US2994399A - Loud speaker system - Google Patents

Description

Aug. 1, 1961 s. P. ZEMMERMAN ETAL 2,994,399

LOUD SPEAKER SYSTEM Filed July 1'7, 1958 INVENTORS Samuel E Zimmerman BY Will/am 6. Madison ATTORNEY United States Patent 2,994,399 LOUD SPEAKER SYSTEM Samuel .P. Zimmerman, Boston, Mass. (1 Merrill Ava,

--.Belmont 78, Mass.); and William G. -Madison, 115 Bancroft .Ave.,.Reading, Mass.

' Filed July17, 1958, Ser.'No. 749,296

7 "Claims. '(Cl. 181-31) Thisinvention relates to a loud speaker system com- :bining'the direct-radiation of high and middle frequencies from -a driver with corner horn back loading of the driver for--low.lfrequenc:ies. The invention relates particularly 'to a loudspeaker structure adapted to be positioned-in'the corner of a room to utilize portions of the room walls to define surfaces of the acoustic system and-to specifically define portions of'an exponential horn. In 'brief, the invention comprises a cabinet structure having-'aclosed resonant cavity and'a driver or speaker :mounted over an opening-in a-substantially fiat wall thereof. The side walls of the cavity are so configured and constructed that theycurve outwardly from the edges -0f1the flat wall, then rearwardly and converge toward resonant cavity through a narrow slot in the rear of the -cavit-ytothe corner of the room.

his, therefore, an=object of this invention to provide a loud speaker structure providing improved low frequency response with any type of driving unit.

Another object of the invention is to provide a speaker strueture 'exhibiting improved low frequency response and which occupies a minimum of space.

Still 'another'object of the invention is to provide a corner horn cabinet utilizing the adjacent fiat walls of a room to definesections of a horn and which horn is a truly'exponential horn.

A-further object of the invention is to provide a speaker system as set forth which is simple in design and economical to construct.

Additional and-further objects of the invention will be apparent to those skilled in the art as the description proceedsinconnection'with the accompanying drawings, wherein:

:FIG. 1'is apersprective view of one embodiment of the inventionplacedinthe corner of a room;

FIG. 2 is afront .elevational view of the structure shown in'FIG. 1;

FIG. 3 is a'hon'zontal transverse sectional view taken along the line 33 of FIG. 2; and

'FIG. 4 is a sectional view similar to FIG. 3, but showinga modified form of the invention.

According to the present invention the loud speaker cabinet structure comprises a top panel or wall 2 and a bottom panel orwall 4, each being of generally square outline buttwith their forward corners cut off as at 6 to define a diagonal forward edge. An upstanding, substantially flat frontwall 8 extends between the top and bottom walls and constitutes a support for a suitable driver or loud speaker 10 of conventional construction. The loud speaker 10 is mounted at the rear of wall 8 in a conventional .manner, overlying an opening 12 in the front wall 8.

Referringnowto FIG. 3, the cabinet of the present invention'includes side walls '14 and 16 of curved configuration. The walls 14 and 16'are convex outwardly and extend from the side edges of the front wall '8 rearwardly and inwardly toward the corner 18 of the room. The rearmost edges 20 of the side walls 14 and 16 terminate short of the corner 1810 define a slot 22 therebetween.

ner, such as by gluing, screws, or both.

Patented Aug. 1, 1961 The edges 20 are furthermore spaced from the walls of the room as clearly shown in FIG. 3.

The walls 14 and 16 are preferably made of a rela tively thin but hard and quite stiif material, for example, a material formed by pressing-ground wood into sheet form and bonding the particles with a suitable cementing material. Such sheet material is readily available under the trade name of Masonite and has proven eminently satisfactory for the present invention. As shown, a plurality of struts 24 extend from the bottom wall 4 to the top wall 2 and are suitably secured to each in the arrangement shown. The panels 16 are readily bent to conform to the curvature defined by the struts 24 and are fixedly secured thereto in any suitable man- In'the form shown in FIG..3, the side panels 14 and 16 extend'forwardly 'past thefront wall 8 to define a'forward cavity 26. .-At least one of the walls 2 or 4, preferably the former, is'provided with edges adapted to abut snugly againstthe walls ofthe room to position the cabinetin thedesire'd relationship to the corner 18.

.The cavity defined by the front wall 8, side walls 14 and 16, and topand bottom walls 2 and 4, constitutes a resonant cavity having an impedance or reflex opening.(slot 22) at the ;rear'thereof. Such resonant cavities are well known in theart and function as tuned circuits whereby only low frequency sounds exhaust from the. opening or slot 22. .As is clearly evident from FIG. 3,, the-sounds exhausting'from the slot 22 are fed directly to the space between the rear edges of the side walls .14 and '16 and the adjacent walls of the room. The spaces between the rear ,edges of the sidepanels and the walls of the room constitute the throats ,of the horn sections, which flareforwardly and occupy the spaces between the side panels and the room walls and between the upper and lower walls 2 and 4 of the cabinet. The mouth of each horn sectionis at the forwardedge of the upper andlower walls and extends from the ends of the edges 6 over to the side walls of the room.

Applicants havefound that increased eiiiciency'of such a system is :attainable by formation of the said walls Hand 16 in the curved manner shown. Specifically, the Walls .14 'and .16 follow an .exponential or logarithmic curve whereby to increase the intensity of sound energy radiated from the .mouth of the horn. The-curvature of thewalls -14 and 16 follows the formula:

A=A (cosh x-l-T sinh x).

In the above formula, A is the transverse sectional area of.a-,horn section measured in a plane perpendicular to the wallof the room. A is the cross sectional area of the throat of .the horn, .i.e., the space between the rear edge of .20 of aside panel and the adjacent wall of'the room. x is a function of the distance from the corner .18..along the room wall to the plane in which the area is being .calculated. T is a parametric constant that determines the shape of the cavity and the degree .of curvature of the wall panels14 and 16. The quantity x is the distance .from the corner 18 to the portionof the horn :under consideration, measured in linear units, and multiplied .by-a factor dependent upon the resonant frequency ,of the resonant cavity defined by .the curved walls of the cabinet and the panels 2 and 4.

Another feature of the invention resides in the .fact that the area of the throat of each section of the exponential horn is equal to one-half the area of the slot 22 previously described. Thus, both portions of the exponential horn function as a single horn structure having a throat area exactlyequalto the area of the impedance slot 22, which results .in direct acoustic coupling of the resonant cavity to .thehorn. In the above formula, A is always equal toone-halfthearea ofthe slot 22. his

from the corner10.45 in.

provides excellent low frequency response. structure the inside height of the resonant cavity 34 would be 14 in.; the square bottom wall 32, 20 in. on each side; and the maximum width of the resonant cavity 34, 18 /2 evident that the above formula will define an exponential curve since the hyperbolic functions can be replaced by their exponential equivalents, thus:

and the equation becomes:

((F;l)e+(12T)e) where e is usually taken as the basic of the Naperian cosh x i logarithms in the frequency range of from 20 c.p.s. to 550 c.p.s.

A cabinet constructed in accordance with FIGS. 1 through 3, wherein the parametric constant T is assigned a value of .6 and wherein the driver unit 18 is a 12-in.

speaker, will have the following dimensions: The width of the cavity of the front wall 8approximately 19 in.; the height of the cabinet between top wall 2 and bottom Wall 424 A in.; the width of slot 22 /2 in.; the

space between the rear edges of the panels 14 and 16 and the adjacent Walls of the room-% in. each; the width of each horn section at plane A (see FIG. 3), in. from corner 181.25 in.; at plane B in. from corner 18-255 in.; the width at plane C 20 in. from the corner5.75 in.; and the width at plane D 24 in. In a cabinet thus constructed, the side panels 14 and 16 extend approximately 3% 'in. forwardly from the front wall 8. Such a cabinet proves to have excellent frequency response in the frequency range of 20 c.p.s. to 550 c.p.s.

While the drawings show a cabinet with the front thereof completely open, it is contemplated that such 'cabinets may be constructed with suitable decorative framing around the forward portions thereof and with the mouths of the horn sections and the front of the cavity '26 covered by suitable decorative acoustic cloth.

FIG. 4 is a horizontal sectional view through a cabinet structure constructed in accordance with the present in- .vention, but wherein the parametric constant T of the equation set forth above is assigned a value of unity (1).

In this form of the invention, the side panels 26 and 28 do not extend forwardly of the front wall 30 but terminate substantially flush therewith. A cabinet of this type may be constructed with a perfectly square bottom wall 32 and a correspondingly shaped top. A cabinet according to FIG. 4 constructed for a 6-in. speaker or driver 34 In such a in. The width of the slot 36 would still be /2 in. and

the distance between the rear edges 38 of the side panels 26 and 28 and the adjacent walls of the room, A in. each.

In both described forms of the invention it is to be noted that the rear portion of the resonant cavity is so 'related to the reflex or impedance opening that smooth entry of acoustic energy from the resonant cavity to the mouth of each horn section is provided and, as previous ly stated, the relation of the areas of the ports 22 and 36 to the areas of the threats of the horn sections is such as to provide optimum coupling between the resonant cavity and the horn sections with a minimum loss of energy through the entire low frequency spectrum.

While a limited number of specific examples of the invention have been shown and described herein it is to be understood that other modifications may be adopted within the scope of the invention defined by the appended claims.

Having thus described the invention, what is claimed is:

1. In a base reflex loud speaker enclosure means defining a base reflex enclosure constituting a resonant cavity having top and bottom walls, a front wall having a driver mounted therein, and horizontally curved side walls extending rearwardly from the side edges of said front wall, said side walls being outwardly convex and converging rearwardly to define a narrow slot between the rear edges thereof and comprising a reflex opening from said enclosure, said enclosure having means thereon to engage the walls adjacent a corner of a room and to hold said rear edges spaced from the walls of said room a distance substantially equal to one-half the width of said slot to thereby define a horn throat whereby said curved side walls and the adjacent walls of said room define forwardly flared horn sections coupled to said cavity through said slot and whose cross sectional areas increase as an exponential function of their lengths.

2. A device as defined in claim 1 wherein the tangent planes at the rear edge portions of said curved side walls are substantially parallel to the adjacent Walls of said room.

3. A device as defined in claim 1 wherein said curved side walls each comprise a plurality of spaced rigid upstanding struts extending between said top and bottom walls and a sheet of relatively stiff and hard material secured to said struts to define said curved side walls.

4. A device as defined in claim 1 wherein said curved side walls extend forwardly past said front wall for a substantial distance to increase the length of said flared horn sections.

5. In a base reflex loud speaker enclosure means defining a base reflex enclosure constituting a resonant cavity having top and bottom walls, a front wall having a driver mounted therein, and horizontally curved side walls extending rearwardly from the side edges of said front wall, said side walls being outwardly convex and converging rearwardly to define a narrow slot between the rear edges thereof and comprising a reflex opening from said enclosure, said enclosure having means thereon to engage the walls adjacent a corner of a room to hold said rear edges spaced from the walls of said room to define a horn throat whereby said curved side walls and the adjacent walls of said room define forwardly flared horns, the curvature of each of said curved side walls being in accordance with the formula:

A=A (cosh x+T sinh x) wherein A is the cross sectional area of the horn in a plane perpendicular to the room wall, x is a function of the distance from the horn throat to the plane of A, A is the cross sectional area of the throat of said horn, having one-half the area of said slot and T is a parametric constant having a value of from 0 to l.

6. A device as defined in claim 5 wherein the value of T is approximately 0.6.

7. A device as defined in claim 5 wherein the value of T is approximately 1.

References Cited in the file of this patent UNITED STATES PATENTS 1,984,550 Sandeman Dec. 18, 1934 2,310,243 Klipsch Feb. 9, 1943 2,338,262 Salmon Jan. 4, 1944 2,373,692 Klipsch Apr. 17, 1945 2,731,10l Klipsch Jan. 17, 1956 2,866,513 White Dec. 30, 1958 FOREIGN PATENTS 143,597 Australia Sept. 27, 1951

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