US1812213A - Loud speaker - Google Patents

Description

June 30, 1931;# J, p MlN-roN 1,812,213

LOUD S PEAKER Filed March 30. 1927 Fig. 2

//` F ,IX S Y wi lfcf @4&5 INVENTOR //////////////////4///////// JOHN P. MINTON Patented June 3o, 1931 UNITED STATES PATENT oFFlcE JOHN P. 4MINTON, OF WHITEPLADI'S, NEW YORK, ASSIGNOR, BY MESNE 'ASSIGNHENTS TO UNITED REPBJODUCERS CORPORATION, OF ROCHESTER, NEW YORK, A CORPORA- TION F NEW JERSEY LOUD SPEAKER Application filed Iaroh 30, 1927. Serial No. 179,433.

This invention relates to sound reproducers, and more particularly to sound reproducers operating from electric currents and converting such currents into sound, and is 5 particularly applicable to sound reproducers of the type generally designated as loud speakers which are desired to reproduce both voice and music and other audible sounds, with a volume sufficient to lill an ordinary room, and comparable in intensity with the original sound.

It has long been realized that fidelity of reproduction is most desirable in loud speakers, and the ideal has been a device which would produce sounds exactly corresponding in intensity at all frequencies to the currents supplied thereto. In the past, however, it has not been found possible to produce such a speaker. It has been found most difficult,

if not impossible, to do away with resonance effects which destroy quality, and still obtain sufficient volume, without the use of excessive power. The use of excessive'power is, however, undesirable because it increases the 25 cost of the loud speaker and the amplifiers necessary to operate it to a point which is far beyond the capacity of the average person to afford.

It has also been proposed to make use of very-large diaphragms operating in unconfined air, such as cones ranging in size from nine inches to three feet or more. These cones are'not satisfactory for several reasons, among them being the presence of a pronounced low frequency resonance which may make the tone drummy, and the absence or reduction of high frequency response which renders speech indistinct and muiiied. Finally, the size of the cone is in itself a serious objection, since the speaker cannot be built in or incorporated as a structural unit of the ordinary loud speaker, by reason of the small space available in such receivers, and is` difficult to place in the home in an artistic and pleasing manner. It has, in the past, been attempted to produce cone loud speakers of less than nine inches in diameter, and operable by means of a vibrating amature type of driving unit from an ordinary type of radio receiver or amplifier, but such devices, as far as'I know,

' cient low frequency response with small diaphragms when mounted to be driven by a vibrating pivoted armature. I have found, however, that it is possible to produce loud speakers having a stiff diaphragm less than nine inches in diameter and driven by a pivotedvibratile armature which will havela performance characteristic equal to, if not superior to, that of any heretofore known type of loud speaker, and which will produce satisfactory| volume on the ordinary receiver or amplifier, and which, also, may be driven from a power amplifier to give a greatly increased Volume without the production of rattling and other noises characteristic of some types of loud speakers when run with high power.

In the copending joint application of Selden E. May and myself, Ser. No. 126,157, filed July 31, 1926, we have shown and described a loud speaker comprising a stiff diaphragm not exceeding six inches in diameter and driven by a pivoted vibratile armature which will have a performance characteristic equal, if not superior to, that of any heretofore known type of loud speaker, and which will produce satisfactory volume on the ordinary receiver or amplifier, which may also be driven from a power amplifier to give greatly increased volume without the production of rattling and other noises characteristic of some types of loud speakers when run with high power.

This invention relates to an improved form of loud speaker of the same type described in the application above referred to and which will give a characteristic performance superior even to the loud speaker described in the said application.

From the foregoing, it will be understood itis an object of this invention to provide a loud speaker, capable of the highest quality of reproduction, operable by an ordinary receiver or amplifier, of a size which will permit it to be readily incorporated or builtv into a cabinet of an ordinary type of radio receiver or amplifier, and which may be Mln built and sold at a price which may be afforded'by anyone who can afford to have'a radio receiver capable of opera-ting a loud speaker. Still other objects will apparent from the specification.

' The features of novelty which I believe to be characteristic of my invention, will be pointed out with particularity in the appended claims.- My invention itself, how-l ever, both as toI its underlying principles and to its practical application, will best be understood by reference to vthe specification f and accompanying drawings, in which:

Fig. 1 is a perspective view of a loud speaker according to my invention.

Fig. 2 is a section on lines 2-2 of Fig'. l..

.sevensquare inches in area, which values I: have found'togive the best results when arranged as described hereafter.

The diaphragm. is preferably mounted on and supported ent'irely by the driving mecha-- nism, which is arranged in a particular manzner, so asto be capable of carrying the weight of the diaphragm Without disturbing the adjustment or position of the armature: and in order to provide for low frequency response, which requires a'large amplitude of movement of the diaphragm, a motion multiplying linkage is provided for multiplying the motion of th'e vibrating armature to the extent desired before applying it to the dia- 'In order to prevent reflection of waves in the material of the cone, which might produce standing waves and thereby destroy the response of the speaker, I rprovide a ring or annulus of iexible inelastic damping material attached as by adhesive to the periphery of the diaphragm, and finally in order-to prevent the slippage of air around the edge of the diaphragm, and to prevent interference between sound waves radiated from the frontand back of the' diaphragm, I enclose one side of the" cone, preferably the convex side to whichl the drive is attached, in a hol? 'low casing. The edge of the annulus of damping material is attached to the casing to provide a complete'separation of the` air space behind the diaphragm from that in front ofthe diaphragm as regards circulation within Ythe casing, but ext'reme care must be taken 4in the attachment o`f this annulus lto the casing to make sure thatffull freedom of motion is allowed to the diaphragm and that no restoring force whatsoever is'exerted upon it by the annulus, as this would tend to dlstort the performance characteristic by decreasing the low frequency response, andby introducing parasitic and undesired resonanceat one or more frequencies. In other words, the diaphragm is at all times'sup- .ported in such manner that it has full and complete freedom of motion between the limits of it's movement: and the position of the diaphragm at any instant determined solely by the driving mechanism, which is spring biased towneutral position. Any ref straint orrestoring force exerted on the edge of the diaphragm other than the damping referred to is avoided, as it would tend to deform the diaphragm and destroy the performance characteristicf A In the application referred to, the back .of the diaphragm is enclosed for all audible.

-fre uencies in such manner that sound radi# ate from the back does not reach the unconned air at any audible frequencies]l In accordance with my invention, I utilize a portion of the radiation from the 'back of the diaphragm, and also-provide va construction which tends to decrease the resonant the response characteristic. l

For this purpse, I provide an opening in the cabinet behind the diaphragm. This peaks in opening is covered with a layer of sound abnever been heretofore reduced, nor has any loud speaker been ro uced so far as I know,

capable of produclng the results obtainable from the combination.

Referring now more vparticularly Fig. 1, .y

1 designates a stiff diaphran, preferably yin the form of a cone of suita le fibrous material such as paper, preferably homogeneous 4paper,stii and smooth, and approximately .0075"` thick: and 2 designates generically a casing or box in which the diaphragm ,andA supporting and driving mechanism are enclosed, and which is'provided with an opening in thefront 5 thereof to expose the front of thediaphragm directly to' unconfined air. 3 designates generically the` diaphragm supporting and drivingl mechanism itself, comprising a vibratile balanced armature mounted in a mannerto be actuated by telephone currents supplied through the leads L. The dia hragm is mounted upon the. driving V1 anismissuch'manner aswillbehereinafter explained, that the entire weight of the diaphragm is carried on and supported by the driving mechanism but without substantially affecting the position and adjustment of the armature. In order to prevent the surging of air back and forth around the outer edge of the diaphragm and in order to damp the edge of the diaphragm and prevent reflection of waves in the material which would produce standing waves on the diaphragm and interfere with its response or modify its characteristic, a ring 4 of suitable damping material is provided suitably attached to the periphery of the diaphragm as by gluing, and suitably attached to the interior of the front 5 of the casing so as to position the diaphragm 1 at the opening in the front 5.

The annulus 4 may be secured to the inner face of the front 5 in any suitable manner, as for example by gluing, but in attaching the annulus, care should be taken to avoid imposing restraint upon the diaphragm. The damping material should be freely iiexible and inelastic, and should be mounted with sufficient slack so that it will not inany way interfere with or influence the forward and backward motion of the conical diaphragm; in other words, it exercises no restraint or restoring force whatsoever upon the diaphragm, the neutral position of which it determined and maintained by the driving unit which is spring biased to neutral position.

As an example of a satisfactory mounting, the ring 4 may be of soft and pliable leather such as kid, cut in strips and glued together to form a freely flexible and inelastic annulus, which is glued to theA diaphragm 1 and to the inside of front wall 5 of the casing 2.

It will be noted that when the cone is secured in position in the casing in the manner above described, there is provided an air space Within the casing behind the diaphragm: in order to prevent this dead air space from acting as a resonance chamber and thereby interfering with the proper action of the diaphragm, the entire exposed interior walls may be heavily coated with a suitable sound deadening material such as felt 10. t

For the purpose of smoothing out the resonant peaks in the performance characteristic and thereby securing a more faithful reproduction of sound from the speaker, I provide for utilizing a portion of the sound lradiated from the back of the diaphragm 1;

for this purpose, instead of providing a solid back for the casing 2, I provide an opening therein which is closed by a. layer of sound absorbing material such as felt 1() enclosed between an inner layer of Sateen or other suitable cloth, and an outer layer 71 of the same. The sound deadening material may be mounted upon a. grille or screen of metal gauze or other suitable arrangement for strengthening and reinforcing the-layer of sound absorbing material without substantially affecting its sound absorbing characteristics.

peak, for example about 300 cycles. If the back were closed tightly with a solid back, there would be a low frequency peak but at a slightly different frequency, which could not be `entirely avoided by lining the entire surface pf the cabinet with sound deadening materia However, the use of the open back covered with a layer of sound absorbing material as described, eliminates these peaks and smooths out the response curve, thereby im- .proving the faithfulness of reproduction.

The sound deadening material used in the manner described acts, it is believed, to apply just the right amount of damping to the cone to prevent it from developing the marked resonance which would otherwise appear as a pronounced resonant peak at certain frequencies.

The diaphragm' supporting and driving mechanism preferably comprises a permanent magnet 11 in the form of a U and having poles of opposite polarity mounted on and carried by a suitable supporting bracket 12, which in turn is mounted withinthe casing. The magnet 11, as already stated, comprises poles 13 and 14 of opposite polarity. The magnetic circuit is completed through a pair of pole pieces 15 andl associated with poles 13 and 14 respectively and a vibratile armature 17 interposed between the pole pieces and mounted in a flat leaf spring 29 and -passing through actuating coils 34. A yoke member 18 of nonmagnetic material is provided of sufficient length to overlap the poles 13 and 14 and the yoke member and poles are suitably drilled to receive screws 19 to secure the members in position. The holes for these screws will be made suiiiciently large to afford clearance to make necessary adjustments in order to position the yoke as desired. v

The exact construction of the driving unit is not per se a part of this invention, and is therefore not described in detail, reference being had to the application above referred to for such details. It will be understood that any suitable armature construction may be l substituted for that described in said application.

Referring now more particularly to Fig. 3, a suitable disc 65 appropriately shaped and preferably of light metal such as alumi fio num, is provided to which the cone 1 may be glued. A driving arm 63 is provided having a suitable screw thread end adapted to receive nuts 64 to mounting disc 65 an Vthe cone 1. A rigid arm 52 is provided to which the arm 63 ma be secured as by soldering or Welding, an .the arm 52 is attached to a support in such manner that it may vibrate in the plane of the paper in Fig. 3 about point 53, and for the purpose of strengthening the arm 52, it is preferably made U shaped in cross section except at point 53. An enlarged end 54 is provided, which may be suitably fastened as by screw 56 to a carrying block 55 adapted to be bolted to the magnet 11. A suitable connecting rod 61 is provided, secured atone end to one end of the armature 17, and, at

the other' end to arm 52. The arrangement.

is 'such that connecting rod 61 is vibrated longitudinally by the vibration of armature 17 thereby causing the vibration of rigidv arm 52, and likewise the longitudinal vibration of the driving rod 63 carrying the cone 1.

It will be seen that by reason of the connection of connecting rod 61 to a point between the fulcrumv oint53 of arm 52 and its connection to driving rod 63, the motion of the armature will be multiplied by approximately 2. This has been found necesi sary in order to provide the relatively large amplitude of movement necessary to give satisfactory low frequency response from a relatively small diaphragm. It will be noted that the static position of the cone 1 is completely independent of the armature 17, the weight of the cone being supported through iso driving rod 63, rigid arm 52 and tcarrier block 55.

While I have shown and described certain referred arrangements of apparatus accordling to my invention, it will be understood that modifications and changes may be made Without departing from the spirit and scope of my invention,` as will be understood by those skilled in the art.

I claim: I

` 1. A sound reproducer for voice and music comprising a housing having an opening in one face thereof, a stiff vibratile diaphragm l mounted in said housing and having one side exposed directly to unconfined air through said opening and having the other side exposed only to air within said housing, said housing having an opening of substantial I, areain back of said diaphragm and said opening being covered with a layer of soundabsorbin ing and r-iving saiddiaphragm, comprising i an electromagnetic unit.v

2. A sound reproducer for voice and music comprisin a housing havin an opening inone ,face t ereof, a stiff conical diaphragm supported entirely at its center and .having osition the diaphragmmaterial and means for support` .comprising a housing having an opening in one face thereof, a stiff, vibratile, conical diaphragm having its concave side exposed .directly to unconned air, and having its convex side exposed only to vair within said housing, said housin having an opening of substantial area in ack of said diaphragm and said openin being covered with a layer of sound-absor ing material, and means for supporting and driving said diaphragm com.- l

prising an electromagnetic unit.

4. A sound reproducer for voice and music, comprising a vhousing having an opening in one face thereof, a stiff vibratile, conical diaphragm supported entirely at its center and aving its concave side exposed directly to unconlined air through said opening and havv in its convex side exposed only to air within said housing, said housing havin an openingof substantial area in back o said diaphra m and said opening being covered by a soun filter arranged to create back pressure on said diaphra m at certain predetermined frequencies, an electromagnetic means for driving said diaphragm.

5. A sound reproducer for voice and music, comprising a housin having an opening in one face thereof, a stiff vibratile, conical diaphragm having one side exposed directly tol -unconlined air through4 said opening and having the other side exposed only to air within said housing, said housing having an opening of substantial area in back of said diaphragm and said opening being covered with {sound-absorbing material, operating to create back pressure on said diaphragm at certain frequencies, and electromagnetic means for driving said diaphragm. v

6. A sound reproducer for voice and music, comprisin a housing having an opening on one face t ereof, a stiff, vibratile diaphragm mounted in said housing, and having one side directly exposed to uiconined air through said opening, and having the other side exposed `only to air within said housing, said housing having an o ning of substantial area in back of said diaphragm and a sound filter interposed between said opening of substantial area and said diaphragm, and operating to create back pressureon said dia-v one face thereof, a' stiff, vibratile dia hragm having a rojected area of substantially 39 square inc es, mounted in said housing and having one side exposed directly to unconined air through said opening and having the other side exposed only to air within said housing, said housing having an opening of substantial area in .back of said diaphragm and said opening being covered with a layer of sound-absorbing material'having a frequency selective damping effect on said diaphragm and electromagnetic means for driving said diaphragm.

8. A sound reproducer for voice and music, comprising a housing having an opening in one face thereof, a stiff, vibratile, conical diaphragm having a surface area of substantially 47 square inches mounted in said housing and having one side exposed directly to unconfined air through said opening, and having the other side exposed only to air within said housing, said housing having an opening of substantial area in back of said diaphragm and said opening being covered with a layer of sound-absorbing material having a frequency selective damping effect on said diaphragm, and electromagnetic means for driving said diaphragm.

9. A sound reproducer for voice and music, comprising a housing having an opening in one face thereof, a stiff, vibratile diaphragm mounted in said housing and having one side exposed directly to unconfined air through said opening, and having the other side exposed oniy to air Within said housing, said housing having an opening of substantial area in back of said diaphragm and said o ening being covered with a layer 4of soun -absorbing material so arranged that the sound radiated from the last-mentioned side of said diaphragm does not substantially exceed va `small part of the sound radiated from said first side for mostof the speech and music frequency range and electromagnetic means Jfor driving said diaphragm.

l0. A sound reproducer for voice and music, comprising a housing having an opening in one face thereof, a stiff, vibratile, conical diaphragm mounted in said housing and having its concave side exposed directly to unconfined air through said opening, and having its convex side exposed only to air Within said housing, said housing having'an opening ofly to unconined air through said opening and having its convex side exposed only to air within said housing, said housing having an opening communicating with the rear of said diaphragm, said opening being of substantial area and covered with a layer of sound-absorbing material so arranged as to absorb a substantial amount of the sound radiated from said convex side and electromagnetic means for driving said diaphragm.

12. A sound reproducer for voice and music, comprising a housing having an opening in one face thereof, a stiE, vibratile, conical diaphragm not substantially exceeding 47 square inches in surface area, supported entirely at its center, and mounted Within said housing and having its concave side, exposed directly to unconiined air through said opening and having its convex side exposed onlypto air confined Within said housing, said housing having an opening of substantial area communicating with the convex side of said diaphragm and said opening being covered with a layer of sound-absorbing material so arranged as to absorb a substantial amount of the sound radiated from said convex side and electromagnetic means for driving said diaphragm.

13. A sound reproducer for voice and musie, comprising a housing having an opening in one face thereof, a stid, vibratile, conical diaphragm not substantially exceeding 47 square inches surface area supported entirely at its center, mounted Within said housing and having one side exposed directly to unconfined air through said opening and having the other side exposed onlyto air Within said housing, said housing having an opening of substantial area communicating with the back of said diaphragm and said opening being covered with a layer of sound-absorbing material so arranged as to absorb a substantial amount of the sound radiated from said side, a balanced armature unit for driving said diaphragm and means for multiplying the motion of said armature interposed between said armature and said diaphragm.

14. A sound reproducer for voice and music comprising a cabinet having an opening in one Wall thereof, a stiff vibratile diaphragm positioned Within said cabinet at said opening in such manner as to have one side thereof exposed directly to unconfined air, and said cabinet having an opening behind said diaphragm, said opening being covered With a layer of sound absorbing material operating to create a back pressure on said diaphragm at predetermined frequencies, and electromagnetic means for driving said diaphragm.

15. A sound reproducer for voice and music, comprising a cabinet having an opening in one wall thereof, a stiff vibratile conical diaphragm positioned Within said cabinet at said opening and having one side thereof exposed to unconfined air, said cabinet having ano ening behind said diaphragm, said opening Ibeingfcovered with 4a layer of sound "absorbing material operating to create back 5 ressure on said dia hragm at predetermined requencies, means or preventing circulation of air from one side of said diaphragm to the other within said cabinet, and electroma` etic means for driving said diaphragm. v v gned at White-Plains, in the county of Westchester and State of New York, this 22nd dayof March, A. D. 1927. A

JOHN P. MINTON.

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