Note: Descriptions are shown in the official language in which they were submitted.
'7~3
SOUNDSTAGE BOUND~RY EXPANSION SYSTEM
The present invention relates to a loudspeaker
system and particularly to a loudspeaker system for
providing an expanded soundstage and three dimensional
effect within a given listening area.
The background of the invention as explained
below makes reference to Figures 1 and 2 of the
accompanying drawings. For the sake of convenience, all
of the drawings will first be introduced briefly, as
follows:
Fig. 1 is a diagram illustrating placement of
speakers relative to a listener, and desired soundstage
expansion,
Fig. 2 illustrates a prior art system,
Fig. 3 is a longitudinal cross sectional view of
a loudspeaker according to an expanslon system of the
present invention,
Fig. 4 is a schematic diagram showing loudspeaker
interconnection in the system of the present invention,
Fig. 5 is a front view, partially broken away, of
a second loudspeaker suitable for the system of the
present invention,
Fig. 6 is a horizontal cross section of the Fig.
5 speaker,
Fig. 7 is a perspective view of a third
loudspeaker suitable for the system of the present
invention,
~k
~2 S ~
Fig. 8 is A horizontal cross section of the Fig.
7 speaker, and
Fig. 9 is a front view, partially broken away, of
a fourth loudspeaker suitable for the system of the
present invention.
In simplest terms, a stereophonic reproduction
system employs plural microphones to pick up sounds
emanating from various areas on a stage, and corresponding
transducers or loudspeakers are driven separately to
reproduce the sounds received at the various microphones.
Of course, signals may be manipulated to varying degrees
and a number of channels may be combined to provide
essentially two output channels which are recorded for
reproduction in a customary stereophonic loudspeaker
system. The concept of providing realistic sound in this
manner is valid in many respects because a person with
normal hearing picks up sounds binaurally. However,
speaker design, speaker location, room acoustics, and
electronic circuitry are all critical factors in
achieving the desired results~ If speakers are
placed farther apart to give the perception of a
larger soundstage, a "hole" may become apparent
between the two speakers, and sound will appear to
-la-
JPD/kml 1o/26/~3
~5~7a~
emanate from the right and/or the lef-t loudspeaker. Ir~ addition ~1jacen
walls will cause Imwanted reaction -to the sound waves and will tend to
interfere with desired wave radiation patte~ns. On the other hand, lf
the speakers are placed too close together, the middle information will
dominate and the so-unds-tage will appeax much narrower. Also, movement
of the listener from the apex of an equal sided triangle formed by the
speakers and himself will cause a perceived shift in the progrPm material
from one side of the soundstage to the other, i. e. deteriorating the
stereophonic e~fect.
If two loudspeakers are fed "out of phase" ~rith the same
signal it is possible to achieve the illusion of sound originating to
the left of both speakers or to the right of both speakers depending
upon which speaker is out of phase from normal. me effect is not a
particularly natural one. It would be desirable to provide a loud-
speaker system presenting the illusion of sound emanating from an
entire soundstage having dimensions beyond the distance between two
loudspeakers, such as speakers 12 and 14 in Fig. 1, e. g. along the
stage 10 be-tween poin-ts 18 and 20 in Fig. 1.
One prior art approach to providing a broadened soundstage
is illustrated in Fig. 2 wherein speaker 12 in Fig. 1 is replaced by
a pair of speakers 26~ 32 and speaker 14 is replaced by a pair of
speakers 28~ 30. The principal speakers 26 and 28 are driven from
conventional stereo amplifier channels 22 and 24, but auxiliary or
enhancement speakers 30 and 32 are d~iven in a reversed phase sense
from the opposite channel~ Enough wavefront subtraction is produced
so th~t sound will ~ppear to originate to the left and to the right
of the gxoup of speakers as well as therebetween, if the speakers
aren't too far ~part 3nd if the auxiliary- speakers 30 and 32 are
oper~ted at ~n ~Iplitude level less than that of the main speakers
26 and 28. Unfortunately, the Fig~ 2 approach has certain
JPD/k~-L 10~26/83
L~
acoustical drawbacks including major shlfts in perceived locations as
well as cancellations of image, app~rently due to phase ~noma~Lies
which occur whenever the listener moves from a given spot~ e. g. a~,ra~
from apex location 16 in Fig. 1, This phenomenon apparently takes
place primarily because the extra speakers ~0 and 32 have different
points of radia-tion from those of the main speakers, even if located
in the same enclosure or cabinet with the main speakers. Thus the ear,
which is phase sensitive, picks up the -time difference in the sound
wave radiation pattern from each enclosure and renders the expanded
soundstage system "believable" on'Ly at certain positions.
It i~ a'Lso possible to perform the function of the Fig. 2
system electronica~Lly, wherein single transducers or loudspeakers are
substituted for the pairs 26, 32 and 28, 30. Thus, the lefthand speaker
in a stereophonic system is driven from an e:Lectronic adder or summing
point which receives both -the output from the lefthand ~mplifier
channel 22 and a reversed and attenua-ted output from the righthand
channel 24. Unfortunately the sub-traction or summation achieved
is frequently not natural enough to provide a sound which the listener
will perceive as coming from a broadened soundstage.
In spite of the various problems, the prior art approaches
do give the listener some sensation of an expanded soundstage, and the
systems are interesting and viable. They do suffer from lack of
realism, p~rticularly if the listener moves frcm the centra~L location
or apex indicated at 16 in ~ig. 1.
Experiments using the technique of ~ig. 2 have led to the
conclusion that optimwn results could be obtained if the two drivers,
such as 26, 32, could occupy the same physicaL space in an enclosure
and be of identicaL design ~nd construction. This is an apparent
impossibility.
Summ~ry of the Invention
In accordance with the present invention in a principaL
emobdiment thereof a soundstage boundary exp msion system for providing
the effect of a sound source charlcteri~ed by apparent sound direction-
JPD/kml 10/26/~3
'7~
aLity b~yond the physicil dimensions of -the system includes ~ ster o
amplifier, with first ~nd second output ch~nnels, and first ar~d seco.-~'
transducers or loudspeakers having movable elements which ~iibrate in
response to -the respective output char,nels~ In addition, the s3ne
physicaLly movable elements are responsive in a reversed phase sense
to the outputs of the opposite output channels. That is, the movlble
vibration~L transducing element of each loudspeaker is driven in a
first phase sense in ~ norm~L fashion from an arnplifier channel out-
put, and the movable element is aLso driven in a reversed phase sense
from the opposite ~.plifier channel output.
In a particlllar embodiment a loudspeaker in accordance with
the present invention is provided with a pair of voice coils disposed
in separate air gaps of the loudspeaker magne-tic circuit, with each
voice coil being at-tached to the same loudspeaker cone. The respective
voice coils are driven from opposite channel outputs in a reversed
phase sense~
It appears the response of a given transducer movable
element, physically driven from the two sources~ better simulates
the response of -the human ear drum, which, after all, is itself a
physicaLly movable diaphragm driven by sound informa-tion originating
from various directions and which is highly sensi-tive to the sound
information for ascertaining the direction from which the sound is
coming. Each loudspeaker in the system according to the present
invention more cLear^ly convinces the ear of the person with binauraL
hearing that sound is legitimateLy produced from a location outside
the soundstage boundaries represented between the two speakers~
and without requiring the speakers be placed so far ap?rt as to produce
a "hole" or void between the loudspeakers. The loudspeakers can even
be placed aLong a relatively short waLl or in a rela-tively smaLl room
3 ~nd still provide the effect of a broadened soundstage which may in
fact be l~rger than the room in which the loudspeakers are located.
~PD/kml 10/3/~3
~5~'7~
The listener is not confined to a smaLl listening area or apex to
achieve the impression of -the large soundstage, and ~rill also percei-/s
a depth -to ths soundstage so that different instruments appear to
reside at for~Jard and rea~Tard locations on the stage as wel] as at
extended left and right locations.
It is accordingly an object of the present invention to
provide an improved soundstage boundary expansion system which is
more effective in providing the illusion of sound beyond the physica~L
dimensions of the system.
It is another object of the present invention to provide an
improved soundstage boundary expansion system for providing the effect
of a sound source characteriYed by apparen-t solmd direction~lit~ beyond
the physica~L dimensions of the system, and wherein the effect is
perceived over a relatively wide area rather than at a specific apex
location or region near an apex location.
It is another object of the present invention to provide
an improved soundstage boundary expansion system that is more
economica~L to produce than systems heretofore proposed.
It is another object of the presen-t invention to provide
an improved soundstage boundary expansion system which retains phase
coherency throughou-t a broad listening area.
It if a further object of the present invention to provide
an improved soundstage boundary expansion sys-tem that permits greater
flexibility in the placement of loudspeaker enclosures.
It is another object of the present invention to provide an
improved soundstage boundary expansion system which provides a tnree
dimensionaL effect and gives the illusion of instrument placement in
the tota~L soundstage.
It is a further object of the present invention to provide
an improved soundstage boundary expansion system without incurring
undesireable sound wave reflections from adjacent waLls or other surfaces.
v
The subject matter which I regard as my invention
is particularly pointed out and distinctly claimed in the
concluding portion of the specification. The invention,
however, both as to organization and method of operation,
together with further advantages and objec-ts thereof, may
best be understood by reference to the following
description taken in connection with the accompanying
drawings wherein like reference characters refer to like
elements.
Detailed D_scriE~i_n
Referring to the drawings and particularly to
Fig. 1, line 10 indicates a soundstage or apparent sound-
stage represented to the listener by stereophonic speakers
12 and 14, wherein 12 represents the left-hand speaker and
14 represents the right-hand speaker. The position of the
listener is indicated in 16. Thus the listener or
,~
JPD/kml 1 o/26/83 ~25~7fL~
audience is typically located in front of the speakers, at a locatio;-i
approximately equidistant from each speakerO Depending upon the
distance of the lis-tener to the front of the line of speakers, the listenGr
will receive an impression of directionality or location of sound
aLong so~ldstage 10, but in prior art sys-tems the li~nit of the apparent
soundstage is ordinarily the distance bet~een the two speakers 12 a,~d
14. A uniforln soundstage ~nay not be presen-ted to the listener in
prior art systems, but rather he may perceive a "hole" or void directly
between the speakers. The system according to the present inven-tion
not only provides a uniform soundstage, but also provides the impression
of sounds emanating to the left ~nd/or to the righ-t of both speakers,
thus giving an impression of a wide soundstage, e. g. between more
widely separated points 18 and 20. The effect according -to the present
invention is not limited to listening location 16.
~s mentioned hereinbefore, Fig. 2 is a represen-tation of a
prior art system including a pair of s-tereo amplifiers or channels
22 and 24 driving principal speakers A and B (numbered 26 and 28).
In addition to the principal speaker 26, amplifier channel 22 drives
an auxilialy speaker A1 (n~mbered 30) physically positioned proximate B
speaker 28. Also, amplifier channel 24 drives an auxiliary speaker B1
(numbered 32) which is physically located proximate A speaker 26. The
leads are reversed to both auxiliary speakers 30 and 32 so they are
fed out of phase with their respective principal speakers, and the
leads to each auxiliary speaker are suitably provided with resistance
25 (e. g. resistors 34 and 36) for attenuating the signal to the auxiliary
speakers. Phase reversal has the effect of placing the ~pparent sound
either entirely to the left or entirely to right of both sets of
speakers, while the resistances 34 and 36 attenuate -the signals to
the auxiliar~ spe~kers such that cancellation does not occur in between
the speakers as would present an apparent sound void~ There may also
be de'lay provided betw-een each of the amplifier channels and each of
JPD/kml 10/26/83
7~
the au~iliary speaTcers. While the system of Fig. 2 is someT,rhat ef~ective
in providing a wide soundstage, as hereinbefore mentioned, the s~stem
is very sensitive with regard to the location where the effect is
perceived. The listener at central position 16 (in Fig. 1) will
lose the impression of a ~ide soundstage ir he moves at all rrom
his central position. The result is believed to be caused by the
phase differences between physically separate but adjacent speakers
such as, for example, speaTcers 26 and 32 in Fig. 2. If the speakers
26 and 32 were located at exactly the same point, then the desired
effect would be produced over a wide area. The ear of the listener
is apparently sufficiently sensitive to the phase differential
resulting from the necessary spacing between the actual sound-
producing means in spealcers 26 and 32 so that only a limited range
of listener positions will provide the desired soundstage effect.
In accordance with the present invention, a soundstage expansion
system employs transducers or loudspealcers with physically movable
; elements that are driven in response not only to a main or principal
amplifier channel output, but also from a reversed phase amplifier
output from the opposite channel. In this manner, there is no
phase difference between generated sounds as was -the case with speaTcers
26 and 32 in Fig. 2, but rather the sounds appear to and do originate
from the same point~ Referring specifically to Fig. 3, a transducer
or ~oudspealcer 38 according to the presen-t invention is provided with
a physically ~ovable element comprising a diaphragm or cone 40
carrying a bobbin 42 around which are wound voice coils 44 and 46.
The voice coil 44 is driven by a given channel amplifier, say the
left channel amplifier of a stereophonic system, while the voice coil
46 is driven from the reversed phase output of the opposite channel
amplifier, as hereinafter more fully desc~ibed.
3 The loudspeaker fl~rther includes a basket or frame 48 which
JPD/kml 1o/26/83
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supports cone 40 therewithin by means of flexible surround 50.
Attached to the cone is a bobbin 1L2 located around c~lindrical pole
piece 52 which extends forwa-rdly from a bottom plate 54. Plate 54
also carries annular magne-t 56~ On the for~rard side of the magnet, i. e.
5 toward the baske-t 48, there is a lower -top plate 58 which is arnular
in construction and an upper top plate 60 which is also cmnular in
construction. The latter top plate is secured to the basket 48, with
-the top plates being supported between the baske-t and magnet
Each of the top plates includes an annular, inwardly facing,
separate end piece (numbered 62 and 64 respectively) disposed in
juxtaposition with the central pole piece 52 to define a pair of
separate air gaps. Magnetic circui-ts are completed to supply
m~gnetic flux across air gaps~ It will be noted voice coils 44
cmd ~6 are respectively located by bobbin ~2 in separate air
gaps whereby current in the respective voice coils reacts with the
magnetic flux across the air gaps to produce movement of the speaker cone.
Referring now to Fig. 4, illustrating schemc~ticc~ the
electrical connections of the sys-tem according to the present invention,
a pair of left and right speakers 38A and 38B are respectively con-
structed in the manner illus-trated in ~ig. 3, i. e. each has a main
or principal voice coil 1~4 and an enhancement voice coil 46. Connec-
tions 70 and 72, comprising the output leads of a left channel amplifier,
are connected in the manner shown with terminaL 72 grounded and terminal
70 coupled through high pass filter 78 to a terminal 80. Terminal 80
25 is connected b~ me~ls of low pass filter 82 to one terminaL of principal
voice coi~ 44A of lefthand speaker 38A, while the rem~ining terminal
of such voice coil is grounded.
Terminal 80 is ~lso connected to an input of low pass filter
~nd attenuator 84 having cn output lead 86 which is cross-connected
30 to the auxiLia~y or enhancement voice coi:L 46B of the righthand
spe~ker 38B. It will be observed that voice coi~L 46B has its connections
JPD/kml 10/12/83
~25~7~
reversed from those of the principal voice coil 44B on the same spea'~er,
i~eO enhancemen-t voice coil 46B is fed in an inverted phase relation
to voice coil 44B and also in inverted phase relation to voice coil
44A of the lefthand spealcer.
Similarly, terminals 74 and 76, comprising the output
terminals of -the righthand amplifier channel, are connected by wa~
of high pass filter 88 to a -terminal 90 which is in tu~n coupled
through low pass filter 92 to the principal or main voice coil 44B
of righthand speaker 38B and the same -terminal 90 is also coupled by
way of low pass fil-ter and attenuation circuit 94 to lead 96 which is
cross connected to the enhancement voice coil 46A of left hand spealcer
38A. It will be observed that enhancement voice coil 46A is driven
180 degrees ou+. of phase with respect to principal voice coil 44A of
the same spealcer and with respect to principal voice coil 44B of the
righthand speaker. Although the system aceording to the present
invention may provide the only sound ou-tput for a sound system, it
is contemplated tha-t spealcers 38A and 38B respeetively eomprise mid-
range audio transdueers for a sterephonie sound system, while left
and right woofers and tweeters will also be ineluded in -the same
enclosures with speakers 38A and 38B.
~ow pass filter 78, suitably comprising serially connected
eapaeitors 98 and 100 and shunt induetance 102, is designed in a
eonventional manner to have a -3 dB attenuation point at a predetermined
frequeney between 100 and 700Hz. More particularly, the attenuation
point is advantageously between 100 and 300 Hz, and in one example 100
- H~ has been found suitable. ~ower frequencies may be adequately pre-
sented by the woofer system and moreover are suitably excluded from
the system aceording to the present invention to avoid cancellation
of low frequencies or a "doppler" like effect. Also undesired resonance
is avoided.
-1 O~
JPD/kmL 10/3/~3
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The 10W pass filter 82 leading to the main or princip~l
voice coil suitably has a -3 dB attenuation po-int at about 3,000 llz
assuming a tweeter system is present for the high frequencies. Of
- course, if no such tweeter system is employed,~the filter 82 may
be adjusted. Filter 82 is illustrated as comprising simply a series
, .
inductance 104, but other filter circuits may be substituted therefor.
; The low pass filter and attenuation circuit 84 is illustrated
as comprising a parallel combination of inductance 106 and re~istor
108, such combination being connected in series with resistor 115,
and has the combined attributes of attenuation in accordance with
the resistance of the resistor 115, a small amount of delay, and low
pass filtering having a -3 dB attenua-tion Foint at a frequency between
600 and 3,000 Hz. The attenuation of the low pass filter represented
by inductance 106 and resistor 108 is suitably designed such that the
signal therethrough is attenuated at 700Hz and above with an approximate
slope of 3 dB per octave, with the response of the enhancement speaker
coil 46B being "contoured". Alternatively, the attenuation point can
be at approximately 900 Hz, this being the frequency, according to
-~ Weiners's defraction measurements, at which decay of high frequency
.
wave pat-terns begin as they encounter the shape of the human face,
passing therearound from one side of the face to the opposite ear.
Consequently, the voice coil 46B is provided with a rolloff simuLating
the frequency contour experienced by the listener's right ear as he
hears sounds ~pproaching from the left side of his head. The resuLt
of this contoured response is a more ~Lifelike and realistic production
of sounds appearing to originate from the left of the listener.
The attenuation provided by resistor 115 decreases the
amplitude of the drive to the enhancement coil 46B to avoid the
appearancc of a hole or a void in front of the :listener between the
two speakers as may be the case with no attenuation. The amount of
JPD/kml 12/27/83
attenuation will depend upon the placement of the speakers -to some
extent.
The component elements of filter circuits 88, 92 and 91~
and their purpose correspond to those of circuits 78, 82 and 8~ and
need not be discussed separately. It ~nLll be obvious from the above
discussion that the operation of righth~md speaker 38B is substanti~lly
the counterpar-t of the lef-thand speaker.
With the speaker construction and circui-t illustrated, an
apparent wide soundstage is presented to the listener, with sounds
appearing to originate beyond the boundaries of the speakers such as
~- 12 and 11~, i. e. fron a wider soundstage for example between points
18 and 20 in Fig. 10 l'he sounds may even appear to originate beyond
the walls of a room in which the speakers are positioned, and the
spea~cers 12 and 1~ need not be spaced widely apart to achieve this
effect. Thus the speakers can be placed against the "short wall" of
a room while still producing a pronounced wide soundstage effectO
Moreover, the effect is not highly dependent upon position of the
listener. The listener need not be located at position 16, at the
apex of the system, but can be nearly anywhere in front of the two
loudspeakers while still receiving the impression of the wide sound-
stage. The effect of the wide soundstage while moving about the
room is more pronounced than for either the prior art electronic
mixing system, or the prior art dual speaker system as illustrated
in Fig. 2.
The dual speaker system of Figo 2, where the main enhancement
speakers are physically separated to some degree even though in the
same enclosure, apparently produces phase effec-ts which are different
as the listener moves and restrict the wide soundstage result to the
location of the listener at point 16 in Fig. 1, or at least in close
proximity thereto~ The phase efPects ch~nge as the person moves
around the room listening to the prior art system, but do not change
with respect to the system according -to the present invention~ As
-12-
JPD/kml 1o/26/33
~ ~5~
also explained, the w;de soundstage effect is atso improved as cGmp~r d
with the prior art electronic mixing system or -the electronic equi~r~len
of the system of ~ig. 2 wherein the signals illustrated in Fig. ~ as
applied to speakers or drivers 26 and 32 (or 2~ and 30) are electronic~1ly
summed and applied to the same driver. It is theorized that the sum~.ation
(or subtraction) of sounds achieved in the electronic miY~ing system
of the prior art produces a type of cross talk or modulation (or
absence thereof) not as comparable with the response of the hwnan ear
as is the case with the present system. In the system according to
the present in~ention, the two separa-te drive signals are applied to
a single dlaphragm in a given speaker or transducer. Thus, referring
to Figs. 3 and 4, a single diaphragm 40 is driven by voice coils 44
and 46 in each case. The response of -the diaphragm is apparently not
too unlike that o~ the human eardrum when encolmtering a Fair of sounds,
for the person wi-th binaural hearing. In the dual voice coil drive
illustrated for the present invention -there is in fact a single
diaphragm or vibrating speaker cone 40 for cach of the left and right
speakers, and therefore the lef-t and right sounds originate from
specified left and right points but have the effect of providing
natural sound to the left and right ears respectively. In addition
to providing a wide soundstage effect, the system according to the
present invention is also perceived by the listener as producing a
three dimensional effect, wherein the listener imagines he can place
the instruments of an orchestra at different locations in front of
him, depthwise as well as transversely across the soundstage.
The loudspeaker according to the present invention
advantageously employs two voice coils 44 and 46 in two separate air
gaps as herein described. However, it is also within the scope of
the present invention to provide a pair of voice coils located on a
3 sin~^le diaphrag~l of a convention~l speaker, e. g. with the voice coils
being bifilar wound or ~ound adj;lcently as understood by those skilled
~13-
JPD/~L 10/26/83
~ ~5~
in the art. The construction as iLlustrated in Fig. 3 is preferred
since when both volce coi~Ls are located in the same gap (bifilar wound~,
each voice coiL tends to see -the gap as being too large. The system
then becomes somewhat less efficient or lossy. But, not on~Ly is the
i~Llustrated duaL voice coil system according to the present invention
more efficient, it a~Lso provides a more striking sound effect than is
the case with the bifilar winding~ Wi-th a bifi~Lar winding there is
apparen-tly too much coupling (i. e. transfo~mer coupling) or a chance
for more interaction between the coi~Ls with the overa~Ll resu~Lt being
a swnmation electronicaLly of the main and enhancement signa~Ls in a
manner similar to the electronic swnma-tion system of the prior art.
There seems to be not onlv too much cancellation, but dampening of
the dynamic range when the coils are bifilar wound. The result
according to the present invention is one of much more pronounced
reaLism and ability to perceive the effect over a greater area in
front of the speakers when the double air gap, double voice coil
construc-tion as illustrated in ~ig. 3 is employed. However, as
indicated, the bifilar winding arrangement is of some advantage and
to a degree provides the resu~Lt of the present invention.
Figs. 5 and 6 illustrate a planar type speaker which may be
employed with the system according to the present invention. A
-tri-laminate frame 110 includes a rear border laminate 112, a centra~L
laminate 11~, and a forward border laminate 116. Between laminates
.
112 and 114 is located a perforated aLuminum plate 118 carrying a
pluraLity of ~trip m~gnets 120~ In this illustration, the strip
m&gnets are disposed in a vertica:L direction and parallel to one
another. Between laminates 114 and 116 there is positioned a ~lylar
diaphragm 122, the vibratory part of the speaker, which carries
bifiLar wound voice coiLs 124 and 126. The two voice coils are
connected in -the same manner as coils 44A ~nd 46A in ~ig. 4. Of
JPD/kml 1 2/27/83
'7'~
course, a second speaker of the planar type would then be utilized for
the remaining channel.
A double diaphragm speaker, which may be employed in con-
junction wi-th the presen-t inven-tion, is illustra-ted in Figs. 7 and
8~ A pair of semi-cylindrical diaphragms 128, suitably formed of
Mylar, are respectively supported by halves 130 and 132 of a plastic
frame~ The semi-cylindrical diaphragms are glued or otherwise
joined together centrally of: the device, and firs-t and second voice
coils 134 and 136 are secured on opposite sides of the double thick-
10 ness of Mylar where the diaphragms are joined. Each voice coil
suitably comprises a multi-turn flat loop which is glued or other-
wise secured to the double diaphragm.
Magnets 138 and 140 of the Figs. 7 and 8 embodiment are
supported or sandwiched between gap pla-tes 142 and 144 respectively,
15 and the gap plates are in turn received in apertures in the inwardly
extending, somewhat pyramidal shaped por-tions 146 and 148 of the
plastic frame so as to position the gap plates adjacent sides of the
voice coils. Gaps formed between opposed ends of the gap plates
thus receive sides of the voice coils causing the voice coils to
20 be linked by magnetic flux from the magnets 138 and 1L~o. Movement
of the diaphragms, when the voice coils are energized in the man-
ner of coils 44A and 46A and Fig~ 4, is primarily in the direction
of arrow 150, i. e. perpendicular to the long sides of the gap
pla-tes.
Fig. 9 illustrates an electrostatic -t~Jpe speaker which
may be employed with the system according to the present invention.
First and second panel frame members 151 and 152 enclose a con-
ductive film diaphragm 153 which is engaged between peripheral
flanges 164 of the panel frame members~ Each of the panel frame
30 members has a grid structure which is recessed away from the con-
ductive film diaphragm, wherein panel frame member 151 is pro-
vided with a principal signal polarizing conductive grid 15ll com-
prisirlg spaced in-terconnec-ted -ver-tical conductors disposed adjacent
... ,l ,r).,.
JPD/kml 1 2/27/83
i3L740
but spaced from diaphragm 153 on the opposite side -thereof.
In between the conductors of conductive grid 154 on panel
frame member 151 are disposed a plurality of parallel interconnected
conductors comprising an enhancement signal polari%ing conduc-tiiJe
grid 155~ On panel frame mamber 152 between the conductors of
., ,
polarizing conduc-tive grid 156 are located parallel in-terconnected
, ~ ~
conduc-tors comprising an enhancement signal polari~ing conduc-tive
grid 1 57 .
In the illustra-ted construction, terminal 162 connects to
conductive film diaphragm 153 while terminal 158 connects to con-
ductive grid 151~, terminal 160 connects -to conductive grid 156, and
terminal 159 connects to conductive grid 157. Another terminal
(not shown) is connected to conductive grid 155.
The electrostatic speaker operates in a conventional man-
15 ner for this type of speaker with respect to conductive grids 15L~
and 156 which are driven from a principal amplifier output. However,
the enhancement polari%ing conductive grids 155 and 157 are driven
from the opposite channel in a reverse phase sense~ A second
electrostatic speaker of this type would also be utili~ed.
It will be seen that a number of different speaker con-
structions are possible according to the presen-t invention, each
emplo~Jing plural voice coils so that each speaker is provided with
principal and enhancement means for operating the same vibrational
member or diaphragm.
While I have shown and described plural embodiments of m~
invention, it will be apparent to -those skilled in the art that manv
other changes and modifications ma~ be made without departing from my
inventlon in its broader aspects. I therefore intend the appended
claims to cover all such changes and modifications as fall within the
true spirit and scope Gf m~ invention~
