“Audio Sound Power from Parametric Array Loudspeaker: Frequency and Aperture Size Dependence, and Low Conversion Efficiency”

https://pubmed.ncbi.nlm.nih.gov/38117125

The audio sound power generated by a parametric array loudspeaker is roughly proportional to the square of the audio frequency and aperture size, and inversely proportional to the ultrasound frequency, with a low conversion efficiency of typically below 0.15%.