The present study describes the development and field testing of a simple apparatus-based diagnostic instrument (SABDI) that examines undergraduate students' understanding of the underlying physics principles that explain how simple acoustic apparatuses work. SABDI comprises 13 items. Based on previous research studies and the history of science, the 38 distractors of SABDI were designed to reflect the following four categories of possible misconceptions: (a) direct and (b) incorrect emergent views of sound; (c) explanations based on a device's salient feature; and (d) wrong applications of physics knowledge. Field testing carried out on 159 participants showed the salient features category to be the most popular. SABDI is a valid and reliable tool that could be used to determine students' thinking regarding acoustic devices.