US1823512A - Loud speaker - Google Patents

Description

' Spt. 15, 1931. V RINGEL 1,823,512

LOUD SPEAKER Filed Oct. 22, 1927 INVENTOR ABRAHAM RlNGEL.

A RNEY Patented Sept. 15, 1931 UNITED STATES PATENT OFFICE ABRAHAM 'RINGEL, OF BROOKLYN, NEW YORK, ASSIGNOR T0 RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE "LOUD SPEAKER :Applicatiouflled October 22, 1927. Serial N0. 228,018.

ever that there is another factor besides the area ofthe vibrating surface which determinesthesound given off from a vibrating surface. This is the amplitude of motion of the surface. I havefound that the lack of low frequency response of a small vibrating surface maybe compensated for by giving the vibrating surface a large amplitude of motion at thelow frequencies. One of the objects of this invention is to provide a means for doing this.

In the-ordinary armature type of electromagnetic unit, the armature is constantly attracted in the direction of the pol'e pieces and is held away from contacttherewith by either the stiffness of the'diaphragm, or by a separate spring. This spring, which is loaded by the armature and its attached diaphragm, constitutes resonant vibrating system. By adjusting thespring stiffness and the mass of the diaphragm the resonant frequency may be arbitrarily determined within certain limits. Should the spring not have suflicient stiffness the system would be unstable, and the armature would be pulled against the pole ;-pieces. Thus the minimum spring stiffness-is limited by the tolerance necessary in the manufacture of the driving unit,'so that a reasonable factor of safety is maintained against this instability.

' The stiffness of the unit below this resonant frequency causes suflicient decrease in the amplitude of'motion, so that this frequency may be considered as an effective measure of the low frequency cut-off of this kind of speaker.

For a given minimum spring stiffness, the frequency of resonance is determined by the effective mass of the diaphragm. Thus the effective mass of the diaphragm must be within certain limitsto assure that the low frequency cut-off willbe such that the low notes will be clearly'reproduced.

With the'lar ediaphragms commonly used the mass is .su cient to bring this resonance to'a frequency which has been considered low enough for the present art of radio reproduction. As a. matter of fact, for convenience in manufacture a step down motion of the diaphragm has usually been used. This actually reduces the effective mass of the diaphragm and results in a still larger vibrating area being required than would otherwise be necessary.

A small diaphragm will not give satisfactory results, when used with one of these driving units. Due to the small mass of the diaphragm, the resonant frequency is so high that the low frequency cut-off is too high to give pleasing reproduction.

I have found that the reproduction from a small diaphragm may be made equal or superior to that from a larger one byproperly increasing the effective mass of the small diaphragm. According to one form of my invention I accomplish this by making the motion-of the diaphragm larger than that of the armature at the pole piece. When the motion of the diaphragm is increased its effective mass is also increased in the ratio ofthe square of the increase of motion. It is therefore obvious that the motion may be sufiiciently increased to make the effective mass of the small diaphragm equivalent to that of the large diaphragm and thus I keep the low frequency resonance at the same value thatit was for the larger diaphragm.

A further study, taking into account this increased motion, the radiation characteriszics of small diaphragms, and the decrease in thickness of diaphragm material which may be obtained by the use of a smaller diaphragm, shows that with agiven motion of the armature neariy equivalent results may be obtained by the use of large and small diaphragms over the low and intermediate frequency range, and that improved radiation ensues from the small diaphragm at high frequencies.

Another object of this invention is to prevent the circulation of sound waves from acts as suflicient bafiie to prevent a large part of this circulation. The small diaphragm however requires additional means for preventing this circulation. In this invention I prevent this circulation of sound waves by means of an enclosure behind the diaphragm, the enclosure being open only at the side most distant from the diaphragm. The diaphragm is'supported in this enclosure, which may be in the form of a box, by a material which is impervious to air, so that circulation of sound waves around the edge of the diaphragm is prevented. At the same time, inorder to allow for the large amplitude of motion of the diaphragm, its'outer rim must be'very loosely attached to the supporting surface.

I have noted that the low frequency cut-off of the loudspeaker is determined by the frequency of the diaphragm-spring resonance.

The presence of this resonance causes an increased acoustic output at this particular frequency which is disagreeable to the listener. It is a still further object of this invention to supply means for so damping the motion of the diaphragm at this frequency, that the output will be reduced to normal. The enclosure described above allows free motion of the diaphragm at all frequencies. I have found,.hoWever, that for small diaphragms as described, the motion may be efiectively damped at the resonant peak and at the same time be maintained substantially unchanged elsewhere by placing a layer of coarse acoustic felt between the diaphragm and the back side of the box enclosure.

If the box had been completely closed by means of stiff material, the stiffness of the confined air added to the spring stiffness wouldhavegi'ven a resonant peak and therefore low cut-off, at a frequency considerably higher than that actually obtained. It is one ofthe objects of this invention to obtain the low cut-off obtained with the diaphragm wibrating in the open box, and the increase in amplitude at the higher frequency, which can be secured by means of the closed box. This may be done by covering the coarse felt described above by a layer of sateen or like material on both sides or by using a felt of a closer texture, which will have similar acoustic properties to this combination. The sateen being more impervious to the air vibrations than the coarse felt, adds the stiffness required to give a diminished semblance of the peak, which would be present if the box were completely closed.

Another object of this invention is to provide a damping means for preventing objectionable high frequency resonances of both the' cone and driving unit.

Other objects of this invention will become apparent upon reading the followingspecilication with reference to the accompanying drawings in which Fig. 1 is a vertical section through a cone speaker built in accordance with this invention, and Fig. 2 is a rear View with the felt backing of the cabinet removed.

Referring more particularly to the drawings, a cone 1 adapted to be operated by a driving unit 2 is mountedinside a box enclosure or cabinet 3. The front wall 4: of the cabinet 3 is provided with a circular opening and the edge of the cone is fastened to the front wall by any suitable-means, such as a rim of thin leather, cloth or any kind of a flexible membrane 5 which is fastened to an annular piece of heavy material 6. The fastening member of leather or the like, is impervious to air so that there will not be a circulation of sound waves from the rear to the front of the cone. The cone may also be fastened to the front member of the cabinet by crimping the edge of the cone in an annular fashion several times and then fastening the cone directly to the front member, the

crimping in this case giving the flexible connection between the main portion of the cone and the cabinet.

The cone may be made from any material that is suiiiciently stiff to prevent the cone from breaking up into undesired modes of vibration and at the same time sufficiently light so that the cone is very sensitive and can readily respond to the electrical Vibrations over a desired frequency range.

A metallic cup member 7 is fastened to the apex of the cone 1 to form a more substantial connection between the cone and the driving unit 2. The cup 7 is normally made of aluminum in order that it will have both rigidity and lightness, and its general shape is that of a frustum of a cone. The bottom of this cupmember 7 is provided with a' small opening for connecting the cup memher with the driving unit-2.

The driving unit 2 which actuates the cone is mounted on a board 8 which in turn is fastened to the walls of the cabinet 3 by any suitable means. The driving unit consists of a permanent magnet 9 to which pole pieces 10 are attached. A soft iron'armature 11, which is provided with windings 12 is supported between the pole pieces 10 by means of a phosphor bronze spring 13. The spring 13 is fastened to the middleof the armature by any suitable means, such as welding. The pole pieces 10 are spaced so that there is an air gap of approximately .01 between the pole pieces and the armature.

ivory flexible at the pivot point 18.

eeann Asseen in Fig. '1, the pole piece at the right hand side of the armature 11 is, say,

, a north pole. while the pole piece at the left hand sideof the armature is a south pole.

I henvariable electric currents, such as those (cans-es each end of the armature to be instantaneously polarized. At the instant that-the upperendof the armature 11, as seen in Fig. '1, is a-north pole, that end of thearmature is repelled by the right hand .pole piece 10 which is-alsoa north pole, but

at the same time it is attracted by the left hand pole piece which is a south pole. At the same instant the lower end of'the armature, which is a southpole, is attracted by so fthe right hand north pole piece 10 and is re pelled by the left hand south pole piece. As a result 'the armature twists in a counter clockwise direction. At the next instant, however, the polarization of'the armature is reversed and the 'reverseaction takes place.

:w' 'tached at one endto one of the pole pieces 10.

A thin rod is fastened to one end of the armature 1'1 and to a point between the ends of the-spring member 14. At the free end ofthe spring member 14 is fastened a rod 16 is "-which is also fastened-through anadjustable connection 'to the cone 1, by means of the metallic cup member 7. In order to retain the desired flexibility and sensitivity of'the system,the connecting rods 15 and 16 should imhave-a very small diameter, just suiiicient to assure rigidity of the rods, and the rods should be set at right angles to the spring lever 14.

The rod 16 is provided with screw'threads,

"and smalllock nuts 17 arranged on both sides of the aluminum cap member to allow the proper adjustment to be made between the driving unit and the cone.

The spring lever 14 is channelled at 'the jpoint where the rod 15 is fastened, and is tapered near'thepivot point 18 of the lever. The channel gives rigidityto the spring memher at the point of connection with the rod 15, and the tapering makes the spring member The spring member 14thus has practically a pure lever action. the lever arms being the drivinglever, or that portion from the pivot'point 18 tothe point of connection of the rod 15,

. and the driven lever or that portion from the pivot point 18 to thepoint-of connection of the rod 16.

It has been found that the ratio of these arms should be Varied, to give the ibest resuits, according ito thesize of theeone, the

mass of the cone and the material from which the cone 1s made, the cone size and'mass being the more important. In the case of a cone having a diameter of aproximately 6" and made of material just stifi' enough to prevent undesired modes of vibration'in the material, a driving arm to a driven arm ratio of 2:3 gives very good results. If the cone should be made with only a 3 diameter, the step up ratio would-have to be materially increased over the 2:3 ratio suggested for 6 cone.

If some material could be obtained that is extremely light and very rigid, such as a material as stiff as paper and only one-fourth as heavy, the lever arm ratio for a 6 cone could be increased from the suggested value of 2: 3 to, say 1 3. In other words the stepping up ratio depends on the mass of the cone. In any case the flexible membrane that is fastened between the edge of the cone and the surrounding member is arranged so that for all practical purposes the cone can be said to be free edged or free floating.

By increasing the lever arm from the 1: 1 ratio or the direct drive heretofore used, the effective mass of the cone is increased. This increase in the effective mass of the cone, with the spring stiffness or restoring force remaining constant, causes a decrease in the natural resonant period of the vibrating system. As a result more low frequencies are obtained below this natural period. Because of the step up lever the amplitude of the cone movement is increased when the cone is vibrating substantially like a piston at'the low frequencies and also when the cone has broken up into modes of vibration at the very high frequencies. However, it should be noted that when the cone is still vibrating like a piston at the ordinary high frequencies,

that is, before the cone has broken up into higher modes of vibration, the amplitude-of motion is not as great as it would be if the same cone was being driven directly from the driving unit. This is because of the increased effective mass of the vibrating system and results in reduced sound radiation at these intermediate frequencies. The use of a lighter cone material makes this effect less pronounced, or in other words, it results in an increase in the sensitivity in the intermediate frequency region.

A sleeve 19 of rubber or some similar material is slipped over the rod 16 to damp out the undesired high frequency resonances of both the cone and the driving unit. This results in a more uniform tone product.

The rear of the cabinet is closed by a layer of acoustical felt 20. This layer, which is relatively thick, is covered or. both sides with sateen. The sateen covered felt serves two important purposes. First,it provides sufficient damping on the cone at low frequenones to ehmlnate any olnectionable resonances of the cone itself, particularly the fundamental cone resonance peak. Second, it damps out injurious reaction of cabinet resonances or anti-resonances on the cone.

The sateen covering'is added to give a slight stiffness to the felt. An ornamental grill of some sort may beused in the front of the cabinet to prevent mechanical injury to the cone.

'1' i' As used in the specification and claims, the

six inches in diameter give especially good results. It is to be understood, of course, that diapl ragms of othc' than the conical shape illustrated, but havingradiating areas approximately equal to the area. of the diaphragm herein described, are within the scope ofthis invention and are intended to be covered by the appended claims.

Having thus described my invention, what I claim is I 1. The method of reproducing sound by means of a vibrating diaphragm actuated by adriving member, which consists in providing a diaphragm so small that it will not normally reproduce notes of low frequency, in stepping up themovement of the driving member to produce an amplitude of dia phra gm movement sufficient to reproduce the desired low notes and in radiating the sound waves from the diaphragm directly to the open air.

2. The method of reproducing sound by means of a vibrating system comprising a small vibrating diaphragm actuated by a driving member, which consists in modifying the driving movement so that the resultant effective mass of the diaphragm will be sufficiently high to decrease the natural resonant period of the vibrating system to a frequency suflic'ently low to allow the clear reproduction of low tones, and in radiating the sound waves directly from the diaphragm to the open air.

3. The method of reproducing sound by means of a small diaphragm actuated by a driving member, which consists in increasing the effective mass of the diaphragm until it is equal to the effective mass of a large diaphragm which will clearly reproduce notes of low frequency. 4 4-. The method of reproducing sound by means of vibratin system comprising a small diaphragm and a driving member connected therewith, which consists in increasing the amplitude of the diaphragm movement to produce av low frequency resonant period for the vibrating system and radiating the sound waves from the diaphragm di-' rectly into the open air.

5. Themethod of reproducing sound by means of a vibrating system comprising a small diaphragm and a driving'member connected therewith, which consists in increasing the amplitude of the diaphragm movement and thereby increasing the effective mass of the diaphragm to produce a natural resonant period. for the vibrating system below 300 cycles, and in radiating the sound waves directly from the diaphragm to the open a1r. 7

6. A loud speaker comprising a small diaphragm radiating directly to the open air, a driving member for said diaphragm and means connected between said driving member and said diaphragm for causing said small diaphragm to have an effective mass equal to the efiective mass of the large diaphragm whereby tones of low frequency ar clearly produced.

7. In combination, a diaphragm under nine inches in diameter mounted to radiate directly to the open air, a driving member, and means for stepping up. the movement of said driving member and for transmitting the stepped up movement to said diaphragm.

8. In combination, a free edged diaphragm under nine inches in diameter, a. vibrating element connected therewith, and means for increasing the effective mass of said diaphragm to equal the effective mass of a diaphragm over nine inches in diameter.

9. A loud speaker comprising a diaphragm approximately six inches in diameter mounted to radiate directly to the open air, a driving member, and means associated with said diaphragm and with said member for increasing the effective mass of said diaphragm to equal the effective mass of a diaphragm over nine inches in diameter whereby low frequency notes are clearly reproduced.

10. A. loudspeaker comprising a cone diaphragm approximately six inches in diameter, means for supporting said diaphragm so that said diaphragm will radiate directly to the open air, a driving member, and means for stepping up the amplitude of movement, operated by said driving member and operating said diaphragm whereby the effective mass of said diaphragm is increased and the natural. resonant period of the vibrating system formed by said diaphragm, said driving member, and said means is decreased so that notes of low frequency are clearly reproduced.

11. In combination, a small diaphragm mounted to radiate directly to the open air, a driving member, and a lever associated with said member and with said diaphragm, the arms of said lever being proportioned so that said diaphragm has a greater amplitude of movement than said member.

12. In combination, a diaphragm mounted to radiate directly to the open air, a driving member, and a spring lever connecting said driving member with said diaphragm, the lever arms of said spring lever being so proportioned that the amplitude of movement of said diaphragm is greater than that of said driving member.

13. In combination, a small diaphragm mounted to radiate directly to the open air, a driving member, and a spring lever rigidly supported at one end for transmitting motion from said driving member to said diaphragm, said diaphragm being connected to the free end of-said spring lever and said. driving member being connected to an intermediate point of said spring lever.

14. In combination, a free edged cone diaphragm mounted to radiate directly to the open air. a. driving means including a member to be vibrated. and means connecting said member with said cone diaphra m so that said cone diaphragm has agreater amplitude of movement than said member. the diameter of said cone diaphra m being approximately six inches and the ratio of the driving member lever arm to the cone diaphragm lever arm being approximately 2 z 3.

15. In combination, a diaphragm under nine inches in diameter mounted to radiate directly to the open air. a driving member and means associated with said driving member and with said dia hragm. said means acting to increase the efl'ective mass of said diaphragm to equal the effective mass of a directlv driven diaphragm over nine inches in diameter.

16. In combination, a diaphragm under nine inches in diameter mounted to adiate directlv to the open air. a driving member for said diaphragm, and means associated with said diaphragm for increasin its effective mass without increasing its actual mass.

17. In a loud speaker. a vibrating system comprising a diaphragm approximately six inches in diameter. a driving member. and means associated with said driving member and with said diaphragm to increase the effective mass of the diaphragm whereby the natural resonant frequency of the vibrating system is obtained near the lower end of the audible frequency range and low frequency notes are clearlv reproduced.

18. In a combination. a vibratile member, fievible restrainin means associated with sai d vibratile member to give the required stability of operation, a small diaphragm radiating directly to the open air, and means associated with said vibratile member and with said diaphragm to increase the amplitude of movement transmitted to said diaphragm at low frequencies. whereby the fundamental resonant period of the vibrating system formed by the vibratile member, the restraining means, the diaphragm and the associated means is obtained at a sufliciently low frequency to reproduce low tones.

19. The method of reproducing sound by means of a diaphragm connected with a driving member to form a vibrating system which consists in the steps of (1) providing a diaphragm having a mass so small that the natural resonant period of the vibrating system would be at an obiectionably high frequency and (2) operatively associating said diaphragm with said driving member in such a manner that the diaphragm has an effective mass sufiiciently large to decrease the natural resonant period of the vibrating system to a frequency near the lower end of the audible frequency range.

20. The method of forming a vibrating system having a natural resonant period at a desired low frequency from a diaphragm and a driving member which consists in the steps of (1) providing a diaphragm having a mass so small that the vibrating system would have a natural resonant period above the desired frequency and connecting the diaphragm to the driving member in such a manner that the effective mass of the diaphragm has a value sufficiently high to decrease the natural resonant period of the vibrating system to the desired frequency.

21. The method of forming a vibrating system having a natural resonant period at a desired low frequency from a diaphragm and a driving member which consists in the steps of (1) connecting the driving member with a diaphragm having a mass so small that the vibrating system would have a resonant period above the desired frequency and (2) decreasing the natural period of the vibrating system by increasing the effective mass of the diaphragm while maintaining the actual mass of the diaphragm constant.

ABRAHAM RINGEL.

CERTIFICATE OF CORRECTION.

Patent No. 1,823,512. Granted September 15, 1931, to

ABRAHAM RINGEL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4, line 13, after the syllable "eter insert a period and the words I have found that practically any size diaphragm under nine inches in diameter; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 26th day of April, A. D. 1932.

M. J. Moore, (Seal) Acting Commissioner of Patents.

DISCLAIMER 1,823,512.-Abraham Ringel, Brooklyn, N. Y. LOUD SPEAKER. Patent dated September 15, 1931. Disclaimer filed February 17, 1932, by the assignee, Radio Corporation of America.

Hereby disclaims from the scope of claims 1, 2, 3, 4, 5, 19, 20, and 21, the method set forth therein except insofar as it applies to acoustic devices wherein the efiective area of the diaphragm has (1) a circular peripheral edge of less than nine inches in diameter, or (2) a peripheral edge defining an area smaller than the area defined by the peripheral edge of a circular diaphragm nine inches in diameter.

Your petitioner further disclaims from the scope of claims 6, 11, 12, 13, and 18, all acoustic devices except those wherein the effective area of the diaphragm has (1) a circular, peripheral edge less than nine inches in diameter, or, (2) a peripheral edge defining an area smaller than the area defined by the peripheral edge of a circular diaphragm nine inches in diameter.

[Ofiicial Gazette March 15, 1982.]

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