Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation
Reexamination Certificate
1998-01-07
2001-12-18
Isen, Forester W. (Department: 2644)
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Reexamination Certificate
active
06332027
ABSTRACT:
The invention relates in general to noise-absorption structures and to walls formed by means of these structures, and more particularly to such structures that are lightweight and compact, applicable specifically to the aviation industry for fitting to jet engines, their nacelles, and airplane cabins, in the transportation industry, in the building industry, etc. . . .
BACKGROUND OF THE INVENTION
Proposals have already been made, in French patent application No. 94 00539 (published under No. 2 715 244) for lightweight noise-absorption structures each comprising a support frame on which a gastight membrane is fixed and tensioned, together with plates disposed beneath the membrane to co-operate therewith to form a passive laminar air-flow damper. Soundwaves incident on the side of the membrane remote from said plates give rise to vibratory deformation of the membrane which in turn gives rise to a laminar flow of air between the membrane and the plates, and thus to energy being absorbed. When the acoustic impedance of such a structure is properly matched to the incident soundwaves, a large portion of the energy of said soundwaves is absorbed by the structure over a relatively broad frequency band.
OBJECTS AND SUMMARY OF THE INVENTION
The aim of the present invention is to provide significant improvements to those structures.
An object of the invention is to provide lightweight structures of the above-specified type of acoustic impedance that is modifiable, adjustable, or controllable, and capable of following changes in the sources of noise to be absorbed.
Another object of the invention is to provide lightweight structures of the above-specified type including means for modifying, adjusting, or controlling their acoustic impedances, which means are themselves controllable by a data processing system.
Another object of the invention is to provide walls that are lightweight and thin, made by juxtaposing and assembling such structures.
To this end, the invention provides a noise-absorption structure comprising a support frame over which a gastight membrane is tensioned and fixed, the outside face of the membrane receiving soundwaves, a gas such as air, for example, filling an internal volume defined by the frame and the membrane, and energy-dissipation means housed in said volume, wherein the energy-dissipation means are of the laminar gas-flow type, of the electrostatic type, or of the electromagnetic type, and area modifiable, adjustable, or controllable in order to modify the acoustic impedance of said structure as a function of the characteristics of the noise to be absorbed.
Because their acoustic impedances are modifiable or adjustable, structures of the invention can be designed or adjusted to absorb incident noise or to deflect it by reflection, e.g. as a function of the positions occupied by the structures in a noise-absorption wall or a wall for providing protection against noise.
In a first embodiment, the energy-dissipation means are of the laminar gas-flow type and comprise plates disposed inside the frame a short distance from the membrane, and means for modifying said distance.
In another embodiment, the laminar gas-flow dissipation means comprise at least one gas flow passage or duct connecting a closed chamber defined inside the frame by the membrane to another chamber inside said structure.
For example, the passage may be a duct formed between two superposed plates associated with means for modifying or adjusting the distance between them or for modifying or adjusting the flow section of the duct.
In another embodiment, the laminar gas-flow dissipation means comprise rods carried by the membrane and extending perpendicularly therefrom inside the frame in fixed tubes which are closed at their ends remote from the membrane and which co-operate with the rods to define annular gas-flow channels.
In yet another embodiment, the energy-dissipation means comprise electrode plates disposed parallel to the membrane at a distance therefrom, and at least one other electrode formed on the membrane and connected together with said plates to bias means such as a DC source associated with an electric or electronic circuit including elements for dissipating energy by the Joule effect.
For example, the membrane may include one or more metal-coated zones facing the above-mentioned electrode plates, or it may be made of an electrically-charged plastics material, in which case the bias means are not necessary.
The elements for dissipating energy by the Joule effect comprise, for example, a resistor, advantageously an adjustable resistor, in which case the structure of the invention then includes controlled means for modifying the resistance of the resistor for the purpose of adjusting the acoustic impedance.
In another embodiment, the energy-dissipation means are of the electromagnetic type and comprise electrical conductors moved by the membrane relative to magnetic elements carried by the frame or constituted thereby, the above-mentioned electric conductors comprising, for example, coils connected to the membrane or one or more electric circuits printed or deposited on the membrane.
In a variant, it is possible to use a magnetic membrane that is movable relative to an electric circuit.
According to yet another characteristic of the invention, each above-mentioned structure is closed in gastight manner and contains an expandable and contractible volume element such as a balloon or a bellows, for example, which is filled with air and which is in communication with the outside via a static pressure equalizing orifice, said element occupying a significant fraction of the volume of said structure.
This characteristic makes it possible to compensate for the influences of variations in the external pressure and temperature on the membrane of the noise-absorption structure.
Each structure of the above-specified type is designed to be juxtaposed and assembled with a plurality of other structures of the same type to form a wall that is plane or curved, convex or concave, and in which the structures have acoustic impedances that are similar or different for the purpose of absorbing noise or of deflecting it by reflection, as appropriate.
In such a wall, the energy-dissipation means of at least some of the structures are associated with modification, adjustment, or control means, themselves controllable by a data processor system.
This makes it possible, in particular, to adjust the acoustic impedances of certain portions or of all portions of a wall to take into account a modification or variation over time in the characteristics of the noise to be absorbed.
REFERENCES:
patent: 5778081 (1998-07-01), Patrick
patent: 6041125 (2000-03-01), Nishimura et al.
patent: 2 482 663 (1981-11-01), None
patent: 2 715 244 (1995-07-01), None
Collin Dominique
Fumoux Christine
Guilloud Jean-Claude
Julliard Jacques
Alston & Bird LLP
Bertin & Cie
Isen Forester W.
Pendleton Brian Tyrone
LandOfFree
Noise-absorption structures and walls constituted thereby does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Noise-absorption structures and walls constituted thereby, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Noise-absorption structures and walls constituted thereby will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2565534