By explaining how an Early Music orchestra produces its sound, we can review Howard Becker's concept of a convention. An orchestra's sound depends on principles incorporated in things (musical instruments, scores) and bodies (musicians' techniques). A common set of principles about interpret-ing a piece of music -principles acquired well before any rehearsal -do not suffice for coordinat-ing a group of musicians. As observations have shown, face-to-face interactions are decisive in this coordination. The conductor is not omniscient and does not impose his interpretation on musicians. Relations based on authority, being unstable, are redistributed among the conductor, soloist and first violin during rehearsals. Recognizing the importance of face-to-face interactions draws attention to the cogency of power relations, which, though omnipresent, are constantly reworked in the situation for producing an orchestra's sound.Keywords: Music; Production; Power; Convention; Orchestra; Early Music; France Although sociology has dwelled on production processes, its analyses has seldom focused on the results thereof. The means for organizing work or regulating labor relations have been studied (Reynaud et al. 1990, Lallement 1999. But studies devoted to concrete situations at the workplace have focused less on the results of production activities than on the cognitive operations performed during interactions (Borzeix and Conein