Spectral analysis of a two frequency driven resonance in a closed tube

The disturbances produced in a closed, rigid, gas-filled tube by the small amplitude oscillations of a piston at one end is investigated for the case when the piston movement is characterized by two frequencies close to reson ance frequencies. Starting with a nonlinear generalization of the one-dimen sional d'Alembert's wave equation together with appropriate boundary condit ions, the acoustic wave field in the tube is calculated by iteration. The f ield is then decomposed into its Fourier components and the amplitudes of t he different combination frequencies are determined. The frequency spectrum is changing rapidly with detuning.