Measurement-Based Modeling of Higher-Order Non-Linearities of the Parametric Loudspeaker

Paper in proceeding, 2019

The so called ”Parametric Audio” effect is a way to create highly directional audible sound using ultrasonic carrier waves. It stems from an acoustical phenomena where two high frequency waves at high intensity will interfere and generate intermodulation tones due to non-linear effects in the wave-propagation. Most analytical models apply a second order approximation to predict the level of the au- dible sound. With a second order approximation it is not possible to compensate distortions in the audible sound caused by higher order non-linear effects. Higher order distortions in the audible sound were observed anecdo- tally by the authors, raising the question if they as well could be compensated.

This paper describes a set of measurements of the am- plitudes of the harmonics of a bifrequency plane wave, and compares the measured results with a simple theo- retical model. The measured results indicate that there is significant nonlinear distortion in the electrical and/or mechanical subsystems. Even if a model is developed to predict and compensate for said distortion the model would be tied to a specific amplifier and transducer com- bination, with very limited real-life applicability.