Abstract:
A high mass speaker enclosure having a speaker mounted to a front escutcheon plate and below which a multi-gated balanced acoustical transmission yoke is mounted and whereby a portion of the enclosure&#39;s interior air pressure is relieved so as to augment the speaker sound, especially at frequencies below 60 hertz. Enclosure resonance is minimized via the use of a high mass enclosure and the filing thereof with a fiberglass material around the speaker and a Dacron filler around the transmission yoke, while front mounted polyester mats preload the speaker and transmission yoke. Speaker resonance, lost sounds and/or extraneous speaker induced sounds are thereby avoided.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to balanced speaker systems and, in particular, to a speaker enclosure having an exterior wall with an elliptically-shaped opening formed therethrough, with the edges of the opening being tapered to cause air pressure waves to exit therefrom in a cone-shaped pattern, and acoustically balanced transmission yolk mounted thereto for relieving interior pressure and augmenting the bass range of the speaker without distortion or dampening at frequencies of 60 hertz and lower. 
     The integrity and quality of sound transfer systems is especially linked to speaker performance, since no matter how faithful a sound is recorded or replayed, distortion induced at the speaker still ruins the sound. While most recording systems do record and replay sounds rather faithfully for the mid-range frequencies, their performance tends to fall off at the upper and lower ends of the audio frequency range. Thus, it becomes especially important that any speaker system associated with any sound transfer system be responsive to this frequency roll off, without inducing any undesired distortion or extra sounds of its own or adding significantly to system losses. 
     Relative to woofer speakers, this becomes even more important, since the bass notes, through their low frequencies and high power output, due to their large surface speaker cones, tend to dominate over other frequencies and thus any speaker induced distortion tends to become rather pronounced relative to the listener. Also, because of the inherent driver losses at these low frequencies, the reproduced frequencies and sounds are not as full or complete as they should be. It is, therefore, desirable that for any system having a variety of speakers accomodating various frequency ranges that the bass speakers or woofers be able to augment the power losses of the driver without adding sounds of their own, creating interference, sympathetically resonating or otherwise distorting the sound. 
     Heretofore, a variety of speaker systems; including tubes, horns, labyrinths, transmission lines, screens, sub-woofers, etc., have been developed for faithfully reproducing recorded sounds and which most popularly have included the &#34;infinite baffle&#34; system wherein a completely sealed speaker enclosure contains the speaker that accommodates induced interior pressures without adding great distortion to the sound. Such speakers, however, suffer from a rather fast roll off at low frequencies and do not induce the high energy content sounds such as are required for frequencies of 60 hertz or less. 
     Theatre speakers, on the other hand, through various structural modifications, couple a portion of the back-pressure-wave induced by the speaker to a horn, a labyrinth or another passive radiator or speaker cone, the output of which augments the driven speaker. A problem attendant with such speakers, however, is high distortion and storage time which makes such speakers unsuitable for systems requiring high fidelity. Such speakers are efficient, however, and therefore may be used for public address systems or the like. 
     Additionally, the bass speaker of the present invention differs from known ported speakers in that in lieu of a circular or square port and a sound collecting tube, it employs an elliptical window which creates an air cone as pressure waves driven by the woofer exit therefrom. Also, an ellipsoidal or wedge-shaped cavity is positioned relative to the elliptical window and possesses a balanced acoustical transmission yoke. Internal speaker enclosure pressure waves are thus collected at the shaped gates opening to the transmission yoke, are formed and then transmitted through the elliptical window with less storage time to reinforce the reproduced sound at the frequencies of operation for which the driver equipment output begins to fall off. Furthermore, the window size and position are selected such that at the selected frequencies of operation, the elliptical window is operative to augment the generated sound in a real time fashion and in time-phase with the speaker&#39;s generated sound, thereby avoiding lost sounds or out-of-phase sounds inherent in the tube connected ported speakers. The window is also large enough so that a meaningful output is obtained thereby. 
     The speaker of the present invention is thus intended for combination in a system of speakers, where the present enclosure is typically used in conjunction with the woofer, while a mid-range speaker and tweeter are successively stacked thereabove. Appropriate bandpass filters separate the speakers and ensure operation at the proper crossover frequencies. For the woofer, a passive crossover with the oval window occurs at 60 hertz while the crossover with the mid-range driver occurs at approximately 130 hertz and while the tweeters crossover at 2,700 hertz. Each speaker, in turn, is separated from the other and the floor via a mat having a linear sound transfer function such as the Fulton Kinetic Barrier™ sound transfer mats sold by Fulton Musical Industries of Minneapolis, Minn. 
     The speakers of the preferred embodiment are also fabricated with a high mass, sound augmenting enclosure. In particular, the enclosures are comprised of a front escutcheon having a speaker opening bored therethrough and an underlying shaped ovaloid window mounted along the same axis as the woofer opening. An ellipsoidal or wedge shaped chamber, formed in a balanced acoustical transmission yoke, is mounted behind the elliptical window interior to the otherwise airtight speaker enclosure and is operative in a push-push fashion at frequencies below 60 hertz so as to augment the produced sound and thereby extend the range of frequency response for the speaker, without inducing additional distortion. 
     System operation is, in turn, enhanced due to the augmented bass response, lower crossover frequency and real time response characteristics of the present woofer. Complex sounds, such as are produced by symphonic orchestras, can now better be distinguished, since the bass sounds do not override the upper bass and midrange tweeter. The system&#39;s dynamic range is also wider and each instrument is better distinguishable from one another without &#34;smearing&#34;, while bass power remains intact so as to permit the playback of the sounds at the same power levels as originally played. 
     The above objects, advantages and distinctions of the present speaker enclosure and system as well as various others will, however, become more apparent upon reference to the following description of the preferred embodiment thereof with respect to the following drawings. Before referring thereto, though, it is to be recognized that the following description is made with respect to the presently preferred embodiment only and thus various modifications (over and above those mentioned) may be made without departing from the spirit and scope of the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a high mass speaker enclosure having a front escutcheon containing a speaker opening and a formed elliptical window opening which acts to create an air cone cooperating with an interiorly mounted multi-gated, balanced acoustical transmission yoke. The transmission yoke is centrally mounted relative to the speaker opening and contains a hollowed ellipsoidal cavity having two balanced gates opening thereto from the air space interior to the speaker enclosure. At the predetermined speaker frequencies of 60 hertz and below, induced air pressure changes interior to the otherwise airtight speaker enclosure produce real time responsive augmenting speaker sounds via the elliptical window. 
     The speaker and enclosure back are also sealed so as to seal the enclosure in an airtight fashion, except for the gates of the yoke while the speaker is surrounded by a dense fibrous material and while the transmission yoke is surrounded by a less dense material. The front of the escutcheon openings are, in turn, covered by correspondingly dense sound permeable and less dense materials such that the speaker is preloaded with a sound deadening or distortion reducing material while at the same time the elliptical window is preloaded with a less dense material. 
     In an alternative embodiment, the hollow chamber of the transmission yoke is comprised of a wedge-shaped region. It is further contemplated that in a system configuration, the present enclosure would incorporate a woofer speaker and additional midrange and tweeter speakers would be stacked and insulated from one another as well as the floor via linear sound transfer mats. Still further, the yoke chamber may be covered or roughened so as to preclude sympathetic resonance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a partially cutaway perspective view of the present speaker enclosure. 
     FIG. 2 shows a cross-sectional view taken along lines 2--2 of FIG. 1. 
     FIG. 3 shows a cross-sectional view taken along lines 3--3 of FIG. 1. 
     FIG. 4a shows a detailed elevation view of the present wedge-like balanced acoustical transmission yoke. 
     FIG. 4b shows an end view of the acoustical transmission yoke of FIG. 4a. 
     FIG. 4c shows an end view of an alternative, elliptical balanced transmission yoke. 
     FIG. 5 shows a schematic diagram of the balanced speaker driver circuitry. 
     FIG. 6 shows a typical system diagram of a plurality of speakers for a single output channel. 
     FIG. 7 shows the combined frequency response of a typical augmented woofer of the present type. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a partially cutaway perspective view is shown of the present speaker enclosure 2. It is preferably fabricated from a three-quarter inch, laminated high density particle board. The enclosure is fabricated with mitred corners and for an eight inch diameter woofer, the outside demensions of the enclosure are approximately 111/2 inches wide by 16 inches high by nine inches deep. It is to be recognized, though, that larger or smaller enclosures may also be fabricated in the present fashion. Mounted to the front of the enclosure is an escutcheon panel having an eight inch speaker hole 6 bored therein, near the top of the enclosure 2. An elliptical window 8 is centered and formed below it in the remaining open space of the panel 4. The elliptical window 8 has its edges chamfer routed inwardly so as to essentially form an air cone for the sound pressure waves which eminates therefrom. 
     The panel 4, like the enclosure 2, may be fabricated from a three-quarter inch high density particle board which tends to minimize undesired resonance of the enclosure itself for the typically encountered frequencies of the woofer speaker that is placed therein. Because the elliptical window 8 is centrally mounted, it produces a balanced sound relative to the interior gates 32 and 34 that are disposed to the right and left sides thereof. For the presently preferred embodiment and assuming the dimensions already set out above, the elliptical window 8 may measure approximately 21/4 inches high by 51/4 inches wide. For an 8-inch woofer, such a construction has been found to produce sounds of sufficient amplitudes at the audio frequencies for which the enclosure 2 augments the sound output of the speaker. 
     From FIG. 1, it is also to be noted that the interior of the enclosure 2 contains a fiber filler of two different materials. In particular, a fiberglass batt or filling 12 surrounds the speaker, while a less dense and more sound porous Dacron batt or filling 14 surrounds the elliptical window 8 and the balanced transmission yoke 10 mounted therebehind. Similarly, individual front panels 16 and 18 of greater and less density materials are mounted respectively in front of the speaker opening 6 and the ovaloid window 8. The fiber material 12 and 14 within the enclosure thus dampens and minimizes any resonance of the enclosure 2 that might otherwise occur, while the front panels 16 and 18 serve to preload the outputs and again dampen any resonance or distortion that might otherwise be generated. 
     Drawing attention next to FIG. 2, a cross-section view of FIG. 1 taken along lines 2--2 is shown. It more particularly depicts the various components of the present enclosure 2 and their relative disposition with respect to each other. FIG. 2 shows a more detailed view of the balanced acoustical transmission yoke 10 that is juxtaposed behind the elliptical window 8. The yoke 10, which will be discussed in greater detail with respect to FIGS. 3 and 4, generally is fabricated in a &#34;T-like&#34; structure that extends across the width of the escutcheon panel 4 so as to contact both side walls of the enclosure 2. The centrally located wedge-like chamber 19 is open to the enclosure 2 on at least two sides and one of which sides for a wedge-like chamber 19 can be seen. The woofer speaker 20, in turn, mounts to the escutcheon panel 4 via a plurality of screws (not shown) and an annular seal 22 is mounted between the speaker and the escutcheon to create an airtight seal. Surrounding the speaker 20 is the fiberglass batt 12, while the more porous Dacron bat 14 surrounds the transmission yoke 10. The enclosure is completed via an airtight seal 26 that is established between the enclosure side walls and the back panel 28 which is screwed thereto. The back panel 28 also contains the necessary terminal strips (not shown) for making appropriate electrical interconnections with the various other speakers of the system and for the present embodiment also includes appropriate cross over circuitry to ensure the proper frequency separation between the speaker 20 and the associated other speakers (not shown). 
     As mentioned, principal to the improved operation of the present speaker is the inclusion of the acoustical transmission yoke 10 in combination with the elliptical window 8 in the escutcheon panel 4. A more detailed view relative to the mounting thereof can be seen upon reference to FIG. 3 which is a cross-sectional view taken along lines 3--3 of FIG. 1. From FIG. 3, the back of the yoke 10 can more clearly be seen relative to its mounting across the panel 4. As mentioned, the yoke is comprised of a &#34;T-like&#34; member and the two longer horizontal arms of which contact the sides of the enclosure 2 while the lower, fatter vertical portion is suspended above the bottom of the cabinet via a spacer block 30. Shown in dotted line are the edges of the wedged-like cavity 19 (FIG. 4b) which have been empirically shown to provide a similar sound quality to that of an ellipsoidal chamber 19. (FIG. 4c) Also, due to the present configuration, the opposed ends of the chamber 19 open to the inside of the enclosure in the regions 32 and 34. This results in the frequency of the reproduced sound being reduced. Also, as the pressure within the enclosure 2 increases, a progressively generated sound is produced at greater and greater amplitudes and eminates from the chamber 19 and elliptical window 8 so as to augment the sound from the speaker 20. For frequencies above 60 hertz, such eminations are nominal, but at approximately 60 hertz, the eminations become more and more significant and correspondingly add to the overall sound eminating from the speaker, thereby augmenting the speaker sound, especially in the range of frequencies where the sound replay or driving equipment frequency response is falling off. In particular, for most sound replay equipment, the frequency response thereof falls approximately seven to ten decibels over the frequency range from 20 to 60 hertz, but which in the preferred embodiment decreases only about three to four decibels. In the prior art tuned ported speakers, 12 to 18 percent distortion is commonly encountered at these frequencies, but for the preferred embodiment is only about 0.06 percent. 
     This augmentation of the sound better defines and makes the bass sounds between 20 to 60 to 60 and 130 hertz more discernable to the listener. Individual bass notes and the instruments generating them are thereby better discernible, rather than sounding as a smeared composite. 
     Attention is next directed to FIGS. 4a, 4b and 4c wherein further details of the present transmission yoke 10 can be seen. In particular, upon referring to FIG. 4, a front elevation view is shown of the present transmission yoke 10. Its end view is shown in FIG. 4b, and an alternative yoke employing an ellipsoidal chamber 19 is shown in FIG. 4c. The yoke 10 may be fabricated from a piece of pine 2×4, although for larger speaker designs, a 4×4 would be employed. The cavity 19 for the 2×4 yoke 10 is approximately two inches high and three-quarters of an inch deep. By adjusting the chamber size, though, various levels of augmentation can be achieved. Also, by varying the vertical placement of the yoke 10 relative to the speaker, the amplitude of the augmenting sound can also be varied. While the ovaloid window is shown in the drawings as being centered below the speaker opening 6 in the escutcheon panel 4, alternatively, it could be formed in the bottom wall of the enclosure 2, the back 28, or on each of the sides, but in any of these cases, the yokes 10 should be symetrically mounted relative to the sound internal to the enclosure so as to augment the speaker sound without distortion. For a bottom mounting, an open pedestal should be employed to ensure that the sound is not muffled. In such an arrangement, the floor becomes a medium by which the sound is further eminated to the room, just as where a back mounted opening utilizes the wall to help distribute the sound. 
     Depending upon the size of the speaker 20 and enclosure 2, it should also be noted that it is desirable to roughen the interior surface of the chamber 19 or line it with the Fulton Kinetic Barrier™ material so as to prevent against the sympathetic resonance of the yoke 10. Irrespective of whether a wedge-shaped cavity (FIG. 4b) or ellipsoidal cavity (FIG. 4c) is used, the sound storage time of the chambers 19 is negligible at the audio frequencies so that a real time frequency response is obtained which does not distort the speaker sound as it is added thereto. 
     Directing attention now to FIG. 5, an electrical schematic is shown of the present speaker 20. It comprises a balanced arrangement of the signal lines to the speaker 20. Specifically, chokes or inductors 36 and 38 are placed in series in the plus and minus input lines, while a balanced, center tapped capactive network is coupled in parallel to the voice coil 44 and the permanent magnet 46 (typically 70 oz.) with the center tap between the capacitors 40 and 42 also being coupled to the equipment ground. Thus, not only is the yoke 10 balanced in the regions 32 and 34 relative to the sound pressure within the enclosure 2, but also the speaker 20 will be driven in a balanced fashion so as to thereby further relieve distortion. The present speaker 20 is specially formed with annilus-like reliefs 47 formed in the speaker cone so as to allow deep excursions without bumping the front grill material and under extreme bass passages reflect tighter control of the moving speaker cone mass itself. 
     Directing attention to FIG. 6, a system representation is also shown for a speaker system including the enclosure 2 of the present invention. Specifically, it is contemplated that for such a system the various speakers thereof would be stack mounted above the woofer enclosure 2 and as shown in FIG. 6 include a midrange enclosure 48 and a tweeter enclosure 50. Each of the speakers would, in turn, be separated from one another and from the floor by the aforementioned Fulton Kinetic Barrier™ sound transfer mats 52. 
     Finally, a representation of the composite frequency response for the present speaker 20 in enclosure 2 is shown in FIG. 7. From this figure, the aforementioned additive effect of the output from the elliptical window 8 can be seen relative to the independent response of the speaker 20 alone. In particular, it is to be noted that elliptical without the window 8, the speaker response is down approximately 24 decibels at 20 herz; but that the net response is down only seven decibels, when the sound output of the elliptical window 8 is added. Up to 60 hertz, the speaker&#39;s response is thus augmented, thereby improving the quality of the total sound over the range of frequencies for which the output of the driving equipment falls off. 
     While the present invention has been described with respect to its presently preferred embodiment, it should be apparent from the above that various modifications may be made thereto without departing from the spirit and scope thereof. It is, therefore, contemplated that the following claims should be interpreted so as to include all those equivalent embodiments within the spirit and scope of the described invention.