Immersive wave propagation experiments in a two-dimensional acoustic waveguide

• Published in: The Journal of the Acoustical Society of America Vol. 146; no. 4; p. 3078
• Main Authors: Becker, Theodor S., Börsing, Nele, van Manen, Dirk-Jan, Haag, Thomas, Donahue, Carly M., Curtis, Andrew, Robertsson, Johan O.
• Format: Journal Article
• Language: English
• Published: 01-10-2019
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.5137682

The physical implementation of immersive boundary conditions (IBCs) allows acoustic or elastic waves to propagate seamlessly between a physical domain, such as a wave propagation laboratory, and a numerical simulation virtually enclosing the physical domain. IBCs correctly account for all wavefield interactions between both domains, including higher-order long-range scattering. In this contribution, IBCs are physically implemented in a two-dimensional (2-D) acoustic waveguide. The boundary surrounding the waveguide is densely populated with hundreds of loudspeakers that apply the necessary boundary conditions. The required signals to be injected at the boundary are predicted in real-time by (1) measuring the pressure field and its gradient on two acoustically transparent auxiliary surfaces of microphones inside the waveguide and (2) extrapolating the wavefields to the boundary by evaluating a Kirchhoff-Helmholtz integral using a low-latency, FPGA-enabled data acquisition, computation and control system. Here, we demonstrate the first real-time, 2-D physical immersive wave propagation experiments. We present the setup, as well as a suite of experiments that demonstrate the ability of IBCs to actively suppress broadband incident fields at the boundary of the waveguide and to correctly reproduce all orders of wavefield scattering between the physical experiment and the numerical simulation.