US2751997A

US2751997A - Low frequency horn

Info

Publication number: US2751997A
Application number: US447943A
Authority: US
Inventors: Jr Edward J Gately
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-08-05
Filing date: 1954-08-05
Publication date: 1956-06-26
Anticipated expiration: 1973-06-26

Description

Juhe26,l956

E. J. GATELY, JR

LOW FREQUENCY HORN Filed Aug. 5, 1954 INVENTOR EdwardJGazefqh QTTORN EYS United States Patent LOW FREQUENCY HORN Edward J. Gately, Jr., Drexel Hill, Pa. Application August 5, 1954, Serial No. 447,943

11 Claims. (Cl. 181-31) This invention relates to the art of acoustic devices and more particularly to horns to be used in conjunction with loud speaker units for amplifying low frequency sound waves.

As conducive to an understanding of the invention, it is noted that to have true reproduction of low frequency audio sound waves, two factors essentially govern the success of a horn operated at such low frequencies. First, the taper or rate of flare of the horn should be such that the propagation of low frequencies through the horn is accomplished easily. For good low-frequency reproduction, the taper should be very gradual. Second, the mouth area of the horn must be adequate to prevent resonances in the air column of the horn if smooth response is to be realized.

Consequently, where the horn, to have such gradual taper and large mouth area, is made of relatively great length, because of the bulk and size of the horn it is undesirable, especially for home use where the size and esthetic eifect of the unit are important factors.

Where the horn is of the folded type to achieve the desired length in a minimum of space, it is relatively expensive to construct and the large mouth area generally makes the unit too large for home use.

Where the horn, to minimize its size, must be located at a particular position in a room, such as in a corner so that it relies on the side walls and floor as an extension of the horn mouth to increase its effective area, its utility is necessarily limited, as in many cases there is no corner available for the unit, due to structural or decorative considerations.

It is accordingly among the objects of the invention to provide a combined cabinet horn which is made from relatively inexpensive components which may readily be assembled at low cost, which is compact in size yet provides the desired gradual taper and effective mouth area for high fidelity reproduction of low frequency sound Waves regardless of the portion of the wall of a room against which it is positioned.

According to the invention from its broader aspect, the horn tapers outwardly exponentially from its throat so as to substantially double its area per discrete increment of length and is designed so that sound waves will be emitted from the front and from both sides of the cabinet in which it is contained. Thus when the cabinet is positioned against the wall of a room, the floor in front and on each side of the cabinet, as well as the portion of the wall against which the cabinet is placed on each side of the latter will serve as extensions of the horn mouth to increase the eifective area thereof, thereby permitting a gradually tapered horn of minimum length and size with high fidelity reproduction of low frequency sound waves.

In the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. 1 is a perspective view of the cabinet horn,

Fig. 2 is a sectional view taken along line 2-2 of Fig. 1,

Fig. 3 is a front elevational view of the unit with parts broken away, and

Fig. 4 is a fragmentary view similar to Fig. 2 of another embodiment.

Referring now to Figs. 1 to 3 of the drawings, in the embodiment shown to illustrate the invention, the unit comprises a cabinet 11 illustratively rectangular as shown, having a front wall 12, a rear wall 13,

side walls

14 and 15, a floor 16 and a top wall 17.

The front wall 12 and

side walls

14 and 15 adjacent their lower edges 18 each has a

rectangular opening

19, 20 and 21 therethrough extending substantially the width of the associated Wall and defining the mouth of the horn.

Positioned in the cabinet 11 is a bafile structure 22 which is substantially a pyramid bisected along a plane perpendicular to its base and extending through its vertex. The baffle structure is illustratively formed from two

side panels

23 and 24 in the form of right triangles having two

legs

26 and 27 and a hypotenuse 28 and a front panel 29 in the form of an isosceles triangle having a base 31 and two

legs

32 and 33.

The leg 255 of each of the

side panels

23, 24 is aflfixed to the floor 16 of the cabinet adjacent the lower edge 13 of each of its

side walls

14 and 15 respectively and the

panels

23, 24 are inclined toward each other with their upper apices meeting as at 34 and with their legs 27 affixed to the back wall 13 of the cabinet. The front panel 29 has its base 31 affixed to the floor 16 of the cabinet adjacent the lower edge 18 of its front wall 12 and the

opposed legs

32 and 33 off front panel 29 are afiixcd to the adjacent hypotenuse 23. of

panels

23 and 24 respectively with the apex of panel 29 meeting the junction 3 of the apices of

panels

23 and 24.

Also mounted in the cabinet 11 between its side walls 14- and 15 is a baffle member 36 illustratively a substantially rectangular panel affixed at its lower edge 37 to the front wall 12 immediately above the upper edge 33 of opening 19. The panel 36 is inclined toward front panel 29 of the ba'i'fie structure 22 with its upper edge 39 lying in substantially the same horizontal plane as the apices of

panels

23, 24 and 25 and spaced therefrom.

Desirably rising from the upper edge 39 of panel 36 is a rectangular baffle panel 42 which also extends between

side walls

14 and 15 and is inclined toward the back wall 13, the area between the upper edge 43 of panel 42 and the back wall 13 and

side walls

14 and 15 defining the throat of the horn.

A speaker 44 is mounted on front wall 12 behind an opening 45 therein with the concave side of the speaker facing toward the opening 45 so that high frequency notes will be radiated directly into the room.

The

panels

36 and 42 together with the baflle structure 22 and the back wall 13 and

side walls

14, 15 of the cabinet form the horn and the dimensions and angles of inclination of the various elements are selected so that from the throat T to the mouth of the horn the rate of taper will be such that the cross sectional area of the horn will double for each increment of length based on the cut off frequency desired. In addition, the dimensions are selected so that the eifective mouth area which is the sum of the actual mouth area defined by

openings

19, 20 and 21 plus the extensions of such mouth caused by the effect of the floor in front and on the sides of the cabinet and the portion of the wall against which the cabinet is placed on each side of the latter, will be equal to the required mouth area, for high fidelity response at the desired cut off frequency.

Generally, the mouth area of the horn should equal ap proximately the area of a circle whose diameter is 1/11 times the wavelength of the lowest frequency to be reproduced and the rate of taper or the distance in which the sectional area doubles expressed in feet is equal to 62.5 frequency in cycles per second As the formulas for determining the desired mouth area and the rate of taper for a given out oif frequency are well known in the acoustic art, they will not be discussed.

Where it is necessary to increase the effective length of the passageway through which the sound waves travel in order to achieve the desired taper and mouth area, additional bafile plates may be provided.

Thus, in the embodiment shown in Fig. 4 which is substantially identical to Fig. 2, a baffle plate 46 extending between the

side walls

14 and 15 may have its lower edge 47 affixed to back wall 13 and its upper edge 48 aff xed to top wall 17. An associated baflle plate 49 also extending between

side walls

14 and 15 may have its lower edge 51 aflixed to the upper edge 43 of bathe plate 42 and its upper edge 52 spaced from the top wall 17.

The

bathe plates

46 and 49 which define therebetween a continuation of the passageway between baffle plate 42 and rear wall 13 and baffle plate 36 and battle structure 22, are so positioned in the cabinet that the sectional area of the combined passageway will increase exponentially from one end to the other.

With the construction above described, by reason of the fact that the three openings defining the mouth utilize the floor in front of and on each side of the cabinet as well as the room wall on each side of the cabinet to increase the effective area of the mouth of the horn, the length of the horn may be a minimum even with the required rate of taper for the low cut off frequency desired.

Consequently, the horn may be relatively compact in size, suitable for home use and as it may be positioned against any portion of the wall of a room its usefulness is enhanced.

Although the cabinet-horn above described is especially suitable for home use, it can also be used in large auditoriums where a large volume of sound is required.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

l. A horn for use with a loud speaker unit, comprising a substantially rectangular cabinet having a floor, a top wall, front and back walls and side walls, a baffle structure rising from said floor adjacent its walls and tapering to a point against the back wall of said cabinet sub stantially midway between its side walls, said front and side walls each having an opening adjacent said fioor, said openings defining the mouth of the horn, an inclined baffie plate in said cabinet spaced from said baffie structure to define a passageway therebetween, said baflle plate having its lower edge substantially aligned with the upper edge of the opening in the front wall and its upper edge spaced from the top of the baffle structure, the sectional area of said passageway increasing exponentially from one end to the other.

7 2. The combination set forth in claim 1 in which the upper edge of said plate lies in the same horizontal plane as the top of said bafile structure.

3. The combination set forth in claim 1 in which said bafile structure has a front panel and two side panels, each of the side panels being a right triangle having one leg against the back wall, a second leg against the floor and its hypotenuse extending from the back wall to the front wall, and the front panel is an isosceles triangle having its base against the floor and its legs against the hypotenuse of each of the side panels.

4. The combination set forth in claim 1 in which said bafile structure has a front panel and two side panels, each of the side panels being a right triangle having one leg against the back wall, a second leg against the floor and its hypotenuse extending from the back wall to the front wall, and the front panel is an isosceles triangle having its base against thefloor and its legs against the hypotenuse of each of the side panels, the upper apices of said three panels lying in substantially the same horizontal plane as the upper edge of the baflle plate.

5. The combination set forth in claim 1 in which said bafiie plate extends from one side wall of the cabinet to the other.

6. The combination set forth in claim 1 in which a second baffie plate is provided, affixed at its lower edge to the upper edge of said first baffle plate and inclined toward the back wall of the cabinet, the passageway defined between the second bafiie plate and the back Wall of the cabinet forming a continuation of the passageway between the first baffie plate and the baifle structure, the sectional area of the combined passageways increasing exponentially from one end to the other.

7. The combination set forth in claim 6 in which a pair of additional spaced baffie plates are provided having their lower edges affixed against the back wall of the cabinet and the upper edge of the second baflle plate, the upper edge of the plate having its lower edge afiixed to the back wall being affixed to the top wall of the cabinet and the upper edge of the other of said pair of plates being spaced from said top wall, the passageway defined between said pair of additional baffie plates being a continuation of the combined passageways, the sectional area of the combined three passageways increasing exponentially from one end to the other.

8. The combination set forth in claim 1 in which each of said openings extends substantially the entire width of the associated wall.

9. A horn for use with a loud speaker unit, comprising a substantially rectangular cabinet having a floor, a top wall, front and back walls and side walls, a baflle structure in said cabinet comprising a front panel and two side panels, each of the side panels being a right triangle having one leg against the back wall, a second leg against the floor adjacent the side walls respectively and its hypotenuse extending from the back wall to the front wall, the front panel being an isosceles triangle having its base against the floor adjacent the front wall and its legs against the hypotenuse of each of the side panels, the upper apices of each of said three panels meeting at a point against the back wall substantially midway between the side walls of the cabinet, said front and side walls each having an opening therethrough adjacent the floor of the cabinet extending substantially the width of the associated wall and defining the mouth of the horn, an inclined baffle plate in said cabinet extending from one side wall to the other, having its lower edge aligned with the upper edge of the opening in the front panel and its upper edge lying in substantially the same horizontal plane as the top of the bafile structure, said baffle plate being spaced from the bafile structure to define a passageway therebetween, the sectional area of said passageway increasing exponentially from one end to the other and a second bafile plate, affixed at its lower edge to the upper edge of the first baffie plate and inclined toward the back wall of the cabinet, the passageway defined between the second baffle plate and the back wall of the cabinet forming acontinuation of the passageway between the first baffie plate and the baffle structure, the sectional area of the combined passageways increasing exponentially from one end to the other.

10. The combination set forth in claim 9 in which a loud speaker is mounted on the front wall of the cabinet on a level substantially the same as that of the upper edge of the second baflle plate.

11. The combination set forth in claim 9 in which a pair of additional spaced bafiie plates are provided having their lower edges aflixed against the back wall of the cabinet and the upper edge of the second baflie plate, the upper edge of the plate having its lower edge afiixed to the back wall being afiixed to the top wall of the cabinet and the upper edge of the other of said pair of plates being spaced from said top wall, the passageway defined between said pair of additional baflle plates being a continuation of the combined passageways, the sec tional area of the combined three passageways increasing exponentially from one end to the other and a loud speaker is mounted on the front wall of the cabinet on a level between the upper edge of the second baffie plate and the upper edge of the other of said pair of additional bathe plates spaced from said top wall.

Wheeler et a1. Apr. 21, 1936 Olson Dec. 17, 1940