Abstract: The invention relates to a method and an equipment for attenuating sound in a duct. Sound propagating in a duct is detected by means of a detector (2) and attenuated by using two successive monopole elements (3, 4) in such a way that both elements function as a dipole approximation and the elements are also used to approximatively produce the monopole radiation needed. A dipole control signal is fed to both elements (3, 4) at a phase shift which is 180° between the two elements. In addition, a monopole control signal is fed to the same elements (3, 4), only this time cophasally. Total volume velocities produced by the two elements (3, 4) are combinations of the portions obtained from the monopole and dipole sources.

Abstract: The invention relates to a sensor for measuring acceleration and sound pressure, the sensor comprising a first pressure sensitive film (2) for measuring pressure (P) and second pressure sensitive film (5) having a mass (6) disposed thereon for measuring acceleration (A). The films are arranged concentrically in the same plane, so that pressure and acceleration are measured at the same point, thereby avoiding a phase difference between the two measurements.