US3166147A

US3166147A - Loudspeaker system

Info

Publication number: US3166147A
Application number: US246096A
Authority: US
Inventors: Daniel K Greenfield
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-05-07
Filing date: 1962-12-20
Publication date: 1965-01-19
Anticipated expiration: 1982-01-19

Description

Jan,19,1965 D.K.GREENHELD J J LOUDSPEAKER SYSTEM Original Filed Feb. 4. 1960 2 Sheets-Sheet 1 4 YEiL.

INVENTOR DANIEL K. GREENFIELD BY mam ATTORNEY Jan. 19, 1965 D. K. GREENFIELD 3,166,147

LOUDSPEAKER SYSTEM Original Filed Feb. 4, 1960 2 Sheets-Sheet 2 I INVENTOR. DANIEL K. GREENFIELD ATTORNEY United States Patent ()7 3,166,147 LOUDSPEAKER SYSTEM Daniel K. Greenfield, Elkins Park, Pa., assignor of onefonrth to Walter B. Udell, Philadelphia, Pa. Continuation of application Scr. No. 6,771, Feb. 4, 1960.

This application Dec. '20, 1962, Ser. No. 246,096

25 Claims. (Cl.181--31) This invention relates to soundreproducing apparatus, this application being a continuation of my copending application, Serial No. 6,771, filed February 4, 1960, now abbandoned. More particularly, this invention relates to a spaced multiple loudspeaker system which in conjunction with a'wall produces an acoustical Wavefront substantially uniform in both the vertical and horizontal planes so that a listener may move freely about a room without experiencing the annoying sensation of having the sound source apparentlys'hift from one loudspeaker to another. The acoustical integration of the sounds from the spaced loudspeakers is such that the character of the composite sound is constant and appears to emanatefrom a broad area beyond the associated wall rather than from a small localized loudspeaker source. Moreover, while the loudspeaker system according to the invention can be constructed relatively inexpensively and so asto occupy only. a very small volume, as for example approximately four cubic feet, the performance of the system insofar as range and efficiency are concerned is the equal of systems substantially more costly and requiring several times the room space, and is unique in its ability to provide very wide angle totally-integrated sound regardles of cost and size factors. a I g In the past, and particularly prior to the inventionof the high quality long playing phonograph records and low distortion phonograph transducers, interest in realistic sound reproduction was generally limited to the relatively few devotees of serious music, an insignificant number of whom were technically competent to advance the, art. These inventions, among other things, stimulated an improvement in the quality of every component of sound reproducing systems by awakening a wide public interest which has increased steadily ever since, until today the manufacture and sale of sound reproducing systems constitutes a considerable industry.

As the quality of sound was improved by the minimization of mechanically and electronically introduced distortions, other and subtler forms ofdistortionbegan to be appreciated. In general it may be fairly stated that one of the major now unmasked forms of distortion is the lack of acousticalrealism caused by the relatively small effective. sound radiating area of the loudspeaker system..

The ear does not receive, and the mind cannot accept, the impression of av large dimensioned sound source such as an orchestra, but instead hears the orchestral sound as though constricted andpassed through an opening of small size compared to that'of the orchestra. This form of distortionhas come to be known as the hole-in-thewall effect.

Attempts to eliminate the hole-inthe-wall have taken either the form of very expensive loudspeaker enclosures of heroic dimensions with complicated internal bafiling systems, or two speaker enclosures spaced apart horizontally from four to eight feet. The former'merely enlarges the hole without eliminating it, while the latter although capable of broadening the apparent sound source only does so when the listener remains within a relatively small area located some distance away from the speakers and on a line approximately midway between them.

Movement laterally of the midline or too close approach to the speakers destroys the illusion by aurally separating I the system into two independent spaced loudspeakers,-one

- reflection and diffusion.

3,165,147 Patented Jan. 19, 1965 of which dominates the other, and having a hole or dead zone between. n

Thus, in' order to experience integrated broad area sound and avoid the hole in the middle, a listener may not move about at random in the room but must remain in a critically located area.

This problem of integrating the sounds from separate horizontally spaced loudspeakers to provide a broad area sound source became acute with the advent of stereophonic sound reproduction which employs at least two somewhat dissimilar separate sound channels. The ultimate objective of stereophonic sound reproduction is to provide not merely a broadened sound source but, most important, to achieve an aural perspective such that the various orchestral instruments appear to be physically locatable, as for example on the left, on the right, or in the center of the apparent sound source. It follows as a matter of necessity that the multiple channel recording techniques employed 'in stereophony require multiple channel playback equipment involving at least two physically independent loudspeaker systems, one for each channel in a typical two channel system. Thegreat failing of all presently known systems employed prior to the instant invention is their inability to produce a broad apparent sound source providing aural perspective which maintains constant sound integration throughout a wide angle in a horizontal plane. The loudspeaker system according to the present invention is not so limited. Accordingly, it is a primary object of this invention to provide-a novel spaced multiple loudspeaker system capable of producing a sound pattern which is completely integrated in both the horizontal and vertical planes so that the movement of a listenerfis not restricted to a relatively small critically located area.

Another object of this inventionis to provide a novel spaced multiplevloudspeaker system for producing wide range totally integrated sound appearing to emanate from a very broad sound source characterized by aural perspective. 3

Yet another object of this invention is to provide a novel spaced multiple loudspeaker system having the foregoing attributes which is relatively inexpensive to manufacture and which occupies a minimum of room space, being unobtrusive in appearance and easily concealed from view if so desired.

Still another object of this invention is to provide a novel spaced multiple loudspeaker system which While employing several discrete sound sources causes the sounds therefrom to be substantially integrated immediately adjacent to a room wall by utilizing acoustical principles of The foregoing and other objects of the inventionwill become apparent from a careful reading of the following specification in conjunction with an examination of the appended drawings, wherein:

FIGURE 1 illustrates in diagrammatic form a plan view of the system according to the invention, showing representationally the system components;

FIGURE 2 illustrates in front elevation the loudspeaker components of the system of FIGURE 1, also indicating thereon a range of positional variation possible with re spect to certain of the loudspeakers;

FIGURE 3 is an end elevational view of the system seen in front elevation in FIGURE 2;

FIGURE 4 is an end elevational view of an alternative system of loudspeaker placement;

FIGURE 5 illustrates in chematic form a very simple method of coupling the loudspeaker system to the output transformer of an electrical power amplifier;

FIGURE 6 illustrates a perspective view of the underside of the base and mid-rangeloudspeaker enclosure which normally occupies the of enclosures;

I FIGURE 7 is a longitudinal vertical section taken through the enclosure of FIGURE 6 as would be seen when viewed along the lines 77 thereof;

FIGURES 8 and 9 are cross-sectional views taken through the enclosure of FIGURE 6 as would be seen when viewed along the lines 8+8 and 9-9 respectively thereof;

central position in the array FIGURE 10 is a front perspective view of one of a" pair of identical loudspeaker enclosures which occupy flanking positions relative to the central elongated bass unit;

FIGURE 11 is a cross-scctional view taken through the enclosure of FIGURE'IO aswould be seen when viewed along the lines Ill-l1 thereof;

FIGURE l2 is'an enlarged fragmentary detail view of a flexiblehinge structure employed in the enclosure of FIGURE 10 and which is enclosed in the phantom circle of FIGURE 11. g

In the several figures like elements are denoted like reference characters.

inent of the invention shown in the drawings, it will be more conducive to a complete understanding to first consider the basic concepts which led tothe evolution of the invention. The overall problem divides itself essentially v into three subsidiary problems, which are:

(1) Broadening of the apparent-sound sourceto eliminate the hole-in-the-wall effect.

' g (2) Achieving aural perspective, and

' (3') Maintaining integration and'aural perspective of the broadened sound source 'througho ut a wide angle a in the horizontal plane. 7 The first'two problems have been previously solved,

after a fashion,'by the before described systems of utilizing at least two physically independent loudspeakers in a spaced apart configuration and need not be further here considered except insofar as they demonstrate that heretofore universal approach tothe total problem which is inherently incapable of yielding a solution. The difiiculty with these systemsappears to reside fundamentally 'in the horizontal sound distribution pattern exhibited by loudspeakers together with the fact that the spatial gap between the separated speaker systems is real and is desources having a controlled sound output frequency spectrum; and finally, the integration of the sound output of all three sources in a plane substantially coincident with a wall of the listening room, the integrated sound being reflected olf of the wall and out into the room;

Referring now to the figures for an understanding of Y the manner in which the above set forth underlying concepts of the invention are achieved, consider first FIG- Before referring to the particularlyillustrated embodiciple embodied in the invention is an important concept,

URES 1 through 4 which illustrate the system aspects as opposed .to the detailed constructional features which will be hereinafter described in connection with the showings of FIGURES 5 through l2.' Considering first FIG- URES 1 and 2, it will be observed that the loudspeaker system according tothe present invention basically corn-v prises three separate physicalunits, a central elongated enclosure 2%) and a pair of flanking enclosures 21, all

three enclosures beingphysically located slightly away from'the plane of a vertically extending wall 22..

As best observed in the showings of FIGURES 2, 3 and 4- the sound radiation from each of the individual loudspeaker enclosures is rearwardlydirected toward the wall 22 and is not, as in conventional loudspeaker systerns, radiated directly forwardly and outwardly into the room toward the listener. The sound radiation from each of the separate enclosures is merged into an integrated wave front closely adjacent to the wall 22 and distributed thereacross'throughout a wide area in both the vertical and horizontal directions, the resulting wave front then being reflected off of the wall 22 and outwardly into the room. While it is realized that the utilization v speaker systems, and indeed runs counter 'to theories expounded by many working in the field, nevertheless it has been found in actual practice under widely varying environmental room conditions that the results achieved by the loudspeaker system according to the present invention depend upon such a system of refiected'sound as one of the principal factors. w

One view adhered to by many is thatreflected sound when employed in a stereophonic system of music reproduction would destroy the aural perspective desired by blending the separate sound patterns into a homogeneous wave front. theory has proved to be completely inaccurate insofar as it relates to a loss of the stereophonic directional qual ity, such directional quality being positively apparent and even made more realistic by virtue of the fact that direc' tionality is associated with relatively large areas ofsound emanation rather than smalland localized sound sources.

As indicated by the radiation pattern arrows 23 associated with each of the enclosures,.it is observed thatthe soundoutput from all three of the enclosures'20and 21 merges along the'wall 22 over a broad central area while the sound pattern produced by each of the flanking speakers 21 laterally outwardly therefrom is predominantly composed of the sound radiation from each of wall 22. It is believed that this is the principal reason why aural perspective is not in actuality lost, the en hancement' of the aural perspective so achieved-being more realistic because there is effected a. graded inte gration of' the sound patterns from the individual en' closures which eliminates the highly objectionable line of demarcation between the, sound patterns of the several'enclosures. i

While the aforedescribed diffusion and reflection prin theme of suchprinciple will not of itself provide the desired end result. For example, merely turning Conventiona-l loudspeaker enclosures toface the wall of aroom, while possibly being somewhat better thandirect radiation, will not produce the desired wave front. It has been found to beef importance to substantially broaden the apparent sound source associated with each of the loudspeaker enclosures so that a proper overlap without discontinuities is achievable. The means by. which the central elongated enclosure 20 is enabled to smoothly and completely fill in the gap between the flanking enclosures 21, and also the means by which 'eachof thei flanking enclosures 21 is made to aurally appear to be many times its actual physical size will be described in detail in connection with the showings of FIGURES 6 through 11. At this point, however, it will be suflicie nt to indicate generally the meansby'which such broad- Each of the llanking enclosures hous es a. loud- Under actual test conditions this speaker 26 in a box 24 of minimum dimensions, just 'large enough to enclose the loudspeaker and a suitable amount of interior acoustical padding to properly absorb radiation from the rear of the speaker cone, the front of the cone facing outwardly toward a nonresonantly mounted reflecting plate 25 mounted at an angle of approximately 45 degrees to the axis of the loudspeaker cone. The reflecting plate or baflie 25 diffuses the energy radiated from the front of the loudspeaker cone upwardly and laterally outwardly in opposite directions so that a portion of the generated sound sweeps up the wall 22, inwardly along the wall22 toward the positions of the central enclosure 20 and opposite flanking enclosure 21, and outwardly along the wall 22 away from the central enclosure 20 and opposite flanking enclosure 21. Some of the radiated sound, of course, sweeps laterally outwardly and downwardly along the wall 22 due to diffraction around the side edges of the baffle plates 25 and thus there does not exist a dead zone at elevations vertically below the position of the flanking enclosures 21.

The elongated central enclosure 20 utilizes at least two individual loudspeakers 27 mounted therewithin so that they face downward toward the floor of the room upon which the enclosure 20 is seated. The downwardly facing loudspeakers 27 do not actually touch the underlying floor but are spaced somewhat thereabove so that their sound output is spread out along the room floor over the entire undersurface of the central enclosure 2t) which is of substantially the same size as the area seen when view ing the enclosure 20 from above. The spread out sound is then forced to travel rearwardly along the underlying surface and through a slot 47 which extends the entire length of the enclosure 20 along the lower edge of the rear or wall-facing enclosure panel, finally emerging out of the slot and travelling upward and laterally outward along the wall 22 and merging in the plane of the wall with the sound output from the flanking enclosures 21.

By constructing the central enclosure 20 to be between approximately four and six 'feet in length, it has been found that the flanking loudspeakers 21 may be laterally spaced apart symmetrically about the system center line 28 of FIGURE 2 at distances from five to twelve feet without noticeable change or disruption of the integrated wave front produced. Such lateral variable spacing is indicated on FIGURE 2 by the arrows 29 directed inwardly from the vertical center lines 39 of the flanking enclosures 21. Similarly, the uniformity of the integration is a vertical direction is so complete that the flanking enclosures 21 may be variably vertically positioned relative to the central enclosure 20 as indicated by the direction arrows 31 relative to the horizontal center line 32 joining the flanking enclosures 21. In practice the vertical positioning of the flanking enclosures 21 relative to the central enclosure 29 has been found to be completely non-critical within a vertical range of zero to six or seven feet above the ceintral enclosure. Consequently, all three enclosures may be set upon the floor in a concealed arrangement, as for example beneath and/or behind articles of furniture already in the listening room, or the central enclosure 20 may be so concealed beneath a sofa while the flanking enclosures 21 may be somewhat elevated and seated unobtrusively upon bookcases or tables.

FIGURE 3 illustrates one possible concealed arrangement of the various enclosures, the central enclosure 28 being located on the floor 33 and concealed from view beneath and behind a cabinet 34, shown in phantom, while the flanking enclosures 21 may be concealed within the back of the cabinet 34. FIGURE 4 illustrates quite a different configuration of the various enclosures, the flanking speakers 21 being shelf or bracket mounted as by means of the bracket 35 secured to the wall 22, while the central encluousre 20 is placed on the floor adjacent the wall 22' oppositely across the room from the wall 22.

. While this across-the-room placement of the central en closure 20 might appear to disrupt the fill-in function associated therewith in the showings of FIGURES l and 2, such disruption may or may not occur and will be determined by the sound output frequency spectrum associated with each of the several enclosures and the configuration of the room in which the system is set up. In general, optimum results may be expected with the orientations illustrated in FIGURES l, 2 and 3.

Under such conditions it has been found that integration in a horizontal plane may be accomplished throughout the extremely wide angular range of at least as indicated in the showing of FIGURE 1. For all practical purposes this constitutes integration completely throughout any given listening area and results in complete freedom of movement for a listener within a room. One unpredicted psycho-acoustical result achieved by the loudspeaker system according to the present invention is that wherein the apparent sound source seems to be physically located at a distance beyond the wall 22 on the side opposite that facing into the listening area. Whatever the cause of this acoustical phenomenon, the result insofar as the listener is concerned is that the received sound emanates from a broad source somewhat removed from the listeners position, as for example when listening to a live orchestra.

Before turning to the constructional aspects of FIG- URES 6 through 12 a final detail of the system will be described in connection with the showings of FIGURES 1 and 5. In FIGURE 1, it will he observed that a source of electrical signals 36 is coupled by means of the

cables

37 and 38 to a pair of

electrical power amplifiers

39 and 40. The output from the amplifier 39, designated as channel 1, is delivered to the loudspeaker 26 in the lefthand flanking enclosure 21 by a cable 41 and is also delivered to the left-hand one of the speakers 27 in the central enclosure 20 by means of a cable 42. Similarly, the electrical output from the amplifier 40, designated as channel 2, is delivered to the remaining

loudspeakers

26 and 27 over the

cables

43 and 44.

As illustrated in the showings of FIGURE 5, the entire frequency spectrum output of the amplifier 39 is routed to the loudspeaker 27 of the central enclosure 20 through the cable 42, whereas the frequency spectrum output from the amplifier 39 which is directed to the loudspeaker 26 of the flanking enclosure 21 is restricted in accordance with the impedance relationship between the loudspeaker 26 voice coil impedance and the impedance of the capacitor 45 connected in series therewith. Since the reactance of the capacitor 45 increases with decreasing frequency, the capacitor acts as a high pass filter element and effectively restricts the driving frequency range for the loudspeaker 26 to the spectrum extending upward from a preselected frequency. In practice, it has been found that chosing the capacitor 45 to restrict the frequency input to the loudspeakers 26 to those frequencies above approximately 200 to 250 cycles results in no deleterious effects whatever in the resultant radiation pattern while at the same time permitting the enclosure 21 for the loudspeakers 26 to be reduced in physical size to the point where they need be merely s-uflioiently large to house the loudspeakers, in accordance with well-known acoustical principles.

The two channel arrangements illustrated in FIGURE 1 is shown to properly reproduce stereophonic program material, the amplifier 39 and

loudspeakers

26 and 27 driven therefrom comprising one of the stereophonic channels and the amplifier 40 and

loudspeakers

26 and 27 driven therefrom constituting the second stereophonic channel. In the event that monaural sound reproduction is desired then the electrical signals from the source 36 is routed to the

amplifiers

39 and 40 via the

cables

37 and 38 may be identical, or alternatively, both of the loudspeakers 27 of the central enclousre 20 may be driven in parallel from cable 42 of amplifier 39 and both of the loudspeakers 26 may be driven in parallel from the cable 4'1 of the amplifier 39, the amplifier 40 being rendered stricted to the bass and mid range frequencies by acoustical filtering. For this purpose several acoustical filters are employed, one of such filters being merely the underlying rug or carpeting 46 upon which the central enclosure is seated and which acts as a high frequency acoustical absorber, a second filter being the restricted volume of the chamber 48 into which the loudspeakers 27 face, and the remaining filter comprising a slot arrangement 49 formed by the rear vertical panel of the central enclosure 20 and the wall of the room 22 from which it is slightly spaced, together with the horizontally extending slot previously described in connection with the means for broadening the apparent sound source associated with the central enclosure.

By moving the central enclosure closer toward and farther from the wall 22 the frequency spectrum in the audible mid range can be controlled to provide more or less mid frequencies, such adjustment, of course, being limited to the range of spacing within which the slot effect is obtained. Spacing the enclosure 20 away from the wall 22 beyond a certain point effectively eliminates this vertical slot effect with a consequent increase in the spectrum and amplitude in the mid range frequencies propagating from the central enclosure. It has been found that the widely varying environmental room acoustical conditions encountered in practice sometimes call for the elimination of this slot effect to provide an augmented mid range but in most cases the preferred treatment is to employ the slot effect to some degree or other. Typically, the spacing of the central enclosure 20 from its associated wall 22 will lie within the range of one and one-half to two inches, this spacing being quite effective when employed with a central enclosure constructed in accordance with the showing of FIGURES 6 through 9 and dimensioned in accordance with the illustrative examples hereinafter set forth.

Understanding now the general principles of the invention and the manner of employing these principles to carry out the objects as previously set forth, attention should "be now directed to the construction details illustrated in the showings of FIGURES 6 through 12. Considering by lock jointing to form a rigid unitary assembly having little tendency to vibrate.

The end panels 50 and front panel 51 extend vertically downward for the same distance from the top panel 52 whereas the rear panel 53 is of shorter vertical extent, terminating a predetermined distance above the lower edges of the front and end panels. It is this shortened construction of the panel 53 which provides the rear slot formation out of which the sound from the enclosure mounted speakers must issue since it should now be clear that the lower edges of the front and

side panels

51 and 50 provide a peripheral seal with the underlying carpet on three sides of the enclosure.

The bottom panel 54 is removably securable to the four walls of the body of the enclosure as by means of screws (not shown) extending through the bottom panel 54 into the furring strips 55 permanently secured to the inside surfaces of the front, rear and end panels and extending I completely about the inside periphery of the enclosure.

As best seen in FIGURE 6, the bottom panel 54 is circularly apertured as at 56 to mount the loudspeakers 27, indicated in dotted outline in FIGURE 1, with the front of the loudspeaker cones facing downward toward the floor. Also cut through the bottom panel at opposite ends thereof are a pair of reflexing ports 57. Centrally rigidly secured to the inside face of the bottom panel and extending completely across the internal width of the enclosure from front to rear is a partition panel 58 which divides the enclosure into two identical compartments 20a and 20b symmetrically oriented relative to the partition.

The enclosure 20 is thus seen to include three separate chambers, two of which are the symmetrical compartments 20a and 20:) just mentioned and the third of which is the chamber 48 between the bottom panel 54 and the floor of the room upon which the enclosure is seated. This third chamber 48, which is also one of the acoustical filters as previously described, provides acoustical loading for and mutual acoustical coupling between the loudspeakers associated with each of the symmetrical chambers and distributes the sound output therefrom for radiation out of the rear slot. The symmetrical compartments are, moreover, themselves directly intercoupled in the bass frequency range in a manner to be described to provide additional acoustical loading in the frequency range where the loudspeaker radiation resistance would otherwise fall off quite rapidly. Within each of the symmetrical compartments the front panel 51, rear panel 53, end panels 50 and top panel 52 are lined with suitable acoustical absorbent material 59.

Completely filling the volume of each of the symmetrical compartments between the inside face of each of the end panels 50 and the proximate edge of the associated loudspeaker mounting aperture 56 is an acoustically porous barrier 60 of layers of resin impregnated long staple fiber glasswool oriented so that the back radiation from the cone of the loudspeaker to be mounted in the associated compartment must travel endwise between the barrier fibers in order to reach the reflexing port 57. The resin impregnated glasswool is employed because it is mechanically stable and has a minimum tendency to deform when subjected to the large pressure variations produced by the loudspeaker cone. The mechanical stability of the acoustical barrier is quite important in order that the acoustical impedance presented thereby to the loudspeaker does not appreciably vary as a function of sound pressure. It has been found that the acoustical barrier 60 not only lntroduces a substantially resistive acoustical loading impedance for the loudspeaker which smooths out the response and extends it smoothly below the forty cycle range, but also permits a substantial reduction in the internal volume of the symmetrical chambers by comparison with the volume that would be required in a conventionally lined type of loudspeaker enclosure. The acoustical barriers 60, of course, absorb the high frequency and mid-range energy radiated from the back of the loudspeaker, thus decoupling the port 57 from the loudspeaker except in the low bass range and in particular in the vicinity of the loudspeaker cone resonance.

The structure of the central enclosure is completed by the acoustically porous barrier 61, best seen in the showings of FIGURES 7 and 9, which intercouples the symmetrical chambers with one another immediately above the partition panel 58. The acoustical barrier 61 is constructed of the same type of acoustical absorbent mate rial whose characteristics have been previously described in connection with the acoustical barriers 60. As in the case of the acoustical barriers 60, the barrier 61 absorbs the high frequency and mid-range energy radiated from the rear of the loudspeaker cones and hence effectively isolates the symmetrical compartments from one another in these frequency ranges. However, in the bass frequency range the degree of energy absorption decreases with decreasing frequency so that the back wave radiation from each of the loudspeakers increasingly loads the other. This progressively increased loading offsets to a substan tial degree the decrease in radiation resistance which naturally occurs with decreasing frequency and augments the URES 6 through 9 when constructed for use with a pair of good ten inch loudspeakers might be as follows: The length, width and total depth may be four feet, fourteen inches and eight inches respectively; the spacing of the .undersurfaceof the bottom panel 54 above the lower edge of the front and end panels may be one and one-half V to one and three-quarter inches; the area of the reflexing ports 57 may be approximately twenty-four square inches shown dimensioned in a rectangle having three inch and eight inch sides, the side of the port closest to the end panel 50 being spaced therefrom a distance between zero and three-inches; the length of the acoustical barrier 60 may be approximately eleven inches; and the length of the acoustical barrier 61 may be approximately five inches and two inches in height.

In general, the following principles and relationships may be used as guides if it is desired to construct an enclosure of dimensions other than those previously given. Firstly, the enclosure should be between approximately four and six feet in length although these limits are not I to be taken as critical. The enclosure width and height 2 need only be sufficiently large to accommodate the loudspeakers to be mounted within the enclosure, and optimally the loudspeakers chosen foruse in the enclosure should have a free air cone resonancepreferably belowforty cycles. The area of the reflexing ports '57 should be equal and ofapproximately the same area as the portv ,intercoupling the compartments above the partitioned panel 58- w'ithin which the acoustical barrier 61 is disposed, these ports being each chosen to; have an area approximately one-half-to two-thirds that-of each of the and 12 which illustrate the constructional details of each of the fianking'loudspeaker enclosures 21, it is observed that each of such enclosures has a top panel 62, a bottom panel 63, a pair of opposite side panels 64, a rear panel 65 and an apertured front panel 66. All of the foregoing mentioned panels excepting the front panel 66 are rigidly secured together in a suitable fashion and the interior of the enclosure is completely lined with acoustical absorbent material 67. The apertured front panel 66 is removable so that the loudspeaker to be housed may be secured to the rear of thepanel for installation therewithin. For purposes of rigidly securing the front panel 66 to the walls of the enclosure 21 a framing of'furring strips 68 is employed. i e

As previously described, the baffle plate is secured to the enclosure 21 by a non-resonant support system which includesa top edge supporting fabric strap 69, as for example made of nylon, secured at one end to the loudspeaker enclosure and at the other end to the top plate 25, and as best seen in the fragmentary view of FIGURE 12 includes a fabric strap 71 secured at one endto the enclosure 21 and at its other end was lower edge of the baflie plate 25 by means of the metal clip 72.

The bafiie plate 25 should be suificientlyrigid so "that it is not vibrationally excited by the sound pressure directed upon it from the loudspeaker, and for this purpose plate glass has been found to be very satisfactory.

Having now described my invention both systemwise and in connection with particularly illustrated embodiments of loudspeaker enclosures evolved in accordance with the general principles hereinbefore set forth, it is to be understood that various changes and modifications may now naturally occur to those persons normally skilled in the art without departing from the essential spirit or scope of my invention, as for example by employing a plurality of loudspeakers within each of the symmetrical compartments of the central enclosure illustrated in the figures, by rendering the central enclosure independent of the floor by providing a bottom panel, by inverting the system to conceal the enclosures above theceiling level of a room, and other now obvious variations. Ac-

cordingly, it is my intention to claim the invention-both broadly and specifically as indicated by the appended claims. I

What is claimed as new and useful is:

l.' A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, each of said sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward a common acoustical reflecting surface located closely adjacent to all of said soundsources, the acoustical sound waves from each source diffusing radially outward therefrom along the reflecting surface and merging in an overlapping pattern with the sound waves from each of the other sources in the plane of the reflecting surface to form an integrated wavefront, which wavefront is reflected outward into the listening area, wherein each of said flanking sound sources comprises a loudspeaker positioned to face said common reflecting surface and housed in an enclosure having a reflecting baffle plate secured thereto, said-baffle being disposed in front of the cone of said loudspeaker at an angle tothe cone axis, whereby the sound Waves produced by said loudspeakerare directed toward and refiected outward from said baffle along said common reflecting surface. i

2. A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources. spaced laterally on opposite sides of' said central sound'source, each of said sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward acommon acoustical reflecting surface located closely adjacent to all of said sources, the acoustical sound waves from each source diffusing radially outward therefrom 'along the reflecting surface parallel to and lying adjacent said reflecting surface,

whereby sound waves propagated from said loudspeakers into said chamber emerge thereout of through said slot and diffuse across said reflecting surface.

3. A' multiple sound source loudspeaker system adapted for the reproduction of two channel stereophonic sound,

comprising a central sound source and a pair of flanking send sources spaced laterally on opposite sides ofsaid central 'sound'source, each of said sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward a common acoustical reflecting surface located closely adjacentto all of said sound sources, the acoustical sound waves from i ll each source diffusing radially outward therefrom along the reflecting surface and merging in an overlapping pattern with the sound waves from each of the other sources in the plane of the reflecting surface to form an inte grated wavefront, which wavefront is reflected outward into the listening area, said central sound source comprising at least twosound wave generators, means elec trically coupling together one of said at least two sound wave generators and the said flanking sound source closest thereto to form a first independent source of sound waves forionc stereophonic channel, and means electrically coupling together the other of said at least two sound wave generators and the remaining flanking sound sourcewhich is closest thereto to form a second independent source of sound waves for the second stereophonic channel, each of said first and second independent sources of sound waves being electrically non-coupled to the other, wherein said central sound source comprises an elongated enclosure disposed with one of its long dimensioned sides parallelto and spaced slightly away from the said reflecting surface, said at least two sound Wave generators being housed within said enclosure so that they face into a chamher having a slotted opening along one side thereof, said chamber slotted opening extending parallel to and lying adjacet to said reflcctig surface, whereby sound waves, propagated'from said sound wave generators into said chamber emerge thereout of through said slot'and diffuse across said reflecting surface.

4. The, loudspeaker system according to claim 3 wherein said at least two sound generators are housed within said elongated enclosure in separate compartments, and means disposed between said compartments for acoustically substantially decoupling said compartments from one 12. each of said symmetrical compartments so that the cones of loudspeakers mounted therein face into the third compartment through the partition apertures, and an elongated slotted opening along said one side of the said third compartment through which all of the sound waves generated by loudspeakers. mounted in said symmetrical compartments must pass to escape said enclosure.

9.' The loudspeaker enclosure according to claim 8 wherein said first means comprises an interconnecting port between said pair of symmetrical compartments which substantially decouples said symmetrical compartments above a preselected frequency and progressively increasingly intercouples said symmetrical compartments with decreasing 7 frequency below said preselected frequency, and wherein said second means comprises port means which intercoupleeach of said symmetrical compartments with said third compartment within a limited frequency band in the bass frequency range. l

10. A multiple sound source loudspeakersystemcomprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, each of said sound sources positioned to direct the sound wave output therefrom awayfromthe listening area directly toward a common acoustical re-- recting surface located closely adjacent to all of said sources, each of said flanking sound sources including a support means and a loudspeaker connectedthereon, the

faces of said loudspeakers being coplanar and positioned so that the speaker cone axesare perpendicular to said. re-

flecting surface and each of said flanking sound sources in-* eluding a reflector means connected on said support means,

another above a preselected frequency and progressively 1 increasingly directly intercoupling said compartments with decreasing frequency below said preselected freq yr I r 5. The loudspeaker system according to claim 3 wherein said at least two sound wave generators are housed Within said elongated enclosure inseparate compartmentsfsaid compartments being each acoustically coupled to said chamber within a limited frequency band in the bass frequency range by means of a port.

6. The loudspeaker system according to claim 3 wherein said chamber slotted opening extends substantially the full length of said elongated enclosure along the enclosure side which is parallel to and spaced slightly away from the said reflecting surface.

7. A multiple sound. source loudspeaker system comprising a centralsound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, each of saidf sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward a common acoustical reflecting surface located closely adjacent to all of said sound sources, each of said flanking sound' sources having a loudspeaker positioned to face said reflecting surface and a reflector meansincluding a surface disposed in front of the cone of said loudspeaker for sweeping sound waves produced by said loudspeaker vertically up and laterally outward along said reflecting surface, the acoustical sound waves from all of said sound sources merging to form an integrated wavefront in the plane of the commonacousti:

'cal reflecting surface, which wavefront is reflected outward from said reflecting surface into the listening areaiin both the vertical and horizontal'planes.

' acoustically intercoupling each of said symmetrical com- I partments with the third compartment, said apertured pan I titiondefining means for mounting a loudspeaker withinflected outward from said reflecting surface into the listen-i 40' said reflector means having a surface disposed at an angle to the cone axis of said loudspeaker for sweeping soundwaves produced by said loudspeaker vertically" up and laterally outward along said reflecting surface, the acoustical sound waves'from all of said sound sources merging to form an integrated wavefront in the plane of the common acoustical reflecting surface, which wavefront is reing area in both the vertical and h orizontal planesJ I 11. Aimultiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, each of said sound sources positioned to direct the sound wave output therefrom away from the 1 listening areadirectly toward a common acoustical reflecting surface located closelyadjacent to all of said sound sources, each of said flanking sound sources includmg support means and a loudspeaker connected thereon to face saidireflecting surface and each of said flanking sound sources including a reflector means connected on said support means, said reflector-means having a surface disposed with respect to the cone axis of theloudspeaker for sweeping sound waves produced by'saidloudspeaker vertically up and laterally outward along said reflecting surface, said central soundsource comprising at least two sound wave generators each of which includes means for coupling the same to different sources of electrical signals,

one of said at least two sound wave generators and one of said flanking sound sources together comprising the source of sound waves for one stereophonic channel, and

the other of said at least two sound wave generators and j the remaining flanking sound source together comprising the source of sound waves for the second 'stereophonic channel, the acoustical sound waves from each sound source merging to form an integrated wavefront in the plane of a common acoustical reflecting surface, which wavefront is reflected outward from said common reflecting surface into the listening area in both the vertical and horizontal planes. Y 12. A multiple sound source loudspeakersystem com-1 prising a central sound source anda pair of flanking sound sources spaced laterally on opposite sides of said central sound source, a commonacoustical' reflecting surface lo cated closely adjacent to all of said sound sources, each loudspeaker vertically upand laterally outward along said reflecting surface, the acoustical sound waves from all of said sound sourcesmerging to form an integrated wavefront in the plane of the common acoustical reflecting surface, which wavefront is reflected outward from said reflecting surface into the listening tical and horizontal planes.

13. A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on, opposite sides of said central sound source, a common acoustical reflecting surface located closely adjacent to all of said sound sources, each of said sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward the common acoustical reflecting surface, each of;

said flanking sound sources including support means and a-loudspeaker connected thereon, the faces of said loudspeakers being coplanar and positioned so that the speaker cone axes are perpendicular to said reflecting surface and each of said flanking sound sources including a reflector means connected on said support means, said reflector means having a surface disposedatan angle-tothe cone axis ofsaid loudspeaker for sweeping sound waves producedby said'loudspeaker vertically up and laterally outward along said reflecting surface, the acoustical sound waves from all of said sound sources merging to form an integrated wavefront in the plane of the common acoustical reflecting surface,twhich wavefront is reflected outward from said refleciing surface into the listening area in both the vertical and horizontal planes. 1

. 14. A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, a common acoustical reflecting surface located closely adjacent to all of said sound sources, each of said sound sources positioned to direct the sound wave output therefrom away from the listening area directly toward the common acoustical reflecting surface, each of said flanking sound sources including support means and a loudspeaker connected thereon to face said reflecting surface and each of said flanking sound sources including a reflector means connected on said support means, said reflector means having a surface disposed with respect to the cone axis of the loudspeaker for sweeping sound waves produced by said loudspeaker vertically and laterally outward along said reflecting surface, said central sound source comprising at least two sound wave generators each of which includes means for coupling the same to different sources of electrical signals, one of said at least two sound wave generators and one of said flanking sound sources together comprising the source of sound waves 1 for one stereophonic channel, and the other of said at least two sound wave generators and the remaining flanking sound source together comprising the source of sound waves for the second stereophonic channel, the acoustical sound waves from each sound source merging to form an integrated wavefront in the plane of the common acoustical reflecting surface, which wavefront is reflected outward from said common reflecting surface into the listening area in both the vertical and horizontal planes.

15. A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, a common acoustical reflecting surface located closely adjacent to all of said sound sources, each of said sound sources positioned to direct area in both the verthe total sound wave output therefrom away from the listening area directly toward the common acoustical reflecting surface, the acoustical sound waves from each source diffusing radially outward therefrom along the reflecting surface and merging in an overlapping pattern with the sound waves from each of the other sources in the plane of the reflecting surface to form an integrated wavefront, which wavefront is reflected outward into the listening area.

16. The loudspeaker system according to claim 15 wherein each of said flanking sound sources comprises a loudspeaker positioned to face said common reflecting surface and housed in an enclosure having a reflecting baffle plate secured thereto, said baflie being disposed in front of the cone of said loudspeaker at an angle to the cone axis, whereby the sound waves produced by said loudspeaker are directed toward and reflected outward from said baffle along said common reflecting surface.

17. The loudspeaker system according to claim 15 wherein the frequency spectrum reproduction range of the flanking sound sources is substantially the same and is attenuated below a preselected frequency, the central sound source reproducing the range'of frequencies below said preselected frequency and additionally reproducing a limited range of frequencies above said preselected frequency, which limited-range of frequencies is of nar rower band width than the rangeof frequencies reproduced by said flanking sound sources.

18. The loudspeaker system according to claim l5 wherein said central sound source comprises an elongated enclosure disposed with one of its long dimensioned sides parallel to and spaced slightly away from the said reflecting surface, said enclosure housing a pair of loudspeakers facing into a chamber having a slotted opening along one side thereof, said chamber slotted opening extending parallel to and lying adjacent said reflecting surface, whereby sound waves propagated from said loudspeakers into said chamber emerge thereout of through said slot and diffuse across said reflecting surface.

the reproduction of two channel stereophonic sound, comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, a common acoustical reflecting surface located closely adjacent to all of said sound sources, each of said sound sources positioned to direct the total sound wave output therefrom away from the listening area directly toward the common acoustical reflecting surface, the acoustical sound waves from each source diffusing radially outward therefrom along the reflecting surface and merging in an overlapping pattern with the sound waves from each of the other sources in the plane of the reflecting surface to form an integrated Wavefront, which wavefront is reflected outward into the listening area, said central sound source com prising at least two sound wave generators, means electrically coupling together one of said at least two sound wave generators and the said flanking sound source closest thereto to form a first independent source of sound waves for one stereophonic channel, and means electrically coupling together the other of said at least two sound wave generators and the remaining flanking sound source which is closest thereto to form a second independent source of sound waves for the second stereophonic channel, each of said first and second independent sources of sound waves being electrically noncoupled to the other.

20.'The loudspeaker system according to claim 19 vwherein the frequency spectrum reproduction range of 19. A multiple sound loudspeaker system adapted for a limited range of frequencies above said preselected frequency,which' limited range of frequencies is of narrower to and lying adjacent to said reflecting surface, whereby sound waves propagated from said sound wave generators into said chamber emerge thereout of through said slot and diffuse across said reflecting surface; I

22. The loudspeaker system according to claim 21 wherein said at least two sound generators are housed within said elongated enclosure in separate compartments, and means disposed between said compartments for acoustically substantially decoupling said compartments from one another above a preselected frequency and progressively increasingly directly intercoupling said ,compartments with decreasing frequency below said preselected frequency.

23. The loudspeakersystern according to claim 21 wherein said at least two sound wave generators are housed within said elongated enclosure in separate cornpartments, said compartments being each acoustically coupled to said chamber within a limited frequency band in. the bassfrequency range by meansof a port.

24. The loudspeaker system according toclaim 21 wherein said chamber slotted openingextends substantiallythe full lengthof said elongated enclosure along the enclosure side which is parallel to and spaced slight- '35 ly away from the saidrefiecting surface.

25. A multiple sound source loudspeaker system comprising a central sound source and a pair of flanking sound sources spaced laterally on opposite sides of said central sound source, a common acoustical reflecting surface located closely adjacent to all of said. sound sources, said flanking sound-sourcesbeing vertically displaced equal distances above said central sound source and having a frequency spectrum reproduction range. in the .audio mid-frequency and high-frequency range,

each of said sound sources positioned to direct the total sound wave output therefrom away from the listeningarea and directly toward the common acoustical reflecting surface, the acoustical sound waves from each source diffusing radially outward therefrom along the reflecting surface and merging in an overlapping pattern with the sound waves from each of the other sources in the plane of the reflecting surface to form an integrated wavefront, which wavefront is reflected outward into the listening area. I r r I References Cited by the Examiner UNITED STATES PATENTS r 2,520,798

8/50 De Boer 2,610,694 9/52 .De Boer 181-}31 2,694,462 11/54 Robbins et a1 18131 2,896,736 7/59 Karlson' 181-[31 2,904,123 9/59 Nigro 181-31" 2,921,135 1/60 Hoodwin. 3,016,424 1/62 Fran'ke 179-1 3,090,462 5/63 Huff et al. 181-31 OTHER REFERENCES Publication: Radio and TV News, December 1958,

page 34. LEO SMILOW, Primary Examiner.

Claims

1. A MULTIPLE SOUND SOURCE LOUDSPEAKER SYSTEM COMPRISING A CENTRAL SOUND SOURCE AND A PAIR OF FLANKING SOUND SOURCES SPACED LATERALLY ON OPPOSITE SIDES OF SAID VENTRAL SOUND SOURCE, EACH OF SAID SOUND SOURCES POSITIONED TO DIRECT THE SOUND WAVE OUTPUT THEREFROM AWAY FROM THE LISTENING AREA DIRECTLY TOWARD A COMMON ACOUSTICAL REFLECTING SURFACE LOCATED CLOSELY ADJACENT TO ALL OF SAID SOUND SOURCES, THE ACOUSTICAL SOUND WAVES FROM EACH SOURCE DIFFUSING RADIALLY OUTWARD THEREFROM ALONG THE REFLECTING SURFACE AND MERGING IN AN OVERLAPPING PATTERN WITH THE SOUND WAVES FROM EACH OF THE OTHER SOURCES IN THE PLANE OF THE REFLECTING SURFACE TO FORM AN INTEGRATED WAVEFRONT, WHICH WAVEFRONT IS REFLECTED OUTWARD INTO THE LISTENING AREA, WHEREIN EACH OF SAID FLANKING SOUND SOURCES COMPRISES A LOUDSPEAKER POSITIONED TO FACE SAID COMMON REFLECTING SURFACE AND HOUSED IN AN ENCLOSURE HAVING A REFLECTING BAFFLE PLATE SECURED THERETO, SAID BAFFLE BEING DISPOSED IN FRONT OF THE CONE OF SAID LOUDSPEAKER AT AN ANGLE TO THE CONE AXIS, WHEREBY THE SOUND WAVE PRODUCED BY SAID LOUDSPEAKER ARE DIRECTED TOWARD AND REFLECTED OUTWARD FROM SAID BAFFLE ALONG SAID COMMON REFLECTING SURFACE.