Study on attenuation in hard-wall acoustic pipe caused by viscosity and thermal conduction

Abstract

Viscous attenuation in the boundary layer of the pipe wall has been considered for acoustic attenuation in closed acoustic pipes. However, the specific acoustic impedance was derived experimentally and compared with the theory considering viscous damping, and the results were inconsistent. Tijdeman's theory of thermoacoustic phenomena，acoustic damping due to thermal conduction, is introduced as a new complex volume modulus. In the reference book "Thermoacoustic Devices," the complex sound velocity and complex wavenumber are finally derived from the basic equations, but the complex density and complex volume modulus are not derived in the process. In this study， the sound absorption coefficient，acoustic impedance, complex sound velocity, complex density，and complex volume modulus of the duct are measured directly by experiment，and the complex density and complex volume modulus are derived for comparison with the theoretical values，and the complex sound velocity and complex wavenumber are derived from these two.