U.S. patent application number 10/429289 was filed with the patent office on 2004-01-15 for acoustically enhanced electro-dynamic loudspeakers.
Invention is credited to Garner, David B., Hutt, Steven W., Steere, John F..
Application Number | 20040008858 10/429289 |
Document ID | / |
Family ID | 30119322 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040008858 |
Kind Code |
A1 |
Steere, John F. ; et
al. |
January 15, 2004 |
Acoustically enhanced electro-dynamic loudspeakers
Abstract
An electro-dynamic loudspeaker is provided with dampening
arrangements that contribute to improved acoustical properties for
the electro-dynamic planar loudspeaker. The dampening arrangements
include providing a frame having a curved sidewall surface for
reducing standing waves. Another design provides for a ferrofluid
being disposed between the diaphragm and magnets of the
electro-dynamic loudspeaker in order to dampen the resonance
frequency of the device. In addition, a diaphragm of an
electro-dynamic loudspeaker is provided with a short turn of
conductor disposed along a fringe zone at an edge of the diaphragm
in order to electro-dynamically dampen the edge resonance of the
film.
Inventors: |
Steere, John F.;
(Martinsville, IN) ; Garner, David B.;
(Indianapolis, IN) ; Hutt, Steven W.;
(Bloomington, IN) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
30119322 |
Appl. No.: |
10/429289 |
Filed: |
May 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60380001 |
May 2, 2002 |
|
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|
60378188 |
May 6, 2002 |
|
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60391134 |
Jun 24, 2002 |
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Current U.S.
Class: |
381/398 ;
381/396 |
Current CPC
Class: |
H04R 2499/13 20130101;
H04R 9/047 20130101; H04R 2400/11 20130101; B60R 11/0217 20130101;
B60R 2011/0288 20130101; H04R 31/006 20130101; B60R 2011/0028
20130101; B60R 2011/0094 20130101; B60R 11/0211 20130101; H04R 1/06
20130101; B60R 11/0205 20130101; H04R 7/04 20130101; H04R 9/06
20130101; H04R 2201/34 20130101; B60R 2011/0017 20130101; H04R
1/025 20130101; H04R 31/003 20130101; H04R 7/18 20130101; H04R
1/026 20130101; H04R 9/025 20130101; B60R 11/0223 20130101; B60R
11/0235 20130101; B60R 2011/0082 20130101; B60R 2011/0003
20130101 |
Class at
Publication: |
381/398 ;
381/396 |
International
Class: |
H04R 001/00; H04R
009/06; H04R 011/02 |
Claims
What is claimed is:
1. An electro-dynamic loudspeaker, comprising: a frame defining a
recessed portion having a pair of sidewalls interconnected by a
pair of end walls, at least one of the sidewalls including a
plurality of curves along a length of the sidewalls; a plurality of
magnets mounted in the recessed portion of the frame; and a
diaphragm mounted to the frame.
2. The loudspeaker according to claim 1, where the plurality of
curves along the length of the at least one of the sidewalls are
sinusoidal.
3. The loudspeaker according to claim 1, where the plurality of
curves along the length of the at least one of the sidewalls are
scalloped.
4. The loudspeaker according to claim 1, where the diaphragm is
mounted to the frame by an adhesive.
5. An electro-dynamic loudspeaker, comprising: a frame defining a
recessed portion having a pair of sidewalls interconnected by a
pair of end walls, the sidewalls being non-parallel to one another;
a plurality of magnets mounted in the recessed portion of the
frame; and a diaphragm attached to the frame.
6. The loudspeaker according to claim 5, where one of the pair of
sidewalls of the recessed portion of the frame is angled relative
to the other of the pair of sidewalls.
7. An electro-dynamic loudspeaker, comprising: a frame; a plurality
of magnets mounted to the frame; a diaphragm mounted to the frame;
and a ferrofluid disposed between the diaphragm and the
magnets.
8. The loudspeaker according to claim 7, further comprising means
for maintaining the ferrofluid on the plurality of magnets.
9. The loudspeaker according to claim 7, further comprising a wall
structure surrounding the plurality of magnets.
10. An electro-dynamic loudspeaker, comprising: a frame; a
plurality of magnets mounted to the frame; a diaphragm mounted to
the frame; and means disposed between the diaphragm and the magnets
for dampening vibration of the diaphragm.
11. The loudspeaker according to claim 10, where the means disposed
between the diaphragm and the magnets is a ferrofluid.
12. The loudspeaker according to claim 11, further comprising means
for maintaining the ferrofluid on the plurality of magnets.
13. The loudspeaker according to claim 10, further comprising a
wall structure surrounding the plurality of magnets.
14. A method of dampening vibration of a diaphragm of an
electro-dynamic loudspeaker, comprising the steps of: mounting at
least one magnet in a frame; placing ferrofluid on an upper surface
of the at least one magnet; and mounting a diaphragm, with an
electric circuit thereon, to the frame such that the ferrofluid is
in contact with the diaphragm.
15. The method according to claim 14, where the at least one magnet
is mounted inside of a wall structure that surrounds the
magnet.
16. An electro-dynamic loudspeaker, comprising: a frame; at least
one magnet mounted to the frame; a diaphragm mounted to the frame,
the diaphragm including a conductor mounted to a film material; and
a shorted turn of conductor disposed along a fringe zone at an edge
of the diaphragm.
17. The loudspeaker according to claim 16, further comprising a
second shorted turn of conductor disposed on an opposite side of
the diaphragm form the shorted turn of conductor.
18. An electro-dynamic loudspeaker, comprising: a frame; at least
one magnet mounted to the frame; a diaphragm mounted to the frame,
the diaphragm including a conductor mounted to a film material, the
film material being a piezoelectric material; and an undriven
conductor applied to both sides of the film material.
19. The loudspeaker according to claim 18, where the undriven
conductor is disposed in a fringe zone at an edge of the film
material.
20. An electro-dynamic loudspeaker, comprising: a frame; at least
one magnet mounted to the frame; a diaphragm mounted to the frame,
the diaphragm including a conductor mounted to a film material, the
film material being a piezoelectric material; and conductor means
for providing an electric current in a fringe zone at an edge of
the diaphragm.
Description
1. CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/380,001, filed May 2, 2002, No. 60/378,188,
filed May 6, 2002, and No. 60/391,134, filed Jun. 24, 2002. These
patent applications are incorporated by reference.
2. CROSS REFERENCE TO CO-PENDING APPLICATIONS
[0002] This application incorporates by reference the disclosures
of each of the following co-pending applications which have been
filed concurrently with this application: U.S. patent application
Ser. No. ______, entitled "Mounting Bracket System," filed May 2,
2003; U.S. patent application Ser. No. ______, entitled "Film
Tensioning System," filed May 2, 2003; U.S. patent application Ser.
No. ______, entitled "Film Attaching System," filed May 2, 2003;
U.S. patent application Ser. No. ______, entitled "Electrical
Connectors For Electro-Dynamic Loudspeakers," filed May 2, 2003;
U.S. patent application Ser. No. ______, entitled "Electro-Dynamic
Loudspeaker Mounting System," filed May 2, 2003; U.S. patent
application Ser. No. ______, entitled "Conductors For
Electro-Dynamic Loudspeakers," filed May 2, 2003; U.S. patent
application Ser. No. ______, entitled "Frame Structure," filed May
2, 2003; U.S. patent application Ser. No. ______, entitled
"Directivity Control Of Electro-Dynamic Loudspeakers," filed May 2,
2003; U.S. patent application Ser. No. ______, entitled "Frequency
Response Enhancements For Electro-Dynamic Loudspeakers," filed May
2, 2003; and U.S. patent application Ser. No. ______, entitled
"Magnet Arrangement For Loudspeaker," filed May 2, 2003.
BACKGROUND OF THE INVENTION
[0003] 1. Field of Invention
[0004] The invention relates to electro-dynamic loudspeakers, and
more particularly, improvements for electro-dynamic loudspeakers
and manufacturing methods thereof.
[0005] 2. Related Art
[0006] The general construction of an electro-dynamic loudspeaker
includes a diaphragm, in the form of a thin film, attached in
tension to a frame. An electrical circuit, in the form of
electrically conductive traces, is applied to the surface of the
diaphragm. Magnetic sources, typically in the form of permanent
magnets, are mounted adjacent to the diaphragm or within the frame,
creating a magnetic field. When current is flowing in the
electrical circuit, the diaphragm vibrates in response to the
interaction between the current and the magnetic field. The
vibration of the diaphragm produces the sound generated by the
electro-dynamic loudspeaker.
[0007] Many design and manufacturing challenges present themselves
in the manufacturing of electro-dynamic loudspeakers. First, the
diaphragm, that is formed by a thin film, needs to be permanently
attached, in tension, to the frame. Correct tension is required to
optimize the resonance frequency of the diaphragm. Optimizing
diaphragm resonance extends the bandwidth and reduces sound
distortion of the loudspeaker.
[0008] The diaphragm is driven by the motive force created when
current passes through the conductor applied to the diaphragm
within the magnetic field. The conductor on the electro-dynamic
loudspeaker is attached directly to the diaphragm. Because the
conductor is placed directly onto the thin diaphragm, the conductor
should be constructed of a material having a low mass and should
also be securely attached to the film at high power (large current)
and high temperatures.
[0009] Accordingly, designing conductors for electro-dynamic
loudspeaker applications presents various challenges such as
selecting the speaker with the desired audible output for a given
location that will fit within the size and location constraints of
the desired applications environment. Electro-dynamic loudspeakers
exhibit a defined acoustical directivity pattern relative to each
speaker's physical shape and the frequency of the audible output
produced by each loudspeaker. Consequently, when an audio system is
designed, loudspeakers possessing a desired directivity pattern
over a given frequency range are selected to achieve the intended
performance of the system. Different loudspeaker directivity
patterns may be desirable for various loudspeaker applications. For
example, for use in a consumer audio system for a home listening
environment, a wide directivity may be preferred. In the
application of a loudspeaker, a narrow directivity may be desirable
to direct sound, e.g., voice, in a predetermined direction.
[0010] Often, space limitations in the listening environment
prohibit the use of a loudspeaker in an audio system that possesses
the preferred directivity pattern for the system's design. For
example, the amount of space and the particular locations available
in a listening environment for locating and/or mounting the
loudspeakers of the audio system may prohibit the use of a
particular loudspeaker that exhibits the intended directivity
pattern. Also, due to space and location constraints, it may not be
possible to position or oriented the desired loudspeaker in a
manner consistent with the loudspeaker's directivity pattern.
Consequently, size and space constraints of a particular
environment may make it difficult to achieve the desired
performance from the audio system. An example of a listening
environment having such constraints is the interior passenger
compartment of an automobile or other vehicle.
[0011] While the electric circuitry of electro-dynamic loudspeakers
may present design challenges, electro-dynamic loudspeakers are
very desirable loudspeakers because they are designed to have a
very shallow depth. With this dimensional flexibility,
electro-dynamic loudspeakers may be positioned at locations where
conventional loudspeakers would not traditionally fit. This
dimensional flexibility is particularly advantageous in automotive
applications where positioning a loudspeaker at a location that a
conventional loudspeaker would not otherwise fit could offer
various advantages. Further, because the final loudspeaker assembly
may be mounted on a vehicle, it is important that the assembly be
rigid during shipping and handling so that the diaphragm or frame
does not deform during installation.
[0012] While conventional electro-dynamic loudspeakers are shallow
in depth and may therefore be preferred over conventional
loudspeakers for use in environments requiring thin loudspeakers,
electro-dynamic loudspeakers have a generally rectangular planar
radiator that is generally relatively large in height and width to
achieve acceptable operating wavelength sensitivity, power
handling, maximum sound pressure level capability and low-frequency
bandwidth. Unfortunately, the large rectangular size results in a
high-frequency beam width angle or coverage that may be too narrow
for its intended application. The high-frequency horizontal and
vertical coverage of a rectangular planar radiator is directly
related to its width and height in an inverse relationship. As
such, large radiator dimensions exhibit narrow high-frequency
coverage and vice versa.
[0013] The frame of the electro-dynamic loudspeakers supports the
magnets, the diaphragm, and the terminal. A ferrous steel frame has
the advantage of carrying magnetic flux that can improve efficiency
over a non-ferrous frame. However, frames constructed from
non-ferrous or non-metallic materials provide other manufacturing
advantages. The frame presents design challenges since it is
preferably rigid enough to keep the diaphragm film tension uniform
and capable of not deforming during handling, assembly, or over
time. The frame also should be capable of withstanding
environmental high temperatures, humidity, salt, spray, etc., and
be capable of bonding with the diaphragm film.
[0014] Other features affecting the acoustic characteristics of the
electro-dynamic loudspeaker include damping of undriven portions of
the diaphragm film in order to help reduce distortion and smooth
frequency response. Damping is required to control film edges by
reducing unproductive or counter productive vibration.
[0015] Furthermore, the controlled directivity of sound is critical
for a good system design and acoustical interaction in the
listening environment. The electro-dynamic loudspeakers exhibit
defined acoustical directivity relative to frequency and to their
shape and also relative to the distance from the source. In
addition, other frequency response enhancements can also be made to
the current electro-dynamic loudspeaker designs.
[0016] With the dimensional flexibility obtained with an
electro-dynamic loudspeaker, various locations in automotive and
non-automotive vehicles may be employed to house electro-dynamic
loudspeakers. Different locations offer various advantages over
other locations. The thin depth of the electro-dynamic loudspeaker
allows them to fit where conventional loudspeakers would not. The
final assembly may be mounted on a vehicle, and therefore, must be
rigid during shipping and handling and should not allow the
diaphragm or frame to deform during installation.
SUMMARY
[0017] The invention provides several arrangements and methods for
enhancing the acoustical properties of an electro-dynamic
loudspeaker. According to one aspect of the invention, the
electro-dynamic loudspeaker includes a frame defining a recessed
portion having a pair of sidewalls interconnected by a pair of
endwalls and at least one of the sidewalls including a plurality of
curves along a length of the sidewall. The curves can be in the
form of a sinusoidal curve or scallops or another shape that is
non-parallel to the opposing sidewall. The curves that are placed
in at least one sidewall are provided in order to reduce standing
waves that contribute to distortion.
[0018] The electro-dynamic loudspeaker includes a frame including a
plurality of magnets mounted to the frame. A diaphragm is mounted
to the frame and a ferrofluid is disposed between the diaphragm and
the magnets and contacts a lower surface of the diaphragm. A
ferrofluid is a stable colloidal suspension of sub-domain magnetic
particles in a liquid carrier. The ferrofluid dampens the resonant
frequency of the diaphragm in order to reduce distortion and smooth
frequency response.
[0019] An electro-dynamic loudspeaker is provided with a shorted
turn of conductor disposed along a fringe zone at an edge of the
diaphragm. The shorted turn electro-dynamically dampens the edge
resonance of the diaphragm.
[0020] A diaphragm of an electro-dynamic loudspeaker is made from a
piezoelectric material, such as PVDF (polyvelydeneflouride) and is
provided with a current carrying conductor and an undriven
conductor applied to both sides of the film material. The undriven
conductors are caused to move by the electromotive force on the
circuit as the diaphragm vibrates, thus creating electric current
through the undriven conductor. The electric current causes the
piezoelectric material of the film to expand and contract in
response to the electric current, and thereby dampens the film
modes to reduce distortion and smooth frequency response. As an
alternative, a PVDF strip can also be glued to a PEN (polyethylene
naphthalate) film.
[0021] Other systems, methods, features and advantages of the
invention will be or will become apparent to one with skill in the
art upon examination of the following figures and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within this
description, be within the scope of the invention, and be protected
by the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The invention can be better understood with reference to the
following drawings and description. The components in the figures
are not necessarily to scale, emphasis instead being placed upon
illustrating the principles of the invention. Moreover, in the
figures, like reference numerals designate corresponding parts
throughout the different views
[0023] FIG. 1 is a perspective view of a electro-dynamic
loudspeaker as it would appear with the grille removed.
[0024] FIG. 2 is an exploded perspective view of the
electro-dynamic loudspeaker shown in FIG. 1 having a grille.
[0025] FIG. 3 is a cross-sectional view of the electro-dynamic
loudspeaker taken along line 3-3 of FIG. 1.
[0026] FIG. 4 is an enlarged cross-sectional view of the encircled
area of FIG. 3.
[0027] FIG. 5 is a plan view of the film having an attached
conductor.
[0028] FIG. 6A is a perspective view of a frame having sinusoidal
curved sidewalls.
[0029] FIG. 6B is a partial plan view of a scalloped sidewall.
[0030] FIG. 6C is a partial plan view of a jagged sidewall.
[0031] FIG. 7 is a perspective view of a frame having an angled
sidewall.
[0032] FIG. 8 is a cross-sectional view illustrating a ferrofluid
disposed on a surface of a magnet and in contact with the film.
[0033] FIG. 8A is a detailed cross-sectional view of the ferrofluid
on the magnet with the diaphragm in an upward direction.
[0034] FIG. 8B is a detailed cross-sectional view of the ferrofluid
on the magnet with the diaphragm in a downward direction.
[0035] FIG. 9 is a perspective view of an electro-dynamic
loudspeaker including an undriven conductor applied to both sides
of the film for providing a dampener for the diaphragm film.
[0036] FIG. 10 is a cross-sectional view taken along line 10-10 of
FIG. 9.
[0037] FIG. 11 is a plan view of an electro-dynamic loudspeaker
having a shorted turn of conductor in the fringe zone at the edges
of the film to electro-dynamically dampen the edge resonance.
[0038] FIG. 12 is a cross-sectional view taken along line 12-12 of
FIG. 11.
DETAILED DESCRIPTION
[0039] FIG. 1 is a perspective view of an electro-dynamic
loudspeaker 100 of the invention. As shown in FIG. 1, the
electro-dynamic loudspeaker is a generally planar loudspeaker
having a frame 102 with a diaphragm 104 attached in tension to the
frame 102. A conductor 106 is positioned on the diaphragm 104. The
conductor 106 is shaped in serpentine fashion having a plurality of
substantially linear sections (or traces) 108 longitudinally
extending along the diaphragm interconnected by radii 110 to form a
single current path. Permanent magnets 202 (shown in FIG. 2) are
positioned on the frame 102 underneath the diaphragm 104, creating
a magnetic field.
[0040] Linear sections 108 are positioned within the flux fields
generated by permanent magnets 202. The linear sections 108 carry
current in a first direction 112 and are positioned within magnetic
flux fields having similar directional polarization. Linear
sections 108 of conductor 106 having current flowing in a second
direction 114, that is opposite the first direction 112, are placed
within magnetic flux fields having an opposite directional
polarization. Positioning the linear sections 108 in this manner
assures that a driving force is generated by the interaction
between the magnetic fields developed by magnets 202 and the
magnetic fields developed by current flowing in conductor 106. As
such, an electrical input signal traveling through the conductor
106 causes the diaphragm 104 to move, thereby producing an
acoustical output.
[0041] FIG. 2 is an exploded perspective view of the
electro-dynamic loudspeaker 100 shown in FIG. 1. As illustrated in
FIG. 2, the flat panel loudspeaker 100 includes a frame 102, a
plurality of high energy magnets 202, a diaphragm 104, an
acoustical dampener 236 and a grille 228. Frame 102 provides a
structure for fixing magnets 202 in a predetermined relationship to
one another. In the depicted embodiment, magnets 202 are positioned
to define five rows of magnets 202 with three magnets 202 in each
row. The rows are arranged with alternating polarity such that
fields of magnetic flux are created between each row. Once the flux
fields have been defined, diaphragm 104 is fixed to frame 102 along
its periphery.
[0042] A conductor 106 is coupled to the diaphragm 104. The
conductor 106 is generally formed as an aluminum foil bonded to the
diaphragm 104. The conductor 106 can, however, be formed from other
conductive materials. The conductor 106 has a first end 204 and a
second end 206 positioned adjacent to one another at one end of the
diaphragm 104.
[0043] As shown in FIG. 2, frame 102 is a generally dish-shaped
member preferably constructed from a substantially planar
contiguous steel sheet. The frame 102 includes a base plate 208
surrounded by a wall 210. The wall 210 terminates at a radially
extending flange 212. The frame 102 further includes apertures 214
and 216 extending through flange 212 to provide clearance and
mounting provisions for a conductor assembly 230.
[0044] Conductor assembly 230 includes a terminal board 218, a
first terminal 220 and a second terminal 222. Terminal board 218
includes a mounting aperture 224 and is preferably constructed from
an electrically insulating material such as plastic, fiberglass or
other insulating material. A pair of rivets or other connectors
(not shown) pass through apertures 214 to electrically couple first
terminal 220 to first end 204 and second terminal 222 to second end
206 of conductor 106. A fastener such as a rivet 226 extends
through apertures 224 and 216 to couple conductor assembly 230 to
frame 102.
[0045] A grille 228 functions to protect diaphragm 104 from contact
with objects inside the listening environment while also providing
a method for mounting loudspeaker 100. The grille 228 has a
substantially planar body 238 having a plurality of apertures 232
extending through the central portion of the planar body 238. A rim
234 extends downward, substantially orthogonally from body 238,
along its perimeter and is designed to engage the frame 102 to
couple the grille 228 to the frame 102.
[0046] An acoustical dampener 236 is mounted on the underside of
the base plate 208 of the frame 102. Dampener 236 serves to
dissipate acoustical energy generated by diaphragm 104 thereby
minimizing undesirable amplitude peaks during operation. The
dampener 236 may be made of felt, or a similar gas permeable
material.
[0047] FIG. 3 is a cross-sectional view of the electro-dynamic
loudspeaker taken along line 3-3 of FIG. 1. FIG. 3 shows the frame
102 having the diaphragm 104 attached in tension to the frame 102
and the permanent magnets 202 positioned on the frame 102
underneath the diaphragm 104. Linear sections 108 of the conductor
106 are also shown positioned on top of the diaphragm 104.
[0048] FIG. 4 is an enlarged cross-sectional view of the encircled
area of FIG. 3. As illustrated by FIG. 4, the diaphragm 104 is
comprised of a thin film 400 having a first side 402 and a second
side 404. First side 402 is coupled to frame 102. Generally, the
diaphragm 104 is secured to the frame 102 by an adhesive 406 that
is curable by exposure to radiation. However, the diaphragm 104 may
secured to the frame 102 by other mechanism, such as those known in
the art.
[0049] To provide a movable membrane capable of producing sound,
the diaphragm 104 is mounted to the frame 102 in a state of tension
and spaced apart a predetermined distance from magnets 202. The
magnitude of tension of the diaphragm 104 depends on the speaker's
physical dimensions, materials used to construct the diaphragm 104
and the strength of the magnetic field generated by magnets 202.
Magnets 202 are generally constructed from a highly energizable
material such as neodymium iron boron (NdFeB), but may be made of
other magnetic materials. The thin diaphragm film 400 is generally
a polyethylenenaphthalate sheet having a thickness of approximately
0.001 inches; however, the diaphragm film 400 may be formed from
materials such as polyester (e.g., known by the tradename "Mylar"),
polyamide (e.g., known by the tradename "Kapton") and polycarbonate
(e.g., known by the tradename "Lexan"), and other materials known
by those skilled in the art for forming diaphragms 104.
[0050] The conductor 106 is coupled to the second side 404 of the
diaphragm film 400. The conductor 106 is generally formed as an
aluminum foil bonded to diaphragm film 400, but may be formed of
other conductive material known by those skilled in the art.
[0051] The frame 102 includes a base plate 208 surrounded by a wall
210 extending generally orthogonally upward from the plate 208. The
wall 210 terminates at a radially extending flange 212 that defines
a substantially planar mounting surface 414. A lip 416 extends
downwardly from flange 212 in a direction substantially parallel to
wall 210. Base plate 208 includes a first surface 418, a second
surface 420 and a plurality of apertures 422 extending through the
base plate 208. The apertures 422 are positioned and sized to
provide air passageways between the first side 402 of diaphragm 104
and first surface 418 of frame 102. An acoustical dampener 236 is
mounted to second surface 420 of frame base plate 208.
[0052] With reference to FIG. 6, an alternative frame 600 is
provided which defines a recessed portion 602 having a pair of
sidewalls 604, 606 interconnected by a pair of endwalls 608, 610.
As described above, the magnets of the electro-dynamic planar
loudspeaker are mounted to the frame and a diaphragm is mounted to
an upper attachment surface 612. One or more of the sidewalls 604,
606 or end walls 608, 610 includes a plurality of curves along a
length of the wall in order to reduce transverse standing waves
across the diaphragm. The curved sidewall 604 or 606 can include a
sinusoidal curve (FIG. 6A), scallops 614 (FIG. 6B), triangular
peaks 616 (FIG. 6C), or any other configuration which reduces
standing waves by varying a diameter of the frame along a
longitudinal length thereof in order to reduce transverse standing
waves across the diaphragm by minimizing the length of parallel
wall lengths.
[0053] With reference to FIG. 7, a frame 700 according to a second
embodiment of the invention, has a recessed portion 702 having a
pair of sidewalls 704, 706 connected to one another by a pair of
endwalls 708, 710. A plurality of magnets are mounted to the frame
700 and a diaphragm is mounted to an attachment surface 712 of the
frame 700. The sidewall 704 is non-parallel to the sidewall 706 in
order to reduce transverse standing waves. In particular, sidewall
704 can be angled relative to the sidewall 706. By varying the
distance across the frame 700 along a longitudinal length thereof,
the production of standing waves is thereby reduced.
[0054] With reference to FIG. 8, another embodiment of the
invention will now be described. In FIG. 8, an electro-dynamic
loudspeaker 800 is provided including a frame 802 having a
plurality of magnets 804 (one shown) mounted to the frame 802. A
diaphragm 806 is mounted to an attachment surface 808 of the frame
802 by an adhesive 810. The diaphragm includes a conductor
including a plurality of elongated traces 812 mounted thereto. A
ferrofluid 814 is provided between the diaphragm 806 and magnets
804. The ferrofluid 814 is in contact with the diaphragm 806 so
that as the diaphragm 806 vibrates, the contact with the ferrofluid
814 dampens the vibration. As illustrated in FIG. 8A, as the film
806 moves upward, the ferrofluid 814 is "stretched" upward while
maintaining contact with the film and as shown in FIG. 8B, as the
film 806 moves downward, the ferrofluid 814 is compressed. The
ferrofluid 814 is maintained on the surface of the magnet 804 by
the magnetic field attracting the ferrous fluid. A wall structure
816 surrounds the magnets 804 in order to isolate the ferrofluid
814 on an upper surface of the magnets 804. The ferrofluid 814 can
be provided on all of or selective ones of the magnets 804. In
particular, putting ferrofluid only on the outermost magnets 804
may provide sufficient damping. The ferrofluid provides a
mechanical dampener for dampening the resonance frequency of the
film 806 instead of the use of felt or another dampener material on
the back of the frame.
[0055] With reference to FIGS. 9 and 10, an alternative damping
arrangement is provided for an electro-dynamic loudspeaker 900. As
shown in FIG. 10, the electro-dynamic loudspeaker 900 includes a
frame 1000 having a plurality of magnets 1002 mounted thereto as
previously described. A film 1004 is mounted to the frame by an
adhesive 1006. A conductor 1008 is provided on the film 1004 in the
same manner as is described above with reference to FIG. 1. The
film 1004 is made from a piezoelectric material such as
polyvelydeneflouride (PVDF) that is available under the trade name
KYNAR. KYNAR exhibits a piezoelectric effect in that when
electricity is applied to conductors attached on opposite sides,
the material contracts or expands. A pair of undriven conductors
1010, 1012 (not part of the conductor 1008) are applied to both
sides of the film 1004 along opposite edges of the film. The
undriven upper and lower conductors 1010, 1012 are each connected
together by a rivet 902 extending through the film 1004. The
undriven conductor is located in order to dampen the film modes.
Specifically, as the film 906 vibrates, the undriven conductor 912,
914 is moved relative to the magnetic field generated by magnets
1002 and generates electric current therethrough which causes the
film material to contract and expand as the current changes so that
the conductors 1010, 1012 act to dampen film modes and behave like
an edged treat. Due to the piezoelectric effect, the PVDF film has
a resultant change in thickness based on the relationship
dta=d33*Vt where: dta is the change in thickness; d33 is the
piezoelectric moduli appropriate for the material; and Vt is an
applied voltage. Conversely, Vt=dta/d33.
[0056] With reference to FIGS. 11 and 12, an alternative dampening
arrangement is provided for an electro-dynamic loudspeaker 1100.
The electro-dynamic loudspeaker 1100, as shown in FIG. 12, includes
a frame 1200 including a plurality of magnets 1202 mounted thereto.
A diaphragm 1204 is mounted to the frame 1200 by an adhesive 1206.
A conductor 1208 is mounted to the diaphragm 1204 in the same
manner as described with reference to FIG. 1. A shorted turn of
conductor 1102 is separately provided in the fringe zone at the
edges of the film 204, as best illustrated in FIG. 11. The shorted
turn 1102 electro-dynamically dampens the edge resonance of the
film 1204 by providing a damping electromotive force.
[0057] While various embodiments of the invention have been
described, it will be apparent to those of ordinary skill in the
art that other embodiments and implementations are possible that
are within the scope of this invention. Accordingly, the invention
is not restricted except in light of the attached claims and their
equivalents.
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