US 6728389 B1
A system for tensioning a membrane within a frame for a loudspeaker or a microphone is characterized by a frame containing an opening, a membrane connected to an exterior surface of the frame and spanning the frame opening, and a tensioning device connected with the frame for deflecting a portion of the membrane within the frame opening. The tensioning device is compliant thereby allowing the membrane to exhibit a high degree of flexure both within and beyond a plane containing the membrane.
1. A membrane support system, comprising:
(a) a frame containing an opening;
(b) a membrane connected to an exterior surface of said frame having a portion of which spans said frame opening;
(c) means for tensioning said membrane including a roller arranged between said frame and said membrane, said roller being rotatable in a plane parallel to a plane containing said membrane portion, whereby excess tension in said membrane portion during excursions thereof is relieved.
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This application is a division of application Ser. No. 09/981,401 filed Oct. 17, 2001 now U.S. Pat. No. 6,577,742 which is a continuation-in-part of application Ser. No. 09/864,425 filed May 24, 2001.
The invention relates to a membrane support system which applies tension to the membrane of a sound producing or sound receiving device, such as a speaker or a microphone, respectively.
The prior art relating to membrane support and tension systems utilize various techniques. The U.S. patents to Selinka U.S. Pat. No. 5,850,461, Carver U.S. Pat. No. 4,803,733, Thigpen U.S. Pat. No. 4,837,838, Torgeson U.S. Pat. No. 4,468,530, and Recklinghausen U.S. Pat. No. 4,037,061 disclose rigidly affixing a loudspeaker membrane to a supporting structure. In other cases, membrane tension is applied by rigidly holding the membrane by the edges and introducing an inelastic deforming protuberance to apply membrane tension. The protuberance is positioned in grooves within the mounting structure. With each of the aforementioned references, the membrane edges are rigidly affixed so that no additional flexure of the membrane material is allowed. Consequently, the tension in the membrane must increase when it moves backward and forward from its center, or rest position. This limits the membrane excursion range, and thus the speaker's maximum acoustic output and dynamic range.
In the Bruney U.S. Pat. No. 4,939,784, front-to-back excursions of the membrane edges are prevented, and the membrane edges are allowed to move inward, in the plane of the membrane, as the central membrane moves back and forth. In this way, tension variation in the membrane is appreciably reduced and the useable excursion range of the membrane is increased. However, an apparatus for applying tension across the membrane is not disclosed.
The present invention is a membrane support system for applying tension to a membrane that is connected to a frame by incorporating a tensioning device that provides mechanical compliance in the direction of the plane of the membrane. The system includes a frame that has an opening, a membrane that is connected with an exterior surface of the frame and spans the frame opening, and a tensioning device that is connected with the frame for deflecting a portion of the membrane within the opening of the frame. The tensioning device includes a clamping member which is secured to the frame and extends over the frame opening, and a support formed of a compliant material that is connected with the end of the clamping member which extends over the frame opening. The compliant material of the tensioning device allows the membrane to exhibit a high degree of flexure both within and beyond, i.e. normal to, the plane containing the membrane.
According to a further object of the invention, the membrane support system includes a compliant roller which acts as a tensioning member for the membrane. The roller tensions the membrane within the plane thereof and the roller rotates in a plane parallel to the membrane plane during excursions of the membrane to relieve excess tension.
Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in the light of the accompanying drawings, in which:
FIG. 1 is an exploded perspective view of the membrane support system according to the invention;
FIG. 2 is a perspective view of the assembled membrane support system of FIG. 1;
FIGS. 3 and 4 are top sectional views of the membrane support system of FIGS. 1 and 2, respectively;
FIGS. 5 and 6 are exploded and assembled top sectional views, respectively, of an alternate membrane support system according to the invention;
FIG. 7 is a perspective view of a membrane support according to another embodiment of the invention;
FIGS. 8 and 9 are exploded and assembled perspective views, respectively, of the membrane support system using the support of FIG. 7;
FIGS. 10-13 are top sectional views, respectively, of a membrane support system including a hollow roller for tensioning the membrane in the plane thereof; and
FIGS. 14 and 15 are top sectional views, respectively of a membrane support system including a compliant tensioning roller according to a further embodiment of the invention.
Referring to FIGS. 1 and 3, a frame 2 formed of a rigid material contains an opening. A membrane 4 is secured to the frame 2 so that the membrane 4 spans the opening, thereby to completely cover the opening in the frame 2. The membrane is formed of any suitable thin film material such as Mylar, Kapton, or piezoelectric film, or an electret material. A clamping member 6 has a compliant support 8 connected thereto, the support 8 being formed of a synthetic or silicone rubber, foam tape, or other elastomeric material.
Referring now to FIGS. 2 and 4, the support 8 is placed through the opening of frame 2, thereby displacing and tensioning the membrane 4 in a direction normal to the original plane of the membrane which coincides with the plane containing an exterior surface of the frame to which the membrane is secured. The compliant attributes of the support 8 are essentially in the direction of the plane of the membrane 4 to allow the membrane to move in a direction normal to the original plane of the membrane when the membrane is activated. The clamping member 6 is connected with one side of the frame 2 by any suitable fastening devices such as nails, staples, tape, screws, or an adhesive, and the support 8 displaces the membrane 4 in a direction normal to the original plane of the membrane 4. In this configuration, the membrane 4 has a direction of compliance both within the plane of the membrane and also in a direction normal thereto.
In the embodiment of FIGS. 5 and 6, a pair of clamping members 6 and supports 8 are connected with opposing ends of a frame 2. The supports 8 tension the membrane 4 within the frame opening in a direction normal to the original plane of the membrane 4. In this embodiment, the membrane 4 is tensioned on two opposing sides within the opening of frame 2.
Referring now to the embodiment of FIGS. 7-9, a clamping member 106 is connected to an angular rigid support 110. The edge of the angular rigid support 110 opposite the clamping member 106 is tapered. A compliant support 112 is connected with the angular rigid support 110 along the tapered edge. The support 112 is formed of a compliant material. The compliant material and angular shape of the angular compliant support 112 when connected with the angular rigid support 110 provides a varying degree of compliance along the length of the support.
As shown in FIGS. 8 and 9, a membrane 104 is connected with the frame 102 and spans an opening therein. The clamping member 106 is connected with the frame and supports 110, 112 thereby to apply tension to the membrane. The stiffness of the membrane suspension is inversely proportional to its compliance. Greater stiffness (lower compliance) corresponds to a higher membrane resonance frequency, and lower stiffness (higher compliance) corresponds to a lower membrane resonance frequency. Because the compliance of the support 112 varies along its length; i.e., the support is more compliant at the bottom and less compliant at the top, the resulting suspension stiffness which the angular compliant support 112 exerts on the membrane 104 varies from one end to the other. The variation in suspension stiffness across the membrane 104 allows the membrane to produce varying degrees of sound from low bass tones to high treble tones.
A compliant support can also be used to apply varying tension to a membrane rather than varying only the suspension stiffness by deflecting different areas or portions of the edge of the membrane by different amounts. The smallest deflection from the smallest tension is suitable for the lowest frequency and the greatest deflection from the greatest tension is suitable for the highest frequency. This allows a membrane to produce varying degrees of sound from low bass tones to high treble tones. Either a compliant material of uniform height or a tapered compliant material may be used. In either case, the edge of the support that deflects the membrane in a perpendicular direction to its original plane is mounted at an angle with respect to the original plane so that one end of the support perpendicularly deflects the membrane more than the other end.
While the frame is illustrated and described as having a rectangular configuration, other shapes may be used as well including triangles, pentagons, circles and the like. Similarly, tension can be applied at any location around the perimeter of the opening, including on adjacent sides, continuously, on opposite sides or the like.
Turning now to FIGS. 10-15, alternate embodiments of the invention including a compliant tensioning roller will be described. In FIG. 10, a frame 202 has offset portions 202 a and 202 b which are offset but spaced to define an opening. A membrane 204 is connected with the frame and includes a portion spanning the opening. The membrane is connected with the frame portion 202 a via conventional fasteners (not shown) and with the frame portion 202 b via a cylindrical roller 214. The roller is hollow and formed of a rigid material or a compliant material such as an elastomeric material, silicone, fluorosilicone, vinyl, foam, and the like.
Surrounding the roller is a fastener film 216 which has a first end 216 a connected with the frame portion 202 b, such as with an adhesive, and a tension end 216 b which overlaps the first end 216 a for connection with the first end as in FIG. 10 or with the frame portion 202 b as in FIG. 11. The degree of tension is governed by the amount of overlap. The membrane 204 is connected with the film by any suitable fastener such as an adhesive. When the membrane 204 undergoes excursions out of the normal plane thereof, the roller 214 rolls to the left as shown by the arrow 218 to relieve additional tension in the membrane resulting from the excursions.
In the embodiment of FIG. 12, the tensioning end 216 b of the fastener film 216 is connected with a separate portion 202 c of the frame so that the tensioning end and the first end of the film are arranged on opposite sides of the roller to improve the tension relief effect thereof.
In FIG. 13, there is shown a fastener film connected with the roller and frame in a manner similar to that of FIG. 10, except that a spacer 220 is arranged between the roller and the fastener film. The spacer increases the torque applied by the tensioning end of the fastener film.
The fastener film is shown as a single film. However, two film strips may be used to achieve the same result.
In FIGS. 14 and 15 are shown a further embodiment of the invention wherein the frame 302 comprises offset portions 302 a and 302 b and the tensioning roller comprises a solid cylindrical roller 314 formed of a rigid or a compliant material. A membrane 304 passes around the roller and is connected with the portion 302 b via a clamp 310 (FIG. 14) or via an adhesive (FIG. 15). The membrane is also adhesively connected with the roller. As the membrane moves out of plane during excursion thereof, the roller is displaced along the frame portion 302 b to relieve tension.
In the embodiments of FIGS. 10-15, the diameter or height of the roller is selected so that the upper edge thereof is co-planar with the exterior surface of the frame first portion.
The roller preferably has a cylindrical configuration for use in tensioning a membrane across a rectangular frame. Other roller configurations are possible. For example, the roller may take the form of an O-ring if the membrane to which it is attached is round or oval.
While the preferred forms and embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various changes may be made without deviating from the inventive concepts set forth above.