Using animations to better understand acoustic impedance

Abstract

It is very common for students to struggle to grasp a conceptual understanding of acoustic radiation impedance and input impedance. Often graduate students need exposure to impedance concepts in more than one course before they start to understand its importance and meaning. Instructors commonly suggest that impedance can be thought of as a resistance, ignoring the imaginary part of the impedance (the reactance), and the word “sloshing” is sometimes used to describe what the radiation reactance represents. This presentation will show some animations that have been developed in MATLAB to help students visualize the motion of the air particles near a vibrating surface. These animations utilize the relevant physical equations to observe the ratio of the pressure to the particle velocity. While these animations are not directly interactive, the user can change things like the frequency, source size, and excitation amplitude and recreate a new animation. Thinking of the impedance as the ratio of a potential quantity to a flow quantity can often be helpful, with this ratio having an in phase component and a component where the two quantities are 90 degree phase shifted.