The spectral element formulations are extended to problems of sound propagation in ducts involving varying cross-sections by introducing tapered spectral elements. Two types of duct cross-section variations are considered: linear and polynomial. The element shape functions are established as well as the dynamic stiffness matrices describing the spectral relation between the acoustic pressure, as the unknown vector, and the volumetric velocity, as the excitation vector. Although the Finite Element Analysis (FEA) is considered a leading procedure for numerical simulations, it still presents disadvantages mainly when dealing with higher frequencies due to the need for fine meshes and, consequently, prohibitive computational cost. On the other hand, the spectral approach describes the acoustic wave-motion exactly at any position along arbitrary multiply connected duct wave-guides within the plane-wave assumption. Each continuous span between two discontinuities can be modeled with one single spectral element, regardless of the frequency. The modeling of tapered duct wave-guides plays an important role in the design of acoustic excitation devices, as the one used in a micro-scanner, which is currently being developed by the authors. 39013908Lyon, R.H., DeJong, R.G., (1995) Theory and Application of Statistical Energy Analysis. 2 nd Edition, , Butterworth-Heinemann, 1995Kinsler, L.E., Frey, A.R., Coppens, A.B., Sanders, J.V., (1982) Fundamentals of Acoustics. 3 rd Edition, , John Wiley & SonsDoyle, J.F., (1997) Wave Propagation in Structures, , Springer-Verlag, New York, NY