US2858377A

US2858377A - Driver unit for loudspeakers

Info

Publication number: US2858377A
Application number: US351962A
Authority: US
Inventors: Sidney E Levy
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-29
Filing date: 1953-04-29
Publication date: 1958-10-28
Anticipated expiration: 1975-10-28

Description

Oct. 28, 1958 s. E. LEVY 2,858,377

DRIVER UNIT FOR LOUDSPEAKERS ATTORNEY Oct. 28, 1958 s. E. LEVY 2,858,377

DRIVER UNIT FOR LoUDsPEAxERs Filed April 29, 1953 2 Sheets-Skaail 2 United rates DRIVER UNrr Fou LOUDSPEAKERS Sidney E. Levy, White Plains, N. Y., assiguor of one-haii to Arthur Blumenfeld, New York, N. Y.

Application April 29, 1953, Serial No. 351,962

19 Claims. (Cl. 179-1155) The present invention relates to loudspeaker driver units, and more particularly to a novel driver unit of .both a direct and indirect radiator type having acoustically isolated dual concentric or coaxial throats.

Heretofore, loudspeaker driver units usually have been so constructed as to utilize the acoustic energy generated from only one surface of the diaphragm by directing this energy to a throat or central orifice for entrance into a suitable horn or trumpet, while the sound energy generated by or radiated from the reverse side of the diaphragm is confined to and trapped in a relatively air-tight chamber, or is trapped within the housing or shell f the driver unit and is not directed into the atmosphere, or is otherwise dissipated as wasted energy.,

Other known driver units have been so constructed as :to utilize the sound generated by the rear vsurface of the diaphragm, in addition to that generated by the front surface thereof, by directing the rear sound generation to a vseparate horn or trumpet which is on a common axis with the front horn or trumpet. 4In this type of construcztion the respective sound generations travel in directions '180 apart.

vIt is an object of the present invention to provide a novel loudspeaker driver unit which is so constructed as to collect the acoustic energy generated by the rear sur- Aface of the diaphragm and direct the same forwardly so that it is directed in the same direction and on the same axis as sound generated by the front surface of the diaphragm.

'A further object is to provide a novel loudspeaker driver unit which collects the sound generated by the rear surface of the diaphragm and acoustically isolates the rear sound generations and directs the same towards a central neck or throat which is coaxial with the direction of travel of sound generated by the front of the diaphragm, this neck being adapted to be connected to a horn through which the two acoustic waves are projected coaxially into the atmosphere.

Specifically, it is an object of this invention to provide a loudspeaker driver unit which includes an outer shell, a magnetic pot assembly suitably mounted in said shell and spaced therefrom, a central pole-piece carried by said pot assembly, said pole-piece having an axially extended opening therethrough communicating with the space between the shell and the pot assembly, a diaphragm mounted in the space between the shell and the magnet assembly, a barrier defining an isolated air chamber in front of the diaphragm and with the shell defining a second isolated air chamber concentric with the first air chamber and communicating with the. opening through the pole-piece through the space between the magnetic pot assembly and the shell, whereby sound generated by the front of said diaphragm is directed axially through the first-mentioned chamber, and sound generated by the back of the diaphragm will be directed through the polepiece and the space between the pot assembly and the v'shell and through the secondmentioned air chamber` Another specific objective of the present invention is ice to provide a loudspeaker driver unit which includes an outer shell, a magnetic pot assembly suitably mounted in said shell and spaced therefrom, said pot assembly including a central pole-piece having a plurality of openings therethrough, a vibratable diaphragm interposed between said pot assembly and the rear wall of said outer shell, and a barrier carried by said magnetic pot assembly at the forward side thereof, said barrier defining a central throat therethrough in communication with theA openings through the pole-piece for conducting sound generated by the forward surface of the diaphragm to a horn, and said barrier defining with the shell a second throat concentric with the first-.mentioned throat and communicating through the space around said pot assembly with the space at the rear side of said diaphragm for conducting sound therefrom to said horn.

Other objects, advantages or features of construction will be hereinafter described or will become apparent t0 those skilled in the art, and the novel features of the present invention will be defined in the appended claims.

In the drawing:

Fig. 1 is a longitudinal sectional view taken on the central plane of a driver unit embodying the present iuvention, said driver unit being adapted to be connected to a horn or other sound directing unit such as that shown in broken lines; i

Fig. 2 is -a view in front elevation of the driver unit alone, with a portion thereof broken away;

Fig. 3 is a longitudinal sectional view taken on the central plane of another form of driver unit embodying the present invention, this driver unit also being adapted to be connected to a horn or other sound-directing unit such as that shown in broken lines in Fig. l; and

Fig. 4 is a view in front elevation of the driver unit of- Fig. 3.

Like reference characters designate corresponding parts in the figures of the drawings and in the following detailed description.

One form of driver unit embodying this invention, as shown in Figs. l and 2 includes an outer housing or shell 1, an inner magnet or pot assembly 2, a diaphragm '3, a partition or baflie 4, and perforated spacer elements 5 and 5'.

The housing 1 is preferably made in two partsand has` a rear, cup-like shell portion 6 disposed in abutting engagement with a forwardly projecting closure 7 having same in abutting engagement, with a compressible annular gasket or washer 4' therebetween.

Suitably mounted in and carried by the housing or shell l is the magnet or pot assembly 2 which includes an annular plate 9 of magnetic material having a central opening 9' therein. provided with a plurality of circumferentially spaced L- shaped ribs 6 which serve to center the pot assembly and maintain the same in spaced relation to the inner rear face and the annular wall of the shell 6. Engaged with the annular member 9 is an annular or ring magnet element 10 which is operatively connected to another annular plate il at the rear side of the member 10, this plate ll having a central opening i2 therethrough. Operatively connected to the plate 11 about the margin of the opening 12 is a central pole-piece13, this polepiece 13 having a rearwardly diverging central opening 14 therethrough. A centering washer 15 of annular form is suitably secured to the plate 9 and projects radially inward into contact with the outer margin of the pole- Patentecl Oct. 28, 1958 The shell 6 at its inner rear side is piece 13, this centering washer being of a non-magnetic material.

The diameter of the pole-piece 13 is less than the diameter of the opening 9 through the annular plate 9, thus providing an air gap 16 therebetween, and a cylindrical voice coil 17 which is suitably secured to the diaphragm 3 in any conventional manner projects into the air gap 16.

The diaphragm 3 preferably has a domed central portion 18 interconnected by compliant ribs 19 with a marginal fiange 20, this marginal ange 20 being secured between the pair of annular spacer washers or gaskets 5, which are interposed between the forward face of the annular plate 9 and the opposing inside surface of the closure portion 7, with the flange of the diaphragm 3 clamped between the washers 5, 5. Y

The bathe or separator 4 is also provided with a niarginal ange 21 which is clamped between the washers 5, 5', this bafiie 4 tapering forwardly and inwardly towards the axis of the driver unit and extending forwardly thereof to form a central throat 21. About the throat portion 21 of the separator 4, the neck 8 of the housing 1 is provided with a centering collar or spider 22 having annularly spaced radial connecting ribs 23 spaced there around. As best seen in Fig. 2, the spaces intermediate the ribs 23 define arcuate passageways 24.

The washers 5, 5 are respectively provided with a suitable number of

radial openings

25, 25 therethrough, these openings as shown in the drawing being in the form of round passageways, and the voice coil 17 is likewise provided with a suitable number of annularly spaced openings 26 therethrough, the latter openings shown in the drawing also being in the form of round apertures.

As is best seen in Fig. 1, the baffle or separator 4 divides the housing 1 into two acoustically

isolated chambers

27 and 28. The chamber 27 is defined between the forward or outer surface of the separator 4 and the inner surface of the closure 7, and the openings 2S through the forward washer 5 establish communication between the chamber 27 and the zone of the housing 1 in which the pot assembly 2 is mounted. The openings 25 through the rearward washer 5 serve to establish communication between the space behind the diaphragm 3 and the space between the pot assembly 2 and the housing, and the openings 26 through the voice coil 17 establish communication between the space within the confines of the voice coil and the space between the compliant section 19 of the diaphragm and the plate 9 of the pot assembly. Communication between these latter spaces is also established through the air gap 16 around the inner or free end of the voice coil 17. The air chamber 28 is defined between the inner or rearward faces of the separator 4 and the forward face of the diaphragm 3, respectively.

The shape or contour of the isolating partition 4 and thecontour of the inner surface of the closure portion 7 of the housing are designed to provide a cross-sectional area for each of the chambers 27 and 2S which will maintain a maximum acoustic efhciency, since abrupt changes in these areas would result in an undesirable restriction or pocket, with attendant deleterious effects upon the frequency response and sensitivity of the loudspeaker driver.

Sound generated by the forward surface of the diaphragm is confined to the chamber 28 and thus is preferably directed to the throat 21 of the separator 4 without any bend or circuitous pass, and thus this direct and relatively short path is primarily for the high frequency sounds generated by the diaphragm. On the other hand. however, the sounds generated by the rear surface of the diaphragm 3 will be caused to traverse a number of bends in its path to the chamber 27, with resultant loss of high frequency energy because of path length differences at the bends which tend to trap or cancel the higher frequencies. Therefore the refiex energy from the rear 4 surface of the diaphragm becomes useful for the middle or low frequency bands of sound waves.

Since the forward portion of the neck 8 defines an annular throat 27 concentrically disposed about the throat 21 of the separator 4, the driver unit produces two acoustic waves, namely, a high frequency wave and a low frequency wave, both emerging from a common outlet. When such a driver unit is associated with a horn such as that shown in broken lines in Fig. 1, sound may be reproduced by a single voice coil and diaphragm and uliimateiy directed into the atmosphere in two separate waves, with both Waves transmitted in the same direction on a common axis.

The horn shown in broken lines in Fig. 1 is the subject matter of my companion application tiled concurrently herewith, and therefore will only be described generai'iy in the present application.

The horn assembly comprises a supporting member or head 31 adapted to threadedly engage the threaded neck S of the housing 1 of the driver unit. This supporting member 31 is provided about its outer margin with a dared bell 32, the forward surface of the member 31 being arcuately formed at 31 so as to merge with the curvature of the bell 32. At its center, the member 31 is provided with a spider-like support 33 having arcuate openings 34 therethrough which correspond substantially to the openings 24 in the spider 22. Suitably coaxially mounted on the member 31 are an intermediate annular wall or partition 35 and an inner annular wall or partition 36, The inner wall 36 is of such a diameter as to substantially match the throat 21 of the separator 4 and ares or diverges gradually towards its forward end so as to provide a relatively short high frequency horn which preferably terminates at its extreme forward end in a widely flared bell 36. The space between the inner wall 36 and the intermediate wall 35` communicates with the chamber-27 and thus constitutes a sound path for low and middle frequency sound waves generated by the rear of the diaphragm 3, and this latter sound path is reflexed at the forward end of the wall 35 3S to the supporting member 31 of the horn assembly.

The arcuate surface 31 of the supporting member 31 reexes the low frequency sound path a second time from whence the low frequency sound path again extends forwardly.

The path of sound waves generated by the forward side of the diaphragm 3 is indicated by solid arrows, and

it will be noted that this path is relatively short and straight. The paths followed by the sound waves.l generated by the rear side of the diaphragm 3 are indicated by broken arrows, and it will be seen that the latter sound paths are circuitous or tortuous.

Tracing out the paths followed by the soundwaves generated by the rear face of the diaphragm, it is seen from the broken arrows in Fig. 1 that sound generated by the central portion of the diaphragm 3 passes rearwardly through the opening 14 in the pole-piece 13 and is then caused to spread by a conical projection l" on the inner face of the housing 1, into the space 40 between the pot assembly 2 and the housing 1. This space 4@ extends completely around the outer periphery of the pot assembly 2, and the sound waves thus are directed to the openings 25 through the forward washer 5 through which the sound waves pass in a radially inward direction into the chamber 27. From the chamber 27, the sound waves pass through the

spider openings

24 and 34 of the assembly and into the reflexed sound passage of the horn.

In addition, some of the sound waves generated by the rear arca of the diaphragm lying close to the voice coil may follow either or both of two paths, Sound waves following one of these paths pass rearwardly through the air gap 16 between the inner face of the voice coil and the outer periphery of the pole-piece and are then reflexed by the centering washer and travel forwardly through the air gap 16 between the outer periphery of the voice coil and the inner margin of the plate 9, where they join with sounds following the other of the two paths which is radially through the openings 26 in the voice coil 17. From here, the sound waves travel radially outwardly through the space 41 between the diaphragm and the plate 9 and then through the openings in the rear washer 5 to the space 40, where they join the sound waves following the path through the central pole-piece and continue along the same path above described through the openings 25 in the washer 5 and so on into the horn.

Inherently, the sounds ultimately reaching the atmosphere from the forward face of the diaphragm 3 will be those of the high frequency range, whereas the sounds generated by the rear face of the diaphragm, by reason of their circuitous paths, will be those of the intermidiate or low frequency range, but these sounds of the different frequency ranges will nevertheless be projected in the same direction on the same axis and on a similar wave front.

Referring to Figs. 3 and 4, there is shown another form of the present invention.

In this form of the invention, the housing or shell 101 includes a pair of

complemental housing parts

102, 103, each preferably having a plurality of radially projecting

ears

104 and 105 through which a threaded fastener 106 extends. An annular, compressible washer 107 is disposed between the opposed faces of the

housing parts

102 and 103 to seal the housing against sound losses and to facilitate assembly of the driver unit.

Mounted within the housing 101 and spaced therefrom is a magnetic pot assembly including a rear annular plate 108 of magnetic material having a central opening 109 therethrough, an annular magnet member 110 and a forward annular plate 111 of magnetic material having a central opening 112 therethrough. A central pole-piece 113 is disposed in the opening 109 in plate 108 and engages at its forward end with the plate 111. At the forward side of the plate 111 is an axially extended barrier member 114 having a radial ange 115 thereon seating on the plate 111 and having an axially extended annular flange 116 seating in the housing 112 through the plate 111. Extending axially through the barrier 114 is a sound passage 117.

At the other side of the pot assembly and engaged with the rear side of the plate 108 is a vibratable diaphragm 118 having a voice coil 119 carried by its central portion, this voice coil projecting into the air-gap 120 defined between the pole-piece 113 and the inner periphery of the plate 108.

The magnetic pot assembly, together with the barrier 114 and the diaphragm 118, are located and maintained in spaced relation to the inside surface of the housing 101 by means of a plurality of circumferentially spaced L-shaped

ribs

122 and 123 at the inside corners of the respective housing parts' 102 and 103. The ribs 122 engage a resilient washer 124 interposed between a marginal flange 125 of the diaphragm 118 and the ribs 122, and the ribs 123 engage the forward surface of the flange 115 of the barrier 114, whereby when the housing parts are secured together by the screws 106, the pot assembly, the barrier and the diaphragm are clamped together between the

ribs

122 and 123. The

ribs

122 and 123 also engage the outer periphery of the pot assembly and hold the `pot assembly in coaxial spaced relation to the housing.

The forward end of the housing part 103 is provided with a reduced threaded neck 126, the inner periphery of which is spaced from the outer periphery of the barrier 114 so as to provide a sound passage 127 communicating through the space 128 between the pot assembly and the housing with space 129 between the rear side of the diaphragm 118 and the housing. The central pole-piece 113 is preferably provided with a plurality of openings 130 therethrough, which openings establish communication between the sound passage 117 through the barrier 114 and space 131 between the diaphragm and the polepiece. Thus, sounds generated from opposite sides of the diaphragm 118 are free to travel through acoustically isolated sound paths to dual

concentric throats

117 and 127, from whence these separate sound waves may pass into a suitable horn such as that shown in broken lines in Fig. l, which horn is adapted to be connected to the threaded neck 126 of this form of the driver unit.

In use, sound waves generated by the rear face of the diaphragm 118 will travel from space 129 around the outside of the pot assembly, through space 128, and out through the throat 127. This sound path is designated by the broken directional arrows, and since this sound path is long and tortuous, it is primarily suited for the conduction of relatively low frequency sound waves.

On the other hand, sound waves generated from the inner or forward side of the diaphragm 118 will pass through the openings 130 through the central pole-piece and through the throat 117, as indicated by the solid arrows, and because of the fact that this' path is relatively short and straight, it is primarily suited for the conduction of relatively high frequency sound waves.

Thus, the driver unit of each of the two illustrative forms of the present invention will direct the sound waves generated from opposite sides of a single diaphragm through acoustically isolated sound paths to dual concentric throats from which these respective sound waves are emitted on the same axis, in the same direction, and on a similar wave front. It is to be understood that in referring to a central pole-piece having an opening therethrough, as described in the specification with respect to the elements designated `13 and 113, and as defined in the claims, any appropriate form of magnet having an opening through a portion thereof disposed over the diaphragm may be employed.

While the specific details have been herein shown and described, the invention is' not confined thereto as changes and alterations may be made without departing from the spirit thereof as defined in the appended claims.

I claim:

1. A loudspeaker driver unit comprising an outer shell, a magnet assembly mounted in said shell in spaced relation thereto, said magnet assembly including a central polepiece having a central sound passage therethrough communicating with the space between said shell and said magnet assembly, a diaphragm mounted in said shell, means engaged about the margin of said diaphragm and projecting axially to form a sound passageway therethrough on one side of said diaphragm, said means together with said shell defining a second sound passageway concentric with the first passageway and acoustically isolated therefrom, and means establishing communication between the second sound passageway and the space between the magnet assembly and the shell.

2. A loudspeaker driver unit comprising a shell, a magnetic pot assembly mounted in said shell, a central pole-piece in said pot assembly and defining an air-gap between the pole-piece and a portion of said pot assembly, a vibratable diaphragm spaced from said pot assembly and from said shell and having a voice coil extending into said air-gap, separator means engaged about the margin of said diaphragm and projecting axially therefrom and forming a hollow sound passage for sound generated from one side of the diaphragm, said shell surrounding said separator means in spaced relation thereto and defining a second sound passage acoustically isolated from the first sound passage and concentric therewith for conducting sound generated from the other side of said diaphragm, and means establishing communication between said second sound passage and the space between the diaphragm and the pot assembly.

3. A loudspeaker driver unit as defined in claim 2, wherein the last-mentioned means comprises a pair of washers having radial openings therethrough, said washers engaging said diaphragm about the margin thereof, with one of said washers disposed on one side of said diaphragm and the other of said Washers disposed on the other side of said diaphragm.

4. A loudspeaker driver unit as defined in claim 2, wherein the last-mentioned means comprises a pair of washers having radial openings therethrough, said washers engaging said diaphragm about the margin thereof, with one of said washers disposed on one side of said diaphragm and the other of said washers disposed on the other side of said diaphragm, and said separator means including a marginal flange secured between said washers with the margin of the diaphragm.

5. A loudspeaker driver unit as defined in claim 2, wherein the last-mentioned means comprises a central opening provided in said pole-piece, and said pot assembly is spaced from said shell to provide an annular space communicating with the opening through said pole-piece and the second sound passage aforesaid.

6. A loudspeaker driver unit as defined in claim 2, wherein the last-mentioned means comprises a central opening provided in said pole-piece, and said pot assembly is spaced from said shell to provide an annular space communicating with the opening through said pole-piece and the second sound passage aforesaid, and said shell having a conical projection extending into the opening through the pole-piece.

7. A loudspeaker driver unit as defined in claim 2, wherein the voice coil is provided with a plurality of openings therethrough.

8. A loudspeaker driver unit as defined in claim 2, wherein a centering washer bridges the air gap in spaced relation t the voice coil and forms a sound passage around the end of said voice coil.

9. A loudspeaker driver unit as defined in claim 2, wherein the last-mentioned means includes a washer supporting the diaphragm in spaced relation to the pot assembly and having a plurality of passages extending through said washer.

l0. A loudspeaker driver unit comprising an outer shell, a magnetic pot assembly mounted in said shell in spaced relation thereto and defining with said shell a sound passage therebetween, a central pole-piece in said pot assembly, said pole-piece having a central opening therethrough, a vibratable diaphragm disposed between said pot assembly and a portion of said shell and overlying said pole-piece in spaced relation thereto, said pole-piece being spaced from a portion of said pot assembly and forming an air gap therebetween, said diaphragm having a perforated voice coil having a free end extending into said air gap, means closing one end of said air gap and forming a sound passage around the free end of said voice coil, a perforated washer interposed between the marginal edge of the diaphragm and said pot assembly, another perforated washer interposed between the marginal edge of said diaphragm and the shell, an annular separator having a marginal flange disposed between the diaphragm and the second-mentioned washer, said separator being in spaced relation to said shell and extending axially to form a throat for sound generated by the adjacent side of said diaphragm, and said shell surrounding the throat of said separator and forming a second throat concentric with the first throat.

ll. A loudspeaker driver unit comprising an outer shell, a magnetic pot assembly mounted in said shell in spaced relation thereto and defining with said shell a sound passage therebetween, a central pole-piece in said pot assembly, said pole-piece having a central opening therethrough communicating at one end with the sound passage aforesaid, a diaphragm disposed between said pot assembly and a portion of said shell and overlying said pole-piece in spaced relation thereto, said pole-piece being in spaced relation to a portion of said pot assembly and defining an air gap therebetween, said diaphragm having a voice coil extending into said air gap, spacer means having sound passages therethrough and interposed between said diaphragm and said shell, and separator means disposed between said diaphragm and said shell and forming therewith a pair of acoustically isolated concentric sound passages, one of said concentric sound passages communicating through the passages in said spacer means with the sound passage between the pot assembly and the shell, and the other of said concentric sound passages being confined between said diaphragm and said separator means.

12. A loudspeaker driver unit comprising a shell, a diaphragm in said shell, means also in said shell for vibrating said diaphragm, a separator dividing said shell into two acoustically isolated sound passages leading respectively to opposite sides of said diaphragm, said shell having a reduced neck forming a throat for one of said sound passages, and said separator having a reduced neck concentric with and spaced from said neck of the shell and forming a throat for the other of said sound passages, and means supporting said separator in said shell in spaced relation thereto.

13. A loudspeaker driver unitas defined in claim l2, wherein the means for supporting the separator means includes an annular gasket having sound openings therethrough disposed between said shell and a portion of the diaphragm.

14. A loudspeaker driver unit as defined in claim 12, wherein the means for supporting the separator means includes an apertured centering spider carried by said shell in the neck thereof and engaged about the neck of said separator means.

l5. A loudspeaker driver unit comprising a shell, a magnetic pot assembly mounted in said shell in spaced relation thereto and defining with said shell a sound passage therebetween, a central pole-piece in said pot assembly, said pole-piece having at least one opening therethrough, a vibratable diaphragm mounted in said shell at one end of said pole-piece and overlying the latter in spaced relation to said pole-piece and to said shell, a barrier at the other end of said pole-piece and having a central opening therethrough defining an outlet throat in communication through the opening in said pole-piece with the space between said diaphragm and said pole-piece, said barrier being spaced from said shell and defining therewith an annular outlet throat concentric with the central outlet throat through the barrier, and the last-mentioned outlet throat being in communication through the space between said magnetic pot assembly and said shell with the space between said diaphragm and said shell.

16. A loudspeaker driver unit comprising an axially extended generally cylindrical outer shell, a vibratable diaphragm mounted in said shell at one end thereof, means in said shell for vibrating said diaphragm, said shell having a reduced hollow neck adapted to be connected to a loudspeaker horn, means defining a pair of acoustically isolated sound passages leading from opposite sides of said diaphragm to said hollow neck, said i last-mentioned means including a barrier mounted in said shell at the other end of the same and on the side of the diaphragm vibrating means opposite said diaphragm, said barrier having a central opening therethrough constituting a central outlet throat for one of said sound passages, said barrier being spaced from said reduced neck and defining with said neck an outlet throat for the other of said sound passages concentric with the first-mentioned outlet throat, the central outlet throat through the barrier and its sound passage being substantially straight and short, and the outlet throat between the barrier and the shell and its sound passage being relatively long and tortuous.

17. A loudspeaker driver unit comprising a shell, a diaphragm in said shell, means in said shell for vibrating said diaphragm, means for mounting the diaphragm vibrating means in spaced relation to said shell to form a sound passage between said shell and the diaphragm vibrating means leading from one side of said diaphragm, said diaphragm vibrating means having means providing a sound passage therethrough leading from the other side of said diaphragm, a neck on said shell forming an out- 1ct throat for the first-mentioned sound passage, and barrier means disposed in said shell and defining an outlet throat for the second-mentioned sound passage, said sound passages being acoustically isolated one from the other, and said outlet throats also being acoustically isolated one from the other and extending coaxially in the same direction.

18. A loudspeaker driver unit as dened in claim 17, wherein said diaphragm and said barrier means are disposed on the respective opposite sides of said diaphragm vibrating means.

19. A loudspeaker driver unit as defined in claim 17, wherein the diaphragm vibrating means comprises a magnetic pot assembly including a central pole-piece having at least one opening therethrough, and having a plate at one end of said pole-piece provided with a central opening therethrough, said barrier means being Supported on said plate, and the throat of said barrier means being in communication with the opening through said pole-piece through the opening in said plate.

References Cited in the file of this patent UNITED STATES PATENTS 1,930,915 Wente Oct. 17, 1933 2,084,944 Cornwell June 22, 1937 2,367,026 Hutter Jan. 9, 1945 2,429,470 Knowles Oct. 2l, 1947 2,440,439 Gilman Apr. 27, 1948 2,534,040 Lindley Dec. 12, 1950 2,549,963 De Buer et al. Apr. 24, 1951 2,642,947 Heidrich June 23, 1953 OTHER REFERENCES Olson et al.: Publication, A Compound Horn Loudspeaker, Journal of the Acoustical Society of America, vol. 8, pp. 48-52, July 1936.