Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1998-12-18
2001-08-14
Tran, Sinh (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S190000, C381S423000, C381S424000, C181S167000, C181S168000, C181S170000
Reexamination Certificate
active
06275598
ABSTRACT:
TECHNICAL FIELD
The invention concerns the arrangement of drive systems in sound reproduction devices that operate in accordance with the flexural wave principle.
BACKGROUND OF THE INVENTION
Sound reproduction devices that operate in accordance with the flexural wave principle are known in the state of the art. Such arrangements are essentially composed of a panel and at least one drive system, where the panel begins to oscillate when sound signals are conducted to the drive system(s). It is characteristic for such sound reproduction devices that a “flexural wave radiation” starts at a critical lower cut-off frequency, where the flexural waves lead to sound being radiated in a frequency-dependent direction along the plane of the respective panel. In other words, a cut through a directivity diagram shows a principal lobe whose direction if frequency-dependent. These relations apply fully to infinitely expanded plates and absorber plates, while the relations for the multiresonance plates treated in this application are clearly more complex because of the strong edge reflexes. This multiresonance plate complexity is due to the fact that the mentioned principal lobe has a number of such principal lobes superimposed on it in a frequency-dependent direction, so that a fan-shaped directivity diagram is created which furthermore is very frequency-dependent. But the multiresonance plates and the absorber plates treated here have in common that the center of their directivity diagram rather points away from the mid-perpendicular. This characteristic allows the room to have a greater effect on the sound wave projection.
The panel is built in accordance with the sandwich principle, where each of two opposite surfaces of a very light core layer are connected to a thin cover layer, for example by means of an adhesive. For the panel to have good sound reproduction properties, the material for the cover layer must have an especially high dilatational wave speed. Suitable cover layer materials are for example thin metal foils or fiber-reinforced plastic foils as well.
The core layer must fulfill special requirements as well. Thus it is necessary for the materials being used to first have a low mass density and low damping. In addition, the core layer materials must have as high a vertical shear modulus as possible with respect to the surfaces that are provided with the cover layers. Finally in the sense of a principal requirement it is necessary for the materials that can be used for the core layers to have a very low modulus of elasticity in the direction in which the subsequently formed core layer has its greatest expansion. These two premises, which at first seem contradictory in reference to the last two requirements, are better fulfilled by a core layer which has a perforated structure with openings of a preferably small cross section extending between the two surfaces to be covered by the cover layers. In addition to the core layers with the perforated structure, hard foams can also be used as the core layer material because these materials have suitable shear and elasticity moduli despite their isotropic properties. In this connection we should not forget to also mention that when hard foams are used as the material for the core layer, the objective of the cover layers is to provide the required anisotropic behavior of the panel.
In order to radiate sound waves by means of a panel as described above, it is necessary to connect the panel to a drive system which produces wave-shaped deformations in the panel that are vertical to the plane of the cover layers. To achieve this the state of the art generally uses magnet systems which are also used for driving conventional loudspeakers. In order for these drive systems to provide the deformation of the panel which is necessary to radiate flexural waves, the drive systems are usually equipped with a corresponding countersupport. This countersupport can for example be formed by a supporting structure which is located away from one of the two cover foils and receives the drive system. Aside from the fact that such a supporting structure not only increases the constructed depth and the weight of such installations, this kind of supporting structure also requires considerable production costs. For that reason the supporting structures which function as a countersupport for the drive systems are now directly connected to the panel. A disadvantage however is that the supporting structures which are connected to the panel impede the generation of flexural waves in the panel and lead to a distorted sound reproduction. This can be attributed to the fact that by comparison with a pure drive system, the attachments required to fasten such supporting structures to the panel stiffen large areas of the panel which extend in the direction of the greatest expansion. It is additionally disadvantageous in such supporting structures that they do not fulfill the properties required by the cover layers and the core layer.
It is therefore the objective of the invention to present a sound reproduction device which eliminates the disadvantages of the state of the art.
SUMMARY OF THE INVENTION
This objective is achieved by a sound reproduction device with a panel essentially composed of a core layer as well as a top and a bottom cover layer, where opposite surfaces of the two cover layers cover opposite surfaces of the core layer, and with a drive arrangement which is connected to the panel and makes it oscillate under the effect of sound signals, wherein the core layer has a cutout, and that the drive arrangement is exclusively integrated into this cutout.
The basic idea of the invention is to provide the panel with a cutout, and to locate the drive system in this cutout. If the sound reproduction device is built in this manner, the core layer itself can be used as countersupport for parts of the drive system. In addition to the savings in weight and construction depth, this also has the advantage that due to the drive system's full integration into the panel, the two surfaces provided with the cover layers can be constructed in a uniform manner. Furthermore, panels in which the drive systems are fully integrated, or which are separated from the environment by the cover layer or layers, can also be used in areas subjected to dirt or humidity without any problems. Finally the area of the panel that is weakened by the cutout causes a particularly good impression of flexural waves in the panel, so that the output required to achieve the flexural wave can be reduced, or the same output can produce the panel oscillations that are required for bass sound reproduction.
Particularly good transmission is achieved in the bass and middle range areas if the drive system is composed of at least one permanent magnet, a voice coil support and a voice coil.
The construction of a sound reproduction device is particularly simple if the core layer has a honeycomb structure where each honeycomb is formed of a number of walls extending between the two cover layers. By locating the cutout in the core layer, the walls of one or of several honeycombs are laid open and in this case it is possible to use them as voice coil supports. It should already be pointed out here that the use of the core layer as the voice coil support is not limited to the honeycomb structure. Rather the walls of circular or polygonal structures that form the core layer, and the walls which are formed by placing a cutout in a core layer of hard foam, can be used in the same manner.
The construction is further simplified if the permanent magnet or magnets are connected directly or by means of holders to the core layer, and the areas of the core layer which are directly connected to the permanent magnet or magnets or the holders have a diameter D
1
that is larger than the diameter D
2
of the voice coil. It should already be pointed out here that the relationship between the two diameters D
1
and D
2
has a decisive significance for the tuning of the panel. Modifications of the diameter D
2
are particularly sig
Bachmann Wolfgang
Krump Gerhard
Regl Hans-Jurgen
Harman Electronic Systems GmbH
Harvey Dionne N.
Tran Sinh
Ware Fressola Van der Sluys & Adolphson LLP
LandOfFree
Sound reproduction device does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sound reproduction device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sound reproduction device will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2459694