An abat-son (usually plural abat-sons) is an architectural device constructed to reflect sound in a particular direction. Typically it takes the form of large louvers which direct the sound of church bells from a bell tower toward the ground.
In general use, any louvers in a bell tower are commonly called abat-sons, whether they are designed to redirect sound or merely to prevent ingress of water.
A church in Trélissac
Church of Saints Peter and Paul, La Tour-Blanche
Church of Our Lady of the Assumption, Échourgnac