Active sound attenuation device to be arranged inside a duct, particularly for the sound insulation of a ventilating and/or air conditioning system

A device for the active sound attenuation of a sound signal propagated in a duct, the device comprising:

• at least first sensor means which are arranged at a first location inside the duct for picking up a first sound signal at least at one point of said first location,
• attenuation actuating means which are arranged in a predetermined geometric relation relative to the duct and upstream of the first sensor means in a direction of propagation of the sound signal in the duct for supplying at least one active sound attenuation signal in response to at least one selected control signal,
• electronic control means for generating the active sound attenuation signal for the actuating means, in order to minimize energy of the first sound signal thus picked up, and
• second sensor means which are arranged at a second location inside the duct, upstream of the first location in the direction of propagation of the sound signal in the duct, for picking up a second sound signal at least at one point of said second location, and wherein the electronic control means generate the active sound attenuation signal for the actuating means, in order to minimize the energy of the first sound signal as a function of the first and second sound signals thus picked up,
• wherein the first sensor means and the actuating means are separated from one another by a distance substantially smaller than the diameter or than the smallest dimension of a cross section of the duct, in order to avoid the first sensor means receiving interfering sound waves from the actuating means including a first angular mode sound wave, and arranged completely inside the duct at a selected distance from an inner wall of a casing of the duct, and
• wherein an axis of symmetry of a radiation of the actuating means and an axis of symmetry of the first sensor means are substantially parallel to the direction of propagation of the sound signal in the duct.

A device for the active sound attenuation of a sound signal propagated in a duct, the device comprising:

• at least first sensor means which are arranged at a first location inside the duct for picking up a first sound signal at least at one point of said first location,
• attenuation actuating means which are arranged in a predetermined geometric relation relative to the duct and upstream of the first sensor means in a direction of propagation of the sound signal in the duct for supplying at least one active sound attenuation signal in response to at least one selected control signal, and
• electronic control means for generating the active sound attenuation signal for the actuating means, in order to minimize energy of the first sound signal thus picked up,
• wherein the first sensor means and the actuating means are separated from one another by a distance substantially smaller than the diameter or than the smallest dimension of a cross section of the duct, in order to avoid the first sensor means receiving interfering sound waves from the actuating means including a first angular mode sound wave, and arranged completely inside the duct at a selected distance from an inner wall of a casing of the duct,
• wherein an axis of symmetry of a radiation of the actuating means and an axis of symmetry of the first sensor means are substantially parallel to the direction of propagation of the sound signal in the duct, and
• wherein the duct is subdivided into a plurality of subducts with or without a casing, each subduct having an associated framework arranged inside said subduct, the plurality of frameworks forming a single structure with or without passive attenuation means.