RESILIENT MOUNTINGS

Abstract: A resilient mounting for a carcass (20) and platter/pick-up arm board (22) of a phonographic turntable comprises an integral silicone rubber moulding providing a diaphragm (12), an upstanding post (14), and a depending shirt (16). The carcass (20) is secured to the periphery of the diaphragm (12) with the skirt (16) acting as a resilient support for the carcass. The board (22) is supported on the post (14). A nut and bolt (24, 26) cooperate with the post (14) to act as a levelling device.

Description: - 1 - "Resilient Mountings" This invention relates to resilient mountings for providing isolation from mechanical vibration. It is particularly, but not exclusively, of application in audio equipment such as phonographi turntable decks, compact laser-read disk players, and tape decks. The invention will be described herein, by way of example, principally in relation to phonographic turntable decks. It is common practice in phonographic equipment to mount the turntable platter and pick-up arm on a board which in turn is mounted in a carcass via resilient means. Most commonly, such resilient means comprises three assemblies each having a coil spring and a screw which can be adjusted to level the platter board. This arrangement is relatively complex and expensive, and is also less efficient than is desirable in isolating the platter from low-frequency interference such as that transmitted through an item of furniture on which the deck is sitting. An object of the present invention is accordingly to provide an improved resilient mounting which provides good audio frequency isolation while being inexpensive to produce and to assemble in the end-use equipment. The present invention ' provides a resilient mounting for use in mounting a first element to a second element to provide audio frequency isolation, the mounting comprising a resilient diaphragm supported at its periphery by the second member or means secured thereto, the diaphragm being formed integrally with an upstanding central post to which the first element may be secured, and a central bore extends through the post and diaphragm for passage of a fixing and levelling screw. In a preferred form for use with a phonographic turntable, the post mounts a turntable/pick-up arm board, a skirt integral with the diaphragm depends therefrom to act as a foot, and a metallic ring is bonded to the periphery of the diaphragm for securement to a carcass. Embodiments of the invention will now be described, by way of example, with reference to the drawings, in which: Fig 1 is a cross-section of a mounting in accordance with 04 - 2 - one embodiment of the invention in position in a turntable deck; Fig 2 is a plan view of the mounting of Fig 1; and Fig 3 is a cross-section of the mounting alone showing preferred dimensions. Referring to Fig 1, a resilient mounting generally designated 10 comprises an integral moulding of silicone rubber forming a circular diaphragm 12, a cylindrical post 14, and a cylindrical skirt 16. A metal ring 18 is secured to the periphery of the diaphragm 12 and is used to secure the mounting to carcass 20 such that the skirt 16 acts as a resilient support for the carcass 20. A platter/pick-up arm board 22 is carried by the post 14. The deck is provided with three such mountings spaced around the centre of gravity of the assembly of the board 22 and parts thereon. A screw 24 and nut 26 in each mounting can be operated to level the board 22. Upper and lower washers 28 and 30, not bonded to the mounting, prevent the diaphragm being unduly displaced. In use, the skirt 16 isolates the carcass 20 from external noise and shocks transmitted via the furniture or other object on which the deck is resting, while the diaphragm 12 and post 14 together provide a resilient suspension of the board 22 in the carcass 20. It will be appreciated that the central part of the diaphragm 12 is in tension, and relative movement between the board 22 and carcass 20 will be damped by flexing of this central part. The isolation characteristics provided by the mounting are a function of its geometry and dimensions and of the resilience of its material. For the present phonograph example, the dimensions (in millimetres) shown in Fig 3 together with a Shore hardness of about 45 have been found to give excellent acoustic isolation, especially at low frequencies around 100 Hz where spring systems tend to resonate. A suitable material for this embodiment is General Electric Grade 4 General Purpose silicone rubber. Pure silicone rubber is preferred as it is resistant to ageing. However other resilient materials may be adequate, eg silicone rubber loaded with filler, or butyl rubber. The principle of the invention can be applied in other forms. For example, the depending skirt could be removed for applications where one part is resiliently mounted to another without a requirement for a supporting foot. It is contemplated that in this form the invention would be of utility in compact disc players where, because of the much lower mass of the turntable/ disc assembly, the dimensions of the mounting would be substantially smaller.

Claims: - 4 - CLAIMS 1. A resilient mounting for use in mounting a first element to a second element to provide audio frequency isolation, the mounting comprising a resilient diaphragm supported at its periphery by the second member or means secured thereto, the diaphragm being formed integrally with an upstanding central post to which the first element may be secured, and a central bore extends through the post and diaphragm for passage of a fixing and levelling screw. 2. The mounting of claim 1, further including a depending skirt formed integrally with the diaphragm to act, in use, as a resilient support for the second member. 3. The mounting of claim 2, including a non-resilient ring bonded into or secured to the peripheral portion of the diaphragm outwardly of said skirt. 4. The mounting of any preceding claim, in which the diaphragm and the parts integral therewith are formed of a material having a Shore hardness in the range 30-60. 5. The mounting of claim 4, in which the diaphragm and the parts integral therewith are of silicone rubber. 6. A phonographic turntable assembly comprising a carcass and a platter board, and a plurality of mountings in accordance with claim 1, each mounting having said diaphragm periphery secured to the carcass and the platter board resting on its post, each mounting having, a screw-threaded fastening means passing through said bore to present relatively movable flange surfaces bearing on the platter board and the diaphragm respectively. 7. The assembly of claim 6, in which three said mountings are equipspaced about the centre of gravity of the platter board and parts carried thereby.

Inventors: DALGLEISH MARTIN, DALGLEISH, MARTIN
Applicants: LINN PROD LTD, LINN PRODUCTS LIMITED
Application year: 1986
Main classification: G11B33
IPC codes: G11B33