fig2

Figure 2. Parameter optimization of loudspeaker unit. (A) Schematic representation of an SPL measurement; (B) Results showing the SPL response of perforated and non-perforated paper substrates at different driving voltages. The excitation frequency is 1,975 Hz; (C) Optical photos and schematic diagrams of paper substrates with varying hole dimensions and densities; (D) Effect of hole diameter on SPL; (E) Relationship between SPL and hole density; (F) Effect of the top paper substrate with varying thickness on SPL; (G) Relationship between the thickness of the middle and bottom paper substrates and SPL; (H) PLA electret film with varying thickness as a function of SPL value; (I) PLA electret film with different surface potentials as a function of SPL value. Unless otherwise stated, the test conditions include a driving voltage of 500 V, a hole diameter of 1.2 mm, and a hole density of 20.25 holes/cm². Error bars in the figures represent the standard deviation for an experimental sample size of three. SPL: Sound pressure level; PLA: polylactic acid.