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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of loudspeakers employing a
plurality of substantially rigid planar diaphragms, driven by cooperating
coil and magnet units.
More specifically, the invention relates to a planar loudspeaker system
having an elongated and substantially planar enclosure, configured to
house tweeter, midrange, and a pair of woofer diaphragms in its median,
longitudinal portion. A pair of quarter-wave woofer labyrinths extends
throughout the remainder of the enclosure's volume. The labyrinths vent
the woofer backwaves forwardly, toward the listener, through a pair of
shared ports in the mid-frontal area of the enclosure.
The invention also relates to electro-magnetic drive units which apply a
distributive driving force to the planar diaphragms, while presenting a
distributive load to the drive amplifiers. Three versions or embodiments
of the drive units are disclosed, each of which utilizes bar magnets, pole
pieces, and thin encapsulated moving coils, all of elongated and
symmetrical configuration, in accordance with the distributive drive and
load design.
2. Description of the Prior Art
a. Planar Loudspeakers
An overview of planar loudspeaker designs is presented on pages 40-47 of
the August, 1987, issue of Audio, Audio Publishing, New York, N.Y. While
by no means complete, this article does present some of the varied
historical and current approaches to constructing and driving, and housing
planar diaphragms. However, none of these designs contemplates the
particular loudspeaker system disclosed in the following application.
The applicant herein has previously described, in U.S. Pat. No. 4,385,210,
an electro-acoustic planar transducer which shares at least some of the
characteristics and goals of the loudspeaker system presented herein.
Specifically, the transducer disclosed in the '210 Patent uses
substantially rigid planar diaphragms, driven by an electro-magnetic drive
system. The design taught in the '210 Patent also addresses the "backwave
problem", in the particular context of a planar loudspeaker mounted
directly upon a rearwardly positioned wall, or other planar surface.
Applicant's prior design, however, was not adapted for multiple transducer
systems to be positioned immediately adjacent one another, as the
laterally directed backwaves of adjacent systems would not be able to vent
properly. Also, in some circumstances, the laterally vented backwaves can
induce undesirable resonances in the rear wall upon which the speaker is
designed for mounting. Lastly, the stationary coil and moving magnet drive
disclosed in the '210 Patent presents such a low impedance to the
amplifier, that even current designs for high fidelity amplifiers have
considerable difficulty in driving the transducers properly. The planar
loudspeaker design herein is directed toward solving each of these issues,
while retaining the segmented, rigid planar diaphragm and electro-magnetic
drive philosophy associated with the applicant's prior design.
b. Electro-Magnetic, Moving Coil Drive Systems
A summary of the construction and operation of a conventional moving
coil/stationary magnet drive system for a direct radiator dynamic
loudspeaker is shown on page 337, Section 9.3 of Music, Physics And
Engineering by Harry F. Olson, Second Edition, Dover Publications, Inc.,
New York, N.Y. The typical electro-magnetic drive unit shown therein
employs a single, conical shaped permanent magnet, a first cylindrical
pole piece on the forward end of the magnet, and a second yoke-shaped pole
piece, extending from the rear end of the magnet around to the forward
portion of the first pole piece. A ring-shaped voice coil, attached to a
cone diaphragm, is positioned within a slightly larger aperture of
corresponding configuration, located between the adjacent ends of the pole
pieces. When an electrical signal is applied to the voice coil, a force to
drive the diaphragm is produced by the interaction between the
electro-magnetic field and the magnetic flux lines flowing between the
pole pieces.
Symmetry is lacking, both in the structure and in the dynamic response of
this single magnet, dual pole drive system. It is evident that the first
and second poles differ considerably in mass, size and configuration. The
resultant flux field, which the coil intercepts and reacts with, is
non-linear from front to rear, causing the dynamic response of the
loudspeaker to be similarly affected.
This non-symmetrical operation is also inherent in alternative
constructions, such as the single ring magnet, dual pole electro-magnetic
speaker drive units of more contemporary design. This construction is
shown in an article entitled "Rebuilding the AR-1", contained in the
February, 1982 issue of SPEAKER BUILDER, Edward T. Dell, Jr.,
Peterborough, N. H. Again, owing to the differences in mass, size, and
configuration of the pole pieces, the driven pistonic action of the moving
coil is non-linear.
Another characteristic of both of the aforementioned drive units is their
application of drive force through a relatively small implement, namely,
the ring-shaped structure supporting and forming the moving coil. While
such a structure may be well adapted for driving a cone-shaped speaker
diaphragm, it is not particularly suited for driving a large,
substantially rigid, planar diaphragm. The obvious expedient of employing
a plurality of such moving coil drive units would add considerable weight
to the planar diaphragm, and would detract from its ability to respond
properly to transients. Furthermore, the application of driving force to
the diaphragm would still be made through a relatively small number of
pressure points, increasing the likelihood of diaphragm flexure under
heavy drive conditions.
Applicant's electro-magnetic drive system addresses the above-mentioned
problems of non-symmetrical operation and point application of force in a
moving coil/stationary magnet construction. And, the present
electro-magnetic drive units are ideally suited to actuate the
lightweight, substantially rigid, planar diaphragms of the planar
loudspeaker system herein.
SUMMARY OF THE INVENTION
The planar loudspeaker system herein includes a plurality of planar
diaphragms housed within separate compartments, all contained within an
elongated, substantially planar enclosure. The diaphragm housings, as a
group, occupy the median, longitudinal section of the enclosure. Each
housing has side walls extending forwardly from the rear wall of the
enclosure, and a diaphragm opening adjacent the enclosure's front wall.
The collective diaphragm openings define an elongated aperture in the
front, or forwardly facing wall of the enclosure.
In the preferred embodiment, an elongated tweeter diaphragm extends along
one long side of the aperture, and a pair of upper and lower woofer
diaphragms, separated by a midrange diaphragm, occupy the remaining
portion of the aperture. Each diaphragm is located within the diaphragm
opening of a respective housing, having its opposing planar surfaces
facing forwardly toward the listener and rearwardly away from the
listener. Each diaphragm is further maintained and supported in that
location by means of a resilient and flexible diaphragm surround material,
which extends around the periphery of the diaphragm. Thus supported, the
diaphragms are adapted for fore and aft pistonic movement; and, when
appropriately driven, will generate sound waves within a frequency band
dictated by the diaphragm's physical characteristics.
The volume exterior to the diaphragm housings and interior to the
loudspeaker enclosure defines upper and lower woofer labyrinths. Each
labyrinth is bifurcated, or split, into a pair of tubes or tunnels, so
that the overall configuration of each labyrinth resembles the letter "U".
The upper labyrinth is vertically aligned, and inverted in orientation,
with respect to the lower labyrinth. The end extremities of opposing
labyrinth tubes terminate at shared labyrinth ports, located in the median
portion of the front wall, on opposing sides of the elongated aperture.
Upper and lower woofer vents, located respectively, within the side walls
of the upper and lower woofer housings, admit the woofers' backwaves into
the median, or middle portion of a respective labyrinth. From there, the
backwaves travel through each respective tube to the terminus, where they
meet the in phase backwave from an opposing tube, and emerge together
through the common port. Owing to the physical characteristics of the
labyrinths, the forwardly, directed backwaves are substantially in phase
with the woofers' front waves, augmenting the overall bass response of the
system.
The labyrinths are filled with wool, or other appropriate sound absorptive
material, to attenuate the amplitude of the midrange frequencies contained
in the backwaves. The wool also acts to retard the speed of the backwaves
which ultimately emerge at the ports. The effective length of each
labyrinth tube or tunnel is selected to be approximately one-quarter of a
wavelength of the lowest frequency at which the woofers are designed to
generate an appreciable amount of low frequency response.
The tweeter and midrange diaphragm housings are sealed, with exception of
the frontal opening where each diaphragm is located. Sound absorptive
material partially fills the volume of the housings behind these
diaphragms, to dampen the diaphragm action while absorbing the backwave.
A symmetrical and distributive electro-magnetic drive system is contained
within each diaphragm housing, to place each diaphragm into fore and aft
pistonic motion, in response to an impressed electrical signal. Each
diaphragm is driven by a plurality of elongated coil and magnetic units,
interconnected in series - parallel fashion to present an appropriate load
impedance of very low inductive reactance to the drive amplifier.
In its simplest configuration, each drive unit includes at least a pair of
elongated bar magnets, oriented with their longitudinal axes in parallel,
and their upper and lower pole faces being both coplanar and of opposite
pole polarity with respect to each other. Further, their adjacent
longitudinal sides are spaced apart a predetermined distance to define an
elongated flux aperture.
Ferrite planar pole pieces are substantially coextensive with and attached
to the upper and lower pole faces of each magnet, to concentrate and focus
the upper and lower flux lines flowing between the opposite poles of the
adjacent magnets and across the flux aperture. The inner, adjacent edges
of opposing pole pieces are preferably slightly closer with respect to
each other than the magnets themselves, to enhance the density of the flux
lines. The bar magnet and pole piece assemblies are rigidly attached to
the diaphragm housings, by means of various support pieces and
cross-members.
An elongated coil, arranged in planar configuration, is positioned within
the elongated flux aperture, and is adapted transversely to intercept the
upper and lower flux lines. A rigid, lightweight, and insulative
encapsulating material is employed both to maintain the coil in the
desired configuration and to interconnect the coil assembly physically
with the rear surface of the adjacent diaphragm. Accordingly, when an
electrical signal is applied to the coil, the diaphragm is alternatively
driven forwardly and rearwardly to create sound waves.
A plurality of coil and magnetic units is arranged generally upon a median,
longitudinal portion of each respective diaphragm, extending substantially
its entire length. The distributive application of driving force upon the
elongated central region of each diaphragm ensures that the diaphragm
excursions are linear, and pistonic in nature. The previously mentioned
diaphragm surround, extending around the entire periphery of each
diaphragm, maintains a degree of control over diaphragm excursions as well
as establishing an "at rest", or normal position for the diaphragm and the
connected coil assembly.
The preferred embodiment of the coil and magnetic drive unit contemplates a
construction similar to that already described, with the addition of
another bar magnet and pole piece assembly adjacent and parallel to the
existing pair, defining a second elongated flux aperture to accommodate a
second coil assembly. To generate the proper flux patterns, the pole
polarity of the added magnet is identical to that of the remote magnet,
and thus opposite to that of the adjacent magnet. The newly added coil
must also be driven out of phase with respect to the adjacent coil drive,
to cause the new coil and support structure to react in phase with the
adjacent coil and support structure.
A third version of the magnet and coil drive is a natural extension of the
first two embodiments, already described. Rather than employing a single
pair of bar magnets, the third version uses two stacked pairs of magnets.
And, since three-distinct lines of flux are created by the quadruplet of
magnets, the coil assembly positioned within the flux aperture includes a
pair of stacked, elongated coils, having adjacent turns of wire of each
coil overlapping. The coil assembly thus presents upper, intermediate, and
lower turns of wire in a plane substantially intersected by a respective
one of the three lines of flux. This third version of the electromagnetic
drive is particularly well suited for diaphragms having a larger mass and
planar surface, or requiring an extended diaphragm excursion range.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front elevational view of the preferred embodiment of the
invention, with the front grill cloth being entirely removed to show the
diaphragm housings, the diaphragms, and the woofer labyrinth ports, a
portion of the front wall being broken away to reveal the sound absorptive
material within one tube of the lower woofer labyrinth;
FIG. 2 is a rear elevational view of the invention with the rear wall, and
all sound absorptive material within the tweeter housing, the midrange
housing, and the upper and lower woofer labyrinths, being removed for
clarity;
FIG. 3 is a transverse, cross-sectional view, to an enlarged scale, taken
on the plane indicated by the line 3--3 in FIG. 1;
FIG. 4 is a transverse, cross-sectional view, to an enlarged scale, taken
on the plane indicated by the line 4--4 in FIG. 1;
FIG. 5 is a transverse cross-sectional view, to an enlarged scale, taken on
the plane indicated by the line 5--5 in FIG. 2;
FIG. 6 is a transverse, cross-sectional view, taken to an enlarged scale,
of one version of the electro-magnetic drive system, showing fragments of
an associated support piece and planar diaphragm;
FIG. 7 is a top plan view to a reduced scale of a bar magnet;
FIG. 8 is a side elevational view to a reduced scale of the elongated
moving coil assembly of FIG. 6, the encapsulated portion of the oval coil
being shown in broken line;
FIG. 9 is a transverse, cross-sectional view, to an enlarged scale, taken
oh the plane indicated by the line 8--8 in FIG. 1, showing the prefered
version of the electro-magnetic drive system;
FIG. 10 is a transverse, cross-sectional view, taken to an enlarged scale,
of a third embodiment of the electro-magnetic drive system, showing
fragments of the associated support piece and planar diaphragm;
FIG. 11 is a side elevational view of the elongated moving coil assembly of
FIG. 9, the dual stacked, and partially overlapped oval coils being shown
in broken line; and,
FIG. 12 is a pictorial representation of the electrical schematic of the
preferred form of the invention, the broken lines representing outlines of
the tweeter, midrange, and upper and lower woofer diaphragms, in
accordance with the general layout of these diaphragms as shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The planar loudspeaker 11 of the present invention includes an elongated,
substantially planar enclosure 12, or exterior housing, with its lower end
preferably resting upon the floor 13 and extending substantially the
height of the room so that its upper end is adjacent the ceiling 14. The
enclosure 12 has a front wall 16 and a parallel rear wall 17, spanned and
joined together by peripheral side walls 18 and peripheral end walls 19
(see FIGS. 1 and 3). Rear wall 17 abuts and is parallel to the surface of
room wall 15. A base 20, or pedestal, having a flared footing for
stability, is provided at the lower end of the loudspeaker enclosure 12,
to support the loudspeaker securely upon the floor 13.
Located within the median, longitudinal portion of the enclosure 12 is a
diaphragm housing assembly 21, including a tweeter housing 22, an upper
woofer housing 23, a lower woofer housing 24, and a midrange housing 26.
As is evident most clearly in FIG. 1, the forwardmost portion of the
diaphragm housing assembly 21 defines an elongated aperture in the front
wall 16. The tweeter housing 22 is located along one long side of the
elongated aperture, and has closed side walls composed of first and second
elongated pieces 27 and 28 spanned at their end extremities by transverse
pieces 29. The pieces 27, 28 and 29 extend forwardly from the rear wall 17
(see FIGS. 1, 2 and 3), to define a tweeter opening 31 (see FIG. 3)
adjacent the front wall 16.
Upper woofer housing 23 and lower woofer housing 24 are located along the
other long side of the elongated aperture, both woofer housings similarly
having side walls extending forwardly from the rear wall 17. Making
reference to FIG. 1, it is evident that the side walls of the woofer
housings are formed on one side by the second elongated piece 28 of the
tweeter housing 22, and on the other side by a third elongated piece 32.
The closed ends of the woofer housings are formed by an upper cross piece
33 and a lower cross piece 34. The forwardmost edges of the cross piece 33
and the upper portions of pieces 28 and 32 define an upper woofer opening
36; and, in like fashion, the forwardmost edges of the piece 34 and the
lower portions of pieces 28 and 32 define a lower woofer opening 37. Both
woofer openings 36 and 37 are adjacent the front wall 16 of the enclosure
12.
The midrange housing 26 is interposed between the upper and lower woofer
housings, and has closed side walls like those of the tweeter housing
previously described. The closed side walls of the midrange housing 26 are
formed by pieces already generally identified, namely, the middle portions
of the second and third elongated pieces 28 and 32, and the cross pieces
33 and 34, all extending forwardly from the rear wall 17. The forwardmost
edges of each of these wall pieces define a midrange opening 38, adjacent
the front wall 16, as shown in FIG. 1.
The loudspeaker 11 further includes a tweeter diaphragm 39, an upper woofer
diaphragm 41, a midrange diaphragm 42, and a lower woofer diaphragm 43.
Each diaphragm is constructed from a lightweight, substantially rigid
material, which is also non-conductive and acoustically impermeable. Rigid
foam material, such as "ROHACELL" Type 51, manufactured by Cyro
Industries, of Orange, Conn., has proven satisfactory for this
application, although other materials meeting the basic requirements set
forth above should also perform well. Since the diaphragms are relatively
large, thin, and elongated in configuration, the diaphragms must be
sufficiently rigid to avoid bending or flexing, while remaining light
enough to be driven quickly and efficiently by an electrical drive system
and the associated drive amplifier. It has been determined that, where
"ROHACELL" is used as a diaphragm material, a diaphragm thickness of 6.35
mm (1/4") or so, represents a suitable compromise between the existing
rigidity and weight requirements.
Each diaphragm is situated within a respective opening existing in the
forwardmost portion of its housing as previously set forth above. Thus, as
most clearly appears in FIG. 3, the tweeter diaphragm 39 is mounted and
maintained within the tweeter opening 31, primarily by means of a
diaphragm surround 44 that extends around the periphery of the diaphragm,
forming a pliant and acoustically impervious bridge between the tweeter 39
and tweeter housing 22. The surround 44 thereby allows the tweeter
diaphragm freedom of movement, while providing an efficient acoustical
seal between the tweeter and its close walled housing 22.
Similarly, the midrange diaphragm 42 is mounted within the midrange opening
38, the upper woofer diaphragm 41 is maintained within the upper woofer
opening 36, and the lower woofer diaphragm 43 is situated within the lower
woofer opening 37, all by means of peripheral diaphragm surround 44
extending between each diaphragm and the adjacent forwardmost surface of a
respective housing (see FIGS. 1 and 3).
Upper woofer labyrinth 46 and lower woofer labyrinth 47 are also provided
within the enclosure 12. These labyrinths are defined by the volume
exterior to the diaphragm housing assembly 21 and interior to the
enclosure 12. The upper labyrinth 46 begins in the region immediately
exterior to the upper end of the upper woofer housing 23, then proceeds to
split into two tunnels or tubes extending downwardly along either side of
the housing assembly 21. These tunnels are generally rectangular in cross
section, as shown in FIGS. 3 and 4. Similarly, the lower labyrinth 47
begins in the contained volume just below the lower end of the lower
woofer housing 24, and then bifurcates into a pair of tunnels or tubes
extending upwardly along both sides of the housing assembly 21.
An upper woofer vent 48 and a lower woofer vent 49 are provided,
respectively, in the uppermost and lowermost side walls of the upper
woofer housing 23 and the lower woofer housing 24 (see FIGS. 2 and 5).
Vents 48 and 49 are generally rectangular in configuration, and are
adapted to pass each woofer's backwave into a median, or middle portion of
a respective woofer labyrinth. From there, each backwave bifurcates to
travel through the pairs of labyrinth tunnels, straddling each side of the
diaphragm housing assembly 21. As is evident from FIGS. 1 and 2, each
labyrinth is thus configured to resemble the letter "U", the upper woofer
labyrinth 46 being vertically aligned and inverted in orientation with
respect to the lower woofer labyrinth 47. The terminus, or end extremity
of each woofer labyrinth tunnel meets a respective end of the labyrinth
tunnel of the other woofer, in shared or common woofer labyrinth ports 51
and 52. FIGS. 1 and 2 show the ports 51 and 52 to be located in the median
portion of the front wall 16, on opposing sides of the diaphragm housing
assembly 21.
Directive arrows 53 and 54, shown in broken line in FIG. 1 and in solid
line in FIG. 2, trace the paths of the upper woofer backwaves and the
lower woofer backwaves. The backwaves initially vent into the middle
portion or volume of a respective labyrinth, then divide to pass through
the adjacent labyrinth tunnels, and finally meet the opposing in phase
backwave of the other woofer, to emerge forwardly toward the listener,
through the woofer ports 51 and 52.
The design of the upper and lower woofer labyrinths 46 and 47 is such that
each acts as a quarter-wave transmission line, constructively to vent the
backwaves of the planar woofers from the middle portion of the planar
loudspeaker 11, toward the listener. The total length of each leg or
component of the woofer labyrinths herein, is selected to be approximately
one-quarter of a wavelength of the lowest frequency at which the woofers
are expected to generate an appreciable amount of low frequency
information. Thus, for example, the distance from the upper woofer vent 48
through a labyrinth tunnel to a respective port would be around 1.22 to
1.52 meters (four to five feet), or so.
As is well known in the art, by filling such a transmission line with sound
absorptive damping material, such as wool, fiberglass or "DACRON", the
effective length of a transmission line can be extended somewhat, since
the sound waves are slowed down by passing through the material. In
addition, such damping material acts to attenuate the backwave,
particularly the lower midrange and midrange frequencies. So designed, the
woofer labyrinths of the present invention provide substantially in-phase
augmentation of the lower frequency frontal waves generated by the woofer
diaphragms. In other words, there is constructive interference in the
listening zone between the "direct" frontal sound waves, generated by the
forward surface of each woofer, and the "indirect" rearward sound waves,
generated by the rear surface of each woofer.
In addition to length considerations, the labyrinth tubes or tunnels, as
well as the labyrinth ports, should be of sufficient cross-sectional area,
so as to prevent substantial back pressure or resistance, to the outward
flow of the woofer backwave. Since the design herein contemplates pairs of
identical tunnels or tubes for each labyrinth, and a pair of identical
ports for releasing the in-phase backwaves from the enclosures, the
effective cross-sectional area for the labyrinth passage is doubled. It is
preferable that the total cross-sectional area, both for the labyrinth
passage and for the port, be the same or larger than the working area of
the woofer diaphragm whose backwaves are to be vented. While it is not
practical in all cases to achieve such a ratio, as size restrictions of
the enclosure come into play, it is important that the ratio be maintained
as close to 1:1 as is possible.
Having presented the basic construction of the enclosure, the diaphragms,
the diaphragm housings, and the woofer labyrinths, the discussion will now
focus on the electro-magnetic drive units designed to actuate the planar
diaphragms of the present invention.
FIGS. 6, 7 and 8 show the first and most basic configuration of an
electro-magnetic drive unit 56. The drive unit 56 includes a pair of
substantially identical, elongated bar magnets 57 and 58, having upper and
lower longitudinal faces 59 and 61, adjacent sides 62 and remote sides 63,
and opposing transverse ends 64 and 66. Magnets 57 and 58 have opposing
magnetic poles situated upon their respective longitudinal faces, and
these poles are indicated in the drawings by the letters "N" for "North",
and "S" for "South".
Mounting pieces are used to support and maintain the magnets 57 and 58 upon
the frame of the loudspeaker. Although, typically, a pair of such mounting
pieces is used, only a single mounting piece 67 is shown in the
fragmentary cross-sectional view of FIG. 6. The magnets 57 and 58 are held
adjacent each other with their longitudinal axes parallel, and their upper
and lower longitudinal pole faces being both co-planar and of opposite
polarity with respect to the adjacent magnet. FIGS. 6 and 7 show that the
upper surface 59 of magnet 57 is of "North" polarity, while the lower
surface 61 of magnet 57 is of "South" polarity. Magnet 58, however, has an
upper surface 59 of "South" polarity, and a lower surface 61 of "North"
polarity.
Fixed upon both the upper and lower longitudinal faces of the magnets 57
and 58, are upper and lower planar metallic pole pieces 69 and 71. The
pole pieces are substantially co-extensive with the adjacent longitudinal
face of a magnet, but are preferably constructed slightly wider than a
magnet face, affording upper and lower inner edges 72 and 73. As shown in
FIG. 6, the inner edges 72 and 73 of pole pieces 69 and 71 are spaced
relatively closer than the adjacent longitudinal sides 62 of the magnets.
The close spacing of these inner edges acts to focus and concentrate the
flux lines flowing from the magnet faces through the metallic pole pieces.
The adjacent longitudinal sides 62, and particularly the inner edges 72 and
73 of the pole pieces, are spaced apart a predetermined distance to define
an elongated flux aperture extending the entire length of the magnets. The
aperture 74 includes upper transverse flux lines and lower flux lines,
indicated repectively by the numerals 76 and 77. Flux lines 76 and 77,
concentrated by the pole pieces 69 and 71, flow between the adjacent
opposite magnetic poles of the bar magnets 57 and 58.
Positioned within the elongated flux aperture 74 is a drive coil 78,
constructed from conductive wire 79 arranged in an elongated planar
configuration, as shown in FIGS. 6 and 8. The coil 78 is encapsulated in
an insulated carbon fiber material 81 , or "KEVLAR", or any other
non-conductive, lightweight material which can be molded and cured to form
a rigid support structure. The material 81 not only maintains the coil and
the attached diaphragm footing 82 as a rigid structure, but also prevents
the wire 79 from shorting out, should the coil inadvertently come into
contact with a pole piece during an overdrive condition. The footing 82 is
preferably adhesively attached to a planar diaphragm 83, constructed from
a lightweight substantially rigid material, as previously described.
It is important to note that the wire 79 is also configured in an elongated
oval shape, having upper turns 84 and lower turns 86 (see FIG. 8). The
upper turns 84 are located in a plane substantially intersected by upper
flux lines 76, and the lower turns 86 are similarly positioned within a
plane substantially intersected by lower flux lines 77. Such a
configuration and location for the conductive wire 79 ensures that a high
degree of coupling with the magnetic flux lines will exist for all normal
drive conditions.
A drive amplifier (not shown), providing an electrical signal at an audio
frequency, is connected to the plus (+) and minus (-) leads of the drive
coil 78. As the coil is actuated, the fluctuating electro-magnetic field
interacts with the static magnetic field represented by the upper and
lower flux lines, causing the coil 78 and the attached diaphragm 83 to
partake in front to rear excursions. The magnets, pole pieces and coil
turns are respectively identical in size, configuration, number, and
position, and the flux lines resulting from the mirrored construction of
the bar magnets and the pole pieces are of equal density across respective
portions of the flux aperture 74. Thus, the excursions of the diaphragms
are linear and symmetrical, regardless of the direction of travel.
Having discussed the basic form of the electromagnetic drive unit 56, a
slightly more complicated drive unit 87, or second version, will now be
presented. Drive unit 87 is shown in FIG. 9, which, in turn is a
fragmentary cross-sectional view to a greatly enlarged scale, taken from
FIG. 1. Thus, drive unit 87 represents the preferred form of the
electro-magnetic drive system for the present invention. Since many of the
components of the drive unit 87 are identical to those components already
identified and discussed in the explanation given above regarding the
first, most basic drive unit 56, these same numerical designations will be
used hereafter, wherever appropriate, to describe the second drive unit 87
and a third drive unit 88, subsequently to be described. Also, since the
respective constructions of the second and third versions of the drive
unit are in many other ways identical to that of the basic drive unit 56,
certain details of identical structures and features which are evident
from the drawings will be discussed only generally for sake of brevity.
The drive unit 87 includes three substantially identical, elongated bar
magnets 89, 91 and 92, having upper and lower longitudinal faces 59 and
61. Bar magnet 89 has an outer side 93 and an inner side 94, adjacent a
first intermediate side 95 of magnet 91. Bar magnet 92 has an outer side
97 and an inner side 98, adjacent a second intermediate side 96 of magnet
91. To generate the proper flux patterns, the pole polarity of magnet 89
is opposite that of adjacent magnet 91, and identical to that of remote
magnet 92 (see FIG. 9).
The magnets are held adjacent each other, with their longitudinal axes
parallel, and their upper and lower longitudinal pole faces being both
co-planar and of opposite polarity with respect to the adjacent magnet.
Fixed upon both the upper and lower longitudinal faces of magnets 89, 91
and 92 are upper and lower planar pole pieces 69 and 71. These pole pieces
are preferably of the size and configuration previously set forth, and
similarly have inner edges 72 and 73 spaced so as to focus and concentrate
the flux lines flowing between the magnets and through the pole pieces.
The adjacent sides of the magnets, and specifically the inner edges of the
pole pieces, are spaced apart a predetermined distance to define a pair of
elongated flux apertures 74 extending the entire length of the magnets.
The apertures 74 include upper transverse flux lines 76 and lower flux
lines 77, flowing between the adjacent, opposite magnetic poles of the bar
magnets 89, 91 and 92.
The predetermined distance between the inner edges of the pole pieces must
be as close as possible to enhance the density of the flux lines, while
being sufficiently spaced freely to accommodate a respective drive coil
78. Each drive coil 78 used for the second drive unit 87 is identical to
the coil 78 already described in FIGS. 6 and 8, used in association with
the basic drive unit 56. Accordingly, each drive coil 78 shown in FIG. 9
includes conductive wire 79, encapsulated in a rigid support material 81,
and a diaphragm footing 82 transversely positioned at one end for
attachment in this case to the lower woofer diaphragm 43.
In each coil, the conductive wire 79 is configured to have upper turns 84
and lower turns 86, as previously identified and explained. Thus, the
upper turns and the lower turns are located in a plane which substantially
intersects the respective flux lines flowing between the adjacent pole
pieces. In drive unit 87, the drive coils 78 must be driven out of phase
with respect to each other, to cause both coils to react in phase with
each other, and drive that attached diaphragm 43 in synchronism. This, of
course, is necessitated by the fact that the magnetic poles of the
adjacent pairs of magnets (89 and 91, and 91 and 92) are reversed with
respect to each other.
When thus properly driven by an electrical signal, the drive unit 87 causes
the diaphragm 43 to move forwardly and rearwardly, in response to the
frequency and amplitude variations of the drive signal. It should be noted
that each diaphragm footing 82 is equally spaced from the median, or
center line of the diaphragm 43, ensuring that the fore and aft movement
of the diaphragm is pistonic and linear in nature. It will also be
appreciated that in the loudspeaker 11, a plurality of such drive units 87
is used to drive each diaphragm, providing a distributive and balanced
driving force about and along the median longitudinal axis of the
diaphragms.
FIG. 2 shows the assembly of drive units 87, as viewed from the rear of the
speaker. Owing to the scale and perspective of FIG. 2, only the pole
pieces 69 and the drive coils 78 can be seen. It should also be noted that
the drive coils of the tweeter are shorter and lighter than those used to
drive the midrange and woofer diaphragms, but they are otherwise identical
in function and operation to the longer drive coils.
FIG. 12 shows a schematic diagram 99 of the loudspeaker in which the broken
lines configured as a narrow, elongated rectangle, represent the tweeter
assembly 101. Within the tweeter assembly are eight drive units 87,
represented by the adjacent pairs of drive coils 78. As will be noted from
the schematic, the drive coils 78 along each side of the tweeter are
respectively connected in series, and then further connected out of phase
and in parallel with the adjacent series of coils. The tweeter drive coils
are then series connected through high pass filter 102, comprised of
capacitors 103 and 104. The feed end of the capacitors is connected to the
output terminals of amplifier 1, identified by the numeral 106.
Connected in parallel with the tweeter drive coils are four midrange drive
units 87, represented by the drive coils 78. The midrange assembly 107, is
similarly shown by broken lines configured as an elongated rectangle
surrounding the drive coils. As with the tweeter coils, the midrange coils
are connected in series/parallel fashion. It should be noted that the
series/parallel interconnections shown in FIG. 12 result in a low overall
speaker impedance, which is also very low in inductive reactance, owing to
the fact that plural inductive loads are connected in series. The midrange
diaphragm, which is capable of reproducing frequencies fairly smoothly
into the mid-bass range, below 100 Hz, is fed a full range frequency
signal.
An upper woofer assembly 108 and a lower woofer assembly 109 are likewise
represented as elongated rectangles depicted in broken line in FIG. 12. As
with the previously mentioned diaphragm assemblies, the woofer assemblies
108 and 109 contain schematic representations of each drive coil 78
employed to drive the diaphragms. In the case of the woofer diaphragms,
two drive units 87 are used for each diaphragm. As is shown in the
schematic, the eight drive coils 78 utilized to drive the upper and lower
woofer diaphragms are connected series in phase, and parallel out of
phase, so that the resultant action of the woofer diaphragms is in phase,
as previously discussed. The upper and lower woofers are fed by a separate
amplifier 2, identified by the numeral 111.
The program material delivered to amplifier 2 is solely low frequency in
nature, say below 100 Hz, so that the upper and lower woofers are, in
effect, performing as sub-woofers. However, the loudspeaker system 11
deviates somewhat from the traditional bi-amplified system in that the
midrange diaphragm drive coils are fed with full range frequency
information, since the midrange diaphragm has usable response below 100
Hz.
As has previously been discussed, and, as shown in FIGS. 1 and 2, the
loudspeaker is preferably of such a height, that it extends substantially
from the floor 13 to the ceiling 14. In a typical room, then, the | | |
