Researchers develop a paper-thin loudspeaker

https://techxplore.com/news/2022-04-paper-thin-loudspeaker.html

"thin-film loudspeaker by mounting it to wall 30 centimeters from microphone to measure sound pressure level, recorded in decibels. 25 volts of electricity passed through at 1 kilohertz... speaker produced high-quality sound at conversational levels of 66 decibels. At 10 kilohertz sound pressure level increased to 86 decibels... Because the tiny domes are vibrating, rather than the entire film, the loudspeaker has a high enough resonance frequency that it can be used effectively for ultrasound applications"