Speakers do not always operate linearly. Linearity of the speaker can affect the quality of the sound produced by the speaker, i.e., causing distortions in the sound, if the nonlinearites are not accounted for. To determine nonlinearities of the speaker, the speaker is often modeled and measurements are made to estimate the characteristics of the speaker based on the model. By using an angle sensor and a light source, a speaker manager can make a direct measurement of excursion or displacement of the speaker. Moreover, when the angle sensor, the light source, and the light beam are configured appropriately with respect to the moving cone of the speaker, the measurement can be substantially linear with respect to the amount of excursion or displacement. Such measurements are far simpler to use and in some cases more accurate than measurements made by other types of systems.