Abstract:
The present invention relates to a unique stereophonic speaker system of unique construction and true left and right speakers assemblies, booth physically and electrically. The speaker assemblies, located to the left and right front sides of a room effectively recreate the sound characteristics of a sound stage. Each speaker assembly includes a plurality of axially aligned speakers supported one above the other in a housing made of flexible material and which can vibrate and resonate. Each speaker assembly includes cutouts in the side wall of the housing, the speakers being positioned such that the side wall with the cutouts are in facing relation. The left channel information must be played in the left speaker assembly and the right channel information must be played in the right speaker assembly.

Description:
FIELD OF INVENTION 
     The present invention relates to a stereophonic speaker system and more particularly to an improved and unique speaker system in which uniquely constructed spaced true left and right speaker assemblies are preferably positioned such that a speaker assembly is located to the left and right front sides of a room or listening area thus effectively recreating the sound characteristics of a sound stage. 
     BACKGROUND OF THE INVENTION 
     Faithful reproduction of sound (music and/or speech) has been the goal of many in the audio industry. Stereophonic reproduction of sound has been with us for over fifty (50) years and is still the basis for most sound reproducing equipment for home entertainment. Introduced in the early sixties was quadraphonic sound, utilizing four discreet channels and four separate speakers. The goal was to immerse the listener in a soundstage environment by surrounding the listener at or in a theater by the four channel sound source. More recently, surround sound for home or theaters in various different forms has been introduced. The surround sound uses multiple speakers positioned in different locations in an attempt, as close as possible, to recreate as close as possible the original performance of the sound stage. Again, the object was to immerse the listener in sound, mimicking the sound characteristics of a sound stage. 
     In a typical sound stage for recording a stereophonic sound, the stage usually consists of two microphones, each located in the front left and front right of the source of the sound, as shown diagrammatically in FIG.  1  and which will be described further. The listener is to the front of the microphones and between the two, as shown. Multi-microphone techniques have evolves over the years enabling the recording engineer to re-locate the positions of the various musicians and/or vocalists to different places on the sound stage in an attempt to emulate the kind and quality of sound which the engineer seeks. The techniques for creating and arranging the sound stage using multiple microphones are well known and discussion thereof is beyond the scope of this invention. However, it is the case that the listener at a sound stage hears a sound reproduction as close as possible to the original performance. 
     The typical prior art stereophonic model is illustrated diagrammatically in FIG.  2  and will be described further below. In its basic form, the system includes two channels of sound information reproduced by a left and right speaker, as shown. The listener in front of and between the two speakers hears an illusionary sound stage between the two speakers, up front and up to the rear wall at the back of the speakers&#39; location. Due to room boundary reflections, speaker cabinet diffraction, and reflection and psychoacoustic effect, the illusion of a sound stage would appear to be centrally located only in front of the spaced speakers. Various forms of signal processing, such as DSP, have been developed to counteract the effects of diffraction and room boundary reflections. These techniques were successful, to some extent, but due to the difference in room layouts, differing acoustic properties of floors, walls and ceilings, the desired result of reliably replicating the sound in a sound stage was not reasonably achieved. Furthermore, the introduction of signal processing in the signal path may produce undesirable artifacts in the electrical signals. 
     It is thus apparent that a need exists for a relatively simple speaker system which emulates the sound characteristics of a sound stage and compensates for the differing acoustic properties of floors, ceilings, walls and room geometry. 
     It is an object of this invention to preserve the original signal in its purest form as generated at the sound stage by utilizing the room boundary reflections and the acoustical blending of R-L and L-R stereo information by the use of a unique speaker system which effectively recreates the sound stage. 
     It is also an object of this invention to provide an improved speaker system including true left and true right speaker assemblies, each having a plurality of axially aligned speakers and a side wall with spaced cutouts in alignment with some of said speakers. 
     Another object of this invention is to provide a relatively simple stereophonic speaker assembly which includes a true left and true right speaker assembly, the left unit receiving left channel information and the right unit receiving right channel information. 
     Yet another object of this invention is to recreate a sound stage reproduction of sound by the use of left and right speaker assemblies, each having facing side walls with apertures therein for faithful reproduction of such sound. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The above and other objects of this invention are achieved through the use of a pair of unique stereo speakers which effectively recreates the original sound stage acoustics. 
     In accordance with this invention, each speaker assembly consists of seven full range drivers vertically mounted, one above the other, with a tweeter located between selected drivers. The speakers are mounted on a tubular column which may be square or circular or other shape having a front and side faces. In a preferred form, the column is constructed of a flexible material such as {fraction (1/16)} inch structural polyvinyl plastic. The column configuration of the drivers creates a diffraction-free baffle board. In a preferred form, the seven drivers are housed in five different and separate chambers. The first three drivers are housed in a single chamber while drivers four through seven are each housed in four separate chambers. The result is the creation of and the provision of a spherical sound field, encompassing the left and right speakers, much like a sound stage. 
     In addition, the chamber containing the first three drivers and the single chambers of the fifth and seventh driver include axial and horizontally disposed cutouts. These cutouts are intended to optimize the sound stage effect and performance of the drivers. In a preferred form each cutout is positioned perpendicular to the forward axis of the drivers and in a side face or wall of the support so that it faces the other speaker assembly on the other side of the listening area. In effect, there is a true right and a true left speaker assembly, each spaced from the other. These cutouts are intended to perform the following functions. 
     In the case of the left speaker assembly, there is cancellation of a certain band of audio frequencies (300 Hz to 3000 Hz) to move the virtual sound source of the left speaker assembly towards the rear and to the left of the speaker assembly. The cutouts in the left speaker also project an opposite polarity sound towards the right speaker assembly, creating a negative-left minus right sound information at the intended sound stage area. The cutouts in the left speaker assembly also effectively reduce enclosure resonance which minimizes sound coloration. 
     In the case of the right speaker assembly, the cutouts cancel a certain band of audio frequencies (300 Hz to 3000 Hz) to move the virtual sound source of the right speaker assembly towards the rear and to the left of the speaker assembly. The cutouts in right speaker assembly also project an opposite polarity sound towards the left speaker assembly, creating a negative-right minus left sound information at the intended sound stage area. Again, the cutouts in the right speaker assembly also effectively reduce enclosure resonance which minimizes sound coloration. 
     Accordingly, the cutouts create a centrally located sound stage behind both speaker assemblies. 
     The present invention is also unique in that there is a true right speaker assembly and a true left speaker assembly; these speaker assemblies are not interchangeable either electrically or physically. Electrically reversing the left and right channel information will produce a detrimental effect on the sound stage; localization of the performers will be skewed. Mechanically reversing the speakers (left to right and right to left) will effectively destroy the sound stage reproduction and the sound stage will revert to a conventional speaker&#39;s sound stage. Thus, the left channel information must be played back to the left channel speaker and the right channel information must be played back to the right channel speaker. The left and right speaker assemblies must be located at their respective side of the listening area (in relation to the listener facing the speaker). 
     This invention has many other advantages, and other objectives, which may be more clearly apparent from consideration of the various forms in which it may be embodied. Certain versions of such forms are shown in the drawings accompanying and forming a part of the present specification. 
     These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is understood that such detailed description is not to be taken in a limiting sense. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic illustration of a prior art sound stage; 
     FIG. 2 is a diagrammatic illustration of a prior art arrangement of stereo speakers; 
     FIG. 3 is a diagrammatic illustration of the speaker system of the present invention; 
     FIG. 4 is a front view of a speaker assembly in accordance with the present invention; 
     FIG. 4 a  is a sectional view along the line  4   a — 4   a  of FIG. 4; 
     FIG. 5 is a front view of a another form of speaker assembly in accordance with the present invention; 
     FIG. 5 a  is a sectional view taken along the line  5   a — 5   a  of FIG. 5; 
     FIG. 6 is a front view of a right speaker assembly in accordance with this invention; 
     FIG. 7 is a front view of a left speaker assembly in accordance with this invention; 
     FIG. 8 is a view of the rear of the speaker assembly of this invention showing the openings for positioning the speakers in the housing; 
     FIG. 9 a  is an illustration of how the speaker assemblies, using speakers with a 4 ohm nominal impedance, are wired in accordance with this invention; 
     FIG. 9 b  is an illustration of how the speaker assemblies, using speakers with an 8 ohm nominal impedance, are wired in accordance with this invention; 
     FIG. 10 is a diagram of the polar response of the speaker assembly of this invention; 
     FIG. 11 is a diagrammatic view of the right and left speakers arranged in accordance with this invention; 
     FIG. 12 is a view of a portion of the housing of a speaker assembly of this invention showing the apertures for the speakers; and 
     FIG. 13 is a diagram of the polar response of the speaker assembly of this invention in which the cut-outs associated with speakers  1  and  2  are not used. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a typical prior art sound stage is illustrated diagrammatically with a generally conventional set up for recording. The listener  10  is in the front of the stage with a left microphone  11  and a right microphone  12  positioned towards the front of the stage and spaced from the listener. This typical arrangement results in sound being recorded in a right and left manner. 
     Referring to FIG. 2 a typical prior art arrangement or placement of stereo speakers for playing stereo sound recordings or broadcasts is shown. The listener  10  is positioned to the front of left and right speakers  14  and  15 . The speakers may be switched with no noticeable effect. The resulting sound is effectively focussed between the speakers  14  and  15  and if one stands in the area of focus, there is fairly good reproduction of sound in a stereo manner. The difficulty, however, is that to replicate the sound of the sound stage, the listener should stand between the two speakers. Positioned as illustrated in FIG. 2, to the front and spaced from the speakers, the sound stage sound is not replicated. 
     Referring now to FIG. 3, the system  20  of this invention is illustrated and includes spaced left and right stereo speaker assemblies  22  and  24 , located where the microphones of a sound stage are located as shown in FIG. 1, with the listener  10  located where indicated and in about the same position as was illustrated in FIG.  2 . In this particular case, however, the left and right speaker assemblies cannot be switched, as will be explained. It will be noted however, that the sound envelope  25 , a spherical sound envelope, is basically the same as the sound envelope of the sound stage illustrated in FIG. 1. A better understanding of the vastly improved performance of the speaker system of this invention will become apparent from the following description. 
     Referring to FIG. 4, a speaker assembly  30  in accordance with the present invention is shown. The speaker assembly  30  includes a plurality of drivers (speakers) shown as numbered  1  through  7 , with a tweeter  33  positioned between speakers  4  and  5  and supported in an elongated support housing  32  which is essentially square, e.g., 2½ by 2½ and about 66 inches high, see FIG.  4 A. It is understood that other dimensions may be used, but those set forth are the preferred dimensions. The speakers may be commercially available speakers such as Maxon 4 ohm generic speakers or Maxon 8 ohm generic speakers or Aura 3×2 Neoradial technology speakers. 
     The material of the speaker housing is preferably a self supporting but flexible material such as a polyvinyl plastic, as contrasted to rigid and inflexible materials used in most other speaker assemblies, such as wood or metal. The reason for flexibility is the need to control the structure&#39;s tendency to resonate or vibrate. This control is achieved by drivers  4  and  6  working out of phase relative to drivers  1 ,  2 ,  3 ,  5  and  7 . Materials other than polyvinyl may be used provided that their tendency to resonate and vibrate is controllable by the method and structure described above. 
     The housing  32  is basically a hollow elongated tubular member and may, for example, be an extruded plastic member in which the tube may be of any of a variety of colors. The color brown is preferred to simulate furniture or other furniture simulating colors may be used. The housing includes a front face  32   a  in which the drivers are positioned, side faces  32   b  and  32   c  and a rear face  32   d . A stockinet type of sleeve and/or a small grill made of metal or plastic is assembled over the housing to cover the drivers and openings in the housing in which the speakers are located and other openings used for assembly purposes. The housing may be supported by a stand  35  or may be hung on or attached to a wall, if desired. Located within the housing are wires  36   a  and  36   b  the latter connected to the speakers, as will be described. 
     As seen in FIG. 4, the axial spacing between speakers  1 - 3  is basically uniform, but different from the spacing between the speaker  3  and speaker  4 , the latter spacing being greater than the uniform spacing between speakers  1 - 3 . The axial spacing between speakers  5 - 7  is also uniform and the same as that between speakers  1 - 3 . The spacing between the tweeter and speaker  4  is the same as that between the tweeter and speaker  5 , each being greater that the spacing between speakers  1 - 3 , but not as great as that between speakers  3  and  4 . This pattern of spacing assists in providing symmetry of sound reproduction. 
     Another form of speaker assembly  40  is illustrated in FIG. 5 in which a tubular support  42  of about 3 inches in diameter and 66 inches long is used as a housing. The support may be of the materials discussed for resonance purposes, as already noted. Again, a series of speakers,  1 - 7  are mounted in the housing with a tweeter between speakers  4  and  5 , as shown, and which have the axial spacing already described. While cylindrical in cross-section, the housing includes a front face  42   a , side faces  42   b  and  42   c  and a rear face  42   d , as seen in FIG.  5 . The housing is supported on a stand  45 , as seen in FIG.  4 . Again, wires  46   a  and  46   b  for connection to the speakers are located within the housing  42 . As with the unit of FIG. 4, the housing may be of extruded polyvinyl plastic, or of other material, and a stockinet and/or grill cover may be used. 
     As mentioned, the speaker system of this invention includes a true right and a true left speaker assembly. In effect, the speaker assemblies are positioned with the front face of each facing forward and the side face with the slots or cutouts in the side faces facing each other. Referring to FIG. 6, the right speaker assembly  50  is shown of a form illustrated in FIG.  4 . The speaker assembly  50  includes a front face  51 , a side face  52 , a rear face  53  and another side face  54 . The left and right speaker assemblies can be distinguished by the fact that in the right speaker assembly, the face to the left of the front face, face  52 , includes a series of slots or cutouts  55 - 59 . The front face  51  includes the drivers  1 - 7  and the tweeter  33  located between speakers  4  and  5 . 
     As seen in FIG. 6, the axial spacing between speakers  1 - 3  is the same. There is an axial gap between speaker  3  and speaker  4 . There is also the same axial gap between speaker  4  and the tweeter  33 . The axial spacing between the tweeter  33  and each of speakers  5 - 7  is the same and basically that of the gap between speakers  1 - 3  and less than any of the other gaps mentioned. The side wall  52  to the left of the front wall  51  includes the slots or cutouts  55  through  59  arranged in predetermined alignment with certain speakers. The slots or cutouts are located about {fraction (3/16)} of an inch from the rear wall and are about ⅝ of an inch wide and 2¾ in axial length. 
     As seen in FIG. 6, slot  55  is associated with and in alignment with speaker  1 , with slots or cutouts  56  and  57  associated with and in alignment with speakers  2  and  3 , respectively. There are no slots or cutouts associated with speaker  4  or the tweeter  33 . Slot  58  is associated with and aligned with speaker  5  and slot  59  is associated with and aligned with speaker  7 . There is no slot associated with speaker  6 . The speakers tend to project sound to the rear. The side slots or cutouts  55 - 59  provide sound opposite to that projected from the front. 
     The left speaker assembly  60  is shown in FIG.  7 . The front face is  61 , with the right side face being  62 , the rear face being  63  and the left side face being  64 . The speakers  1 - 7  and tweeter  33  are located in the front face  61  with a series of slots or cutouts  65 - 69  located in the right side face  62 . The spacing of the speakers and tweeter and the alignment of the slots or cutouts is as already described in connection with FIG. 6, save for the fact that in the right speaker assembly, the slots or cutouts are located in the left side face and in the left speaker assembly the slots or cutouts are located in the right side face. In use the speaker assemblies are positioned such that faces with the slots or cutouts face each other while the front faces face forward. 
     The tweeter augments the sound produced by the full-range speakers  1 - 7  beginning at 8 kHz. The speaker assemblies may be driven by a 35 watt amplifier, although amplifiers in the range of 20 watts to 120 watts may be used. The system may also use base or subwoofer whose output is in the range of 30 Hz to 200 Hz and positioned in the bottom of the support members or in close proximity to the speaker assemblies. A woofer having an output in the range of 50 Hz to 200 Hz may also be used. The output of the speakers  1 - 7  is in the range of 200 Hz to 19 kHz. 
     To enhance the reproduction of the sound stage effect, in addition to the structures already described, speaker units  4  and  6  are isolated from each other and from the remaining speaker units by baffles. Referring to FIG. 8, the baffling on each side of speaker  6  is illustrated. Such baffling includes baffle elements  70  and  71 , each composed of a sound proof foam such as rigid polystyrene foam. The baffle elements are pre dimensioned to fit between the side walls, between the front and rear face and are inserted between speaker  7  and speaker  5  to isolate speaker  6 . The baffling for speaker  4  is basically the same with the baffle elements being inserted between speaker  3  and the tweeter  33 . The purpose of the of speakers  4  and  6  and their baffles is twofold: First to cancel the resonance and vibration of the enclosure by producing a signal that is opposite in polarity to the driving signals for speakers  1 ,  2 ,  3 ,  5  and  7 . Second, speakers  4  and  6  and their baffles prevent a back sound wave. It is to be noted that the speakers  4  and  6  which are baffled do not include a side slot. The baffling described is used in both the left and right speaker assemblies and for the speakers identified. 
     In addition to the physical arrangement of the speaker and speaker assemblies, one aspect of this invention relates to the manner in which the speakers are wired. Referring to FIG. 9 a , the schematic wiring diagram is shown for speakers having a 8 ohm nominal impedance as receiving a positive and negative input, as indicated at  70 . This results in a total impedance of 4 ohms for the whole speaker assembly. The input for the left speaker assembly is the left channel input while that for the right speaker assembly is the right channel input. Each of the speakers is identified by the numbers already used Each speaker includes a conventional positive and negative mounting terminal as indicated. Speakers  1 ,  2 ,  3 , the tweeter  33 , and speaker  5  are wired with the positive input  70   a  to the positive terminal of the speaker. The positive input to the tweeter  33  includes a 3.3 microfarad capacitor. The negative input line  70   b  is connected to the negative terminal of speaker  5 , there being a 7.5 ohm, 5 watt resistor in the negative line. The negative input line  70   b  is also connected to the positive terminal of speaker  4 . The negative side of speaker  1  is connected to the positive side of speaker  7 , while the negative input line is connected to the negative side of speaker  7 , the line connected between the negative terminal and the negative input line of speaker  7  including a 15 ohm 5 watt resistor. 
     The negative terminal of speaker  2  is connected to the negative terminal of speaker  4 . The negative terminal of speaker  3  is connected to the negative terminal of speaker  6 . The negative terminal of the tweeter  33  is connected to the negative input line downstream of the 15 ohm 5 watt resistor which is in the line, as shown. 
     If a speaker assembly with speakers having a 4 ohm nominal impedance is used, the speakers may be wired as shown in FIG. 9 b , (in which the same reference numerals have been applied to the same components) and will result in a total nominal impedance of 8 ohms. As shown, speakers  1 ,  2 , tweeter  33 , and speaker  5  have their positive terminals connected to the positive input line  70   a . The negative terminal of speaker  1  is connected to the positive terminal of speaker  7 , while the negative terminal of speaker  7  is connected to the negative input line  70   b , there being a 7.5 ohm 5 watt resistance in the line, as shown. The negative terminal of speaker  2  is connected to the positive terminal of speaker  3 . The negative terminal of speaker  3  is connected to the negative terminal of speaker  4 . 
     The positive terminal of speaker  4  is connected to the negative terminal of speaker  6 . The tweeter includes a 3.3 microfarad capacitor in the line between the positive input line and the positive terminal. The negative terminal of the tweeter  33  is connected to the line connected to the negative terminal of speaker  5  between the 12 ohm 5 watt resister and the negative terminal. 
     The speakers of the assembly, wired as above described, cooperate with the cutouts and speaker isolation to achieve the results discussed. 
     FIG. 10 illustrates the linear polar response at 1 KHz of an open speaker assembly (cutouts) versus a closed system of the same type of speaker assembly with no cutouts. The intensity is indicated as decibels at the 50 db, 60 db and 70 db level. What is significant is the symmetrical nature of the readings from the open system (cutouts) all of which are above 60 db in essentially all points of the circle, as indicated by the plots at every 15□ around the circle. The plot of the open system is the solid line and that of the closed system is the dashed lines. It can also be seen that the closed system is far from symmetrical as compared to the open system. 
     FIG. 11 illustrates the back wall with the various speakers mounted in the housing. Speaker  1  is at the top of the unit and speaker  7  is at the bottom, the space or closed section between speaker  3  and  4  being shown as well as the relative spacing between adjacent speakers as already described. The rear face includes four elongated openings,  90 - 93  to provide access to mount the speakers in the housing. After the speakers are mounted in the housing and wired as described, the openings are closed with a cover, such as plastic or the like. 
     FIG. 12 is a fragmentary view of the front face with a plurality of axially aligned cutouts  100  showing the top three speakers apertures, the spacing between the third and fourth speaker, the tweeter opening  33   a  and the remaining three openings below  33   a , only one being illustrated. The speakers and the tweeter and mounted such that they are flush mounted on the front face, with the wiring connectors being located in the interior of the housing. After mounted and wired, the opening in the rear face are covered and a stockinet and/or grill may be assembled over the housing and the latter mounted on a stand or mounted on a wall with the proper orientation of the right and left speaker assemblies. 
     It is also possible in accordance with the present invention to eliminate the openings with speakers  1  and  2  and use only the opening of speaker  3  with the top three speakers. It was noted that with the speaker assemblies described, having openings associated with the top three speakers, the sound envelope was good with respect to listeners that were standing, as shown in FIG.  10 . However, for a sitting audience there was a need to reduce the intensity in the 300 to 3000 Hz range in order to provide a sound envelope that was appropriate for an audience that was sitting or standing. 
     The effect of covering or eliminating the openings associated with speakers  1  and  2  and retaining the opening with speaker  3  is shown in Figure which is a polar plot at a test frequency of 1000 Hz. Here the reference level is 0 dB=52.75 dB SPL. As seen, the plot  100  in short dashed lines shows a rather unsymmetrical response, especially at the 210 degree position, for a speaker assembly in which there are no openings associated with speakers  1 ,  2 , and  3  (the remaining structure being as described). By contrast, the plot  103  in longer dashed lines represents a rather symmetrical response for a speaker assembly in which the openings associate with speakers  1  and  2  were eliminated or covered. The result was a much improved sound envelope profile in both the vertical and horizontal direction. 
     It should be understood that this invention is not limited to the detailed descriptions set forth herein which describes in detail the preferred forms of the present invention. Modifications thereof will be apparent to those skilled in the art, based on the above detailed disclosure, but such modifications based on this disclosure may not be deemed to depart from the spirit and scope of the present invention as set forth in the appended claims.