This book examines nonlinear coupling mechanisms in acoustic oscillator systems that can lead to synchronization phenomena, with particular focus on organ pipes. Building on the questions addressed in previous studies, the elements involved in sound generation are identified through detailed experimental and theoretical investigations, as well as numerical simulations. Furthermore, the interaction mechanisms underlying the mutual coupling of organ pipes are investigated. This leads to the development of a nonlinear coupled-oscillator model based on first principles of aeroacoustics and fluid dynamics. The model calculations are compared with experimental results from previous studies. It is shown that the sound-generation and coupling mechanisms are adequately described by the developed nonlinear-coupled model of self-sustained oscillators. In particular, the model provides an explanation for the nonlinear boundaries of the Arnold tongue of the coupled two-pipe system.

Building on this new knowledge, the influence of various spatial geometries on the sound generation of organ pipes is investigated. Numerical simulations are used to study the interaction between an organ pipe and different spatial geometries, including plane, convex, concave, and ridged surfaces. The influence of so-called swell boxes on the sound generation and radiation pattern of an organ pipe is also investigated.

In further synchronization experiments with precisely equally tuned pairs of organ pipes, as well as with mixed pairs, synchronization is examined for various horizontal and vertical pipe distances in the two-dimensional plane of sound radiation. The spatial discontinuities observed in the oscillatory behavior of the coupled pipe systems indicate transitions between anti-phase and in-phase synchronization regimes depending on the distance between the pipes.

Finally, the feasibility of realistically describing the synchronization phenomenon between two organ pipes by numerically solving the compressible Navier–Stokes equations is demonstrated.