Experimental demonstration of thermophones in vibro-acoustic noise cancellation scenario for varying gaseous media

The paper focuses on an analytical and experimental study of global noise cancellation between two co-planar thermo- and vibro-acoustic sources in varying gaseous media. To address the experimental uncertainty in thermophone thermal boundary condition, the previously developed theoretical model is expanded to consider oscillating temperature at the solid-fluid interface, beyond the previously studied oscillating heat flux boundary. The results of the analysis indicate that at the point of optimal cancellation, the ratio of acoustic sources’ powers correlates to the specific heat ratio γ of the surrounding media through γ/(γ−1) relation. Then, a thermophone device is designed using commonly available materials and is deposited on a conventional vibro-acoustic loudspeaker, which acts as the noise source. Both acoustic sources are placed in a sealed acoustic chamber and are experimentally studied in several fluid media with different specific heat ratio values (argon, nitrogen, carbon dioxide and norflurane). The constructive and destructive interferences of the two emitters are analyzed at an exemplary frequency for varying phase differences, and global noise cancellation is demonstrated in all gases using microphone measurements in different spatial locations. The empirical results are observed to fully agree with the theoretical predictions.