US3080013A - Speaker enclosure - Google Patents

Description

March 1963 w. s. BATEMAN, JR 3,080,013

SPEAKER ENCLGSURE Filed Aug. 16, 1960 2 Sheets-Sheet i INVENTOR. WILLIAM J. 15/178144, JR.

March 5, 1963 w. s. BATEMAN, JR

SPEAKER ENCLOSURE 2 Sheets-Sheet 2 Fild Aug. 16, 1960 IN VEN TOR.

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@M M M WWW f/M ATTORNEYS 3,i 3t),tii3 @PEAKER ENCLGSURE Wiiiiam S. Bateman, in, Summitvilie, @hio Fiied Aug. 16, 196%, Ser. No. 49,945 It) Shims. ((li. Ebb-31) This invention relates to an improvement in enclosures for loudspeakers, and provides for an improved reproduction of sound from such speakers.

The invention aims primarily to provide an inexpensive speaker enclosure of small size which will give a true response over the high and middle sound frequencies, and which will give added range in the bass frequencies, while producing an over-all result which is pleasing to the ear.

Numerous attempts have been made in the past to achieve these objectives in a simple and inexpensive structure, but it is believed that the device of the present invention provides a better response with an extremely simple and inexpensive construction.

In general, the present invention provides an enclosure which is completely closed on all sides except for an opening which coincides with the front face of the speaker, and for a narrow, tapered control slot in a wall of the cabinet other than the wall on which the speaker is mounted. This control slot is provided primarily to permit passage of air to and from the interiorof the enclosure, and not for the emission of sound.

An additional feature resides in the positioning of the speaker so that it is equidistant from the bottom and sides of the enclosure, thus giving an even distribution of sound. The speaker should be placed so that the distance from the top is greater than the distance from the sides and bottom. This spacing provides an equalizing air space above the speaker, and permits the enclosure to operate on the theory of a tuned pipe. To obtain maximum benefit from this tuned pipe theory, the height of the enclosure is /a greater than the length of the slot.

These, and other objects and advantages will become apparent as the description proceeds.

in the drawings:

FIG. 1 is a front elevation of the enclosure.

FIG. 2 is a vertical section on line 11-11 of FIG. 1.

FIG. 3 is a plan view of the bottom of the enclosure.

' FIG. 4 is a view similar to FIG. 3, but showing a modification.

FIG. 5 is a diagram showing the portion of the cissoid curve used in the invention.

in view of the confused state of theoretical knowledge concerning the operation of speaker enclosures, the construction of the enclosure of the present invention will be described with a minimum of theoretical explanation.

Referring to the features in detail, the enclosure includes a front panel iii, two side panels 11, a top panel 12, and a bottom panel 13. These panels are all preferably made of spruce wood varying in thickness from for an enclosure for a 6 in. speaker to 1 in. for an enclosure for a 15 in. speaker. Spruce is used because it is a strong, yet flexible wood and is placed with the grain running lengthwise of the long dimension of the panels in order to permit the panels to bulge on their short dimensions and thus transmit sound through these surfaces.

be back panel 14 is made of spruce wood of a thickness varying between i g in. for an enclosure for a 6 in. speaker and in. for an enclosure for a 15 in. speaker, so that it can give optimum transmission of sound without structural breakdown. Improved results are obruined it the lower part of the back panel is formed as a resonant panel 14a thinner than the upper part of the back panel.

Patented Mar. 5, 1953 The speaker 15, which is a conventional cone speaker,

Dimensions of Cabinet The dimensions of the cabinet are of great importance in obtaining optimum results. These will, of course, vary, with the size of the speaker, but will be of the same proportions. The dimensions are important because they control the volume of air inside the cabinet which must be acted upon by the cone of thespeaker.

The speaker should be mounted on the inside of the front panel it) in such a position that the outer edge of the speaker cone is equidistant from the sides and bottom of the cabinet. This is to get an even emission of sound, since a note originating at any point on the cone travels the same distance to the sides and the bottom. This distance in a rectangular enclosure should be the same for all sizes of speakers, and an optimum distance has been found to be 1% in. on the inside.

To take full advantage of the sound productive characteristics of a slotted pipe, the slot should be /3 of the height of the pipe. However, here we are concerned, not with production of sound, but with, among other things, an enclosing device which will be in tune with the already full-fledged sound emanating from the speaker. Therefore, the slot is placed in the bottom of the enclosure so as to cause minimum disturbance to the air column in the pipe. Maximum length of the slot is obtained by running it diagonally between corners. An additional advantage of this position is that the slot is near, and approximately parallel to, the angle of the speaker cone or source of sound.

To obtain full benefit of the tuned pipe theory, the inside height of the enclosure should be /3 greater than the length of the slot.

Based on this dimension and the other factors already noted, the inside dimensions (these are the important dimensions since we are concerned with the internal air volume) may be calculated as follows:

Let D equal the diameter of the speaker diaphragm and hence the hole for the speaker.

Width =D+(1 A in. 2) Depth (dimension from front panel to back panel)= /2 width or the hypotnuse of a right triangle whose legs are the width and the depth.

Height:

or /3 greater than said hypotenuse.

By using the above equations we obtain the following dimensions for an enclosure for an S in. speaker (whose cone diameter is usually 7 /8 in.):

By making the height /3 greater than the length of the slot, we take full advantage of the organ pipe effect. But it with this dimension we use a back panel having uniformly A tapered control-slot 17a is formed in the bottom panel 13. This slot has its sides slightly curved in horn shape, i.e., each side is mine. shape of part ofa cissoid curve. The slot 17:: crossesthe bottorndiagonally from one corner 'toanother, as stated above, and has its narrow end 17 at the corner a' djacent to the front panel This narrow end. 17, is approximately .015 in. wide. for a 6 in.

speaker, andapprOXimatelyjOSQ in. ,wide for a in.,

speaker. Theslot graduallytaperstoa greater. Width-at therear corner of the enclosure.

The width of the slot at its wide end 13 will vary slightly. with, the-size of thespeaker, For an 8; in. speaken, it is,

approrrimately .1875 I in. wide. at its Wideend;

Each side of the slot is ior ned as a portion o f a cissoid curve generated from a circlehav-inga diameter of '1 /2 in., as shown QinF lG. 5. The extremely curved section at thefinitialend of the cissoid isnot used, as a very small change in position of thisextrerne degree ofcurvaturel not useful in time adjustment.

'Itis preferred to usethe portion of thecurve lying approximately between the numerals 1 7 and 18, The porchanges the area oi the slot very rapidly andithereiore is tionat 17,is used atthe. narrow end of .theslot, and the.

pprtion at .18 is used at the wide endof the slot,

. The'cissoid is a relatively finite curve since, unlike the conics, it rapidly, becomes parallel to its asyrnpto-te.

Therefore, the small end i 7 'used atthe large onbass' end o f'the cone produces a slot: with nearly parallel sides. As this slot must havesut licient over-all area to damp the free air peak'present in speakercones, and at the same time have asmall cross section at the bass end of the cone to give air stiifness atthat point in order to enhance sound production, useof this .curve gives nice control. In other words, by horizontal movement of this slot along its longitudinal axis, with very little change in, cross section atthe bass end, the wider end can be opened or closed quite rapidly. It has been found that there is very little variation in' end openings for different sizes; the necessary variation is produced almost entirely bythe length of the slot.

It would be possible theoretically to tune the enclosure by a large, extremely flexible, bagzk panel, butlthisisimpractical for bothstructural and musical reas ons, although large volume is generated.

Again the back panel could be madevery rigid and a larger slot used for control, but volume output and sound distribution would suffer. 'lhereferepa comproniise is used to give best overall results. Optimum seems to be a thin panel behindthe speaker, as high as it is wide with the upper section ofiback panel of thicker construction and with a slot of minimal area inthe bottom panel.

The slot may beeconornically formed as shown in FIG. 3 by cutting a Wider slot22 of uniform widthinthebottom panel 13, and attaching to the panel two thin strips of wood 19 which have their .confrontingedges formed.

is formed in a metal stamping 20,:and5the stamping is se-.

cured over the wider uniform slot in the bottom panel 13. It is important to note that this tapered control slot is primarily for air control, as will be exlained later more fully.

In order to permit: free movement of air through the cissoid slot, thenspeaker enclosurexmust beamounted so i.- that the bottom panel 13 is above the surface on which it issupported. This can be done by providing the enclosure with legs '21.

Mode of Operation As stated previously, the particular features of the improved speaker enclosure have been arrived at empirically, and applicant does not wish to be limited to any particular theory as to why the improved results are obtained. However, it is believed that the following may be some of the reasons.

The extra, airspace in.the cabinet above the speaker is believed to serve two purposes:-

. too narrow to serve as an outlet for sound. It 18 designed,

(1;) Tuning-- efjec t;-In some: respects the enclosure acts; like; atuned pipewith; an. air exit slot having an exponential taper. ltvis; well known that such a pipe will, give uniform response throughout the audible range while at ;the same timeretaining theacoustictransformer effect of a quarter wave length matching section of transmission line, Hence this; construction extends the rangepfthe speakerto lower; frequencies, and produces Pleasing harmonics.v

(2); Equalizing air, cushiom-It: is; desirable to maintain constant air pressure. Within the cabinet,v and the extra volume oi air providesarcompressive cushion.

The location: of the speaker equidistant from the bottom andsideshelpsto give aneven distribution of sounds respnated from the, cabinet. This. is, because .a' musical noteoriginating at anypoint on the cone travels the same distani e to the sides andv thebottom. Thus the soundmoves outward in phase;

By using theiback panel-14 as a sounding board, sound isdirected rearwardly from the enclosure, so .that in the usual rectangular room, the enclosure acts like a source of sound 'inan auditorium, sending sound toward all Walls.

The tapered, preferably cissoid, slot in the. bottom panel serves; these purposes:

(1) Tunes the column of air in the-uenclosure'so that the enclosure acts likea closed-endpipe.

(2) Allows air to; move in andout of .the enclosure, relieving pressure changes caused by pulsations of the speakerfdiaphragm, .butnot to the extent of preventing proper loading of the. speaker diaphragm.

(3) By placing the narrow end of the 'slot at the front corner, provision is made for a stiffer air'volume adjacent,the -outer'periphery of the'cone, where the bass notes are generated. Hence this part of the cone acts against a stiffer resistance, withthe result that a stronger I Advantages The speaker enclosure of the present invention has the following advantages:

(1) Occupies small space. (2) Is simple and inexpensive (3) Gives superior sound reproduction, with clarity of tone, good illusion of space, .and evendistribution of sound.

As anexample, an enclosure embodying theprinciples ofthis inventionwas cons tructed to house an 8 in'. speak,

er of a well-known make and of low cost and whichis normally rated at 45 to 15,000 c.p.s. When housed in the enclosure, it reproducedfrom 30 to 19,000 c.p.s. with adequate volume, nearly fiat response, and pleasingtonal q ity,

Possible Variants It should be understood that while the combination of features described above gives the best results, certain .5 variations may be made in the construction and arrangement of parts, while still retaining important advantages of the invention.

For example, the use of the materials and thicknesses described above make important contributions to the improved result, since sound is transmitted through the walls, the side panels and especially the back panel. However, it is possible to change the thickness or the material of the walls while retaining many advantages of the invention.

Similarly, the arrangement of the speaker as described relative to the different walls has been found to contribute to the best results. But this arrangement may also be varied within reasonable limits and still provide advantages.

The slot in the bottom panel is preferably of cissoid shape as described, but the use of a tapered slot whose sides do not conform strictly to this shape, or are even straight, will retain some of the advantages of the cissoid slot.

It is also possible to use another damper above the speaker in the pipe chamber. It consists of thin cloth 22 (such as a well-worn line napkin) hung vertically from the center of the top panel parallel to the speaker axis and extending downward to the top of the speaker. Occasionally a note predominates, possibly when wavelength becomes /2 of a pipe dimension. Use of this damper eliminates this defect.

According to the provisions of the patent statutes, 1 have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. In a speaker enclosure of the type having known features defined as Features (a) and (b) the improvement that comprises Features (c) and (d), said Features being defined as follows:

Feature (a): a plurality of side walls, a top wall and a bottom wall;

Feature (b): a cone-type speaker located within the enclosure and facing an opening in one of the side walls;

Feature (c): the bottom wall having a tapered slot with its narrow end adjacent the wall which has the opening for the speaker, and with its wider end farther removed from the Wall which has the opening for the speaker;

Feature (d): all of said walls being closed to the passage of air except the bottom wall and the wall which has the opening for the speaker.

2. A device as specified in claim 1 in which the sides of the slot have the form of portions of a cissoid curve.

3. In a rectangular speaker enclosure having a front panel, a back panel, two side panels and top and bottom panels, with a speaker mounted on the inside of the front panel and facing an opening in the front panel, the improvement which comprises:

the bottom panel having a narrow tapered slot which extends diagonally from a front corner to a rear corner, and with the narrow end of the slot at the front corner.

4. A device as specified in claim 3 in which the sides of the slot have the form of portions of a cissoid curve.

5. A device as specified in claim 3 in which the speaker is located equidistant from the bottom and side panels, but at a greater distance from the top panel.

6. A device as specified in claim 5 in which a portion of the back panel is of thin resonant wood.

7. In a rectangular speaker enclosure having a front panel, a back panel, two side panels and top and bottom panels, with a speaker mounted on the inside of the front panel and facing an opening in the front panel, the improvement which comprises:

the front, side, top and bottom panels being formed of wood, and each of these panels being of uniform thickness;

the rear panel having its upper part formed of wood of the same thickness as the other panels just specified, and having its lower part formed of spruce wood thinner than said other panels;

the speaker being located equidistant from the bottom and side panels but at a greater distance from the top panel;

and the bottom panel having a narrow tapered slot which extends diagonally from a front corner to a rear corner, and with the narrow end of the slot at the front corner.

8. A device as specified in claim 7 in which the sides of the slot have the form of portions of a cissoid curve.

9. In a rectangular speaker enclosure having a front panel, a back panel, two side panels and top and bottom panels, with a speaker mounted on the inside of the front panel and facing an opening in the front panel, the improvement which comprises:

the front, side, top and bottom panels being formed of wood, and each of these panels being of uniform thickness;

the rear panel having its upper part formed of wood of the same thickness as the other panels just specified, and having its lower part formed of spruce wood thinner than said other panels;

the speaker being located so that the outer edge of the speaker diaphragm will be at a distance of 1 A in. from the side and bottom panels;

and the bottom panel being formed with a narrow tapered slot which extends diagonally from a front corner to a rear corner, and with the narrow end of the slot at the front corner;

the parts being so proportioned that the inside height of the enclosure is greater than the length of the slot.

10. A device as specified in claim 9 in which the sides of the slot have the form of portions of a cissoid curve,

and the width of the narrow end of the slot is between .015 in. and .030 in.

References Cited in the file of this patent UNITED STATES PATENTS 2,642,948 Olson et a1. June 23, 1953 2,840,181 Wildman June 24, 1958 2,973,824 Pinski Mar. 7, 1961 FOREIGN PATENTS 102,888 Australia Dec. 23, 1937 1,065,126 France Dec. 30, 1953

Claims (1)

1. IN A SPEAKER ENCLOSURE OF THE TYPE HAVING KNOWN FEATURES DEFINED AS FEATURES (A) AND (B) THE IMPROVEMENT THAT COMPRISES FEATURES (C) AND (D), SAID FEATURES BEING DEFINED AS FOLLOWS: FEATURE (A): A PLURALITY OF SIDE WALLS, A TOP WALL AND A BOTTOM WALL; FEATURE (B); A CONE-TYPE SPEAKER LOCATED WITHIN THE ENCLOSURE AND FACING AN OPENING IN ONE OF THE SIDE WALLS; FEATURE (C): THE BOTTOM WALL HAVING A TAPERED SLOT WITH ITS NARROW END ADJACENT THE WALL WHICH HAS THE OPENING FOR THE SPEAKER, AND WITH ITS WIDER END FARTHER REMOVED FROM THE WALL WHICH HAS THE OPENING FOR THE SPEAKER; FEATURE (D): ALL OF SAID WALLS BEING CLOSED TO THE PASSAGE OF AIR EXCEPT THE BOTTOM WALL AND THE WALL WHICH HAS THE OPENING FOR THE SPEAKER.

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