US2269284A - Signal translating apparatus - Google Patents

Description

Jan. 6, W42. H OLSON v 2,269,284

SIGNAL TRANSLATING APPARATUS Filed Dec. 8, 1957 5 Sheets-Sheet 1 Jan. 6, 1942. H. F. OLSON 2,2692% SIGNAL TRANSLATING APPARATUS Filed Dec. 8, 1937 5 Sheets-Sheet 2 Jan. 6, 1942. H. F. OLSON SIGNAL TRANSLATING APPARATUS 5 Sheets-Sheet 3 Filed Dec.

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SIGNAL TRANSLATING APPARATUS Filed Dec. 8, 1937 5 SheetsSheet 4 V) L; I

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SIGNAL TRANSLATING APPARATUS Filed Dec. 8, 1957 5 Sheets-Sheet 5 Snnentor V" dttorneg Patented Jan. 6, 1942 SIGNAL TRAN SLATIN G APPARATUS Harry F. Olson, Audubon, N. Corporation of America,

ware

J., assignor to Radio a corporation of Dela- Application December 8, 1937, Serial No. 178,802

3 Claims.

This invention relates to signal translating apparatus, and more particularly to a loudspeaker of the dynamic type.

In the field of sound reproduction, there has been a steady extension of the frequencyrange over which reproduction of sound with good fidelity has been realized. The most common form of loudspeaker which has come into extensive use is the direct radiator cone loudspeaker. The efficiency of such a loudspeaker in the range in which the diaphragm, or cone, vibrates as a piston depends upon the diameter and mass of the cone, the material and mass of the voice coil, and the flux density. It is Well known that a mass controlled cone mounted in an infinite baffle delivers constant output in the frequency range below the point of ultimate impedance. From the standpoint of uniform output, a very small cone could be used and thereby a smooth response characteristic obtained overv a wide range. However, the power handling capacity of a small cone is inadequate at the low frequencies and a relatively large cone must ordinarily be used in order to include the low frequencies.

When using paper as the material for the cones, large cones must be made of heavy paper in order to prevent rattle, breaking up, subharmonics, etc. As a consequence, in order to obtain a reasonable efiiciency, voice coil must be employed. Thus, in a practical direct radiator loudspeaker, large diameter heavy cones and heavy coils are required for reproduction of low frequencies. For good performance at the high frequencies, however, cones of small diameter and light coils are required.

In order to take advantage of the foregoing principles, various loudspeakers have been suggested heretofore. Thus, in order to obtain large power handling capacities, good efficiency over a fairly wide range, and uniform directional characteristics, it has been suggested to use a combination of several loudspeaker systems, namely, large cones and coils for low frequency reproduction and small cones and coils for high frequency reproduction. A disadvantage of using several loudspeakers, each covering a certain portion of the audio frequency range, is that such a system requires elaborate filter systems and separate magnetic structures for each cone and coil. Furthermore, when the loudspeakers are mounted in a bafiie or cabinet, the separation in the overlap region is usually several wave lengths. As a consequence, the directional characteristics in the overlap regions consist of several lobes. This a relatively heavy type of directional characteristic introduces frequency discrimination in the response characteristic for various points in space.

To eliminate some of these disadvantages, it has been proposed to employ a single cone loudspeaker provided with a large, heavy coil, and a small, light coil, the two coils being separated by a compliance. Such a system is shown, for example,.in my Patent No. 2,007,748. At low frequencies, the cone is driven by forces generated in both coils. At the same time, the mechanical reactance due to the compliance between the two coils is large compared to the mass reactance of the heavy coil. Therefore, both coils move in phase, or as a rigid unit, in the low frequency region. At the high frequencies, most of the electric current flows through the light coil. Furthermore, the reactance of the compliance between the two coils is small compared to the mass reactance of the large coil. Hence the large coil does not move at the higher frequencies, and the cone is driven by the forces generated in the small, light coil.

With the double coil arrangement just described, it has been possible to double the range of the conventional single coil, single cone loudspeaker without introducing any of the disadvantages heretofore noted. However, this arrangement has certain other inherent disadvantages. First, a heavy and rugged compliance is needed between the two coils because all of the force generated in the large coil is transmitted through this compliance. Since the light coil must carry part of this heavy compliance at the high frequencies, a loss in response occurs due to the added mass reactance. Secondly, the light coil must drive the centering suspension system, as well as a relatively heavy cone, at the high frequencies. The result i a loss in high frequency response, due to the large mass reactance which the small coil must drive.

The principal object of my present invention is to provide an improved loudspeaker system which will be free from the aforementioned disadvantages inherent in loudspeakers of the prior art.

More specifically, it is an object of my present invention to provide an improved loudspeaker system in which the range of reproduction will be considerably extended.

Another object of my present invention is to provide an improved loudspeaker system as aforesaid in which the loss in high frequency response is obviated.

Still another object of my present invention is which is simple in construction,

wide range. A single field structure may for the entire system. By employing mechanical filters for allocating the ranges, simple electrical I circuits: can be used for effecting the transfer of 'quently, there are no lobes to provide an improved loudspeaker system which is highly elficient in use, which will have :a large power handling capacity, and which can be easily f'ab' ricated, I I a In accordancewith my present invention, 1

employ a plurality of driving coils separated by 1' electrical energy, the being suitable capacitors,

only additional elements tion, and preferably very closetogcther. Conseinthe directional characteristics. Furthermore, by choosing cone diameters appropriate to the ranges, it ispossible The cones are. 'ar-' ranged concentrically in nested, overlapping relashown in Fig. 21, but employing four cones and associated voice coils, and

a Figure 23 is a circuit diagram showing-the manher in which the several voice coils'of the modification of Fig. 22 may be coupled together.

Referring more particularly to the drawings,

'wherein similar reference characters designate 7 corresponding parts throughout, there is shown,

in Fig. 1, a loudspeaker system having a pair of vibratile elements comprising a relatively large I cone or diaphragm I' and a relatively small cone or diaphragm 3, each comprising a conical vibration radiating section and a cylindrical driving coil supporting section of known construction.

' The large cone 1 is particularly adapted to reproduce the lower frequencies, and the small cone 3, which mayhave an inverted central portion, as shown in Fig. 1, is particularly adapted to reproduce the higher frequencies. The two cones I and 3 are arranged'in'nested, overlapping relation,'with their cylindrical driving coil supporting 'sections arranged concentrically and in radially to obtain uniform directional characteristics. Q

Withsystems of this sort, it is possible to cover, with very good eificiency,a range of from to 15,000 cycles, and even higher.

The novel features characteristic of my invention are setforth with particularity in the ap The invention itself, however,

pended claims.

I both astoits organization and method of operation, as well a's'additional objects and advantages thereof, will best be understood from the follow ing description of a number of embodiments thereof, when read in connection with the accompanying drawings, in which Figure 1 is a sectional view of one form of my invention,

Figure 2 is a wiring diagram of a circuit which may be employed for energizing the two voice coils shown in Fig. 1,

Figures 3 to 9, inclusive, are sectional views showing various other forms of my present invention,

Figures 10 and 11 are circuit diagrams showing the manner in which the voice coils of the modification of my invention shown in Fig. 9 may be coupled,

Figure 12 is a sectional view of a modification of the arrangement shown in Fig. 9,

Figures 13 to 16, inclusive, are sectional views of further modifications of my present invention, all employing various forms of horns in association with the cones,

Figures 17 and 18 are sectional views showing still further modifications of my invention wherein the field strength for the small, light coil is made stronger than that for the large, heavy coil,

Figure 19 is a sectional view of still another form of my invention wherein three cones and associated voice coils are employed, the previously identified modifications of my invention all employing two cones and coils,

Figure 20 is a circuit diagram showing the manner in which the three coils of the system of Fig. 19 may be connected,

Figure 21 is a modified form of the system shown in Fig. 19,

Figure 22 is a modification similar to that of rings, 9, while spaced relation in the air' gap formed between the'pole pieces 5 and l of a suitable magnetic structure. a The large cone 1 may riphery in any suitable manner between a pair connected to the supporting section, of the diaphragm l for properly centering the system within the air gap of the magnetic structure; Thesmall diaphragm 3. is connected at its periphery to an intermediate portion of thelarge diaphragm l by a compliance I I3, so that the small cone 3 may vibrate inde pendently of the cone 1. A large, heavy voice 5 coil l5 particularly suitable for low frequency reproduction is connected directly to the large cone I, while a small, light coil 11 particularly suitable for high frequency reproduction is connected on one side to the'heavy coil 15 by means of a compliance [9, and on the other side to the small, light cone 3. At low frequencies, the heavy coil 15, the large cone 1, the light coil 11, and the small cone 3 all move in phase, and the system behaves very much like a single coil system. At the high frequencies, the mass reactance of the large coil l5 and the large cone 1 is so large that there is very little motion in this part of the system. The compliance separating the light and heavy coil allows the light coil and small cone to vibrate independently of the large cone and heavy coil when the reactance of the compliances is small compared to the impedance of the large cone and the heavy coil. Furthermore, by connecting a capacitance 2| across the large coil [5, as shown in Fig. 2, practically all the current will then fiow in the light coil 11. Therefore, all the motion takes place in the high frequency system. Now, since the small cone is not driven hard at the low frequencies, it can be made very light. The same is true of the compliances l3 and I9. Either the compliance l3, or the compliance l9, or both these compliances can be made controlling. In any event, the high frequency portion of the system described is light, and, therefore, very efficient. It has been found that a loudspeaker of this type has good response up to about 15,000 cycles.

Fig. 3 shows a modification in which the outer suspension, or compliance I3, is omitted, and also the centering suspension is in the form of the conventional centering spider 23. The advantage of this construction over that of Fig. 1 is that it provides a lighter system due to the elimination be supported at its pee a suitable'suspension ll may be 7 voice coil form, or driving coil of the compliance I3 at the outer edge of the cone 3. The cone 3 may also be made somewhat lighter by omitting the reversely directed central portion shown in Fig. 1.

Fig. 4 shows a system in which the voice coil supporting section of the cone 3 is shorter than that of the cone I and in which the light coil I1 is centered by means of a radially extending suspending compliance I9 of very small stiffness, which connects the lower end of the voice coil form of the cone 3 with an intermediate portion of the voice coil form of the diaphragm I instead of being centered by the voice coil I5, as in the case of Figs. 1 and 3. In this modification, the controlling compliance is the compliance I3.

Fig. 5 shows a system in which the small cone 3 is of the inverted type. In other respects, this modification is similar to that shown in Fig. l, and the electrical connections of the two voice coils may be the same as in Fig. 2.

In manufacturing a loudspeaker according to my present invention, it may be desirable to place one coil in radially spaced relation to the other, instead of in axially spaced relation, as in the modifications heretofore described. By placing the voice coils in radially spaced relation, it also becomes possible to arrange them coextensively axially of the air gap whereby they occupy a symmetrical position in the air gap. Systems of this type are shown in Figs. 6 and 7. The compliance I9 which joins the two cones is located at the bottom of the two coils in Fig. 6, or it may be placed at the top of the two coils, as shown in Fig. '7. In either case, the compliant coupling I3 may either be omitted or, by choosing the proper constants, it may be included, as desired.

In the modification of Fig. 8, which is a modified form of the systems shown in Figs. 4 and 5, the two coils I5 and II are again disposed in axially spaced relation, and the light coil IT and its cone 3 are connected to the heavy coil I5 and its cone I by means of rubber or other plastic material 25 which acts as a compliant coupling. As in Fig. 4, the compliant coupling 25 of Fig. 8 connects the end of the voice coil form of the cone 3 with an intermediate portion of the voice coil form of the cone I to center the coil I! in the air gap.

All the systems thus far described are equipped with two driving coils and a condenser shunting the low frequency coil, as shown in Fig. 2. Actually, it is possible to transfer the energy from the large coil I5 to the small coil I! by induction. That is to say, the small coil I! may be made the secondary and the large coil I5 the primary of a transformer. In one form of the device, the light coil I! may consist of a single turn, or a band of material, as shown in Fig. 10. Of course, this acts as a short circuited turn at the low frequencies, but this, in general, does not introduce any serious loss. To obviate this objection, however, the circuit shown in Fig. 11 may be employed. In this case, the light coil I! is shunted by a capacitance 21, and it does not act as a short circuited turn at the low frequencies because the reactance of the capacitance 21 is large at the lower frequencies. At the high frequencies, the reactance of the capacitance 21 is small and the current flowing in the coil I1 sets up a field which interacts with the steady field in the air gap to produce a force for driving the small cone 3. The system may be arranged as shown in Fig. 9, with the coils I5 and I1 in radially spaced relationand inductively coupled in the manner shown in Figs. 10 and 11, and with the compliance I3 at the outer or peripheral edge of the small cone 3 being the sole connection between the cones 3 and I. The modification of Fig. 12 is similar tothat of Fig. 9, except that, in place of the compliance I 3, the coils I5 and I! are connected by a compliant coupling I9 of rubber or other plastic material to hold the coils together.

It is quite well known that it is possible to increase the radiation load upon a cone by means of a horn, and thereby increase the output. Of course, the length of the horn must be comparable to the wave length to yield an appreciable improvement in efficiency. In a compact, direct radiator loudspeaker, the horn is a practical adjunct at the high frequencies. A double cone, double coil loudspeaker according to my present invention and employing a horn is shown in Fig. 13. The horn is made in two parts 29a and 29b to reduce the path lengths in the air chamber between the base of the horn and the cone 3, thus preventing interference in this part of the system. In general, the length of any path parallel to the cone surface should be less than A; wave length at the highest frequency to be reproduced. A sound impervious suspension or compliance 3I between the horn portion 29a and the diaphragm I surrounds the base of the horn portion 29a and is used to prevent sound radiated by the small cone 3 from leaking outside of the horn.

Fig. 14. shows another modification of the horn type of loudspeaker according to my present invention wherein the large cone I is used for the outer surface of the horn and corresponds to the horn section 29a of Fig. 13, and an insert 33 is provided to obtain a small throat and, therefore, a large load on the small cone 3.

Fig. 15 shows a modification of the structure shown in Fig. 14 in that the insert 33 is made hollow so that two sound channels result, one between the insert 33 and the diaphragm I, and the other through the insert 33. In this arrangement, the path lengths in the air chamber between the insert 33 and the small cone 3 are shorter than those shown in Fig. 14.

Fig. 16 shows another modification wherein the small diaphragm is loaded by a horn, this modification being similar to Fig. 13 except that the small diaphragm 3 is of the conventional type instead of being of the inverted type, as in Fig. 13.

In the several modifications of my invention thus far described, the flux density in the air gap between the poles 5 and I is the same for both coils. It is well known that the efficiency at the high frequencies is dependent upon the flux density. At the low frequencies, the emciencies can be improved by making the voice coil larger, as Well as by increasing the flux density. The mass reactance of the coil is usually negligible compared to the mass reactance of the remainder of the system. Since it is more economical to increase the size of the voice coil than the flux, it is logical to use a large coil operating in a moderate flux density at the low frequency portion of the system. At the high frequencies, however, increasing the voice coil mass also increases the mass reactance because, in this range, the voice coil mass is comparable to the cone mass. Therefore, in this range, it is logical to use a high flux density and a light coil, and the modifications of my invention shown in Figs. 17 and 18 are designed to take advantage of this- In Fig. 17, which is generally similar to the modification of my invention shown in Fig. 1, the center pole piece 5 is provided with a cap 5a of larger diameter than the pole piece 5, and the small voice coil [1 is mounted in the region of the air gap between the cap 5a and the outer pole piece I, while the large coil I1 is mounted in the region of the air gap between the center pole piece 5 and the outer pole piece I. This provides a stronger field for the voice coil ll than for the voice coil H5. The modification shown in Fi 18 is similar to that shown in Fig. 17, the pole piece 5 here also being provided with the cap 5a, but the outer pole piece I is made of two sections 1a and 1b, the section Tb being reduced at the air gap to a thickness substantially equal to the height of the coil I5 and the section la being aligned with the cap construction shown in Fig. 18 is that it provides a field between the section la and the cap 5a in which the coil I! may be centrally aligned axially of the smaller air gap and a field between the reduced edge of the section lb and the pole piece 5 in which the coil i5 may be similarly aligned, so that each coil is symmetrically disposed in its own air gap portion in an axial direction.

All of the preceding modifications relate to systems employing two coils and two cones. Obviously, these systems can be extended to more than two coils and more than two cones. Thus, a system may be built up, according to my present invention, having the equivalent of large cones and coils for the low frequencies, medium size cones and coils for mid-range reproduction, and small cones and coils for high frequency reproduction. One such system is shown in Fig.

19 wherein, in addition to the large cone i and the small cone 3, the latter of the inverted type. there is included an intermediate cone 35 which is coupled to the cone 1 by a compliance 3?. As in the other modifications, the cone 3 is driven by the small voice coil H, the large cone l is driven by the voice coil 15, and the intermediate cone 35 is driven by a Voice coil 39 which is larger than the coil I! but smaller than the coil 5. The compliance 59 connects the coil l'! with the coil 39, and a compliance 4i connects the coil 39 with the coil l5. The voice coils l5, I1 and 39 may be connected as shown in Fig. 20, with the capacitance 2| connected across the coil i5 and a second capacitance 43 of suitable value connected across the coil 39. quencies, current flows through all three coils l5, l1 and 39. At the same time, the reactance of the compliances l9 and M are small compared to the mass reactance of the several coils; hence, all parts of the system move with the same phase. In the mid-range, very little current fiows through the coil i5. Furthermore, the mass reactance of the coil I5 isthen large compared to the compliance 4!. In this range, therefore, the cones 33 and 35 are driven by the coils, l1 and 39. At the high frequencies, the compliance I9 between the coil H and the coil 39 is small compared to the mass reactance of the coil 39. Moreover, considering the electrical circuit of Fig. 20, practically all the current flows in the coil 11 at the high frequencies. Accordingly, the light coil H and its cone 3 vibrate to produce the radiation at the higher frequencies. The modification of my invention shown in Fig. 21 is similar to that of Fig, 19, except that '50.. The advantage of the At the low frefill three conventional cones are employed instead of the inverted type small cone 3 of Fig. 19. In all other respects, the two modifications are alike, the large cone I being suspended as in Fig. 1, and the entire system centered in the air gap either by a suspension similar to the suspension ll of Fig. 1 or by a centering spider similar to spider 23 of Fig. 3.

Fig. 22 shows a system employing four cones and four associated driving coils, the component parts of this system covering four different ranges. The additional cone is constituted by the cone 45 which is coupled to the cone l by the compliance 4'! and which carries a driving coil to, while the cone 35 is connected, through the compliance 3?, to the cone 45. Also, the voice coil 39 is connected by the compliance 4| to the voice coil 49, and the latter voice coil is connected to the voice coil [5 by a compliance 5|. The electrial circuit shown in Fig. 23 also divides the driving current into four ranges and includes a suitable capacitance 53 across the driving coil 49.

Although I have shown and described a number of modifications of my invention, it will be readily apparent to those skilled in the art that many other modifications are possible. I desire, therefore, 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. In a loudspeaker, the combination of a plurality of diaphragms each including a vibrating section and a voice coil supporting section, said diaphragms being of relatively lesser and greater diameter and particularly effective, respectively,

to reproduce higher and lower ranges of the audio spectrum, a separate driving coil on each of said coil supporting sections, said voice coils being correspondingly particularly effective, a compliant coupling between said diaphragms, and a horn loading the smaller of said diaphragms.

2. In a loudspeaker, the combination of a plurality of diaphragms each including a vibrating section and a voice coil supporting section, said diaphragms being of relatively lesser and greater diameter and particularly effective, respectively, to reproduce higher and lower ranges of the audio spectrum, a separate driving coil on each of said coil supporting sections, said voice coils being correspondingly particularly effective, a compliant coupling between said diaphragms, a horn loading the smaller of said diaphragms, and compliant means connecting said horn to the larger of said diaphragms.

3. In a loudspeaker, the combination of a plurality of diaphragms each including a vibrating section and a voice coil supporting section, said diaphragms being of relatively lesser and greater diameter and particularly effective, respectively, to reproduce higher and lower ranges of the audio spectrum, a separate driving coil on each of said coil supporting sections, said voice coils being correspondingly particularly effective, a compliant coupling between said diaphragms, a horn loading the smaller of said diaphragms, and compliant means connecting said horn to the larger of said diaphragms, said last named compliant means comprising a sound impervious member surrounding the base of the horn and serving to prevent leakage of sound around the exterior of said horn which emanates from said small diaphragm.

HARRY F. OLSON.

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