US1861222A - Loud speaker - Google Patents

Description

y 31,1932 J. P. MINTOIQ 1,861,222

LOUD SPEAKER Filed June 25 1925 Fig. 1

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I I I & I 1 I INVENTOR g I JOHN P. wmou IA I By FREdl/f/VC'Y (la 44 TTORNEY Patented May 31, 1932 UNITED STATESPATENT OFFICE JOHN P. MINTON, 01 WHITE PLAINS, NEW YORK, ASSIGNOB TO RADIO CORPORATION OI AHEBICA,'A GOBIORATION' OI! DELAWARE LOUD SPEAKER Application filed Jane 25, 1925. Serial No 39,583.

The invention concerns an acoustic device particularly adapted to loud speakers for radio recelvers or electric phonographs and.

has for its principal object to replace the usual 3 diaphragm and amplifying horn of such a device with a vibrating element of suflicient size to set in motion a column of air large enough to maketlieuse of a horn or-other amplifying means unnecessary. .10 A further object of the invention is to provide an acoustic device of this character in which the vibrating element will respond readily even to the lowest frequencies within its range of operation. 7

Still another object of the invention is to provide a vibratory system in which the vibratory element'will freely vibrate substantially as a piston for the lower frequencies within its operating range and as 9. dia- 20 phragm for the higher frequencies, thereby giving more uniform response throughout its range.

Still another object of the invention is to provide a vibratory system in which the vibratory element will freely vibrate at frequencies whose wave lengths are lar e compared with the size of the element itsel so that all of its parts vibrate substantially in phase and with equal amplitude and which at higher fre- Rfi quencies will vibrate as a diaphragm.

v Still another object of the invention is to provide an acoustic device whose vibrating element is supported by springs or other devices having just enough tension to return it to andmaintain it in normal rest position when not subjected to any operating forces. It has been found thatthe use of suitable diaphragms of large area in acoustic or electro-acoustic devices makes it unnecessary to provide a horn or other sound amplifying means as the large column of air set in motion by such a diaphragm furnishes sufiicient aeoustic energy to make amplification unnecessary. The large diaphragm moreover. has an advantage over the small one in that there is less interference between the sound waves from its two sides. A vibrating diaphragm, of course. emits sound 'waves from its opposite sides which are out of phase with each other and as these waves spread out in position when it has been displaced. In this all directions those from one side cause interference with those from the other, resulting in considerable diminution and distortion of the sound. A large diaphragm will evince thischa'racteristic to a much less extent than a small one and as a result give more intense radiation with less distortion. These efiects are further reduced according to the inven: tion by surrounding the diaphragm with a bafile, comprising a substantially rigid barrie'r about the edge of the diaphragm so that sound waves from one side will beprevented to a considerable extent from reaching and inerfering with those emitted from the other 51 e.

Another feature of the invention resides in the method of supporting the vibratory element. The ordinary diaphragm or cone which is attached to its support by inflexible means or by means possessing an appreciable amount of restoring action will respond very well to the intermediate and higher frequencies within the ran e of audibility but it either fails to respond altogether to the lower frequencies or responds so feebly to them that small intensity of sound only is obtainable and considerable distortion is introduced into the speech or music being reproduced. The present inventi on contemplates attaching the diaphragm or cone to its support by springs or flexible means which have minimum possible elastic restoring action, such action being just suflicient to maintain the element inits normal rest position and restore it to this 85 respect it is analogous to a so called dead heat instrument whose moving element will move to a certain position and then stop dead without any appreciable overthrow. In the present case the diaphragm or cone will be returned to its normal rest position by just suilicient restoring force to cause it to reach its rest position and there will be substantially no overthrow. v

An element supported in this manner and hereinafter referred to as a freely supported body will have its restoring force confined almost wholly to the supporting means itself and will have two distinct modes of o ration within the range of audibility. At t elower 1m 7 that is the displacementsfrom rest position set up at its center will travel'to its edge and back again 'to the center causing flexure of the element and setting up sound waves in the usual manner. As the piston action is obviously well suited to the reproduction of low frequency sounds and as the diaphragm action is well suited to the reproduction of high and intermediate frequency .sounds it will be clear that this device will respond to all frequencies within its range in a manner admirably adapted to the particular frequencies being reproduced and that consequently there w ill be a more uniform response over the complete range of audibility, resulting in a very faithful reproduction substantially free from distortion.

A more complete understanding of the invention may be had from the following detailed description which should be read in connection with the accompanying drawings in which Fig. 1 showsa specific embodiment according to the invention,

Figs. 2 and 3 a section and elevation respectively of a modification and Fig. 4 shows aplurality of curves illustrat ing the action of the freely supported vibrator element. 1i.

Fig. 1 is shown a'cabinet comprising a base 2, sidewalls 3 and 4 and top 1. This cabinetmay include a radio receiver, electric phonograph or similar device indicated diagrammatically at A and B, itbeingunderstood that the output circuit of this device represented by wires 14 has undulating currents therein corresponding to sounds which it is desired to reproduce from the vibrating system. The side wall 4 of the cabinet has an aperture 15 formed therein which should preferably be as large as possible. This aperture is covered by the grille 5 supported by suitable brackets on the sidewall 4. Within the aperture 15 is supported the vibratory element or diaphragm 6 from whosevibrations result the sounds corresponding to electric currents in the wires 14. The element 6 is supported by springs 8 attached to lugs 7 on the vibratory element and to lugs 9 in the sidewall 4 thus providing a slightly resilient support for the vibratory element.

The vibration of the element 6 is caused in the example shown by the electromagnetic device 12 whose coils are connected to the outfor even the lowest audiput conductors 14. This magnetic device as shown consists of a permanent magnet having electromagnets associated therewith, but it-isobvious that other actuating'means, such as the balanced armature or electrodynamic types, for example could readily be used. These devices are well known in the art and therefore further description of them is unnecessary. To the vibratory element 6 is fastened an armature 10 responsive to the magnetic field of the device 12. The armature 10 is fastened in any suitable manner to the element 6 by adjusting means including a thumb screw. 11 by which its position with respect to the magnetic device 12 may be varied. thereby controlling the response of the vibratory element to the I magnetic device. The magnetic device is supported from the base 2 by the bracket 13, although obviously any other convenient method of support could be adopted.

The supporting springs 8 should be made as light as ossible as their purpose is to support the dlaphragm with minimum ossible elastic restoring force. They shoul therefore possess ust sutlicient resiliency to main-- tain the element 6 in its normal rest position and restore it to this position without appreciable overthrow when it has been displaced. When these conditions are satisfied this vibrating element alone will have a natural frequency below its operating range that is below the range of audibility, and in responding to the lower audible frequencies substantially as a vibrating'piston it will reproduce low' frequency sounds faithfully without appreciable distortion. The intermediate and higher frequencies in the audible range will cause the element 6 to operate as a vibratory diaphragm in the well known manner and its natural characteristics will make the piston 'action'negligible at these frequencies according to well known physical laws.

The action of a body thus sup orted will be clearer after a consideration of the curves shown in Fig. 4 in which abscissas represent frequency and ordinate a function of the sound intensity which for lack of, a better name has been designated as diaphragm response. The audible frequencies in this graph extend from the point A to the point C and the response of the body acting as a piston has been respresented by curve P and its response as a true diaphragm by curve D.

The diaphragm response necessary to give faithful and substantially distortionless rcproduction of sound has .been designated by the dotted line E E, that is any diaphragm response which deviates from this line may be considered as undesired operation and any response which is similar to it may be considered as desirable operation. This is of course only an approximation as in practice the change over from desirable to undesirable operation will not occur for a definite type of response but will be gradual. The closer the actual curve approximates the line E E the more satisfactory will be the performance. This approximation, however,

is close enough to the actual operation to assist in understanding the actual conditions. Returning now to the curves it is apparent from curve D that if the vibratory element acted as an ordinary diaphragm throughout the audible range there would be very good 7 sound reproduction in the region from B to C examination of the curve but very poor reproduction in the region from A to B. There would then be very desirable reproduction of the intermediate and higher frequencies but very poor repro- From an duction of the lower freqienci'es.

representlng the action of a vibratory element as a true piston that is such reproduction as depends on the movement of the diaphragm as a unit to cause all sound waves, it will be obvious that a-vibratory element with piston action would give very good reproduction in the region from A to B but very poor reproduction in the region from B to C. In other words the vibratory piston would reproduce the lower frequencies very well but the intermediate and higher frequencies very poorly.

A freely suspended body such as 9, diaphragm supported as explained above partakes of the nature of a piston as well as a diaphragm. At the lower frequencies the piston action will predominate and at the intermediate frequencies the diaphragm action will predominate and the resultant response curve will be somewhat of the form P.--F.D. From this it will be seen that the freely suspended element will reproduce faithfully, without undue distortion and with desirable intensity all frequencies with in the audible range covering entirely the region from A to C.

The structure shown in Fig. 1 possesses further advantages in that the walls of the cabinet,' particularly the portions of the side wall 4 surrounding the aperture act as a bafiie to prevent interference between the sound waves leaving the, front of the diaphragm and those emitted from the rear.

These two sets of waves on leaving their respective sides of the diaphragm will be 180 out of phase; that is as a wave, of condensation is emitted from the front face a wave of rarefaction will simultaneously leave the rear face. These waves spread out in all directions and, if thevibrating element were not surrounded by some baflle means, it is obvious that the waves from its rear face would reach the area covered by waves from its front face considerably out of phase with the latter and thereby cause considerable distortion and diminution of sound intensity. This may be corrected by providing a rigid barrier around the acoustic element so that q the waves from the rear. face will be cut off that the path through which they must travel to reach this area will be so lengthened that their effects in interfering with the waves emitted from the front face will benegligible. In the present structure the wall 4 surrounding the vibrating element acts as a rigid barrier or baflie cutting off the waves emanating from the rear of the element from the area in front of it. Maximum sound intensity and minimum distortion is therefore obtained from the sound waves emitted by the front of the vibratory body.

A modification of thedevice is shown in Figs. 2 and 3 which is entirely analogous in its operation and possesses all the advantages of that shown in Fig. 1 but which differs from the latter in that the loud speaker is a separate unit and not incorporated-in the cabinet of an associated radio receiver or similar device. Referring to these figures the reference numeral 20 designates a base on which is mounted the vibrating element 22 shown as of the double cone type and supported by a flat ring 21 to which it is attached by strips 23, which may be of flexible material such as rubber or leather or slightly resilient material as metal. The strips 23 are secured to the ring 21 by suitable clamping members 24. While four of these attaching members have been shown in the present instance it is obvious that more or less could be used as desired. In some cases a single one at the top may be suflicient while in other cases an annulus of soft leather or rubber completely closing the space between the cone element and the supporting ring may be desirable. Whatever form of attachment is chosen however it must possess substantially the same properties as to its restoring characteristics as the springs 8 in Fig. 1. That is the system must possess just suflicient elastic restoring force. to maintain the cones in normal rest position and to return them-to this position when they are displaced therefrom. As long as these conditions are satisfied it is evident that the cones will behave as a freely suspended body and act substantially as a piston in response to low frequencies and as an unclamped diaphragm in response to intermediate and high frequencies as explained in connection with the device in Fig 1.

The supporting ring 21 is attached to the base 20 and held upright thereon by means of brackets 27. v The operating mechanism 25 is supported on a bracket 26 and has an operating rod 28 fastened to the double cone 22 as shown. It is immaterial What particular form of operating mechanism is used, it being Moreover. the vibrating elements need not be' enclosed in a cabinet and therefore the supporting rin 21 must be of sufiicient width to act as a ba e for preventing the sound waves emitted from the rear of the cone member from interfering with those emitted from the front. It will probably be necessary to make it with an outside diameter of perhaps two feet for the large cones'now in use. If desired however the operating mechanism of this device can be enclosed in a casing in which case the supporting ring 21 can be replaced by onewall of the casing making the structure very similar to that in Fig. 1.

While I have disclosed the invention in several particular forms it will be obvious to those skilled in the art that it is capable of many modifications, for example, the modification shown in Figs. 2 and 3 can be used in connection with a radio cabinet as that in Fig. 1 and the vibratory system of Fig. 1 can be used as a unit as suggested in Fig. 2.

limited to the forms shown but can be of any other shape or style as long as their supporting system possesses the characteristics explained above. I intend to be limited in the invention therefore only as indicated in the following claims.

Having described my invention, I claim:

1. In an acoustic device the combination of a vibratile body, means for vibrating said body, a supportingmem'ber, and means for suspending said body from said supporting member, said suspending means having the minimum amount of restoring action which will return said bod to its position of rest when moved there rom by the vibrating a means.

2. In an acoustic device the combination of a vibratile body, a supporting member, a plurality of springs for positioning said bory in a predetermined position with respect to said member, and means responsive to operating forces for moving said body from said predetermined position against the action of said springs, said springs having the minimum amount of resiliency necessary to restore said body to said predetermined position when no operating forcesare acting on said body.

In a device for reproducing sound the combination of a diaphragm, a supporting member forming an opening slightly larger than. said diaphragm, means connected between the periphery of said diaphragm and said supporting member for holding said diaphragm in its inoperative position, and .a driving unit for moving said diaphragm from its inoperative position in response to operating forces, said means having a min: mum. restoring action to return said diaphragm to its inoperative position when no operating forces are acting upon .it.

4. In a device for reproducing sound the,

combination of a diaphragm having a circular periphery, a member forminga circular aperture slightly larger than the periphery .of said diaphragm, a plurality of lugs fastened to said diaphragm near its periphery, a corresponding number of ln s fastened to said member adjacent to sai aperture, springs fastened between the lugs on said diaphragm and the lugs on said member for supporting said diaphragm in its inoperative position, and means responsive to operating forces for moving said diaphragm from its inoperative position, said springs having a minimum restoring action to return said diaphragm to its-inoperative position when no operating forces are acting upon it.

5. A sound reproducing devicecomprising a vibratile diaphragm, a support, and means comprising a thin, flat, flexible strip for connecting the diaphragm and the support whereby the diaphragm hasfreedom of vibration.

6. A sound reproducing device comprising a vibratile diaphragm, a support, thin, flat, flexible elements secured to the edge of said diaphragm and to said support for holding the diaphragm in a free vibratile position.

7. A sound reproducing device comprising a vibratile diaphragm, a support, said diaphragm having its edge spaced fromsaid support, thin, flexible strips in the space between said edge and said support and connected-to said edge and said support for supporting the diaphragm for free vibrations thereof.

8. A sound reproducing device comprising a vibratile diaphragm, a support surrounding the same and spaced from the edge thereof, spaced flexible elements in said space, means for securing said elements to the edge of said diaphragm, and means for securing said elements to said support, whereby said diaphragm has substantially free vibration. I

9. Sound reproducing apparatus comprising a cabinet having side walls forming an enclosure with the top and bottom thereof,

an opening of material size in one of said side walls, a grille covering said opening, a sound reproducer of the diaphragm type housed within said cabinet with the diaphragm thereof adjacent saidopening, said diaphragm being sufficiently large to reproduce sound without the aid of a horn, a

elements of substantially thin, flat material,

means for connecting said elements to said diaphragm, and means. for connecting said elements to said structure. I

11. Asound reproducing device comprising avibratilc diaphragm having a substantially conical surface, a structure spaced from said diaphragm, spaced flexible elements of thin, flat material extending outwardly from said diaphragm to said structure, means for connectin one end of each of said elements with said diaphragm, and means for connectin the other end of each of said elements with said structure.

12; Sound reproducing apparatus comprising a cabinet, radio receiving apparatus housed within said cabinet, an opening in said cabinet, a loud speaker electrically connected with said radio receiving apparatus and housed within said cabinet with its 15 diaphragm adjacent to said ening, said loudspeaker including a diap ragm sufficiently large to reproduce sound at loudspeaker volume without the aid of a horn, supporting means adjacent to said opening, and flexible suspending means having a low restoring force connected between sald sup porting means and said diaphragm, whereby said diaphragm is. supported substantially adjacent to said opening.

L3. Sound reproducing ap aratus comprising a cabinet having a wa 1, an opening of'material size in said wall, a loudspeaker 7 including a diaphragm and operating means therefore housed within said cabinet, said 30 diaphragm being sufliciently large to reproduce sound at loudspeaker volume without the aid of a horn, radio receiving apparatus housed within said cabinet, electrical connections from said radio receiving apparatus to the diaphragm operating means, supporting means adjacent to the opening in said wall, and flexible suspending means having a low restoring force connected substantially between the peripheral portion ofsaid diaphragm and said sup orting means whereby the peri hery of said diaphragm is positioned a jacent to said opening but spaced therefrom.

14. Sound reproducing apparatus comprising a cabinet, radio receiving apparatus house within said cabinet, an opening in said cabinet, a louds aker electrically connected with said ra io receiving apparatus and housed within said cabinet with its diaphragm adjacent to said 0 ning, said loudspeaker including a diap ragm suflicientl large to reproduce sound at loudspeaker vo ume without the aid of a horn, sup orting means for the diaphragm having a ow restoring force and operating means for the diaphragm housed within said cabinet.

JOHN 1 MINTON.

15. Sound reproducing apparatus comprising a cabinet having a front wall, an opening of material size in said front wall, a loudspeaker including a diaphragm and a driving unit housed within said cabinet, said diaphragm being sufiiciently lar to reproduce sound at loudspeaker vcfi ume without the aid of a horn, sup orting means adjacent to said opening in e front wall,

hery of sald diaphragm is posilac

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