US2580916A - High fidelity sound reproducing unit with resiliently suspended baffle plate - Google Patents

Description

Jan. 1, 1952 M. K. HODGE 2,580,916

HIGH FIDELITY SOUND REPRODUCING UNIT WITH RESILIENTLY SUSPENDED BAFFLE PLATE Filed Sept. 20, 1950 4 Sheets-Sheet 1 Murry Kelly Hodge, INVENLQ/R.

BY (Wavy 3M 4 Sheets-Sheet 2 Q & 3 K 5 M. K. HODGE HIGH FIDELITY SOUND REPRODUCING UNIT WITH RESILIENTLY SUSPENDED BAFFLE PLATE Murry Kelly Hodge INVENTOR.

BY dywqvM Jan. 1, 1952 Filed Sept. 20, 1950 Jan. 1, 1952 M. K. HODGE HIGH FIDELITY SOUND REPRODUCING UNIT WITH RESILIENTLY SUSPENDED BAFFLE PLATE 4 Sheets-Sheet 3 Filed Sept. 20, 1950 Murry Kelly Hodge INVENTOR.

BY WW Em v Em Jan. 1, 1952 HQDGE Y 2,580,916

HIGH FIDELITY SOUND REPRODUCING UNIT WITH RESILIENTLY SUSPENDED BAFFLE PLATE Filed Sept. 20, 1950 4 Sheets-Sheet 4 Murry Kelly Hodge INVENTOR.

BY 2mm Patented Jan. 1, 1952 HIGH FIDELITY SOUND REPRODUCING UNIT WITH RESILIENTLY SUSPENDED BAFFLE PLATE Murry Kelly Hodge, mm Little Rock, Ark.

Application September 20, 1950, Serial No. 185,834

12 Claims. 1

This is a continuation in part of the earlier pending application, Serial No. 90,014, filed April 27, 1949, now abandoned.

This invention relates to sound reproducing and distributing devices and it has ior its main object to provide a high fidelity sound or tone equalizing, harmonizing and distributing unit to be used in connection with a suitably selected high fidelity loud-speaker or with loud-speakers or the conventional type which unit improves materially the performance of the speaker with respect to fidelity and quality of the tone or sound produced and with respect to the distribution of the sound or tone emanating from the reproducing device within a. room.

According to the invention the usual baflle grille arrangement of a radio set, a musical instrument or other sound reproducing unit is replaced by a special multiple baflle assembly, one member of which projects into the interior of the conical loud-speaker membrane and divides the sound beams produced by the membrane at or near the point at which they originate, while a further member intermingles the divided beams emanating from the loud-speaker and is so placed with respect to a grille that the columns of the grille produce a further intermingling of the said beams.

A further object of the invention consists in so arranging the baffle-grille assembly that both are practically acoustically independent of and not influenced by the cabinet housing the sound reproducing unit.

It is a still further object of the invention to suspendthe entire assembly and especially the battle assembly and all its supporting parts solely on the front side. of the cabinet, making the rear of the cabinet entirely free, so that the back wall of the cabinet may be removed.

It is a still further object of the invention to insert between the cabinet proper and the bailie assembly separate sound boxes or com-- partments attached only on their front sides which sound boxes carry the supports for the baflle assembly and which eliminate completelyany efiects which may be due to the reaction of the cabinet.

It is a further object of the invention to provide a two point resilient adjustable suspension arrangement for the baflle assembly which suspension arrangement permits to cutout completely the transmission of sound waves over the'supports or which permits, it suitably adjusted, the transmission or a very limited amount 01* lound energy throu h the sound boxes in order to adjust the pitch of the prevailing background tone of the sound reproduction.

Other objects of the invention are more specific andwill be set forth in the detailed specification.

The invention is illustrated in the accompanying drawings showing one embodiment of the invention and one modification thereof. It is, however, to be understood that the modifications which have been illustrated are shown by way of example only in order to explain the principle of the invention and the best mode of applying the principle. The specification and drawings do not make an attempt to illustrate and describe the various modifications by means of which the invention may be carried into eliect and a departure from the examples illustrated and shown in the drawings will therefore not necessarily constitute a departure from the principle of the invention.

In the drawings:

Figure l is a perspective view of a console radio combined with a phonograph;

Figure 2 is an exploded perspective view of the speaker and the entire baffle and grille assembly used according to the invention;

Figure 3 is a sectional plan view of the console radio and phonograph illustrated in Figure l, the section being taken along the plane which is indicated at 3-3 in Figure 1;

Figure 4 is an elevational sectional view through the unit, the section being taken along the plane of symmetry indicated at 4-4 in Fig. ure 1;

Figure 5- is a fragmentary elevational view of the bafile arrangement seen from the front;

Figure 6 is a fragmentary elevational view of the baiile arrangement when seen from the rear;

Figure 7 is an elevational view of a modified arrangement showing the baflle assembly in cooperation with two loud-speakers; and

Figure 8 is a diagrammatic representation of a sound reproduction unit according to the invention, within a room showing the dispersion of the sound waves and the distribution of the reflected and the directly emitted beams.

To explain the nature of the invention more fully it may be mentioned that in those cases in which high fidelity reproduction of music and the highest possible quality of reproduction of speech has been attempted the units to which most attention was hitherto paid were-apart from the electrical transducing equipmentthe of parasitic oscillations in the conical membrane and to other and similar causes. 7

Other defects of the tonal quality of the reproduction were ascribed to the cabinet and more specifically to the resonance of the cabinet favoring the development of certain low frequencies and suppressing or attenuating other frequenc es and also to the deleterious influence of some walls of the cabinet, especially of the back wall,

the ideas about the nature of-thesedeleterious influences being, however, based on contradictory views, as the elimination of the back wall of the 4 tive sound radiation along the cone due to other effects such as a variable resistance at various points which is partly caused by the forcing in and out of air around the voice coil and the unequal reaction of the back side waves along the cone. Moreover, parasitic oscillations of the cone will also produce beam effects at certain points. a

The usual baffle and grille arrangement,with a grille consisting in openings in the front wall of the. cabinet, rarely succeeds in improving this unequal distribution of the radiations from the cone and'in removing the impression of a pointlike source of sounds.

cabinet has been proposed by some experts, while others recommend special sounding boards behind the loud-speakers. Also, a lining of the entire cabinet with absorbing textiles has been recthe rear side. Moreover, the arrangement included a grille which usually also formed an integral part of the cabinet and merely consisted in openings in a wall of the cabinet and which established communication between the space acted upon and put under pressure by the loudspeaker membrane' and the outer air to which said sounds were transmitted. A piece of textile fabric was usually inserted between the grille and the speaker. The dispersion of the sound waves within the room in front of the set or unit were always considered as a matter connected with the acoustics of the room.

As the quality of the reproduction of music and of speech is an extremely elusive factor which can be gaged by measurements only to a very limited extent, the principles which are mentioned below are mainly based on actual ex perience and on experimentation, their theoretical basis being to a large extent conjectural. It was, however, found that a loud-speaker of good quality was a more perfect sound reproducing means than expected and that it was mainly the irregularity in the distribution of the radiation which lowered the tonal quality or which caused lack of uniformity in the tonal quality and in perfect reproduction. a

One of the sources for inferior production is the fact that with an electrodynamic loud-speaker in which a moving voice coil drives a piston-like conical membrane, the higher frequencies are practically amplified at or near the central portion of the cone, and are projected outwardly in a straight beam from the front in the usual arrangement. There is, therefore, a marked high frequency beam effect which may be most troublesome especially as the radiation of power at high frequency is much greater than at lower frequencies. quencies which are distributed over the cone have in their turn a tendency to vibrate the support in the cabinet and to produce special and localized resonance effects.

Moreover, there isunequal power transmission or. otherwise expr,66d, anunequal loss of effecquality of. a re- The lowest fre- I Equalization, if any, is mainly produced by the textile fabric between the loud-speaker and the front wall which absorbs sound waves and thereby causes lowering of the efficiency.

According to the invention most of the above defects are eliminated by the introduction of a bailie assembly which is acoustically independent of the cabinet and which is mechanicallysupported but otherwise not connected with the cab-- inet. The cabinet may have a special configuration insofar as it is practically without a back wall and as it supports the Whole structure on its front side using none of its other walls for said supports.

The main feature of the baffle assembly used according to the invention, consists in having in front of the loud-speaker a square bafile resiliently suspended at two points, with an opening approximately the size of the cone Opening or only slightly smaller which opening is providedv :with means for carrying a fin assembly consisting of preferably triangular fins arrangedin the form of. a cross which project rearwardly towards a common apex. The outer edges of the fins thus form a pyramid erected on the rear surface of the baflle over the opening arranged in front of the loud-speaker cone and the base points of the pyramid are arranged in acircle concentric with the said openingwhilethe apex of the pyramid is locatedclose to thebase or voice coil end of the conical or frusto-conical membrane of the speaker. The space encircled by the conical membrane is thus subdivided into a plurality of beams or arms, said further baflle plate being pro- 4 vided with a number of circular openings arranged inthe center and along a circle around said center, respectively. -In front of this further baflie member a grille is arranged which consists of a double row of trapezoidal columns which leave obliquely directed passages between them. The grille columns are carried by the cabinet but they form separate elastic members secured merely at their upper and lower ends by .friction so that they are acoustically not to be considered as a part of the cabinet.

In order to explain the above-named features I in detail reference may now be had to the example illustrated. Thesound producing or repro ducing unit as illustrated'consists of a radio, a

phonograph, atelevision unit, an electric organ or. of any other electrical musical instrument in which sounds are ultimately emitted from al0ud-' speaker II] which is only diagrammatically indie ,cated inthe drawings as an e1ectro-. dynamica1.=

speaker with a piston-like action imparted to a conical or frusto-com'cal membrane moved by a voice coil. The nature of the loud-speaker is immaterial for this invention, except that it must be a suitable high fidelity speaker. However, it has been found by experience that with a baflie assembly according to the invention most types of high quality loud-speakers give satisfactory results and elaborate constructions for high fidelity reproduction are therefore not necessary.

The example shown in the drawings is a combined radio and phonograph. unit housed in a cabinet I l which is suitably sub-divided, the two upper compartments 14, I housing the phonograph and the radio set, respectively, while the side compartments l6 may be used for storing records. The side compartments and the central compartment of the cabinet may be provided with separately operable doors l1, I8, l9 concealing the interior completely when the unit is not used.

The cabinet is preferably open at the back and it may be closed by a textile fabric if desired. The front of the cabinet, to the exclusion of all other parts thereof, holds the entire sound reproducing structure and there is practically no other support on an other place.

The cabinet supports at the front two sound compartments or sound boxes which form the structure to which the bafile assembly is attached. The sound boxes are hollow compartments which are open at the front, as seen in Figures 3 and 4, which do not touch the cabinet but are arranged in substantial parallelism with the transverse walls 23 and are fixed to the cabinet by means of blocks and screws 2|.

These hollow structures 20 form the supporting means for the brackets which in their turn support the bafile device 40. The brackets 30 are of arcuate shape covering an arc of about 90, and one end 24 of the bafile is fixedly held on the sound box structure 20 by means of screw bolts 25, while the other end 26 is at right angles thereto and is provided with a stepped bore 21 with the wider portion in front and the smaller bore in the rear. Through this bore 21 a screw bolt 3| passes which supports the bafile arrangement generally indicated at 40. The screw bolt 3! does not fill the bore 21 but is freely mounted within the bore and is held by a rubber sleeve 32 inserted into the wider portion of the bore 21 and projecting outwardly therefrom and it is further held on theother side by a rubber washer 33 seated on the rear surface 01' the end portion 23 of the bracket 30.

The resiliently supported screw bolts 3| hold the baffle assembly which consists of three members arranged directly behind a grille 50, described below, with which the baffle arrangement cooperates.

The baffle assembly comprises a square bafile plate member 42 which is solely supported by two, screw bolts 3| held by the brackets 30. This baffle plate member 42 is prevented from moving transversely or from tilting with respect to the resilient supporting means by small springs 4'4 attached to the lower edge of the baiile plate member 42 and counteracting any force applied to said baiile plate member, thus holding the latter in a vertical position. The springs 44 are attached to bolts 45 projecting from the lower ends of the walls of compartments 20.

The bafile plate member 42 is moreover provided with a circular opening 46 which is approximately equal or somewhat smaller-than.

the largest diameter ofithe loud-speaker cone.

This opening is preferably located above'the center of the bafile plate member 42. The opening. is not a full .circular opening but is traversed by two cross arms 48, 49 arranged at right angles to .each other and formed by leaving the cross arms intact when cutting the opening. The circular opening is therefore, in fact, composed of four separatesectors, separated by thecross arms The cross arms carry the second baflie member 50 of the assembly on the rear side of the baffle plate 42, said second member being turned towards the loud-speaker. This member 50 consists of four triangular fins or lamellae 5| which are projecting rearwardly and which are arranged at right angles to each other, each fin 5! being centered on the middle line or axis of a cross arm 48,59. Each fin 5| is also triangular incross section. The four edges of the four fins 5! therefore delineate a pyramid, the axis of which is coincident with a line at right angles to the square baffle plate 42 and passing through the center of the circular opening 46. Ijhe fins join in the vicinity of said axis so that the four fins form-a cross. The apex 52 of the pyramid is located in the rear of the balile plate 42 on the side of the loud-speaker and when the speaker is mounted it is so adjusted that said apex 52 of the pyramid formed by the fins is close to the base portion of the conical membrane of the loud-speaker, which is usually formed by the apex of the conical membrane or by a small base plate near the voice coil. Therefore, the fins divide the conical interior of the loud-speaker membrane. v

The fins 5| may be solidary with the cross arms 48, 49 of the 'bafile plate 42 or they may preferably be fixed on the same by means of glue or by other fixation means. For the purposes of the present invention the fins 5| may be considered as being part of the baflie plate member 42.

The third member of the bafile assembly 40 consists of a circular disk 55 which is firmly secured on the baffle plate member 42 in such a position that it covers the opening 46 and its center is concentric with the center of the opening .46 and is located in the axis of the pyramid formed by the fins 5|. Thefixation of this disk 55 maybe obtained by screws 51. The disk 55 is provided with a central circular opening 58 and with a number of peripheral circular openings 59 arranged in a circle surrounding the central opening 58, eight such openings being shown. The openings 59 are so arranged that they are not obstructed by the cross arms 48, .49 and offer more .or less a free passage, while the central opening is so arranged that only its center is covered by the'said cross arms.

The peripheral openings 59 are moreover arranged within the area covered by the circular opening 45 so that free air passage from one side of the baflle plate member 42 to the other side is possible through said openings 46, 58 and 59. The area of this passage is therefore practically defined by the sum of the cross sections of said openings.

The three members of the baffle assembly 40, viz. the members 4-2, 50 and 55 thus form a unit which is resiliently suspended at two points only and which is therefore not in an acoustically effective connection with the cabinet, while the acoustically effective connection with the sound assoprow the column is turned outwardly and the small surface faces inwardly- The front portion, moreover, is grooved or is provided with a nearly semi-circular channel so that the columns 62 are concave prismatic bodies. The two rows of columns ,are set in such a manner that the columns of the front row are arranged between the columns of the back row so that channels 64 are formed between the lateral or side faces which are inclined toward the front. The columns are preferably made of wood and are elastic and they are only held by tenons placed in holes at the top and the bottom. wall of the cabinet. They are therefore not integral with the cabinet, but may be flexed in the panel.

The inclined side faces of the columns are parallel and the channels 64 which are formed are inclined in two different directions toward the axis of the speaker. These inclined channels-64, as will be noted, are the sole communication openings between the space in front of the baffle assembly 46 and the exterior.

It has-already been mentioned that the type of loud-speaker which is used is not material. However, it is well known that is some high fidelity I arrangements a plurality of loudspeakers H, 12 (Figure '7), with different frequency characteristics are arranged, one of the speakers reproducing mainly tones of a frequency above and the other tones of a frequency below a certain limit, this being, for instance, obtained by corrugations in the membrane of one of the speakers. A bailie assembly for such a speaker is illustrated in Figure '7. The figure shows that a preferably oblong baffle plate 42 is used in such a case with the two speakers H, 12 arranged at different heights and approxi: mately along a diagonal of that portion of the square baflle 42 which 'is' contained between the two supporting brackets 30.

Each of the two speakers has its conical membrane arranged in front of an opening such as the opening 46 traversed by two cross arms 48, 49 and provided with fins 50 and with a disk 55 in front-of the opening in the manner shown in Figures 2 to 6.

The operation of the device has partly been described and it has again to be emphasized that the explanation of a detailed operation is partly conjectural and that it is not intended to limit the invention by this explanation.

The cooperation of the grille 60 and of the baiile plate assembly 40 is necessary to obtain best results as was established by experiments. The effect of the grille is, however, two-fold as it not only contributes to the tonal quality by its cooperation with the bafiie arrangement but also influences the sound dispersion.

The sound waves produced by the conical membrane of the electro-dynamic speaker are divided near the point at which they start into at least fourbundles, which four bundles have to pass separately through the opening- 46 and through the disk 55. By these means the sounds, produced at different points will interminglethus;

preventing frequency beam emission and suppressing one of the main sources for the deterio-s ration of quality. As has already been explained the high frequencies are likely to be emitted the center or near the center where the projecting pointed portion of the fin assembly is located.

lower. and lowest frequencies which are capable of utilizing a major portion of the cone or the fullsurface of the cone cannot reach the cable net in thiscase on account of the resilient'susr pension of the baffle assembly and thus cabinet resonance and any reaction of the cabinet due: to such resonance is suppressed. It is, however, possible to tighten the suspension of the .baiile.v

assembly 40 on the brackets to acertain ex;-

tent so as to obtain the transmission of energyto the sound boxes 20 to a limited degree and this will result in lowering or raising the pitch of the background waves which may thus be adjusted in the way which seems most agreeable to the listener.

The openings .59 in the disk 55 cause further This is due to the fact that the sound waves gen-v erated at different spots of the conical membrane, are of different frequencies and,.a1though'.

intermingling' occurs, it is far from. complete and if only the conventional grille forming part of the cabinet is used this causes a prevalence or concentration of certain frequencies in certain directions and an insufficient formation of harmonics of higher frequencies in other direcv With the baffle arrangement described the intermingling of the beams is however complete.

tions.

The disk 55 arranged in front of the baffle plate 42 also reduces air blasts coming from the cone and prevents the cone from vibrating too much at the lower frequencies. These low or bass'frequencies,if allowed to develop too freely, drown the middle and high frequencies. If thedisk is removed a booming or rippling quality of thetone is immediately noticeable.

The inclined channels 64 formed between the side faces of the columns BI and 62 of the grille 60 in addition to the effect they have on the;

sound waves which penetrate from the cone to the outside, also have a favorable effect on the dispersion of the sound and distribution in the room.

speaker are in most cases not independent of the frequency so that the tonal quality in the space in front of the set is partly dependent on the spot at which the listener is located. The baffie system and especially the grille used has all the effect of equalizing the tonal quality in directions completely.

Figure 8 shows diagrammatically the influence of the grille on the dispersion of the sounds.

The beams which are formed and which penetrate into the space in front of the bafile'arrangement and enter the grille all consist of sound waves which have been crossed and intermingled so that frequency beaming is suppressed. The beams a, b formed'by the columns of the grille 60 are directed sideways at an angle; and they are moreover directed towards both- It is especially from these centers that. beams which are concentrated emanate. The.

It is well known that the directional characteristics of a radio set including the loud-.

sides. Those beams c which-lareformed by the interaction of two beams intersecting in front of the columns 62 are more or less propagated in a direction which is either perpendicular to the are most perfect. This point'i's at a considerable distance (depending on local conditions) and not merely at a distance not exceeding a couple of feet from the opening of the loudspeaker where only propagated sounds will be received. I

The arrangement and especially'the grille 80 thus improves the acoustics of a room automatically under normal conditions.

It may also be mentioned that. the result is. a

much better dispersion and distribution of the sound and that it is'especially to be noted that with orchestral music the tonal quality of each instrument may be reproduced with equal faithfulness at practically every point in front-of the set.

It will be noted that, 'whilesomeconstructive features above-described are essential others may be changed and modified without in any way departing from the essenceof the invention as defined in the annexed claims.

Having described the invention, what claimed as new is:

1. A sound reproducing unit with anelectrodynamic loud-speaker having a substantially conical membrane, comprising a baffle assembly arranged in front'of'the membrane of the loudspeaker, said baffle assembly including a resilient- 1y suspended square baffle plate provided with an opening located in front of the loud-speaker membrane, a rear baflle member having wedge shaped fins, projecting into the cone of the loudspeaker and an outer baffl member provided with a plurality of openings and fixedly mounted on the said square bafile member in front of the opening of the same.

2. A sound reproducing unit with an electrodynamic loud-speaker having a substantially conical membrane, comprising a baffle assembly arranged in front of the membrane of the loudspeaker, said baflie assembly including a resiliently suspended square bafiie plate member provided with a circular opening substantially of the size of the conical membrane of the loud-speaker, cross arms traversing said opening, a plurality of fins fixedly mounted on the square baflle plate member and projecting towards the loud-speaker into the conical space enclosed by the conical membrane, and an outer disk shaped baflle member fixedly mounted in front of the opening in the said -square baffle plate member mounted on the same, said disk shaped member being provided with a plurality of openings.

3. A sound reproducing unit with an electrodynamic loud-speaker having a substantially conical membrane, comprising a baifle assembly arrangedin front of the membrane of the loudspeaker, said baflle assembly including a resiliently suspended square bafile plate member provided with a circular opening substantially of the size of the conical membrane of the loud-speaker. cross arms traversing said opening, a plurality of wedge shaped triangular fins projecting towards the rear side into the conical space enclosed by the conical-liloud-speaker membrane, and an outer disk shaped baille member fixedly mounted in i to front of the opening in the said square baflie plate member mounted on the same, said disk shaped member being provided with a plurality of openings.

4. A sound reproducing unit with an electrodynamic loud-speaker having a substantially conical membrane, comprising a bafile assembly arranged in front of the membrane of the loudspeaker, said'baffle assembly including a resilient- 1y suspended square bafiie plate member provided with a circular opening substantially of the size of the conical membrane of the loud-speaker, cross arms traversing said opening, a plurality of wedge shaped triangular fins, arranged diametrically with respect-to the opening in the square baffle plate member and projecting from the cross arms of said opening, the edges of said fins forming a pyramidthe apex of which is located on an axis passing through the center of said circular opening, said apex being located near the apex of the conical membrane, said fins thus sub-dividing the space of the cone through which sound beams emanate, and an outer disk shaped baffl member fixedly mounted in front of the opening in the said square baifieplate member mounted on the 1 same, said disk'shaped member being provided dynamic loud-speaker having a substantially conical membrane, comprising a battle assembly arranged in front of the membrane of the loudspeaker, said baifie assembly including a resiliently suspended square bafiie plate provided with an opening located in front of the loud-speaker membrane, means for substantially sub-dividing the space in the interior of the conical membrane carried by and projecting from said resiliently suspended square bafile plate, and an outer baflie member provided with a plurality of openings arranged and fixedly mounted on the said square baffle member in front of the opening of the same.

6. A sound reproducing unit with an electrodynamic loud-speaker having a substantially conical membrane, comprising a cabinet, a resiliently supported baffle assembly supported by said cabinet, a grille in front of said baiile assembly consisting of elastic columns frictionally held in the cabinet, said baflie assembly consisting of three members, one member being a square baffle plate supported at two points, resilient means for holding said square baffle member at these two points, said square baffle plate member being provided with an opening arranged in front of the conical loud-speaker membrane, a second member consisting of a number of fins, projecting towards the rear and into the interior of the conical membrane of the loud-speaker, said fins being arranged transversely with respect to said opening, so as to cross the same, and the third member consisting of an outer disk shaped baffle member fixedly mounted in front of the opening in the said square baiile plate member mounted on the same, said disk shaped member being provided with a plurality of openings.

'7. A sound reproducing unit with an electrodynamic loud-speaker having a substantially conical membrane, comprising a cabinet, a resiliently supported bailie assembly supported by said cabinet, said baflle assembly consisting of three members, one member being a square baiile plate member provided with a circular opening, supported at two points, rigid supporting means, supported by the cabinet, and resilient supporting means, the latter inserted between the rigid supporting meaiis and the said square bafile plate of triangular fins mounted across th opening of the square baifie plate, the outer edges of said fins forming a pyramid projecting into the interior of the conical membrane of the loud-speaker so that said fins sub-divide the space within said conical membrane, and a third member consisting of an outer disk shaped bafiie membrane fixedly mounted in front of the opening in the said square bafiie plate member mounted on the same, said disk shaped member being provided with a plurality of openings.

8. A sound reproducing unit as claimed in claim 2 in which the disk shaped outer bafiie member is provided with one central opening and with a number of circular openings arranged in a circle around said central opening all last obstructed portion of the opening of the square baffle plate so as to provide air circulation be-v axis and arranged'across the opening in the square bafile member, said fin assembly projecting rearwardly into the cone of the loud-speaker lit membrane, and a third member of the baflle assembly being a disk with a plurality of openings fixedly mounted on the square bafile plate in front of the circular opening of the same and of the fin assembly.

10. A sound reproducing unit as claimed in claim 9, wherein the resilient means for supporting said square baflle plate consist in cushioning rubber sleeves and washers held in the bracket and in adjustable screw bolts and nuts pressed against said baflie plate, brackets and'cushioning rubber sleeves and washers, for adjusting the resiliency of the support.

11. In a sound reproducing unit as claimed in claim 6, a grille consisting of two rows of prismatic columnsof trapezoidal cross section, the

tween the space between the fins and the space in front of the baflle.

9.-A sound reproducing unit with an electrodynamic loud-speaker having a substantially". conical membrane, comprising a cabinet, box

. vided with a circular opening, resilient means for supporting said square baflle member on said brackets, a second member of the assembly being a star shaped fin assembly with wedge shaped triangular fins radiating from a common columns'of one row bein g'arran ged between the columns of the other row and the side faces of the columns being arranged at a distance, so as to form channels inclined with respect to the plane of the bailie assembly in two directions, said channels forming the escape ducts for the sound waves passing through the opening of the bafile plate.

12. A'sound reproducing unit as claimed in claim 6, wherein a plurality of loud-speakers is used, and wherein the baffle plate is provided with a plurality of openings, a second and a} third member being arranged in the rear and in the front of the baille plateat each opening.

' MURRY KELLY HODGE.

No references cited.

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