CA1251740A - Soundstage boundary expansion system - Google Patents
Soundstage boundary expansion systemInfo
- Publication number
- CA1251740A CA1251740A CA000500500A CA500500A CA1251740A CA 1251740 A CA1251740 A CA 1251740A CA 000500500 A CA000500500 A CA 000500500A CA 500500 A CA500500 A CA 500500A CA 1251740 A CA1251740 A CA 1251740A
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- loudspeaker
- diaphragm
- transducer
- soundstage
- movable element
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Abstract
Abstract:
A system for providing the effect of an extended soundstage comprises a pair of stereophonic loudspeakers, each having a movable or vibrational element driven by a pair of voice coils including a principal or main voice coil and an auxiliary or enhancement voice coil. The principal voice coil of each speaker is driven in a customary manner from one channel of a stereophonic amplifier, while the enchancement voice coil is driven in a reversed phase sense from the output of the opposite channel, and sound is effectively provided over an extended apparent source having dimensions beyond the spacing between the loudspeakers.
A system for providing the effect of an extended soundstage comprises a pair of stereophonic loudspeakers, each having a movable or vibrational element driven by a pair of voice coils including a principal or main voice coil and an auxiliary or enhancement voice coil. The principal voice coil of each speaker is driven in a customary manner from one channel of a stereophonic amplifier, while the enchancement voice coil is driven in a reversed phase sense from the output of the opposite channel, and sound is effectively provided over an extended apparent source having dimensions beyond the spacing between the loudspeakers.
Description
'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 ~ S~7~
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 ~5~7~
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 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~
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 ~ S~7~
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 ~5~7~
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 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~
Claims (9)
1. A soundstage boundary expansion system for providing the effect of a sound source characterized by apparent sound directionality beyond the physical dimensions of the system, said system comprising:
an amplifier with first and second channel outputs respectively representing sound information intended to give the impression of originating from different directions, first and second sound transducers positionable at spaced locations and responsive to said first and second channel outputs of said amplifier, the first transducer having a physically movable element which vibrates in a first phase sense in response to the first amplifier channel output, and the second transducer having a physically movable element which vibrates in a first phase sense in response to the second amplifier channel output, means for additionally physically driving said physically movable element of the first transducer in proportion to said second amplifier channel output but in a reversed phase sense, and means for additionally physically driving said physically movable element of the second transducer in proportion to said first amplifier channel output but in a reversed phase sense.
an amplifier with first and second channel outputs respectively representing sound information intended to give the impression of originating from different directions, first and second sound transducers positionable at spaced locations and responsive to said first and second channel outputs of said amplifier, the first transducer having a physically movable element which vibrates in a first phase sense in response to the first amplifier channel output, and the second transducer having a physically movable element which vibrates in a first phase sense in response to the second amplifier channel output, means for additionally physically driving said physically movable element of the first transducer in proportion to said second amplifier channel output but in a reversed phase sense, and means for additionally physically driving said physically movable element of the second transducer in proportion to said first amplifier channel output but in a reversed phase sense.
2. The system according to claim 1 wherein each of said trans-ducers is provided with a main driving coil and wherein a said means for additionally driving comprises an enhancement driving coil for substan-tially independently vibrating the corresponding movable element, the driving coils for a given physically movable element being energized in response to the first and second amplifier channel outputs.
3. The system according to claim 2 wherein each transducer comprises a loudspeaker and said driving coils comprise voice coils associated in driving relation with the diaphragm of the same loudspeaker.
4. The system according to claim 3 wherein said pair of voice coils are bifilar wound on the same loudspeaker cone bobbin.
5. The system according to claim 3 wherein a said loudspeaker includes a magnetic circuit adapted to produce magnetic flux, said magnetic circuit having a pair of air gaps, said pair of voice coils being respectively positioned in separate air gaps in said magnetic circuit in linking relation to said magnetic flux.
6. The system according to claim 5 wherein said magnetic circuit includes a central pole piece and a pair of top plates radially spaced from said central pole piece to define said separate air gaps, said loudspeaker including a bobbin attached to the diaphragm of said loudspeaker and extending between said central pole piece and said pair of top plates, with one of said voice coils being located on said bobbin in each air gap.
7. The system according to claim 3 wherein the diaphragm of said loudspeaker is substantially planar and said voice coils are bifilar wound in a circuitous path on said diaphragm.
8. The system according to claim 3 wherein said loudspeaker includes a second diaphragm joined to the first diaphragm, and having a common diaphragm area where the diaphragms are joined, said voice coils being attached to said common area, and a magnetic circuit adjacent said common area adapted to provide magnetic flux linking said voice coils.
9. The system according to claim 1 wherein the movable element of each said transducer is substantially planar and conductive, each transducer being provided with main electrostatic elements and wherein a said means for additionally driving comprises enhancement electrostatic elements for substantially independently vibrating the corresponding movable element, the electrostatic elements for a given transducer being driven in response to the first and second amplifier channel outputs.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000500500A CA1251740A (en) | 1986-01-28 | 1986-01-28 | Soundstage boundary expansion system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000500500A CA1251740A (en) | 1986-01-28 | 1986-01-28 | Soundstage boundary expansion system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1251740A true CA1251740A (en) | 1989-03-28 |
Family
ID=4132352
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000500500A Expired CA1251740A (en) | 1986-01-28 | 1986-01-28 | Soundstage boundary expansion system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1251740A (en) |
-
1986
- 1986-01-28 CA CA000500500A patent/CA1251740A/en not_active Expired
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