2020 Volume 41 Issue 6 Pages 865-876
In this paper, we discuss methods of designing parametric speakers consisting of a small number of transducers. The developed parametric speaker unit includes peripheral acoustic structures, such as radial cones and a waveguide comprising a sonic crystal. The purpose of this study is to fabricate small parametric speakers that can be installed in various equipment. To achieve this purpose, it is essential to minimize the sizes and numbers of transducers. Parametric speakers must fulfill two goals: (1) high sound pressure levels of ultrasonic waves and (2) narrow directivities of ultrasonic waves. These two design goals are accomplished by two measures: (1) two close resonant frequencies and resonant mode control function and (2) an external adapter to obtain narrow directivities and high sound pressure. The first measure was achieved equipping the piezoelectric transducer with double-linked diaphragms and two radial cones. The second measure was embodied by the waveguide consisting of a sonic crystal, which was named the loop horn in this paper. Details of the design and experimental data of a four-transducer parametric speaker unit including the loop horn were presented.