Analysis of the spatial elements of popular music recordings can be made by way of the ‘sound-box’, a concept that acknowledges the way sound sources are perceived to exist in four dimensions: laterality, register, prominence, and temporal continuity. By late 1972 producers working across a range of styles and in different geographical locations had adopted a normative positioning of sound sources across these dimensions. In 1965 no such norm existed. This article contextualizes the notion of the sound-box within academic discourse on popular music and explores the methodology employed by a research project that addressed the gradual coming-into-existence of the norm, which the project defined as the diagonal mix. A taxonomy of types of mix is offered, and a chronology of the adoption of the diagonal mix in rock is presented.