Sound waves ? like light waves ? travel in straight lines, but can be bent through reflection, diffraction, or refraction. In the case of the Berkeley Lab experiments, the researchers bent sound waves using an array of acoustic transducers ? effectively high-frequency loudspeakers ? some 1.5 cm (0.6 in) in diameter, spaced 2.5 cm (0.98 in) apart and operating at a frequency of 10 kHz. This array was able to directly alter the phase and direction at which each sound wave was generated so that a defined set of pressure fields with distinct trajectories were created in the air.
As a result, the team claimed to have produced an acoustic bottle beam whose sound waves travel through the high pressure wall of its curved shell to flow around a zero pressure center. In this way, the sound waves are held together and are able to travel on in this fashion over some distance. The acoustic bottle beam is also uninfluenced by solid objects that are placed in its path, with the shape and characteristics of the sound waves reforming after flowing around the object.