Note: Descriptions are shown in the official language in which they were submitted.
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INERTIAL VOICE TYPE COIL ACTUATOR
Background of the Invention
Field of the Invention
The present invention relates generally to inertial type voice coil actuators
capable of
converting energy between electrical and mechanical form and, more
particularly, to an
inertial type voice coil actuator that utilizes radially polarized biasing
magnets and a
multicomponent suspension for alignment of the moving coil.
Description of the Prior Art
Inertial voice coil actuators have been used in the past to acoustically
stimulate semi-
rigid structures to radiate sound. In this application, voice coil actuators
have been attached to
structures that are relatively large to act as a soundboard such as a wall in
a room, where the
wall of the room, when acoustically driven radiates sound. As is well known in
the art, the
force generated by an electrodynamic transducer is a product of the current,
I, length of coil
wire, L and flux density, B so that F=iL B. The length of the coil wire that
is within the
annular magnetic gap is defmed as the length, L. This force is what creates
the movement of
the coil and subsequently generates sound.
These inertial type voice coil transducers are built upon magnetic circuit
designs that
have classically been used for conventional cone type loudspeakers and not
optimized for
driving soundboard type structures. These voice coil actuators often require
the use of an
external housing to support the heavy magnet assembly relative to the voice
coil. The voice
coil is in communication with the external housing at a location coincident
with an acoustic
output system that permits the transducer housing to be mechanically attached
to a
soundboard.
Loudspeaker motors such as used in the past comprise a magnet circuit assembly
including a permanent annular magnet, polarized in the axial direction, and
sandwiched
between two magnetizable plates. One of the plates carries a cylindrical post
that extends
through a central space defined by the annular magnet, generally referred to
as a cylindrical
pole piece. The other plate has an annular opening, somewhat larger than the
diameter of the
pole piece, such that an annular magnetic gap is formed between the post and
the inner edge
of the associated annular plate. The height of the gap is formed by the
thickness of the
annular plate having the annular opening.
Voice coil actuators have a moveable voice coil disposed within the annular
magnetic
gap. For speakers that use a large body such as a wall to generate sound, the
coil has a
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suspension system that typically utilizes an external housing to which the
annular magnet and
magnetizable plates are also attached. The external housing provides radial
stiffiiess and axial
compliance to the coil. The moving coil has a first end fixedly secured to a
radially central
portion of the inner surface of the external housing wall. A mounting screw
secured to an
exterior well portion of the exterior housing may be attached to the wall.
In practice, the annular magnet, magnetizable plates, external housing and
structural
attachment point comprise a system that is large and heavy relative to the
total dynamic force
the actuator is capable of generating. If the external housing is mounted on a
vertical facing
surface e.g. a wall, large bending moments are placed on the structural
attachment point and
the housing must accommodate these moments without translating them to the
coil.
Increasingly, high fidelity audio recordings are being made where the upper
frequency
range is over one (1) octave higher than normal human hearing at 20 kHz.
Accurate
reproduction of these frequencies is often not addressed or is only poorly
accomplished by
earlier speaker systems.
It is therefore an object of the present invention to provide a novel voice
coil actuator
with a high force density. It is a second object of the present invention to
minimize flux
leakage while providing a smaller and more efficient device for driving
relatively large
structures. A third objective of the invention is to minimize sound distortion
by providing a
multi component voice coil suspension system. A fourth objective of the
invention is to
provide an inertial voice coil actuator equipped with a simple mounting system
for
transducing sound to a soundboard.
A fifth objective is to provide an inertial voice coil actuator equipped with
means to
quickly and removably affix the voice coil actuator to various surfaces
without the use of
adhesive bonding between the output disk and the soundboard and without the
need for tools
thereby minimizing assembly and repair time.
Yet another object is to provide a method of enhancing the system for extended
high
frequency response.
Summary of the Invention
According to the present invention, the novel voice coil actuator includes a
magnetic
flux conductive material core, a magnet, and an electrical current conductive
coil uniquely
arranged. The core has a first surface and a continuous channel disposed in
said first surface.
The channel has a pair of opposing walls. The magnet is radially polarized and
disposed in
intimate contact with either one of the channel walls and spaced from the
opposing channel
wall so that a gap remains between the magnet and the opposing wall. The
magnet has two
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faces of opposite magnetic polarities; one faceg the gap. The magnet is
further spaced from
the bottom of the channel so that magnetic flux is substantially normal from
the face across
said gap to the wall. The electrical current conductive coil is disposed
around a coil former
and moveably positioned in the gap such that an electrical current in the coil
develops a
magnetic force on the coil in a direction substantially normal to the magnetic
flux to displace
the coil in response to the magnetic force.
A feature of the present invention is the unique arrangement of the
components. One
pole or face of the magnet is adjacent the gap. This construction ensures that
the magnetic
flux will be uniformly distributed substantially along the length of the gap
since the flux
emanating from the face is inherently substantially uniform. The spacing of
the magnet from
the bottom of the channel also ensures that leakage flux is minimized since
the flux will
follow the path of least resistance and will prefer to be confined through the
core and gap.
The minimizing of leakage obviates the need for bulky shielding which allows
for simpler,
lighter and smaller packaging than existing actuators.
A second feature according to the present invention is a multi-component
suspension
system that supports the electrical current conductive coil in such a manner
that the coil has
high radial stiffness along with appropriate axial compliance. The electrical
current
conductive coil is wound on the coil former that is typically formed of
polymeric material to
form a cylindrical shaped object. The coil former has a first portion that is
external to the
magnetic gap and suspended by a disk shaped member known as a spider
suspension that
provides radial stiffness while providing a restoring force to an axial
displacement. The
spider suspension of the first embodiment includes a concentric corrugation
that provides
additional compliance in the axial direction. The compliance of this spider
suspension is
tuned to first resonant frequency that is below the low pass (fo) frequency of
the signal sent to
the inertial type voice coil actuator. In addition the suspension provides
sufficient stiffness to
support the mass of the magnetic circuit in a vertical orientation without
displacing the voice
coil from neutral position more than about 10% of its total axial
displacement. A second
embodiment includes a second spider suspension spaced vertically from the
first, having the
same general configuration as the first suspension.
The spider suspension has an annular opening that is sized to the outer
diameter of the
voice coil former. The spider has an outer diameter that is mechanically
associated with a
surface of the core. The spider suspension system in a preferred embodiment is
formed of an
elastic or visco -elastic material such as polyurethane, polypropylene, or
other polymeric
material. More than one spider may be used for added suspension control.
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A second portion of the coil fcirnier is iriteinal to the gap and, in one
embodiment, a
viscous magnetic fluid suspension and an antifriction bearing suspend the
second portion.
The viscous magnetic fluid suspension is a fluid that fills any space between
the inner and
outer surfaces of the voice coil former, the coil, the face of the magnet, and
the wall of the
channel. The suspension system may also comprise an antifriction bearing
surface disposed
in intimate contact with one wall of the channel to support the surface of
voice coil former.
The antifriction bearing is sized to provide sufficient clearance for the
voice coil former, but
in the event of a large radial force, it prevents the voice coil from striking
or rubbing the wall
of the channel or the face of the magnet. This bearing also provides a spring
of infinite
compliance along the axial length of the electrical current conductive coil.
In the preferred embodiment, the magnetic fluid is a low viscosity oil, having
microscopic ferrous particles such as magnetite, homogeneously suspended in
the fluid. The
oil-magnetic emulsion is attracted to and held in the magnetic field within
the magnetic gap
by reason of the magnetic flux across this gap. The viscous magnetic fluid
provides a heat
dissipating mechanism and a radial restoring force when the voice coil is
radially displaced.
In the event of substantially larger radial forces that will overcome the
radial restoring force
of the viscous magnetic fluid, the antifriction bearing acts as a bearing for
the voice coil
former.
A third feature of the present invention includes a unique integrated mounting
apparatus providing both quick installation and quick removal features. The
mounting
apparatus transduces vibrations through the coil to the soundboard through an
output disk. In
a preferred embodiment the integrating mounting apparatus comprises the output
disk
acoustically associated with the soundboard and the coil former.
Another preferred embodiment includes an integrating mounting apparatus
comprising the output disk and a receiver designed to interlock one with the
other in such a
way as to accurately translate the vibrations without attenuation or
distortion to a sound body.
One way of accomplishing these objectives uses an interlocking mechanism which
comprises
at least one wedge-like element on the output disk and at least one
complementary
engagement opening on the receiver. In operation, the wedge-like elements on
the output
disk are positioned to be in communication with a base formed in the receiver
thereby
providing accurate transmission of vibrations. In the preferred embodiment the
output disk
further registers into the receiver rotationally via pins, tabs or other
registration means which
assist in placement of the engagement wedge on the wall of the receiver. The
output disk can
then be rotated and pressured into the receiver. In the preferred embodiment,
there is a
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locking means for holding the output d'isk agairist counter-rotation and in
its downward
pressured position against the receiver in order to accurately transmit
vibrations and forces
created by the voice coil actuator to the receiver, and then through the
receiver to the
substrate or soundboard.
To evenly distribute the downward pressure forces between the output disk and
the
receiver exerted by the interface, the distal surface of the output disk can
be molded with a
very slight convexity. When pressured into the receiver by the rotation of the
tab elements
into the openings on the receiver, the output disk would compress downward,
flattening the
convexity of the outer surface rendering it flat and causing even forces to
propagate
throughout the surface.
Adhesive or conventional fixative means may be used to acoustically couple the
receiver and the soundboard. No adhesives between the output disk and receiver
are
necessary. This mounting arrangement is particularly useful when the voice
coil actuator is to
remain exposed and minimizes the need for tools and time for assembly,
installation, and
repair.
In order to accurately reproduce the extended frequency response of the
system, a
high frequency speaker element may be mounted in near proximity to the
inertial voice coil
actuator assembly. These high frequency speaker elements can be comprised of
any electro-
dynamic, piezo-electric, or magnetostrictive type systems.
In one configuration providing extended frequency response, the integrated
mounting
apparatus includes the output disk which comprises an annular opening. A high
frequency
speaker element is co-axially located with the output disk of the voice coil
actuator opposite
the voice coil actuator assembly and mounted in such a manner that the
acoustic output of the
high frequency speaker element is directed away from the side on which the
inertial type
voice coil actuator is mounted. The output disk may be mechanically or
adhesively affixed to
the soundboard.
The high frequency speaker element is electrically connected with the inertial
type
voice coil actuator so that the high frequency components of the audio signal
are
preferentially sent to the high frequency speaker while limiting the low
frequency
components to the inertial type voice coil actuator.
Another embodiment of the inertial type voice coil actuator with extended high
frequency speaker system uses a plurality of higli frequency speaker elements
configured in a
spatial array. The spatial array can be configured in any single, two or three-
dimensional
geometry.
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The present invention provides a'voice coil actixator with superior suspension
system
and novel construction, which results in a lighter and smaller package, more
accurate sound
reproduction, and faster, simpler installation for use with large or small
soundboards.
Other objects, features, and advantages of the present invention will be
readily
appreciated as the same becomes better understood after reading the subsequent
description
taken in conjunction with the appendant drawings.
Brief Description of the Drawino
Fig. 1 is a perspective view of the present invention as installed on a large
sound body.
Fig 2. is a fragmentary cross-sectional perspective view along line 2-2 on Fig
1 of the Inertial
Type Voice Coil Actuator of the present invention showing its suspension
system and
construction;
Fig. 3 is a cross sectional view along line 3-3 of Fig. 1 of the Inertial Type
Voice Coil
Actuator of the present invention including an acoustic mechanical interface
between the
output disk and receiver of the present invention;
Fig. 4 is an exploded perspective view of the present invention showing the
integrated
mounting apparatus;
Fig. 5 is a top view of the locking portions of the receiver and output disk
elements of the
integrated mounting apparatus;
Fig. 4a is an exploded perspective view of another embodiment of the
integrated mounting
apparatus;
Fig. 5a is a top view of the locking portions of the receiver and output disk
elements of the
second embodiment of the integrated mounting apparatus;
Fig. 6 is a cut away perspective view of the receiver and output disk
interlocked, particularly
showing the interlocking elements of the integrated mounting apparatus;
Fig. 6a is a cross section of the output disk along line 6-6 showing a convex
surface;
Fig. 7 is a cross sectional view of a third embodiment of the present
invention wherein an
additional element in the suspension system is shown;
Fig. 8 is a cross sectional view of an inertial type voice coil actuator of an
embodiment
showing a high frequency speaker element co-axially mounted within the output
disk; and
Fig. 9 is a cross sectional view of the fourth embodiment of the present
invention showing a
multi element, hemispherical, high frequency array.
Detailed Description of the Preferred Embodiment
Referring now to FIGS. 1-2, there is shown a novel inertial type voice coil
actuator
constructed according to the principles of the present invention. A voice coil
actuator
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assembly 90 includes a core 101, a magnet 105, an electrical current
conductive coil 106, and
a multi-component suspension system 92 comprising a coil former 107, an
antifriction
bearing 104, a spider suspension 111, and a spacer 110. The core 101 is
constructed from
magnetic flux conductive material and has a first surface 102 and a continuous
channel 103
disposed in the first surface 102 which leaves a center column 120 with a top
surface 122.
The channel has a first wall 108, a second opposing wall 109, a bottom wall
116 and an anti-
fringing groove 121. An integrated mounting apparatus 94 of a preferred
embodiment of the
voice coil actuator comprises an output disk 112 (see Figs. 1,2 and 3). The
integrated
mounting apparatus of another embodiment includes an output disk 247 and a
receiver 114
with means for interlocking 149 said output disk and said receiver (see Figs.
4-6a). A fmal
embodiment includes an output disk 112 having an annular hole 310 as the
integrated
mounting apparatus (see Figs. 8 and 9).
The magnet 105 is disposed in intimate contact with the second wall 109 so
that a
magnetic gap 124 is formed between the magnet and the first wall 108. (See
Fig. 2) The
magnet 105 is cylindrical in shape, is of radial polarization, and comprises a
first face 126 of
a first magnetic polarity and a second face 128 of a second polarity. The
first face 126 is
adjacent the second wall 109 and the second face 128 is disposed within the
gap 124. The
magnet 105 has a lower edge 115 spaced from the bottom wall 116 of the channel
103
forming an anti-fringing groove 125 and an upper edge 117 coextensive with the
top surface
122 of the center column 120. It should be understood that magnet 105 may be
disposed on
either first wall 108 or second wall 109. A higher performance design of the
present
invention will have the magnet 105 disposed on the outer first wall 108 of the
channel 103.
This alternative arrangement creates a stronger magnetic flux across the gap,
thus improving
its force output for a given current.
Shown best in Fig. 2, the coil 106 is moveably suspended in said gap 124 such
that an
electrical current in the coil 106 develops a magnetic force on the coil 106
in a direction
substantially normal to the radial magnetic flux caused by magnet 105 to
displace the coil
106 in response to such magnetic force. Of course, when the coil 106 is
coaxially suspended
in the gap, the force will be axial and linearly proportional to the current,
as is well known.
The coil 106 is wound on the coil former 107 that is used to mechanically
couple the
electro-magnetic force between the magnetic flux from the permanent magnet to
the output
disk 112. The suspension of the coil former 107 in the present invention is
designed to
maintain radial alignment of the coil 106 within the gap 124 without causing
sound
distortion. This suspension system 92 prevents the coil 106 from striking or
rubbing against
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the wall 108 of the channel 103 or lhe seeand face 128 of the magnet while
still allowing
axial compliance.
Referring now to Figs. 1-3, the suspension system 92 comprises the coil former
107, a
first portion 130 of the coil former 107, the spider 111 with a concentric
corrugation 119, the
spacer 110, a groove 132 in the output disk 112, a viscous magnetic fluid 134,
and the
antifriction bearing 104. The first portion 130 of the coil former is radially
suspended by the
spider 111 which is disk shaped in the preferred embodiment. The spider 111
may contain a
concentric corrugation 119 that provides additional compliance by the coil
former 107 in the
axial direction. The concentric corrugation 119 will also permit additional
axial displacement.
This additional displacement is required for improving the low frequency
response, or
alternatively increased sound pressure level. The spacer ring 110 comprises
means for
attaching a distal portion 138 of the spider suspension 111. Means for
attaching the distal
portion 138 of the spider 111 to the spacer 110 can be through overmolding,
ultrasonic
welding or other bonding or mechanical methods. Alternatively, spider and
spacer can be
integrally associated as a single element.
The antifriction bearing 104 has a first face 140 in intimate contact with the
second
wall 109 of the gap 124. An upper surface 142 of the bearing 104 is in
intimate contact with
the lower edge 115 of the permanent magnet 105 and a lower surface 144 is in
contact with
the bottom wall 116 of the channel 103. A second face 146 of the bearing 104
is facing a first
inner surface 148 of the coil former 107. The bearing 104 of the preferred
embodiment is
made from a low friction material such as Teflon by DuPont or similar
material.
The acoustic output of the present invention is to the output disk 112 and
best shown
in Figs. 2 and 3. The output disk 112 comprises a groove 132 in which the coil
former 107 is
bonded. The output disk 112 serves to stabilize the thin wall coil former from
transverse
radial forces between the coil former 107 and the output disk 112. The output
disk 112 is a
lightweight component to preferentially increase the velocity of the output
disk 112 relative
to the core 101 based on the relative mass. The output disk 112 may be
attached mechanically
or adhesively to a soundboard.
As best seen in Fig. 3 a second portion 149 of the coil former 107 may be
radially
suspended by the viscous magnetic fluid 134. The magnetic fluid 134 is held in
suspension
by the resulting magnetic flux from the permanent magnet 105. The magnetic
fluid will
provide a radial restoring force if the coil former 107 is radially displaced
in the magnetic gap
124. The antifriction bearing 104 is provided for the coil 106 to land upon if
a large radial
force is imparted to the coil former 107 causing large radial displacements.
The bearing 104
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will prevent the coil former 107 frorii striking zir rabbing the magnet 105 or
the outer wall
108 of the channel 103.
Figs. 4, 5 and 6 depict an integrated mounting apparatus of one embodiment.
The
output disk 112 and its receiver 114 and means for interlocking them are
shown. In the
preferred embodiment, there is a distal surface 150 of the output disk 112 on
which are at
least one and preferably a plurality of tab elements 152. In the preferred
embodiment, each
tab element 152 is generally spaced equidistant from other tab elements.
The receiver 114 of this embodiment has an annular hole 160 with a depth 162
and a
base 164. A protruding segmented wall 250 is characterized by an inner surface
161 and at
least one and preferably a plurality of openings 251. The openings 251
comprise an adjacent
opening 253 having a vertical wal1253a. For installation, one of said
plurality of tab elements
152 on said distal surface 150 is inserted fully in opening 251 whereupon the
output disk 247
is rotated such that the tab element 152 is moved in the adjacent opening 253
to engage the
vertical wall 253a which frictionally engages the receiver 114 and the output
disk 247 and
serves to transmit sound vibrations as well as mount the unit on the sound
body. (Some
elements alternatively seen in Fig. 4a or Fig. 5a)
In a second embodiment, (see Figs. 4a and 5a) the plurality of tab elements
152
comprise segmented helical wedges. Each of said plurality of segmented helical
wedges 152
tapers from a first leading edge 154 to a second trailing edge 156. Each of
said plurality of
segmented wedges is generally spaced equidistant from others. Furthermore,, in
this
embodiment, the openings 251 are flanked by angled receiving surfaces 252
which ease
accurate placement of said segmented helical wedges 152. Each of said
plurality of openings
251 in this second embodiment comprises an adjacent helicoidal opening 253
with a surface
170 complementarily shaped to the segmented helical wedges 152.
For installation of the segmented helical wedge embodiment, the receiver 114
is
mounted on a soundboard by conventional means. The wedges on the output disk
247 on the
voice coil actuator 90 are then aligned with the openings 251 on the receiver.
The voice coil
actuator is moved toward the receiver 114 such that the engagement wedges are
in a position
to rotationally engage helicoidal openings 253 and the surfaces 170. Next, the
voice coil
actuator assembly 90 is rotated a partial turn which frictionally engages the
receiver 114 and
the output disk 247 and serves to transmit sound vibrations as well as mount
the unit on the
sound body. To evenly distribute the downward pressure forces between the
output disk 247
and the receiver 114, the distal surface 400 of the output disk can be convex
as shown in Fig.
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6a. As the output disk is compressed downward during installation, the
convexity will flatten
and disperse the downward forces more evenly.
The output disk is removably engaged with the receiver 114 using the tab
elements
152. As shown in Figs. 4 and 5 in order to secure the position of the voice
coil actuator and to
maintain positive contact between the output disk 247 and the receiver 114,
locking means
are employed. Said locking means comprises at least one protrusion 284 on said
distal surface
150 and at least one rib-like element 285 on said inner surface 161 of said
segmented wall
250. Said at least one protrusion 284 is positioned relative to one of said at
least one rib-like
elements 285 such that, upon insertion of each tab 152 into one of said
openings 251 and
rotating said output disk to engage said tab and the vertical wall 253a in
said adjacent
opening 253, the distal surface 150 flexes inward enough to allow the
protrusion 284 to move
past said rib-like element 285. By virtue of resilience or memory, said distal
surface 150 then
returns the protrusion to its extended position thereby frictionally
preventing the output disk
from counter rotating.
In a second embodiment seen in Figs. 5a and 6a, the locking means comprises at
least
one locking snap wedge 184 comprising a curved sloped wedge surface 183 which
when
engagably rotated into receiver 114 will deflect inward until said locking
snap wedge 184
attains a recess 185 in the protrading segmented wall 250 At this point the
locking snap
wedge 184 finds relief to the inward deflection and springs into the recess
185 where a
locking surface 186 engages said wa11250 which prevents the output disk from
counter
rotating. As shown in FIG. 6a and FIG. 4a, at least one wedge 152a and
preferably two
wedges 152a arranged in opposition, are hinged by way of dedicated flexural
hinges 182
associated with said distal surface 150 and openings 181 in said distal
surface 150 of said
output disk which permit inward deflection of the locking snap wedge 184. To
facilitate
disengaging the voice coil actuator assembly 90, release tabs 187 are provided
in an opposed
position. Compressing release tabs 187 deflect the portion of the distal
surface 150 between
the openings 181 and cause the locking snap wedges 184 to deflect inward
disengaging the
locking snap wedges 184 and permitting counter rotation of the voice coil
actuator 90 for
easy removal.
An alternative coil former suspension is shown in FIG.7. The electrical
current
conductive coil 106 is wound on a coil former 107 that mechanically couples
the electro-
dynamic force into the desired acoustic structure. The coil former 107 in this
configuration
uses multiple spider suspension 111 and 111a elements to radially align the
coil former 107
with the magnetic gap 124. The spider elements permit axial displacement of
the coil former
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107 while restricting rocking motion or other out of plan.e motions that will
cause the coil
former 107 to strike or rub the permanent magnet 105 or the outer wall 108 of
the channel
103.
Another embodiment is shown best in Figs. 8 and 9. In Fig. 8 the integrated
mounting
apparatus includes output disk 112 comprising an annular hole 310. Said output
disk 112 is
attached to a soundboard member 306 by means of a clamping mechanism 302. Co-
axially
located with and generally covering the annular hole 310 of the output disk
112 is at least one
high frequency speaker element 301. Said at least one high frequency speaker
element 301 is
mounted in such a manner that the acoustic output side 312 of each said
speaker element 301
is facing the preferred direction for transmitting the acoustic response of
the high frequency
element of the system. A vibration isolation pad 304 may be positioned to be
in
communication with said output disk 112 and with each said high frequency
element 301.
The pad 304 will reduce the dynamic mass experienced by the voice coil
actuator and
minimize the structural vibration each high frequency speaker element 301.
Each said at least one high frequency speaker element 301 is positioned
relative to the
output disk 112 such that it penetrates through the soundboard 306 to minimize
the protrusion
of the high frequency speaker element 301 from the face of the soundboard 306.
The speaker
element 301 may be mechanically fixated through conventional means to either
the
soundboard 306 or the output disk 112.
This embodiment may also include the co-location of a plurality of high
frequency
speaker elements 301 mounted on a fixture 305 to fixedly position the high
frequency speaker
elements in relationship to each other. Acoustic radiation from a speaker
element typically
shows a focusing of the energy as the excitation frequency of the speaker
element is
increased. In an effort to reduce the focusing of the acoustic radiation with
increasing
frequency the elements are arranged generally so that the main response axes
of the elements
are not parallel. This may be accomplished through many orientations. A hemi-
spherical
arrangement drives the high frequency elements 301 in phase so that it behaves
in similitude
with a pulsating sphere. The acoustic soundboard 306 in this instance acts as
a baffle,
increasing the overall efficiency of the system.
The inertial type voice coil actuator illustrated in the drawings is to be
viewed as
having some important advantages, including improved force density, power
rating and
relatively constant sound quality, due to the radially polarized permanent
magnets, uniform
magnetic field, and heat dissipating characteristics of the magnetic viscous
fluid and linear
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bearing system. In addition, advantages of simplified installation elements
and high
frequency response capability have been incorporated.
The present invention has been described in an illustrative manner. It is to
be
understood that the terminology which has been used is intended to be in the
nature of words
of description rather than of limitation. Many modifications and variations of
the present
invention are possible in light of the above teachings. Therefore, within the
scope of the
appended claims, the present invention may be practiced otherwise than as
specifically
described.
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