Acoustic Directivity Characterization of a Smartphone System with Piezoelectric Speakers

Piezoelectric speakers offer several advantages over traditional electrodynamic speakers, particularly in applications involving portable devices. Features such as low power consumption and a thin profile suggest that these speakers could see widespread use. However, their adoption is often hindered by issues such as suboptimal low-frequency response and harmonic distortion. In addition to these challenges, an important but frequently overlooked factor is the spatial acoustic response of the transducers. In this paper, we propose a method to characterize the directive sound propagation of a smartphone system equipped with piezoelectric speakers. Specifically, we measure the spatial response of a smartphone featuring two piezoelectric transducers mounted beneath its screen, resembling a flat-panel loudspeaker configuration, and we show how the directivity changes by considering three orthogonal axes. In this study, we also compare the directivity obtained using only one of the transducers with the one obtained using both of them, in a dual-mono configuration. The knowledge of said radiation patterns sets the basis for the development of spatial audio algorithms tailored to the specific device under test.