Abstract: This paper describes a predictive model for acoustic transverse transmission loss from ducts with flat oval configuration of finite length. The transmission mechanism is essentially that of mode coupling, whereby higher structural modes in the duct walls get excited because of non-circularity of the wall. Effect of geometry has been taken care of by evaluating Fourier coefficients of the radius of curvature. Emphasis is on understanding the physics of the problem as well as analytical modeling. Effects of the flat ovality, curvature have been demonstrated. With Anechoic termination, progressive approach modeling has been adopted in this paper.