Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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.
Backiaround 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
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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.
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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.
SummarX 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
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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
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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.
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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 Figurel 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
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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
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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
5 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
10 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
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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 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 1K 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
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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
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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
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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
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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 colurnns. 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).
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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
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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.
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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.
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