Audio Equipment Storage Device

Field of the Invention

The present invention relates generally to the field of vibration isolation mechanisms in a shelving unit or cabinet, and, more particularly, to vibration control devices which provide improved inherent vibration control in a shelving unit or cabinet in an economical fashion. The shelving unit or cabinet is well suited for use with, for example, audio equipment or other vibration sensitive equipment.

Background of the Invention

People who spend a significant amount of time listening to music often become particularly astute to hearing extraneous variations, which can be caused by a number of factors. One of the main causes of such performance variations in such equipment is vibration, particularly that which is referred to as "micro" vibration within the audio equipment, such as with compact disk ("CD") players, preamplifiers, amplifiers, phonograph stages, and turntables. A primary source of vibration in audio equipment is caused by the sound waves generated by the audio equipment, particularly if the equipment is operated at louder volumes, or repeatedly generates audio frequencies at selected harmonic frequencies.

Other, "macro" vibrations may also happen when a door is slammed, the equipment is bumped, or even from floor movement caused by a person walking in the room.

These vibrations can cause the extraneous variations which are detected by the listener.

The same may be said of the effect of vibration on video equipment, such as laser disk and digital video display ("DVD") players, which become subject to similar vibrations. The irregularities in sound or visual quality of the product caused by the vibration are very distracting to the experienced observer and significantly decrease the quality of the listening or viewing experience for these individuals.

Similarly high technology and laboratory equipment such as microscopes, scales, etc. may likewise be negatively affected by vibrations, even to the extent of causing data produced or collected thereon to be unreliable.

Minimizing the effect of vibration from these "vibration sensitive" pieces of equipment is a constant goal of the audio or video user, or equipment operator.

In the prior art, reducing or eliminating these types of vibration are commonly addressed by providing supports or component attachment means that include vibration isolation devices, such as mounting feet, that isolate the equipment from any vibrations that are transmitted from the shelf on which the equipment rests, or from the cabinet which houses the audio equipment.

Previously, attempts to address the above problem have included use with the performance equipment of such items as isolation cones, spikes, sheets or balls of vibration absorbing material, air isolation platforms, seismic "sinks", and sand boxes, in attempts to dampen the vibrations. However, each of these different methods has certain limitations or disadvantages. Some of the known methods, such as air isolation devices and some seismic sinks are quite expensive and also require a source of pressurized air.

Vibration absorbing materials are limited in the capability to attenuate vibration. Spikes and cones "drain" vibration to the ground or other support surface, rather than actually isolating the performance device from the vibration; and sand boxes, by definition, include the use of sand, which can be very messy and

necessarily creates the risk of inadvertent introduction of sand particles and dust into expensive performance equipment, accessories, tapes, compact disks, and anything else in the vicinity of use of the sand.

Examples of these types of devices are described in, for example, US patent Nos. 3337167, 4718631, 5400998, 6155530, 6357717 and 6655668. Other devices, such as that described in US Patent No. 6845841 seek to minimize vibration from a speaker cabinet by isolation of the speaker cabinet itself from the shelf on which it is resting by use of a foam member as an acoustic isolator.

However, little has been done in the area of providing a shelf structure or cabinet structure which aids in the reduction of vibration. US Patent No. 6550879 does provide a cabinet structure which attempts to address this issue, but merely relies on a series of strengthening pieces to be added to a traditional cabinet. These strengthening materials preferably have a honeycomb structure in order to dampen the vibration from the sound waves. As such, it would be desirable to provide additional means to isolate the vibration sensitive equipment from extraneous vibrations, and preferably accomplish this isolation by features inherently present in the shelving unit or cabinet on or in which, the equipment rests.

Summary of the Invention With the above problems and limitations of the known art in mind, the present invention was developed with the goals of providing a vibration isolating device which inherently provided in the cabinet or support shelf on which the vibration equipment rests, so as reduce, ameliorate, or eliminate the deleterious effects caused by vibration in vibration sensitive equipment. It is further among the advantages of the present invention that the new vibration reduction devices be suitable for manufacture in a variety of sizes or models so as to be capable of handling various sizes of loads and a variety of applications.

It is further among the objects of the invention, having the features indicated, that the vibration control devices be an inherent feature of the cabinet or a support shelf which are used to house or support the vibration sensitive equipment.

The advantages set out hereinabove, as well as other objects and goals inherent thereto, are at least partially or fully provided by the vibration control devices of the present invention, as set out herein below.

Accordingly, in one aspect, the present invention provides a vibration control support structure for use with vibration sensitive equipment, wherein said support structure comprises a shelf and a shelf support device and either or both of said shelf and said shelf support device comprise a vibration attenuating structure.

The shelf and shelf support device can be free standing, or alternatively, can be part of a complete cabinet structure. In a further aspect, the present invention also provides a support shelf for use in the vibration support structure, wherein said support shelf comprises a vibration attenuating structure.

In particular, the shelf of the present invention is provided with at least one surface feature which attenuates the vibration resonant in the shelf structure. Preferred surface features include providing a zone of a vibration absorbing structure or materials, and in a most preferred embodiment, the surface feature is provided by a plurality of grooves or ridges which have preferably been created on at least a portion of one side of said shelf. In a preferred structure, the surface feature is provided by a series of regularly spaced, parallel grooves which have been cut or milled into the lower surface of the shelf.

In a still further aspect, the present invention also provides shelf support device for use in the vibration support structure, wherein said shelf support device comprises a vibration attenuating structure.

In particular, the shelf support device of the present invention is provided with at least one surface or composition feature which attenuates the vibration which is ultimately resonant in the shelf structure. Commonly, prior art shelf support devices are made of a materials such as wood, or tubular aluminum, tubular steel or the like, which can aid in the transmission of any vibration to the shelf. The shelf support device of the present invention is preferably made of a vibration absorbing material or a vibration dispersive material. A preferred vibration absorbing material is a composite fiber material, and most preferably, a hollow tube which has been

fabricated from a carbon fibre material. A vibration dispersive material is a solid metallic rod, and most preferably, a solid aluminium rod, which acts to cause increased radial dispersion of the vibration within the support and thus, less propagation of the vibration along the support. The shelf support device can be a single support or a plurality of support devices, such as, for example, a plurality of carbon fibre tubes or a plurality of solid aluminium rods.

As a result, the vibration control device of the present invention provides a method and apparatus for attenuating the vibrations typically encountered on shelf which is used to support vibration sensitive equipment, and/or which is in contact with such equipment..

Brief Description of the Drawings

Embodiments of this invention will now be described by way of example only in association with the accompanying drawings in which: Figure 1 is a top perspective view of a storage shelf according to the present invention;

Figure 2 is a bottom view of a shelf used in the present invention; and Figure 3 is a cross sectional view of a portion of the shelf of Figure 2.

Detailed Description of the Preferred Embodiments The novel features which are believed to be characteristic of the present invention, as to its structure, organization, use and method of operation, together with further objectives and advantages thereof, will be better understood from the following drawings in which a presently preferred embodiment of the invention will now be illustrated by way of example only. In the drawings, like reference numerals depict like elements.

It is expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

Throughout this discussion, and the description and claims below, it is to be

understood that references to "vibration sensitive equipment" and the like are meant to include sound equipment, as well as video and other sophisticated or scientific equipment which is subject to negative effects of external and internal vibrations. For simplicity of the discussion, "audio" or "sound production" equipment will often be used inclusively of any and all types of equipment, the performance of which will benefit from support of the equipment on the new noise reduction devices described below. Further, for simplicity, the new vibration control device of the present invention will sometimes hereafter be referred to simply as the "device".

Referring to Figure 1 a vibration control device 10 is shown having 3 support shelves 12, and 4 vertical shelf support devices 14. The support shelves and vertical support devices are used in the construction of racks or stands for stereo and video system components. The primary design of device 10 consists of medium density fibreboard (MDF) shelves 12 supported by circular support sections 14 in the shape of circular rod or tubes. The shelves are stacked one above another and individual electronic components are placed on each shelf.

In this embodiment, shelves 12 are fabricated from any of a variety of materials, including, wood laminates, composite wood materials such as MDF, particle board, chip board, or the like, metal, plastic, or glass panels, composite materials such as carbon fibre materials, or various epoxy, fibreglass or acrylic resin based materials, or stone such as granite, or combinations thereof. The skilled artisan will readily be able to determine any one of a number of suitable shelf materials. In the present embodiment, shelves 12 are manufactured from a 16 mm thick sheet of wood veneer MDF (Medium Density Fibreboard).

Shelves 12 are shown all having the same overall dimensions, however, in alternative configurations, each of shelves 12 can have different shapes or sizes.

In the embodiment shown in Figure 1, shelves 12 have a width of 75 cm wide, a depth of 50 cm deep, and a thickness of 2 cm. In alternative embodiments, shelves 12 can have a wide variety of dimensions, but typically, the shelves are between 50 and 125 cm wide, 45 to 60 cm deep, and 1.25 to 3 cm thick. On their top surfaces 16, shelves 12 are preferably substantially flat.

However, as best seen in Figure 2, the lower surface 18 of shelves 12 are fabricated

so as to have a plurality of channeled grooves 20. These grooves are preferably routered into the underside of the shelf, and can be set at any angle between 1 and 179 degrees, relative to the front surface of the shelf. In Figure 2, the grooves are set at an angle of 45 degrees to the front surface 24 of the shelf. The channeled grooves 20 can vary in depth, but preferably are between 1 mm and 55 mm. Preferably, the depth of channeled grooves 20 is such that they do not extend through more than 75% of the thickness of shelf 12, and more preferably, through no more than 50% of the thickness of shelf 12. In the present embodiment, channeled grooves 20 have a depth of 5 mm. All of channeled grooves 20 in the present embodiment have a common width of 8 mm, and all grooves 20 are triangular, or V-shaped, as shown in Figure 3. Other groove shapes, such as semi-circular, square or the like, might also be used. The channeled grooves 20 are also spaced 25.4 mm apart (center to center), although this value can vary depending on the shelf design. Typically, the shelves are spaced between 10 and 50 mm apart, and more preferably, between 15 and 30 cm apart.

The channeled grooves 20 preferably extend to cover at least over 50% of the surface area of the lower surface 18 of shelf 12. More preferably, however, the channeled grooves cover an area of over 70% of the shelf lower surface area 18, and even more preferably, cover an area of over 80% of the lower shelf surface area 18. Preferably, a rim 28 is left around the outer edge area of lower shelf surface

18 for appearance and strength purposes.

The depth, width, number, and spacing design features can all be varied depending on the nature of the shelf design, the shelf construction material or other factors. However, by simple measurement of the shelf vibration during testing, these design parameters can be optimized.

Vertical shelf support devices 14 are fabricated from hollow carbon fiber tubes. However, they might also be fabricated from solid metallic rods, and in particular, solid aluminium rods. The ciruclar support devices are particularly useful in the shelf arrangement shown in Figure 1 , but are also suitable for use in any "rack" mounted arrangements or designs.

Vertical support devices 14 are manufactured to fit within the spaces 28 in

shelves 12, and while support device 14 has a diameter of 2.5 cm, the support device diameter can vary from 1.25cm ID to 7.62cm ID. The height of the vertical support devices 14 can also vary depending on the proposed application, but typically vary from 2.5 cm to 46 cm depending of the shelf design of the rack or platform. The improvement in sound of electronic components supported on shelves 12 with carbon fiber vertical supports 14 is a result of the carbon fiber dissipating the vibrations traveling through the upright supports. It is believed that the carbon fiber resonates at such a low frequency that there is very little stimulation within the uprights. This result in a more stable support for the shelves. Carbon fiber can refer to carbon filament thread, or to felt or woven cloth made from those carbon filaments. By extension, it is also used informally to mean any composite material made with carbon filament, such as for example, graphite-reinforced plastic.

A typical carbon fiber support comprises carbon filaments, wherein each carbon filament is made out of long, thin sheets of carbon similar to graphite. A common method of making carbon filaments is the oxidation and thermal pyrolysis of polyacrylonitrile (PAN), a polymer used in the creation of many synthetic materials. Like all polymers, polyacrylonitrile molecules are long chains, which are aligned in the process of drawing fibres. When heated in the correct fashion, these chains bond side-to-side, forming narrow graphene sheets which eventually merge to form a single, jelly roll-shaped filament. The result is usually 93-95% carbon. Lower-quality fiber can be manufactured using pitch or rayon as the precursor instead of PAN. The carbon can become further enhanced, as high modulus, or high strength carbon, by heat treatment processes. Carbon heated in the range of 1500-2000°C (carborizing) exhibits the highest tensile strength (820,000 Psi), while carbon fibre heated from 2500-3000 ⁰ C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 Psi).

These filaments are stranded into a thread. Carbon fiber thread is rated by the number of filaments per thread, in thousands. For example, 3K (3,000 filament) carbon fiber is 3 times as strong as IK carbon fiber, but is also 3 times as heavy.

Carbon fiber is most notably used to reinforce composite materials, particularly the

class of materials known as graphite reinforced plastic. The carbon fiber thread is typically woven into a carbon fiber cloth. The appearance of this cloth generally depends on the size of thread and the weave chosen.

The carbon fiber cloth, or the like, can then be used to prepare a hollow tube or solid rod by blending it with a suitable polymeric material to produce a graphite- reinforced plastic (GRP). For a tube, a filament winder can be used to make pieces.

Alternatively, materials such as fibre-reinforced plastic (FRP) might also be used. FRP is a composite material comprising a polymer matrix reinforced with fibres usually of glass, carbon, or aramid and is commonly used in aerospace, automotive and marine industries. The term FRP is a more general description of materials like GRP. The polymer is usually an epoxy, vinylester or polyester thermosetting plastic.

Graphite-reinforced plastic or carbon fiber reinforced plastic (CFRP or CRP), is a strong, light and very expensive composite material or fibre reinforced plastic. Like glass-reinforced plastic, which is sometimes referred to as fiberglass, the composite material is commonly referred to by the name of its reinforcing fibers (carbon fiber). The plastic is most often epoxy, but other plastics, like polyester or vinylester, can also be used.

The choice of the GRP matrix can have a profound effect on the properties of the finished composite. A preferred plastic for this application is graphite epoxy.

Improvements in sound quality from music played from components placed on shelf s or platforms supported by carbon fiber supports is substantial when listening tests are conducted. Vibration tests show that there is less resonance when carbon fiber tubes and rods are used for supporting shelf s or platforms, as shown in the attached Examples.

Switching from hollow aluminum tubes to solid aluminum rods as support elements between the shelves was subjectively found by most listeners to cause a general improvement in sound, with a 'tighter' bass response.

Further, placing a series of routered triangular grooves on the underside of the shelves was found to significantly improve the sound quality produced by the electronic components, with most listeners finding large improvements in the treble

response.

Without being bound by theory, it is believed that the results of the improved sound quality from the shelf grooves results from a decrease in standing wave propagation, or vibration, within the shelves. A simple shelf for an audio rack could be a simple rectangular plate with a given thickness. This shelf would have parallel faces on top-bottom, front-back, and side-side. Standing waves, resulting from either surrounding sounds or the harmonic operations within an audio component transferred through the feet of the component to the shelf, could bounce back and forth between faces, muddying the sound. This is analogous to the standing waves within a listening room.

In the example of an audio rack shelf shaped as a simple rectangular plate, there would be internal standing waves between the top and bottom faces of the shelf, as well as the side-to-side and front-to-back faces.

By altering the shape of the shelf to minimize parallel faces, standing waves within the shelf could be minimized. Consequently, instead of a few frequencies causing large resonances in the shelf, the significantly-smaller-magnitude resonances would be spread among many more frequencies, with a corresponding improvement to the clarity of the resulting sound.

With respect to the vertical support columns, it is believed that the vibrations transmitted from either the floor to the rack or from one shelf to another must obviously travel primarily through the support columns.

When a vibration/sound source is present at either the floor of a rack or on a shelf, it causes the end of a support column to vibrate. This vibration then travels through the support column to cause an adjacent shelf to vibrate, and distort the sound produced.

When a vibration 'enters' one end of a prior art tube, it is confined to the narrow walls of the tube. If it is to propagate through the material of the tube, it must travel essentially longitudinally, almost directly towards the opposing end of the tube.

With a solid rod, however, vibrations can propagate to a much larger degree radially, resulting in a less direct path of travel from shelf to shelf for parts of the vibrations. Also, using a solid rod compared to prior art hollow tubing results in

having approximately twice the material in which to absorb the heat from vibrations. Using a solid rod instead of prior art hollow tubing not only create less direct paths of propagation for the vibrations, but the solid rods act as more effective 'heat sinks' to reduce the amount of time a vibration will maintain a sound-affecting amplitude. Since the vibrations produced by bass sound and by 50 Hz or 60 Hz electrical supply 'hum' in audio components have longer wavelengths compared to treble frequencies, fewer cycles are required to cover the distance from one end of a support column to the opposite end.

High frequency/small wavelength frequencies are more likely to dissipate between ends of a support column due to the greater number of cycles required to travel the length of the support column no matter whether the support column is solid or hollow. For bass frequencies, with their longer wavelengths, improvements in vibration dissipation of support columns should result in more pronounced improvements in sound quality compared to higher frequencies. Additionally, or alternatively, the large mass of the solid rod might be the result of better energy dissipation, and the larger mass of the solid rod is able to dissipate the energy more effectively than a tubular metallic support.

Similarly, a carbon fiber tube, for example, is better able to absorb the vibration energy than a tubular metallic support since the vibration energy is contained, and then absorbed within the carbon fibre, and preferably the tubular carbon fibre, support.

Examples

A series of support configurations were tested to evaluate the propagation of vibration within the stand.

Testing Parameters

Since every electronic component used for the subjective listening tests was receiving a 60 Hz, 117 V electrical input, the test frequencies chosen were multiples of 60 Hz. As such, the test frequencies used were 60 Hz, 120 Hz, 240 Hz, 600 Hz, 1200 Hz, 3000 Hz, and 6000 Hz.

To increase the likelihood of finding significant differences in vibration response between different test racks, instead of merely varying the input AC frequency, a loudspeaker was placed on the top shelf, with the drivers facing directly downward. This loudspeaker (System-Audio S2K) consisted of a tweeter and a mid-bass driver. It was supported by a two-piece stabilizing cone/spike on each corner. The location of each cone/spike was consistent for each test rack configuration. As a result, both acoustic vibrations and direct mechanical vibrations from the loudspeaker would be transmitted into the top shelf of the test racks.

The voltage of the signal fed to the loudspeaker produced a sound pressure level (SPL) of approximately 96 dB @ 1 m, A- weighted.

Test Rack Design

The test racks consisted of two shelves separated by four support columns placed approximately at each corner. The shelves consisted of 5/8 in. (16 mm) MDF,

508 mm deep and 660 mm wide. The support columns were circular in cross-section, with a diameter of 25.4 mm (1.00 in.). The distance between the support columns was 354 mm in the depth direction, and 558 mm in the width direction. The basic shape of the shelves was altered slightly for the different test configurations.

A small (76.2 mm) 'foot' was fastened to the underside of the bottom shelf directly underneath the support columns. The entire rack was placed on a wooden test bench, and the location of the 'feet' marked to ensure each rack was placed in the same position.

Measurement Points

Four points were measured on each shelf. The first point was the centre of the shelf (Point A/1). The second test point was the centre between the support columns (Point B/2). This was 26 mm rearward of the first point. The third point (Point C/3) was 7 mm from the side edge of the shelf, in-line with point B. The fourth point was 0.618 of the distance from one side to the other, and 0.618 of the distance from the rear to the front of the shelf (Point D/4).

Measurement Equipment

The vibrations generated in the shelves were measured using a scanning laser vibrometer. The velocity amplitude of the vibrations in the shelves were recorded, both with the loudspeaker 'on' and with the loudspeaker 'off. This was done to determine the noise of the system.

The data was recorded and saved. The data was then used to generate logarithmic graphs comparing velocity amplitude to frequency.

Rack Test Configurations

For testing, the 'base' shelf was the shelf was a CORE rack product that had radiused corners, bevelled edges, and the routered grooves on the underside. A second shelf consisted of the CORE shelf, but with smaller grooves. A third shelf consisted of the CORE shelf, but without grooves. A fourth shelf consisted of a simple rectangular MDF shelf with the same outer dimensions as the CORE shelf. The base CORE shelf was tested with a solid aluminum rod 228.6 mm long vertical support. In another test, the solid aluminium tubing was 228.6 mm long. In a further test, carbon fibre tubing of 228.6 mm was used. In still a further test, a solid aluminium rod of 205.5 mm length was used. In a final test, a carbon fibre tube with a length of 213.0 mm was used. This length was based on a multiple of the approximate wavelength of a 60 Hz sound wave at room temperature, multiplied by 1.618.

For comparison, a standard proprietary OEM design was tested. However, it was tested only to compare with a base model.

Test Results

The forced vibration analysis of the various test rack configurations indicates that the greatest effect on subjective sound quality by the support rack is caused by frequencies greater than 60 Hz and less than approximately 1200 Hz.

The use of routered grooves on the underside of shelves significantly reduces the vibration at 120 Hz.

The use of solid rod supports, compared to hollow supports, results in a slight

decrease in vibration between 120 Hz and 600 Hz.

The carbon fibre tubing exhibited lower vibration velocity amplitude between 120 Hz and 600 Hz than for the solid aluminum rod supports.

The rectangular shelves exhibited greatly larger vibrations as a result of ambient/external vibrations. Carbon fibre tubing generally had the best dampening of ambient/external vibrations.

Choosing specific spacing between shelves based on a ratio of 0.618 can significantly reduce vibrations at approximately 120 Hz.

Choosing aluminum rod lengths for supports based on the 'Golden Section' ratio of 0.618 can reduce vibrations for 120 Hz and 240 Hz.

The subjective improvements in sound quality primarily for the treble region appear to be based on minimizing internal vibrations at 120 Hz. More general improvements in subjective sound quality appear to be based on minimizing vibrations from 240 Hz to 600 Hz. As such, it is apparent that the use of routered grooves on the underside of the shelf provides a reduction in the vibrations observed. Further, the use of solid metallic, and in particular, solid aluminium rods for the vertical support devices also reduces the vibrations observed. Finally, the use of carbon fibre vertical support devices provides an even greater reduction in the vibrations observed. Thus, it is apparent that there has been provided, in accordance with the present invention, a vibration control device which fully satisfies the goals, objects, and advantages set forth hereinbefore. Therefore, having described specific embodiments of the present invention, it will be understood that alternatives, modifications and variations thereof may be suggested to those skilled in the art, and that it is intended that the present specification embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.

Additionally, for clarity and unless otherwise stated, the word "comprise" and variations of the word such as "comprising" and "comprises", when used in the description and claims of the present specification, is not intended to exclude other additives, components, integers or steps.

Moreover, the words "substantially" or "essentially", when used with an

adjective or adverb is intended to enhance the scope of the particular characteristic; e.g., substantially planar is intended to mean planar, nearly planar and/or exhibiting characteristics associated with a planar element.

Further, use of the terms "he", "him", or "his", is not intended to be specifically directed to persons of the masculine gender, and could easily be read as "she", "her", or "hers", respectively.

Also, while this discussion has addressed prior art known to the inventor, it is not an admission that all art discussed is citable against the present application.