L'objet de l'article est de rendre compte des mecanismes qui concourent a la production du son d'un orchestre de musique ancienne, et de faire ainsi retour sur la notion de convention telle qu'elle est developpee par Howard Becker. Le son de l'orchestre depend de principes incorpores dans les choses (les instruments de musique, les partitions) et dans les corps (les techniques du corps mobilisees par les musiciens). Le partage de principes d'interpretations acquis en amont de la situation de travail ne suffit cependant pas a assurer la coordination in situ des musiciens, lors du travail collectif de l'orchestre. Les observations realisees montrent ainsi que les interactions de face a face pendant le travail de l'orchestre constituent un facteur decisif pour la coordination des actions des musiciens. Le role reconnu aux interactions de face a face permet par ailleurs de souligner la pregnance des rapports de pouvoir, omnipresents et en perpetuelle recomposition, dans les situations de production.
By explaining the means whereby an early music orchestra produces its ''sound'', we can review the concept of convention as developed by Howard Becker. An orchestra's sound depends on principles incorporated in things (musical instruments, partitions) and in bodies (musicians' techniques). A common set of principles about interpreting a piece of music, principles acquired well before any rehearsal, do not suffice for coordinating the musicians as a group working together. As observations show, face-to-face interactions are decisive in coordinating musicians' actions. The conductor is not omniscient and does not impose his interpretation on musicians, because relations based on authority, being labile, are redistributed between the conductor, solists, and the heads of instrument sections during rehearsal. Recognizing the importance of face-to-face interactions draws attention to the cogency of power relations, which, omnipresent, are constantly reworked in the situations where an orchestra's sound is produced.