset.org\/pdf\/15236","abstract":"Headphones and earphones have many extremely small\r\nholes or narrow slits; they use sound-absorbing or porous material (i.e.,\r\ndampers) to suppress vibratory system resonance. The air viscosity in\r\nthese acoustic paths greatly affects the acoustic properties. Simulation\r\nanalyses such as the finite element method (FEM) therefore require\r\nknowledge of the material properties of sound-absorbing or porous\r\nmaterials, such as the characteristic impedance and propagation\r\nconstant. The transfer function method using acoustic tubes is a widely\r\nknown measuring method, but there is no literature on taking\r\nmeasurements up to the audible range. To measure the acoustic\r\nproperties at high-range frequencies, the acoustic tubes that form the\r\nmeasuring device need to be narrowed, and the distance between the\r\ntwo microphones needs to be reduced. However, when the tubes are\r\nnarrowed, the characteristic impedance drops below the air impedance.\r\nIn this study, we considered the effect of air viscosity in an acoustical\r\ntube, introduced a theoretical formula for this effect in the form of\r\ncomplex density and complex sonic velocity, and verified the\r\ntheoretical formula. We also conducted an experiment and observed\r\nthe effect from air viscosity in the actual measurements.","references":null,"publisher":"World Academy of Science, Engineering and Technology","index":"Open Science Index 78, 2013"}