On sound transmission into an orthotropic infinite shell: Comparison with Koval's results and understanding of phenomena

Abstract Koval has presented an expression for the transmission loss (TL) by an orthotropic infinite cylindrical shell with one layer, excited by an external plane wave with an angle of incidence θ. We initiated an extension of this calculation in the case of two independent angles θ and ψ, in order to calculate the diffuse field transmission coefficient (Rd). For a plane wave with an angle of incidence θ, some large differences are found between Koval's results and our own. This leads us to analyze in detail the transmission mechanisms, especially the frequencies at which TL is minimum. At the end of this paper, we lay stress on the interest of the orthotropy for a strategy of internal noise reduction into large shells.