M. Watanabe and T. Yamaguchi and M. Sasajima and Y. Kurosawa and Y. Koike
Theoretical Analysis of Damping Due to Air Viscosity in Narrow Acoustic Tubes
679 - 683
2013
7
6
International Journal of Electronics and Communication Engineering
https://publications.waset.org/pdf/15236
https://publications.waset.org/vol/78
World Academy of Science, Engineering and Technology
Headphones and earphones have many extremely small
holes or narrow slits; they use soundabsorbing or porous material (i.e.,
dampers) to suppress vibratory system resonance. The air viscosity in
these acoustic paths greatly affects the acoustic properties. Simulation
analyses such as the finite element method (FEM) therefore require
knowledge of the material properties of soundabsorbing or porous
materials, such as the characteristic impedance and propagation
constant. The transfer function method using acoustic tubes is a widely
known measuring method, but there is no literature on taking
measurements up to the audible range. To measure the acoustic
properties at highrange frequencies, the acoustic tubes that form the
measuring device need to be narrowed, and the distance between the
two microphones needs to be reduced. However, when the tubes are
narrowed, the characteristic impedance drops below the air impedance.
In this study, we considered the effect of air viscosity in an acoustical
tube, introduced a theoretical formula for this effect in the form of
complex density and complex sonic velocity, and verified the
theoretical formula. We also conducted an experiment and observed
the effect from air viscosity in the actual measurements.
Open Science Index 78, 2013