US2201073A

US2201073A - Horn type loud-speaker

Info

Publication number: US2201073A
Application number: US261357A
Authority: US
Inventors: Lloyd J Bobb
Original assignee: Philco Radio and Television Corp
Current assignee: Philco Radio and Television Corp
Priority date: 1938-03-25
Filing date: 1939-03-11
Publication date: 1940-05-14
Anticipated expiration: 1957-05-14
Also published as: GB513940A

Description

HORN .TYPE LOUD-SPEAKER Filed March 11, 1939 Patented May 14, 1940 UNITED STATES PATENT OFFICE Philco Philadelphia,

Radio and Television Corporation, Pa., a corporation oi Delaware Application March 11, 1939, Serial No. 261,357 In Great Britain March 25, 1938 4 Claims.

This invention relates to a novel cabinet structure for a radio receiver and has for its principal object the provision of a cabinet structure where in a. highly eff cient horn coupling between the back of theloud-speaker diaphragm and the outside air is obtained by a novel arrangement of partitions or bafiles which define successive chambers or passages whose respective volumes vary substantially exponentially, giving the effect of an exponential horn. The arrangement of the partitions or bafiles is such that a minimum number of these elements are made to serve the desired purpose.

Another object of the invention is to provide a novel cabinet structure of this character wherein provision is made for accommodating parts of the radio receiver, such as the receiver chassis and batteries, in such manner that these parts reduce the volume of certain of the horn chambers or passages, thus causing such radio receiver parts to serve an additional purpose.

A further object of the invention is to provide a. cabinet of novel construction wherein certain radio receiver parts are judiciously disposed and wherein the space which is not occupied by such parts is utilized for a novel baffle structure which, together with the cabinet walls, provides an effective horn as above mentioned.

Other objects and features of the invention will be apparent as the description proceeds. The invention may be clearly understood by reference to the specific embodiment shown in the accompanying drawing, wherein Fig. 1 is a perspective view of a preferred form of the cabinet structure with certain parts broken away for the sake of illustration; and

Fig. 2 is a perspective view of one form of device employing the cabinet structure.

Referring first to Fig. 1, there is shown. a boxlike cabinet structure comprising a bottom I, a top 2, side walls 3 and 4, and a back 5. The height and width of this structure are substantially equal and are about twice the depth. In other words, the height, width and depth are related substantially in the ratio 222:1. Extending between the side walls 3 and 4, there are provided two superposed horizontal partitions or bafiles 6 and l, the upper bafile 6 extending from the back of the cabinet forward about twothirds of the depth of the cabinet, while the lower baiile 1 extends from the front of the cabinet backward about one-half the cabinet depth. The distances between the top 2 and upper baffle 6, between the two

battles

6 and 1,

(Cl. ISL-31) and between bailie l and the bottom I, are related substantially in the ratio 2 :3210

There are also provided two spaced L.--shaped vertical baflies 8 and 9 having front portions extending between the baifie 'l and the top 2 and having rear portions extending between baifieii and the top 2. The distance between bafiles 8 and 9 and the distances between these baflles and the side walls are substantially equal. A small vertical bailie Ill extends between the baffles 8 and 9 and between the

baffles

6 and 1. The front central space a defined by the baflie l, the top 2, the front portions of baflies 8 and 9, and the small baflie it! is sufliciently large to serve as a chamber or receptacle for the loud-speaker II, as illustrated. A front panel I2 extends between the side walls and between panel I and the top 2. This panel has an opening adjacent the speaker diaphragm.

In further accordance with the invention, the radio receiver proper, in the form of a unit l3 may be disposed. on the bottom 5 centrally between. the side walls 3 and 4 within the space defined by the bottom I, the baffle l andthe side walls 3 and 4. There are also provided batteries within battery cases It and 15 which may be disposed in the rear corners at the bottom of the cabinet, as illustrated. These battery cases are preferably of the shape illustrated, each having an oblique wall It, the purpose of which will be explained presently. Behind the radio receiver unit 13, there may be provided another battery ll.

In operation, the small space a in which the speaker diaphragm is disposed constitutes the throat of a horn for the sounds emanating from the rear side of the speaker diaphragm and, from this space, these sounds pass rearwardly through the somewhat larger space 19 defined by the top 2, the baffle 5, and the rear portions of bafiies 8 and 9. From the space I), the sounds divide and pass divergently toward the side walls 3 and 4 between the top 2 and bafile 6, and then pass forwardly through the spaces 0 around the front edge of baffle 6 and then rearwardly through the spaces d between babies 6 and 'I. From the spaces (1, the sounds again pass downwardly around the rear edge of bafiie l, and then for-- wardly through the larger spaces 6 between the baflle I and the bottom I. The arrows indicate the directions of the sound waves. Thus, there are formed a plurality of successive spaces or chambers of increasing size or volume, such that a horn effect is obtained. It may now be noted that the receiver unit [3 and the batteries l4, l5

and I! reduce the vohune of the last space or chamber from which the sounds emanate and cause the effective vohune of this space or chamher to be in proper relation to the other spaces or chambers formed by the bafiles. The oblique surfaces IS on the battery cases M and i5 assist in the provision of a horn mouth of increasing volume. These surfaces form a flaring soundemitting mouth for the horn and also serve to deflect the sounds.

In order to obtain maximum efficiency, the construction of the cabinet and the arrangement of baffles, as above described, should be rather critically adhered to, and the receiver unit l3 and the associated batteries should be so dimensioned that they reduce the volume of the soundemitting space or horn mouth just sufiiciently to provide the desired acoustic effect at the mouth of the horn structure. The cut-off frequency of the cabinet structure will depend upon the dimensions employed in any instance. In order to vary the cut-off frequency, all of the dimensions should be varied in inverse proportion to the variation in cut-off frequency desired. For example, assuming that a cabinet of given dimensions has a cut-off frequency of about 150 cycles per second, if it is desired to reduce the cut-off frequency by one-half, that is to '75 cycles per second, all linear dimensions, including the diameter of the loud speaker, should be increased by a factor of two.

It will be apparent that the cabinet structure with the parts assembled therein, as shown in Fig. 1, forms a compact unit containing all of the radio receiver parts and with the horn structure built into the casing or housing of the unit. This structure may itself form the cabinet of a radio receiver, in which. case the front may be finished in any desired manner, such as shown in Fig. 2, and be provided with an opening H3 adjacent the speaker, an opening l9 to accommodate the tuning dial, and

openings

20 and 21 to emit sound from the mouth areas 6. Obviously, the front may be of any suitable design and appearance, that shown in Fig. 2 merely being illustrative of one possible form.

Alternately, the structure shown in Fig. 1 may be placed within a larger cabinet adjacent the front panel of such cabinet, the panel being provided with suitable openings. In such case, the receiver unit and the batteries may or may not be disposed in the unit of Fig. 1. If these elements are not so disposed, the height of spaces 6 should be decreased so that the ratio of the heights of spaces c, d, and e is substantially 2%:318. In the specific example given below, this is done by decreasing the height of space c two inches. Other methods of utilizing the structure of the invention will be apparent to those skilled in the art.

Preferably, the baffles 6. l, 8, 9 and 10 are assembled together to form a latticework structure or unit separate from the cabinet in order that this unit may be inserted bodily within the cab?- net to provide the desired horn structure. Where the structure of Fig. 1 forms the radio cabinet and has a front panel closing the front thereof, the entire structure is preferably assembled as follows: The baffles are assembled to form a separate unit as above mentioned. The loud-speaker is inserted within the latticework and is mounted on the panel [0 thereof. The baffle structure is then inserted bodily from the rear of the cabinet, the back wall of the cabinet having been removed previously, The radio receiver parts are also inserted in the cabinet from the back thereof, and finally the back wall is mounted in place.

In a specific example, the inside dimensions of the structure of Fig. 1 were as follows:

Bottom I and top 2 each were approximately 16 inches by 8% inches.

Sides 3 and 4 each were approximately 16 inches by 8%.

Back 5 was approximately 16 inches square.

Baffle 6 was approximately 16 inches by 5% inches.

Baffle l was approximately 16 inches by 4% inches.

The distance between battle 6 and top 2 was approximately 2 inches.

The distance between baffles 6 and l was approximately 3 inches.

The distance between baffle 1 and bottom I was approximately 10 inches.

8 and 9 each were approximately inches deep at the top.

The distance between baflles 8 and 9, and the distance between these baflles and the side walls, was approximately 5 inches, allowing about inch for the thickness of the baffles.

The diameter of the loud-speaker diaphragm was approximately l inches in diameter.

The magnet structure of the speaker was approximately 3 inches in diameter and approximately 1 inches deep.

device had a cut-off frequency of about 180 cycles per second. The resonant frequency of the speaker diaphragm in air was about 175 cycles per second.

When the structure of the invention is employod, the loud-speaker may be modified by in creasing the magnetic flux density in the air gap and decreasing the mass of the speaker cone. This increases the speaker efficiency at high he quencies with some loss in efficiency at low fre quencies. However, this loss is balanced by the improved coupling between the air and the speaker cone brought about by the use of the cabinet structure, with the result that the overall efficiency of the entire acoustic unit is materially improved. Since the direct radiation at low frequencies from the front of the speaker is low, no trouble with interference patterns, due to phase differences in sound waves from the front and back of the loud-speaker, will obtain.

The structure provided by the invention also increases the power capabilities of the sound rcproducing system. As is well known, in the conventional loud-speaker the power output is limited, due to the fact that the maximum possible excursion of the voice coil of the speaker is limited by the dimensions of the magnetic field. and the acoustic power is proportional to the square of this excursion. The present invention permits a much smaller movement of the voice coil [or a given acoustic power output, and, therefore, the power capabilities of the sound reproducing system are materially increased.

Although a single form of the invention has been illustrated and described for the purpose of disclosure, it will be apparent that various modifications of the structure and various embodimcnts are possible without departing from the scope of the invention. For example, the structure may be embodied in a cabinet of the console type and may, if desired, form a part of such cabinet, in which case the receiver unit and the batteries may be positioned differently than shown.

I claim:

1. A sound reproducing apparatus, comprising a cabinet having front and rear panels, said front panel having at least two openings therein, a pair of vertically-spaced horizontal baffles within said cabinet, the lower one of said baffles extending from the front of said cabinet rearwardly and terminating in a rear edge spaced from the rear of the cabinet, the upper bafile extending from the rear of said cabinet toward the front of said cabinet and terminating in a front edge spaced from the front of the cabinet, a loud-speaker disposed above said lower bafile in front of said upper baffle adjacent one of said openings at the front of the cabinet for emitting sound from the speaker, a pair of vertical baffles arranged on opposite sides of said loud speaker to form a speaker compartment and extending rearwardly above said upper baffle to direct sounds rearwardly, and a panel extending between said vertical baiiies and between said horizontal baffles, the said loud-speaker being characterized by having more eificient response at high frequencies than at low frequencies, and the said baffles being arranged to provide successive sound chambers of increasing cross-sectional area from the rear of the laud-speaker to the other opening in the front of the cabinet whereby to reproduce efficiently the low frequency sounds.

2. A sound reproducing apparatus, comprising a cabinet having front and rear panels, said front panel having at least two openings therein, a pair of vertically-spaced horizontal baffies within said cabinet, the lower one of said bafiies extending from the front of said cabinet rearwardly and terminating in a rear edge spaced from the rear of the cabinet, the upper bafile extending from the rear of said cabinet toward the front of said cabinet and terminating in a front edge spaced from the front of the cabinet, a loudspeaker disposed above said lower baffle in front of said upper baffle adjacent one of said openings at the front of the cabinet for emitting sound from the speaker, 21, pair of vertical baffles arranged on opposite sides of said loudspeaker to form a speaker compartment and extending rearwardly above said upper baffle to direct sounds rearwardly, and a panel extending between said vertical baflies and between said horizontal bafiies, the said loud-speaker being characterized by having more efficient response at high frequencies than at low frequencies, and the said bafiies being arranged to provide successive sound chambers of increasing cross-sectional area from the rear of the loud-speaker to the other opening in the front of the cabinet whereby to reproduce efficiently the low frequency sounds, the lastof the said successive sound chambers being of sufficient volume to accommodate one or more radio receiver components which reduce the volume of said chamber to cause its effective volume to be in proper relation to the preceding sound chambers.

3. A sound reproducing apparatus, comprising a cabinet having front and rear panels, said front panel having at least two openings therein, a pair of vertically-spaced horizontal baflles within said cabinet, the lower one of said bafiles extending from the front of said cabinet rear- Wardly and terminating in a rear edge spaced from the rear of the cabinet, the upper baiiie extending from the rear of said cabinet toward the front of said cabinet and terminating in a front edge spaced from the front of the cabinet, a loud-speaker disposed above said lower baffle in front of said upper bafiie adjacent one of said openings at the front of the cabinet for emitting sound from the speaker, a pair of vertical baffies arranged on opposite sides of said loudspeaker to form a speaker compartment and extending rearwardly above said upper baffle to direct sounds rearwardly, and a panel extending between said vertical baffles and between said horizontal baflies, the said loud-speaker being characterized by having more efficient response at high frequencies than at low frequencies, and the said bafiies being arranged to provide successive sound chambers of increasing cross-sectional area from the rear of the loud-speaker to the other opening in the front of the cabinet whereby to reproduce efficiently the low frequency sound, the last of the said successive sound chambers being of sufficient volume to accommodate one or more radio receiver components having oblique surfaces forming a flaring soundemitting mouth, said radio receiver components reducing the volume of said chamber to cause its effective volume to be in proper relation to the preceding sound chambers.

e. A sound reproducing apparatus, comprising a cabinet having front and rear panels, said front panel having at least two openings therein,

a pair of vertically-spaced horizontal bafiies within said cabinet, the lower one of said bafiies extending from the front of said cabinet rearwardly and terminating in a rear edge spaced from the rear of the cabinet, the upper baffle extending from the rear of said cabinet toward the front of said cabinet and terminating in a front edge spaced from the front of the cabinet, a loud-speaker disposed above said lower baflie in front of said upper baffle adjacent one of said openings at the front of the cabinet for emitting sound from the speaker, a pair of vertical baffles arranged on opposite sides of said loudspeaker to form a speaker compartment and extending rearwardly above said upper bafiie to direct sounds rearwardly, and a panel extending between said vertical baffies and between said horizontal baffles, the said loud-speaker being characterized by having more efficient response at high frequencies than at low frequencies, and the said bafiies being arranged to provide successive sound chambers of increasing cross-sectional area from the rear of the loud-speaker to the other opening in the front of the cabinet whereby to reproduce efficiently the low frequency sounds, the last of the said successive sound chambers being of sufficient volume to house a radio receiver chassis and associated elements which reduce the volume of said chamber to cause its effective volume to be in proper relation to the preceding sound chambers.

LLOYD J. 30133.