Acoustics – Sound-modifying means – Sound absorbing panels
Reexamination Certificate
2002-04-11
2003-12-30
Nappi, Robert (Department: 2837)
Acoustics
Sound-modifying means
Sound absorbing panels
C181S289000, C052S144000, C052S786130
Reexamination Certificate
active
06668974
ABSTRACT:
The present invention relates to the acoustic insulation of a glazing unit.
It is common practice in the building industry to use insulating glazing units for improving the thermal insulation of rooms. The glazing units generally comprise two glass sheets combined by means of an insert frame which keeps them at a certain distance apart, while trapping an air or gas layer between them. For example, the glass sheets may have a thickness of 4 mm and be separated by an air or gas space generally of between 6 and 24 mm in thickness. However, as constructed, the acoustic performance of these glazing units is limited, it being appreciably inferior to that of a monolithic glass pane of the same overall mass per unit area and, in particular, the acoustic performance of double-glazing units having 4 mm sheets is mediocre.
Various means are used in the industry to improve the acoustic performance of these insulating glazing units. The means most commonly employed consists in increasing the thickness of the glass sheets, but the effectiveness of this technique is limited and it increases the weight of the glazing unit.
Another means consists in increasing the thickness of the air layer, but the effect is appreciable only for air thicknesses of several centimetres, something which prevents sealed insulating glazing units to be produced.
Patent EP 0,100,701 teaches a glazing unit whose glass sheets are formed by special laminations incorporating special polymer films. This type of glazing unit results in a very substantial improvement over the ordinary insulating glazing unit but the cost of manufacturing it is also considerably higher.
Some publications have proposed glazing units formed from monolithic glass sheets of standard thickness, outside which are fitted Helmholtz resonators tuned to the resonant frequency of the air layer trapped between the glass sheets to which the said resonators are connected. It will be recalled that a Helmholtz resonator consists of a cavity which communicates with the outside via a narrow orifice. When an acoustic pressure acts on the said orifice, it tends to make the mass of air contained in the cavity vibrate at a certain frequency which is a function of the dimensions of this cavity. The Helmholtz resonator is used to attenuate the low-frequency oscillations; its efficiency is at a maximum around its acoustic resonant frequency and around its harmonics.
An example of this technique is described in Patent Application WO-A-85/02640. This application relates to a box fitted with spherical Helmholtz resonators located outside the box and communicating with its internal cavity via ducts of small cross section. However, this system is completely unsuitable for insulating glazing units since external spherical resonators are expensive to produce and difficult to implement. In addition, these resonators are relatively bulky compared with the volume of the air layer of the glazing unit and therefore would result in a large assembly.
Patent DE 3,401,996 relates to a variant of the above system, applied to a glazing unit, which uses a single Helmholtz resonator, again outside the glazing unit, mounted on its periphery, the cavity of the resonator communicating with the air layer via a continuous slot, but this system has the same drawback as the previous one.
Finally, Patent EP 0,579,542 teaches a glazing unit fitted around its periphery with a waveguide which communicates with the air layer via several orifices whose shape, cross section and position are determined so as to detune the acoustic and mechanical waves which are created in the air layer and on the glass sheets, respectively, when the glazing unit is exposed to an incident acoustic field.
This waveguide is formed by a single section going around the insulating glazing unit, placed along the sides of the insert frame, internally with respect to this frame, with holes preferably in the middle of the sides in order to ensure communication between the inside of the waveguide and the air layer. In another embodiment, this waveguide is formed from several straight sections whose ends are not touching, thus leaving additional communication passages between the inside of the waveguide and the air layer.
Whatever the embodiment, the acoustic performance is quite limited and it is complicated to fit the waveguide section or sections.
The present invention aims to remedy the drawbacks of the prior art presented above and its subject is an acoustic insulating glazing unit formed from two glass sheets, which are monolithic or otherwise, having improved acoustic efficiency, leaving a large daylight, being more compact and being easy to manufacture, and for a cost barely greater than that of conventional insulating glazing units.
The invention is based on the observation that a glazing unit which is formed from two glass sheets and is exposed to an incident acoustic excitation is the seat of several vibroacoustic modes but that one of the acoustic modes which carries the most energy from one sheet to the other is the &lgr;/2 mode. Therefore, if this &lgr;/2 mode is essentially attenuated, most of the acoustic energy transmitted from one glass pane to the other is eliminated.
The invention relates to an acoustic insulating glazing unit of the type described in Patent EP 0,579,542, that is to say formed from two glass sheets separated by a peripheral insert frame, containing a cavity filled with gas, especially most often air, and having an internal waveguide, characterized in that this waveguide consists of at least one straight tubular section placed on the periphery of the cavity, along one side of the glazing unit, this section being provided with a transverse partition which closes the latter along its length direction and is placed at a point along this length which depends on the acoustic mode that it is desired to attenuate.
Thus, the glazing unit is combined with a double tubular Helmholtz resonator tuned to the wavelength of the acoustic mode that it is desired essentially to disorganize, for example &lgr;/2 if it is desired to disorganize this vibration mode or &lgr;/i (i being an integer) if it is desired to disorganize this other vibration mode. It is known that &lgr; is given by the formula &lgr;=c/l where c is the speed of sound in the internal cavity of the glazing unit and 1 is the length of the tubular Helmholtz resonator, which depends on the position of the partition.
Advantageously, for greater efficiency, four sections are placed in the cavity, around the periphery of a rectangular insulating glazing unit along the sides of the said glazing unit, each section being provided with a transverse partition.
The position of the partition depends on the acoustic mode to be disorganized: it is placed approximately in the middle of the length of the section in order to act on the &lgr;/2 mode or one third along the length in order to detune the &lgr;/3 acoustic mode.
The central partition may be produced by any appropriate means. It may be manufactured with the section when the latter is being extruded or it may be produced subsequently, especially by fitting two sections of lengths slightly less than half the length of one side of the glazing unit onto a partition connector, that is to say a connector provided with a partition, or else, in particular in the case of thermoformable plastic sections, by restricting the cross section and welding, or else a partition may be slid into a smooth section and be fastened therein.
Moreover, it is possible to insert an absorbent material into the waveguides so as to improve their acoustic performance. It is then judicious to use this absorbent instead of a partition and to make it act as a partition. The waveguide will then be performed, for example, by internally smooth tubular sections into which buffers of absorbent material are inserted and positioned at the desired points especially halfway along the length of each section, respectively.
The principle of sections fitted onto a connector which contains a buffer of absorbent material is also a useful prac
Mottelet Beatrice
Rehfeld Marc
Nappi Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobain Glass France
Warren David
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