This lecture covers the concepts of doublets and dipoles in audio engineering, focusing on the acoustic radiation impedance and the superposition principle. It explains the properties of doublets, the field they generate, and their directivity. The lecture also delves into the field of dipoles, discussing how they are computed using the superposition principle and their far-field characteristics. Additionally, it explores the properties of cardioid sources, which combine monopoles and dipoles to create directional sound emission patterns.