GB2471369A

GB2471369A - Evacuated record player platter

Info

Publication number: GB2471369A
Application number: GB1009476A
Authority: GB
Inventors: Craig Milnes
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-06-07
Filing date: 2010-06-07
Publication date: 2010-12-29
Also published as: GB201009476D0

Abstract

A sealed gas impervious platter made from multi axial carbon fibre 1,2 fashioned by a combination of a resin transfer mounding process and a high compression core 1,1 that is comprised of an open internal cell structure that is permanently evacuated in order to exploit the damping and pre-stressing effects that result from a vacuum to atmospheric pressure differential. The platter is for a gramophone record player turntable. The platter may have an extraction valve for further evacuation should the vacuum deplete. Additional shielding materials may be used to reduce the effects of stray magnetic fields and radio waves. The core may be manufactured using stereo lithography. The pre-stressing elevates the first natural resonant frequency of the structure making it less likely to resonate. Any resonant activity is exposed to high levels of damping. This is realized without adding damping material or added mass.

Description

I

Title of the Invention

Multi axial carbon fibre, S.T.L. generated core, vacuum damped, record player platter.

Field of the Invention

This invention relates to a platter for the purpose of supporting a vinyl record in order to facilitate the highest accuracy transcription of data stored in the groove of the vinyl record.

Background of the Invention

This invention relates to the support structure commonly described as a platter for gramophone record players. A wide variety of materials have been used in prior art of platter assemblies of record players. Notably, with regard to this invention, one of the main concerns that has governed the design of platters in prior art has been the ability of the structure to damp or control by absorbing and directing away from the stylus any resonant energy created by the mechanical reactions of the stylus when it reads the micro groove. To meet this, goal prior art is broad and varied and some notable examples are described below in order to clarify the key criteria that govern the success of the platter. Designed to be in intimate contact with the vinyl and by using a material with a similar acoustic impedance, acrylic has been used as a material that can move the energy away from the vinyl due to its near identical acoustic impedance with vinyl. Unfortunately this "virtue" also provides the ideal path back to the stylus. Acrylic is less than ideal having a very low first natural frequency that is not intrinsically well damped. The exact opposite concept sees the use of a broadband resonant energy damping mechanism, typically a felt or rubber mat, being placed between the platter itself and the vinyl. The mat material acts to provide damping of the unwanted energy that is produced when the stylus is working in the groove. This is quite a good solution that can mask the sound of the platter material to some extent. Alternative designs see high mass metal or mixed material structures as being the best way to deal with any resonance driven by the idea of providing a high mass sink or void for any energy entering the structure and so defeating any energy from returning to impact upon the vinyl. Most of the above designs are based upon material based solutions. More complex systems have manifested as vacuum systems that see a vacuum pump being connected through an elaborate bearing in order to create a pressure differential between the vinyl and a vacuum beneath the vinyl through holes in the platter. The clamping effect generated by the vacuum provides damping of the vinyl only and not the whole platter structure. Mechanical clamps that exploit a simple screw thread provide a degree of clamping that is a much more simple alternative to the above but does not provide the full benefit of the vacuum acting upon the whole surface area of the vinyl.

Generally higher mass platter systems and more complex platters often gain in some ways but are then flawed due to the complexity of the adjacent structural systems that are required to provide support for the higher mass. These more complex systems provide flanking paths for energy to return to the stylus and in some cases create more noise as in the case of vacuum pumps or through the noise generated by the bearing as it tries to cope with the high loads of the platter. Conversely all the low mass, simpler systems tend to made from materials with less than ideal mechanical properties resulting in a low first resonant frequency they also tend to be intrinsically not very well damped. Carbon fibre provides a notable exception, but in all prior art, the use of carbon fibre has not been optimised according to the author's invention that will now be described in more detail. It is important to note that the platter design is governed by a number of requirements that are often conflicting. Specifically with regard to this invention the examples above all have one thing in common and that is, they all recognise the that there are two key Control Criteria that should be considered when designing any platter I Control by damping the resonant energy or 2 Control by conducting away as quickly as possible any resonant energy.

It is the realisation of a single system that is not as severely compromised as prior art that is the subject of this invention and that the invention provides a significantly superior performance according to the above two criteria.

Object of the Invention The object of this invention is to overcome the limitations that have been found in the examples noted above and in all other prior art. The invention seeks to provide a structure that is optimised in terms of its ability to control any unwanted energy created as a result of the stylus reading the groove. By reducing these artifacts to levels that were previously impossible the invention provides a structure that reduces more than all prior art the distortions found in vinyl replay that are attributable to unwanted energy finding its way back to the groove that the stylus is attempting to transcribe. The resulting lower mass system also impinges less on the bearing system that is used to allow the rotation of the platter and as a direct result provides the opportunity for the bearing to perform its function with lower levels of bearing noise.

Summary of the Invention

According to the present invention the preferred design should provide for the vinyl to be clamped across the surface that is usually 100mm diameter at the centre so as to place the vinyl in intimate contact with the micro thin layer of epoxy resin on the surface of the carbon fibre shell of the platter structure. The platter structure should be comprised of a sealed shell structure, which is itself comprised of three key constituent parts. Part 1: The skin of the structure. This should be manufactured to a large extent but not exclusively from a woven multi-axial carbon fibre that is consolidated by epoxy resin. (The nature of this element of the structure and its function is described in more detail later.) Part 2: The core should be created by a high precision, additive manufacturing process or stereo-lithography or similar additive manufacturing technology. The core structure plays an important role in forming and holding the carbon fibre dry fabric during resin infusion when it is formed in the RTM process.

(This moulding process is described in more detail later) Once moulded into the carbon, the core becomes an important structural part of the system providing a cross linking mechanism that is perpendicular to the shell skin, so creating an I section. This cross linking promotes damping and adds significantly to the structural stiffness enabling it to withstand the atmospheric pressures that will be subjected to the whole structure when a vacuum is introduced. Without adding significant additional mass, the increase in stiffness elevates the first natural resonant frequency by several orders of magnitude. As referred to earlier a RTM (Resin Transfer Moulding Technology) manufacturing process is required to realise the structure. The core provides a manufacturing function by providing support structure to the multi axial fabric that should be bonded to it. When closed within the mould the fabric is compressed both against the core and the internal surface of the precision machined moulding tool and so governs exactly the proportion of carbon to epoxy resin ratio that is required to link all the fibres using the least amount of epoxy resin. Prepreg fabrics can be used also but require that a core material that is capable of withstanding higher temperatures be used. Prepregs do not offer the same level of drapability over complex forms when compared to the dry highly drapable fabric that has been determined by the author. Other alternatives like wet lay up would not be appropriate as this would be far too inaccurate in all regards. Part 3: A simple valve that faciltates the extraction of air from the resulting gas impervious shell structure. Once evacuated the structure is sealed to maintain the vacuum.

The structure is now damped across its whole surface due to atmospheric pressure differentials typically in the region of 101.325 kPa or 14.7 lbf/sq or 4.45 Newtons, being the typical pressure available at sea level. The pressure differential pre-stresses the carbon fibre putting it under tension across each cell of the internal core which are themselves placed under compressive forces. This pre-stressing elevates the first natural resonant frequency of the whole system making it less likely to resonate further, any resonant activity that might occur will be exposed to extremely high levels of damping when compared to all materials used in prior art. Significantly, these important benefits are realised without any need to add damping materials or added mass. The net result is a very low mass structure that is damped across its entire surface in a way that was impossible with prior art.

The carbon fabric that is used in the shell structure is now discussed in more detail.

Governed by the maxim, the lower the mass, the easier it is to damp the material, the preferred option is for higher modulus fibres (120 GPa). Higher modulus fibres also provide greater disparity between themselves and the resin that is used to link the fibres which is important for reasons that are explained in more detail below. How the fibres are orientated is important which is why a multiaxial fabric should be used so that fibre orientation is optimised to provide the highest velocity transfer function for the resonant energy from the stylus. It has been found that a key factor in the performance of the carbon fibre when constructed according to the description above, relates to the velocity of sound transfer along the length of the fibre. Carbon fibre and Zylon are second only to Carbon nano tubes in terms of their ability to conduct resonant energy at high speeds. In fact the resonant energy transfer function along the fibre axis of high modulus carbon fibre is approximately 3000 mIs.

Compare this to almost every metal where the maximum possible will be around 800 m/s and there is clearly a significant difference. Conversely, the energy transfer function perpendicular to the fibre is very poor. Like the speed of sound along the fibre, the characteristic of damping within carbon fibre is directly related to the modulus of elasticity and density. When structural borne resonant energy attempts to travel from one medium with impedance zi to another with impedance z2. The first medium being carbon fibre, the second medium being epoxy resin, transmitted energy goes to zero if there is a large mismatch between zi and z2. (After Fletcher and Rossing, 1991) It follows that by using a multiaxial fabric any unwanted resonant energy in the vinyl will be communicated directly to the carbon fibre where it will be rapidly conducted away in multiple axis. Any remaining energy attempting to return towards the stylus will be required to cross trillions of boundaries that will rapidly convert the energy to heat. With reference to the design goals of the platter the resulting structure is then fully optimised so as to provide the highest resonant energy conductivity immediately in the vicinity of the stylus and cartridge but once the cartridge and stylus has moved the multi-axis fabric remains as the only available route that the energy can take in order to return to the cartridge. Since with only a small change in the position of the cartridge, the carbon fibres function changes from being a good conductor of energy to being a very high impedance material in fact a change that increases exponentially with distance. It follows that the skin provides a very high impedance path for any flanking resonances attempting to return to the vinyl where the cartridge is now reading.

To this end the form and geometry of the authors structure, plays a key role in fully exploiting the unique properties of the multi-axial carbon fibre fabric.

When the vinyl is clamped to the structure described above, it is able to benefit from the unique and highly desirable properties of the platter structure. With most of the un wanted energy emanating from the stylus being conducted rapidly away from the vinyl and damped by combination of material and vacuum related features the vinyl can be transcribed with

much higher levels of accuracy than any prior art.

Advantages of the Invention The invention exploits known advantages of anisotropy to achieve near optimum use of the multi axial carbon fibre in shell structure to be used as a platter. The invention exploits the anisotropic properties of carbon fibre to provide a single structure imbued with both high conductivity and high impedance in terms of structural borne energy. The atmospheric pressure differential exerted on the whole surface of the platter is sufficient to provide very high levels of damping with no added mass. The energy that is communicated to the platter by the cartridge stylus mechanism is effectively controlled, firstly by conducting it at the highest speed away from the cartridge and then increasingly dissipating that energy by virtue of the change in fibre alignment, avoiding the need for additional mass damping. Being pre-stressed by the vacuum pressure differential, the low mass, high modulus material is damped at the frequencies where it would normally begin to resonate first of all. The net effect of these advantages translates directly in to superior transcription, being able to measure more effectively the modulations at higher frequencies in the region of 20Khz and above. Crosstalk is improved and background noise relating to vinyl resonance is reduced.

The lower overall mass of the platter will ensure a lower level of bearing noise.

Preferred or Optional Features The preferred design would use a multi axial carbon fibre. Although other methods of manufacture are possible this is the most elegant way of determining the exact alignment of the fibres with a view to achieving a balanced structure that is stiff in more than three axis and so meet the conflicting requirements of the platter.

The preferred fibre would be a high modulus carbon fibre although alternative fibres can be used, as can mixed fibres. Zylon for example has similar properties to high modulus carbon fibre but is adversely affected by ultraviolet light.

The preferred design might also exploit Carbon nano tubes to further enhance the stiffness of the epoxy resin elevating the stiffness of the consolidated matrix, although a reduction in damping would occur if it were used throughout the structure.

The preferred design would exploit the structural benefits to be gained by a low mass open cell cross linking structure that will form a high compression core inside the shell structure.

The preferred method of manufacture of this core would be by stereo-lithography as this would enable high precision sealed system that is also very stiff due to its honeycomb structure.

The preferred design would incorporate into the hollow structure towards and as close as possible to the bearing at the centre of the platter a tube to allow a vacuum pump to be attached so that a vacuum might readily be introduced into the internal cavity of the structure to achieve the pressure differential that will provide the pre-stressed damped structure. The system would be detached once the vacuum had been realised and terminated in such a way as to maintain the vacuum indefinitely.

The preferred design would be a comprised of a matrix that exhibited low levels of off gassing when subjected to a vacuum. Before the final vacuum is introduced the tube would be conditioned by a number of pre vacuum states that would minimise the effects of future off gassing. Calculations show that even a significant drop in vacuum still provides high levels of pressure differential.

The preferred design might also exploit mu metal or other shielding incorporated into the matrix to provide additional shielding of the cartridge, to eliminate any spurious effects of stray magnetic fields or other wave energies such as radiowaves or microwaves.

Brief Description of the Drawing

Drawing I of 2 shows a cross section through the platter core including the location of the vacuum valve.

Drawing 2 of 2 shows a cross section through the platter core including the location of the multi axial carbon fibre

Detailed Description of the Drawing

Drawing I I 2 A core structure 1 that has been grown by additive manufacturing process commonly described as Stereo lithography. Drawing shows section through the core as seen from the side showing the skin of the core 2 that is linked by an internal honeycomb 3 with vacuum valve shown 4 Drawing 2 / 2 Drawing shows section through the core as seen from the side showing a core 1.1 with multi axial carbon fibre 1.2 enveloping the whole surface of the core.

Claims

CLAIMS1. A low mass, high modulus gas impervious, sealed platter structure that benefits from high levels of zero mass damping of the materials from which the platter is made as a direct result of a high atmospheric pressure differential brought about by evacuation of the structure.
2. A structure as claimed in Claim 1, and any claim appendant thereto, wherein the shell is provided with an extraction valve whereby further evacuation may be effected should any vacuum depletion occur.
3. A structure as claimed in Claim 1, wherein, the platters outer shell is manufactured from one or more layers of multi axial carbon fibre cloth that is fashioned by a precision mould so as to cover the entire surface of the platter core during manufacture in an R.T.M. system.
4. A structure as claimed in Claim 1, wherein, the platter core is manufactured by Stereo-lithography or similar additive manufacturing process that sees components that are grown.
5. A structure as claimed in Claim 1, wherein, the platter is manufactured from a multi axial carbon fibre cloth formed around a core structure as according to claim 4 that is then consolidated within precision matched tooling and the resin transfer moulding process which provides for a very accurate infusion of epoxy resin.
6. A structure as claimed in any preceding claim, wherein additional shielding materials are also deployed around, and/or in association with the audio structure, to eliminate the polluting effect of other wave energies such as magnetic, radio waves or microwaves.