US2224919A

US2224919A - Loud-speaker

Info

Publication number: US2224919A
Application number: US134100A
Authority: US
Inventors: Harry F Olson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-03-31
Filing date: 1937-03-31
Publication date: 1940-12-17
Anticipated expiration: 1957-12-17

Description

H. F. OLSON Dec. 17, 1940.

LOUD-SPEAKER 2 Sheets-Sheet 1 Filed March 51, 1937 3nnentor H. F. OLSON LOUD-SPEAKER Dec. 17, 1940.

Filed March 31, 1957 2 Sheets-Sheet 2 Gttorneg Patented Dec. 17, 1940 UNITED STATES PATENT OFFICE LOUD SPEAKER ware Application March 31, 1937, Serial No. 134,100

17 Claims.

This invention relates to loud-speakers, and more particularly to loud-speakers of the compound type.

It has long been recognized that the efiicient transformation of electrical variations into corresponding acoustical vibrations over a wide frequency range is, in general, restricted by practical limitations. Experience has shown that most eflicient reproduction over a wide frequency range may be obtained by an arrangement wherein a cone or other suitable diaphragm is employed to drive both a short horn for reproduction of high frequencies and a long horn for reproduction of low frequencies, and various arrangements of this sort have been proposed heretofore.

It is also well known that high frequency waves are highly directional and are easily absorbed and affected by reflection. With compound horn type loud-speakers of the prior art, little attention has been given to minimizing attenuation of the higher frequencies in inexpensive horn loud-speakers, and as a result, the efficiency of distribution of high frequency sounds where such loud-speakers have been used has suffered.

The primary object of my present invention is to provide an improved compound horn loudspeaker of the type referred to above which is particularly suitable for reproduction over a wide range.

More particularly, it is an object of my present invention to provide an improved loud-speaker as aforesaid which will reproduce the high fre- 35 quencies ina manner not to cause them to suffer serious attenuation or reflection.

Another object of my present invention is to provide improved acoustic filters for discriminating between the range of frequencies supplied by 40 the respective high and low frequency systems of the loud-speaker.

A further object of my present invention is to provide an improved loud-speaker of the type set forth which is very simple in construction, yet highly efficient in use, and which is relatively inexpensive of manufacture.

In accordance with my present invention, I provide a cabinet having upper and lower openings in one of its walls and divide the cabinet 50 into two chambers or compartments. A small,

straight axis horn adapted to particularly transmit high frequencies is placed in the upper compartment and fits into the upper openings, while a long, folded, low frequency horn is disposed partly in the upper and partly in the lower compartment and terminates at the lower opening, a single driver feeding both horns. The small horn is arranged at substantially the level of the listeners ears, whereby very little loss of high frequencies is obtained as a result of absorption and reflection. If desired, the small horn may be omitted and the cone or diaphragm of the single driver arranged to feed directly into the atmosphere as a direct radiator. In either case, the low frequency horn is preferably provided with an acoustic filter which eificiently passes only the low frequencies, and the high frequency horn, in the first modification referred to above, may be provided with an acoustic filter which eificiently permits transmission of only the high frequencies.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of several embodiments thereof, when read in connection with the accompanying drawings in which Figure 1 is a front elevation of one form of my invention,

Figure 2 is a sectional view taken on the line IIII of Fig. 1,

Figure 3 is a sectional view taken on the line III-III of Fig. 1,

Figure 4 is a circuit diagram of the electric equivalent of the acoustic arrangement of this modification of my invention,

Figure 5 is a front elevation of another form of my invention,

Figure 6 is a sectional view taken on the line VIVI of Fig. 5,

Figure 7 is a sectional view taken on the line VII-VII of Fig. 5,

Figure 8 is a diagrammatic illustration of a horn embodying a low pass filter and acoustic capacitance according to my present invention, and

Figure 9 is a diagrammatic illustration of a modified form of combined low pass filter and acoustic capacitance according to my invention.

Referring more particularly to the drawings, wherein similar reference characters designate corresponding parts, there is shown, in Figs. 1, 2 and 3, a cabinet I, the front wall of which is provided with a relatively small opening 3 at the top and a relatively large opening 5 at the bottom, and the cabinet being divided into upper and lower compartments I and 9, respectively, by a partition II. Mounted in the upper compartment is a suitable electro-acoustical driver I3, such as an electro-dynamic loud-speaker which includes a cone or diaphragm I5 and which is preferably adapted to reproduce acoustic signals over a wide range. A short, straight-axis horn H, which preferably is of the exponentially expanding type, is. also located in the compartment I and loads one side (for example, the front) of the diaphragm I5, and, by terminating at the small opening 3, serves to establish communication between front side of the diaphragm I5 and the opening 3 as well as the atmosphere. Also mounted in the upper compartment 1 are the two divided sections I9a and I9'b'0f' a long, folded horn I9 which loads the rear side of the diaphragm I5. The sections I9'a. and I91) are. disposed symmetrically with respect tothe diaphragm I5 and each communicates, through openings 2| in the partition II, withthe single section I90 of the. horn I9 located in the lower compartment 9. The hornv I9, preferably also of the exponentially expanding type, terminates at the large opening 5 and thus serves. to establish communication between the rear side. of the diaphragm I5. and the opening. 5 as well as the atmosphere.

The horn I1 is employed to transmit high audible frequencies with great efiiciency and the horn I9 to transmit low frequencies within the audible range with great efficiency. For this purpose, I provide one or more openings 23 in the horn. I! in proximity to its throat and place about the throat end of the horn H a partition or casing which provides a closed chamber 25 in parallel relation to the horn II, the chamber 25 having communication with the horn II only through the opening or openings23, as the case may be. The opening 23 and the chamber 25 form a series resonant circuit and they are so designed as to resonate at the lower cut-off frequency of the horn I'I. Thus, only substantially those vibrations above the resonant, or predetermined cut-off, frequency of the resonant circuit will be transmitted by the horn I1, and in order to minimize the loss, of the transmitted high frequencies, the cabinet I and the partition II- are so arranged that the horn I1 is substantially at the level of the listeners ears. In this way, the loss of the high frequencies by absorption and reflection is very greatly reduced,

As stated previously, the horn sections I9a and ISbare disposed symmetrically with respect to the driver I3, one on eachside thereof. separating these two sections which, in effect, constitute but a single horn portionwith each section of half the cross sectional area of the combined horn portion in the compartment I, a chamber 21 is formed immediately behind. the diaphragm I5. The chamber 21 has a cross sectional area which is appreciably greater than the total throat area ofthe combined sections I 9a and I9?) and provides an acoustic capacitance which is comparable to the impedance of the horn I9 at the high frequencycut-off frequency of the horn I9, and this is preferably in the vicinity of the low frequency cut-off frequency of the horn H. To further insure against transmission of high frequencies by the horn I9, it may be provided with one or more axially spaced baflies 29 (Fig. 8) each provided with an opening 3| therein of an area smaller, of course, than the cross sectional areas of the horn I9 at the points where thebaflies 29 arelocated and each opening 3| preferably of progressively larger diameter as the cross sectional area of the horn I9 increases. Theeffect of the baffles 29 is to cut down radiation of high frequency vibrations by reflection thereof back toward the chamber 21 and by attenuation due to the constrictions at the openings 3|. In the modification of my invention illustrated in Figs. 1 to 3, the baffles29 are constituted by those portions of the partition II which border on the openings 2| and the openings 2| correspond to the openings 3| of Fig. 8, being of an area appreciably smaller than the cross sectional areas of the horn sections I9a and |9b at the points where the openings 2| are provided. The combined effect of the chamber 21 and the openings 2| is to keep the response of the horn I9 down below its intended, or predetermined, high-frequency cut-off frequency. Thus, the horn I9 will transmit only the lower frequencies and the horn I'I only the higher frequencies, and each with great eiiiciency.

The equivalent electrical circuit of the modification of my invention just described is shown in Fig. 4. If m1 represents the combined mass of the diaphragm I5, its voice coil support and the voice coil, m2 the mass of air in the opening 23, C1 the capacitance of the suspension of the cone l5, C2 the acoustic capacitance of the chamber 21., C3 the acoustic capacitance'of the chamber 25, Z1. the impedance of the horn I1 and Z2 the impedance of the horn I9, the electrical analogues will be arranged as shown. It will be noted that the inductance m2 and the capacitance C:- form a series resonant circuit in shunt with the impedance Z1 and that the capacitance C2 is shunted across the impedance Z2. This arrangement is essential to provide efficient cutoffs for the two horns.

The modification of. my'invention shown in Figs. 5', 6 and 7 is practically identical with that previously described insofar as the low frequency horn I9 is concerned. However, in this modification, the high frequency horn I1 is omitted and the diaphragm I'5'is mounted immediately behind the small opening" 3 to have direct communication therewith and with the atmosphere, whereby it acts as a direct radiator. Sucha construction is preferable to. that previously described in certain cases, as. in radio receiver loud-speakers, monitoring loud-speakers, with centralized radio systems, and the like,since a direct radiator isusuallyv sufficiently efiicient in the midand high-frequency ranges. Also, since the intensity level of reproduction in small rooms is considerably less than the intensity level of the original sound, some accentuation. of lowfrequency response may be required. Coupling the horn I9 to one side of the diaphragm. I5 provides a good systemof low-frequency efliciency and, since the diaphragm I5 is adirect radiator in the arrangement shown. in Figs. 5 to 7 and covers a wide angle of distribution, it is possible to use a small and light vibrating system for the efficient reprodi-iction and distribution of the midand high-frequency ranges from the open side of the cone I5. While I have shown and described but two modifications of my invention, I am fully aware that many other modifications thereof and changes therein may be made within'the spirit of my invention. For example, in 'place of a single driver, two separate drivers may be employed, as may also adriver having a. single field supply for'two separate cones andvoice coils' of the type disclosed and. claimed, forexample, in

the copending application of Frank Massa, Serial No. 113,475, assigned to the Radio Corporation of America. It will also be obvious that the horns I! and [9 may be of any desired shape in cross section instead of square as shown, and that these horns may be made to expand in any desired way. Also, if desired, the baflles 29 may be placed in the chamber 21 instead of in the horn I9, as shown in Fig. 9. Many other changes will, no doubt, readily suggest themselves to those skilled in the art. I, therefore, desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. Signal translating apparatus comprising, in combination, a hollow cabinet, a partition therein dividing said cabinet into a pair of compartments, said cabinet including a wall provided with a pair of openings one of which establishes communication between the atmosphere and one of said compartments and the other of which establishes communication between the atmosphere and the other of said compartments, an electro-acoustical driver in one of said compartments, said driver having a diaphragm one side of which is in communication with the opening associated with one of said compartments, and a horn coupled to the other side of said diaphragm, said horn extending through said partition and having its terminal at the other of said openings.

2. Signal translating apparatus comprising, in combination, a hollow cabinet, a partition therein dividing said cabinet into upper and lower compartments, said cabinet including a wall provided with a relatively small opening which establishes communication between the atmosphere and said upper compartment and with a relatively large opening which establishes communication between the atmosphere and said lower compartment, an electro-acoustical driver in said upper compartment, said driver including a diaphragm one side of which is in communication with said small opening, and a horn coupled to the other side of said diaphragm, said horn extending through said partition and having its terminal at said large opening.

3. The invention set forth in claim 2 characterized in that the first named side of said diaphragm has direct communication with the atmosphere through said small opening.

4. The invention set forth in claim 2 characterized by the addition of a second horn which is coupled to said first named diaphragm side and which terminates at said small opening.

5. The invention set forth in claim 2 characterized in that said horn is of the folded type and is relatively long, said horn being particularly adapted to transmit low frequency vibrations, and characterized further by the addition of a relatively short, straight-axis horn particularly adapted to transmit high frequency vibrations, said second horn being coupled to said first named side of said diaphragm and terminating at said small opening.

6. The invention set forth in claim 2 characterized in that said horn is provided with one or more perforated baffles therein constituting an acoustic filter adapted to pass only vibrations below a substantially predetermined frequency.

7. The invention set forth in claim 2 characterized in that said horn is provided with a chamber behind said other side of said diaphragm constituting an acoustic capacitance ad jacent said diaphragm.

8. The invention set forth in claim 2 characterized in that said horn is so constructed and arranged within said cabinet that it cooperates with said cabinet to provide a chamber behind said other side of the diaphragm constituting an acoustic capacitance immediately behind said diaphragm.

9. The invention set forth in claim 2 characterized in that said horn is provided with one or more perforated bafiies therein constituting an acoustic filter adapted to pass only vibrations below a substantially predetermined frequency, and characterized further in that said horn is provided with a chamber behind said. diaphragm constituting an acoustic capacitance, the capacitance of said chamber being comparable to the impedance of said horn at substantially said predetermined frequency.

10., Signal translating apparatus comprising, in combination, a hollow cabinet, a partition therein dividing said cabinet into upper and lower compartments, an electro-acoustical driver in said upper compartment, said driver including a diaphragm, a relatively short, straight-axis horn in said upper compartment coupling one side of said diaphragm with the atmosphere, and a relatively long, folded horn coupling the other side of said diaphragm with the atmosphere, said last named horn extending through said partition and having a portion located in said upper compartment and a portion located in said lower compartment and communicating with the atmosphere from said lower compartment.

11. The invention set forth in claim 10 characterized in that the portion of said long horn which is located in said upper compartment is divided into two sections symmetrically disposed with respect to said diaphragm, said sections each terminating into the portion located in said lower compartment.

12. The invention set forth in claim 10 characterized in that said small horn is provided with at least one opening in the wall thereof adjacent its throat and characterized further by the addition of means providing a chamber in parallel relation to said small horn, said chamber communicating with said small horn through said opening.

13. The invention set forth in claim 10 characterized in that said small horn is provided with at least one opening in the wall thereof adjacent its throat, and characterized further by the addition of means providing a chamber having communication with said horn through said opening, said chamber constituting an acoustic capacitance and the mass of air in said opening constituting an acoustic inductance in series with said capacitance, and said chamber being so arranged with respect to said horn that said series connected capacitance and inductance form a resonant circuit in shunt with the impedance of said horn, said resonant circuit being such as to resonate at the low frequency cut-off frequency of said small horn.

14. Signal translating apparatus comprising, in combination, a cabinet including a side wall, a partition in said cabinet dividing it into upper and lower compartments, said lower compartment having an opening in said wall whereby communication is established between the atmosphere and said lower compartment, an electroacoustical driver in said upper compartment, and

a horn coupled to said. driver and terminating at said opening, one portion. of said horn being located in said upper compartment and another portion. thereof being located. in. said lower compartment, said partition constituting a wall common to all of said hornportions, and said partition having at least one opening therein for establishing communication between said horn portions.

15. The invention set forth in claim 144 characterized in that said horn increases uniformly in cross-section along its length and characterized further in that the opening in said partition is of smaller area than the cross-sectional area of the horn at the same point, the area of said opening being so related to the cross-sectional area of the horn at said point as to constitute an acoustic filter adapted to pass only vibrations below substantially a predetermined frequency.

16. The invention set forth in claim 14 characterized by the addition of means in said upper compartment providing a chamber interposed between said driver andthe throat of said horn, the cross-sectional area of said chamber being appreciably greater than the cross-sectional area of said throat whereby said chamber constitutes an acoustic capacitance, and characterized further by the addition of an acoustic filter in said horn adapted to pass only vibrations below substantially a predetermined frequency, said acoustic capacitance being comparable to said horn impedance at substantially said predetermined frequency.

'17. Signal translating apparatus comprising, in combination, an electro-acoustical driver, a horn loading one side of said driver, said horn having a small opening therein in proximity to said driver, and means providing a chamber about the throat end of said horn having communication with said horn through said opening, said chamber constituting anacoustic capacitance and the mass of air in said opening constituting an acoustic inductance, said chamber and said opening being so related to said horn as to form a series resonant circuit in shunt with the impedance of said horn, and said: resonant circuit being such as to resonate at a predetermined frequencyl y HARRY F. OLSON.