Demonstration of a length limited parametric array

• Published in: Applied acoustics Vol. 148; pp. 423 - 433
• Main Authors: Skinner, Elizabeth, Groves, Matthew, Hinders, Mark K.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2019
• Subjects: Directional sound beam; Length-limited sound beam; Nonlinear sound propagation; Parametric acoustic array; Parametric loudspeaker; Directional sound beam; Parametric acoustic array; Parametric loudspeaker; Length-limited sound beam; Nonlinear sound propagation
• ISSN: 0003-682X; 1872-910X
• DOI: 10.1016/j.apacoust.2019.01.001

We describe a series of measurements to assess the practicality of a length limited parametric array in air. This study shows that the length limited effect is a measurable phenomenon that can be produced using pairs of commercial off the shelf parametric array speakers. We generated the effect using parametric arrays mounted so that two directional audio beams were simultaneously co-propagating through the open air. Parametric arrays work such that after the ultrasound frequencies have attenuated, the remaining audio range acoustic frequency is linear. We used this principle to propagate 2 kHz signals from two parametric array speakers, adjusting the relative phase of the resulting audio-range signals to produce varying amounts of constructive or destructive interference in the resulting linear sound beams. We demonstrated that increasing the overlap of the audible sound beams increased the effectiveness of the length limited phenomenon. We also found that changing the magnitude of the sound projected through one of the speakers did not have significant impact on the length limited effect.