An assembly constituting an acoustically absorbent material and including a first panel, a second panel pierced with holes, an intermediate panel pierced with through-holes and arranged between the first panel and the second panel, a first structure between the first panel and the intermediate panel and including first cages, a second structure between the second panel and the intermediate panel and including second cages, and for each through-hole of the intermediate panel, a tube opening out at the two ends thereof, where one of the ends of the tube is fixed to the intermediate panel at the through-hole, and where the other end of the tube is accommodated inside a first cage. Such an assembly makes it possible to obtain broad-band attenuation and is easy to manufacture.

An assembly constituting an acoustically absorbent material and including a first panel, a second panel pierced with holes, an intermediate panel pierced with through-holes and arranged between the first panel and the second panel, a first structure between the first panel and the intermediate panel and including first cages, a second structure between the second panel and the intermediate panel and including second cages, and for each through-hole of the intermediate panel, a tube opening out at the two ends thereof, where one of the ends of the tube is fixed to the intermediate panel at the through-hole, and where the other end of the tube is accommodated inside a first cage. Such an assembly makes it possible to obtain broad-band attenuation and is easy to manufacture.

The present invention relates to a method for acoustically detecting at least one malfunction (DYS) of a motor, the motor generating a primary noise Po that is treated by an active noise control system emitting, at the noise reduction targets, an acoustic signal Pc produced by at least one actuator and connected by a transfer function H to a signal Y produced by said active noise control system, said malfunction (DYS) having an acoustic signature identifiable in the primary noise Po at the noise reduction targets, characterized in that it comprises the following steps: acquisition of said signal Y produced by the active control system; identification of the appearance, if any, of a malfunction by a monitoring means that uses the knowledge of Y and H and emits an alert message if warranted.