*U.S. Patent No. 1,787,946 , 01/06/1931 (app. 05/14/1925) [DjVu272KB]
MEANS FOR CONVERTING ELECTRICAL VIBRATIONS INTO SOUND WAVES (class: 381/152; 181/163; 381/166; 381/186; 381/337)
LaRue, William D. (assignee: Victor Talking Machine Company)
Abstract: This invention relates to means for converting electrical vibrations into sound waves and more particularly to a device employing a large sized diaphragm for use in combination with electrical circuits, such, for example as radio receiving circuits, for converting electrical waves into sound waves of large volume. It has heretofore been proposed to provide devices of this character with a diaphragm of such large size that the use of a horn or amplifier is unnecessary in order to produce the desired volume of sound. One of the difficulties that is encountered in the construction of a loud speaker employing such a large diaphragm results from the relatively large mass of the moving or vibrating parts. Usually these latter comprise a diaphragm of large diameter mechanically secured to an armature or "flapper". When producing loud notes, or when the period of the electrical vibrations approaches the natnral period of one or all of the moving parts, the inertia of the latter so increases as the amplitude of vibration that the flapper strikes the pole pieces and there is produced an objectionable rattling noise. If the air gap between the flapper and the pole pieces is increased to prevent the contacting of these elements, the sensitiveness of the device is greatly decreased. An object of the present invention is to produce a loud speaker of the large diaphragm, hornless type which is so constructed as as to overcome the above difficulties.

*U.S. Patent No. 1,820,956 , 09/01/1931 (app. 11/27/1925 & in Germany 12/24/1924) [DjVu40KB]
LOUD SPEAKER (class: 181/148; 340/388.3)
von Arco, Georg (assignee: Gesellschaft Fur Draht-Lose Telegraphie M. B. H., Berlin)
Abstract: This invention relates to means for converting electrical impulses into sound or speech waves, which said devices are commonly known in the radio art as loud speakers. Common objections to the usual type of loud speaker are that they are unsightly in appearance, directional in their results and lacking in true quality reproduction. This invention has for its object to eliminate these undesirabilities and its purpose is to make it possible to construct a loud speaker of pleasing design and capable of giving non-directional and true reproduction.
If two telephones are mounted parallel with reference to one another at a small distance apart, say 1/2 to 1 cm. with their openings turned towards each other, they exhibit a considerable amplification of their acoustic actions. It is upon this discovery and principle upon which the idea underlying the present invention is based. instead of the conventional funnel-shaped structure, an acoustic space is created for the reinforcement of the sound vibrations which is bounded by means of two surfaces placed opposite one another, each of which constitutes a surface of revolution, and in which the telephone, or a similar instrument whose acoustic actions are to be reinforced, is mounted. The simplest case of such an acoustic space is the space between two circular flat plates in the center of each of which a telephone is arranged. If both telephones produce co-phasal vibrations of sound, there is obtained a reinforced action. To avoid disturbing natural vibrations of the surfaces bounding the acoustic space a good and suitable plan is to divide the acoustic space by means of radial partitions, into different compartments, with the result that the whole arrangement forms a sort of individual composite sound funnel.

*U.S. Patent No. 1,830,402 , 11/03/1931 [DjVu156KB]
Electromagnetic Sound Reproducer
Miessner, Benjamin F. (assignee Miessner Inventions, Inc.)
     An object of the invention is the provision of an arrangement whereby the field producing coil of such a reproducer can be excited with a uni-directional pulsating current without disturbing effects on the dynamic coil, and in particular excited with incompletely filtered rectified alternating current, as is had in the now usual practice of energizing the three-electrode vacuum tubes of amplifying systems from commercial alternating current sources.

*U.S. Patent No. 1,841,101 , 01/12/1932 (app. 03/06/1930) [DjVu102KB]
LOUD SPEAKER (class: 181/166)
Flanders, Paul B and Harrison, Henry C. (assignee: Bell Telephone Laboratories, Inc.)
Abstract: This invention relates to loud speakers of the direct radiating diaphragm type and more particularly to mountings for inertia controlled speakers having piston diaphragms of the cone or stiff plate type.
   These diaphragms as used, for instance, in moving coil loud speakers, are usually of comparatively small dimensions and must be provided with some form of baffle arrangement or its equivalent. If this is not done the response particularly at low frequencies, will be unsatisfactory due to the cancellation effects between the air waves set up by the opposite sides of the diaphragm. These speakers, therefore, were at one time usually mounted in an opening in a large plane surface which acted as a baffle board between the front and rear waves. The diaphragm was supported at its periphery by a mounting member of low elasticity which gave it a low natural period and since the radiation resistance of the air is also low at low frequencies, this construction gave a large low frequency peak in the response curve and was, therefore, not entirely satisfactory even aside from its disadvantage due to its large dimensions.
   To obtain the required baffle effect at very low frequencies without resorting to an execssively large structure it is now common pratice to mount such cones in a cabinet or box of moderate size open at the rear side. While it is possible in this way to reduce the cancellation effect materially, it is found that this construction has the decided disadvantage of producing other irregularities in the frequency response due to reflection from the walls of the box. Some of these reflected waves return to the diaphragm out of phase with this motion, thereby retarding it, while others are in phase thereby increasing the amplitude of its natural movement and producing the so-called "barrel tone" or resonant effect. It has been proposed to reduce these irregularities by lining the box or otherwise disposing sound absorbing material within it. In this way resonances in the upper portion of the frequency scale can be largely eliminated but this form of damping is not Very effective at lower frequencies due to the relative thinness of the damping layers With respect to the wave lengths of low frequencies.
   It might be thought advantageous merely to seal up the open side of the cabinet and thereby prevent the waves radiated from the rear side of the diaphragm from cancelling those set up by the front side, but, if this is done, the air confined within the box acts as an elastic reactance tending to retard the diaphragm and since this effect is inversely proportional to frequency the response is unduly decreased at low frequencies.
   The variation of the radiation resistance Of the air with frequency has already been mentioned. It is well-known that, while this resistance is comparatively constant for all sound frequencies having wave lengths greater than one-third the diameter of the diaphragm to be used, it falls off very rapidly for frequencies having wave lengths greater than this diameter. For the steady State condition of vibration this is not objectionable. The variation of velocity of vibration with frequency is such that for constant energy input the sound output, (V²R) is also substantially constant over the range of interest. It will be evident however, that while a low frequency vibration is being built up in the diaphragm, the energy stored in the diaphragm (1/2 MV²) is relatively large compared with the energy radiated (V²R) so that the diaphragm must continue to vibrate for an appreciable time after the driving force has ceased in order to dissipate this excess energy. This results in an "overlapping" or reverberation effect similar to that obtained in an excessively "live" room. Since the impedance of diaphragms of the type under discussion is almost entirely mass reactance, considerable resistance damping can be introduced to suppress these transients without materially increasing the total impedance of the system, that is, without substantially reducing the response of the diaphragm.
   It is therefore the object of the present invention to so design the air chamber of such a loud spcaker as to obtain a satisfactory baffle effect and at the same time to reduce the transient period to a point where it is no longer objectionable.

*U.S. Patent No. 1,868,607 , 07/26/1932 [DjVu88KB]
Electromagnetic Sound Reproducer System
Kolster, Frederick A. (assignee Federal Telegraph Company)
     Still another object of my invention is to provide a construction of electrodynamic loud speaker which includes a plurality of voice coils connected in separate circuits responsive to different ranges of tone frequencies for securing uniform response over a wide range of frequencies.

*U.S. Patent No. 1,878,162 , 09/20/1932 (app. 11/30/1931) [DjVu77KB]
CONICAL DIAPHRAGM FOR SOUND REPRODUCING AND RECORDING APPARATUS (class: 369/160; 181/163; 381/186; 381/432)
Mead, Harold Bertram
Abstract: This invention has reference to conical diaphragms for sound, reproducing and recording apparatus. The present invention provides a novel construction of diaphragm which is characterized by its capacity to move or expand freely under the slightest pressure. The invention is especially applicable to the diaphragms of gramophone sound boxes, and enables a sturdier diaphragm to be used than heretofore possible, whilst at the same time increasing the sensitiveness of the diaphragm so that it readily responds to the oscillatory movements of the stylus bar during tracking.
   Broadly, the invention consists in a diaphragm for the sound-box of a gramophone made from a shaped flat blank which is bent to conical form so that the radiating edges slidably overlap one another to permit of the free expansion of the conical member under the slightest pressure, and the contraction of said conical member to its normal size when pressure is removed.
   The blank constituting a diaphragm is preferably an aluminium blank, or an alloy thereof, and the amount of overlap is gauged so that the maximum degree of pressure, resulting either from the movement of the stylus bar (as in a sound-box) does not cause the overlapping edges of the conical member to slide too far or gape open.
   Figures 1 and 2 are, respectively, a front view and a side view of a main diaphragm for a sound-box. Figures 3 and 4 are, respectively, a sectional view and a rear view of an insulating diaphragm for use in conjunction with the main diaphragm. Figure 5 is a vertical sectional view illustrative of a sound-box fitted with the said diaphragms.

* U.S. Patent No. 1,907,723, 05/09/1933 [DjVu286KB]
Sound Reproducing Device
Bostwick, Lee G. (assignee Bell Telephone Laboratories)

     This invention relates to loud speaking telephone receivers and has for its principal object extending the range of efficient sound reproduction to include the highest frequencies of speech or music.

*U.S. Patent No. 1,931,235 , 10/17/1933 [DjVu113KB]
Sound Reproducing System
Nicolson, Alexander McLean (assignee Wired Radio, Inc.)
     This invention relates to sound reproducing apparatus and more particularly to such apparatus arranged to be operated by electrical oscillations corresponding to the sounds to be reproduced, and adapted to reproduce audible sounds corresponding' to speech, music and the like.
     It is an object of this invention to provide improved sound reproducing apparatus having a response characteristic which is flexible, so to speak, in that it may be controlled as to any part or parts, by prodetermination and design, or by adjustment of the apparatus in operation, or both.

*U.S. Patent No. 1,967,223 , 07/24/1934 (app. 01/06/1933) [DjVu187KB]
VIBRATION TRANSMITTING DEVICE (class: 181/173; 381/386)
Bostwick, Lee G. and Chatham, N. J. (assignee: Bell Telephone Laboratories, Inc.)
Abstract: This invention relates to vibration transmitting devices and more particularly to a mounting for large direct acting diaphragms in sound translating devices.
   One object of this invention is to fiexibly support a diaphragm in sound translating devices so that the diaphragm may vibrate as a whole, analogous to a piston, With large amplitude and with low energy loss in the supporting means.
Another object of this invention is to render a sound translating device particularly efficient throughout a limited range of frequencies in the audio spectrum.
   In one embodiment illustrative of this invention, a loudspeaker comprises a dished diaphragm sufficiently large to reproduce speech and music without the aid of a horn, an actuating device therefor, a support adjacent the periphery of the diaphragm, and a flexible annular mounting connecting the periphery of the diaphragm to the support. The mounting is preferably of light weight sheet material, such as duralumin, and may be divided into a plurality of sections by uniformly spaced slots. The slots are preferably sealed, for example, by strips of felt, to prevent the leakage of sound waves therethrough.
   In accordance with one feature of this invention, the annular mounting is provided with a plurality of linear corrugations arranged in polygonal formation about the periphery of the diaphragm, certain of the corrugations being approximately tangent intermediate the ends thereof to the periphery of the diaphragm.
   In accordance with another feature of this invention, the mechanical motional resistance at the actuating device and the impedance of the vibratory system, that is, the diaphragm and associated parts such as the actuating device and the supports therefor, are made substantially equal in magnitude at or near the natural or resonance frequency of the vibratory system so that a maximum vibrational velocity and maximum sound radiation throughout a limited range of frequencies is obtained.

*U.S. Patent No. 1,988,250 , 01/15/1935 (app. 02/17/1934) [DjVu89KB]
LOUD SPEAKER AND METHOD OF PROPAGATING SOUND (class: 381/184; 181/147; 181/163; 381/89)
Olson, Harry F. and Collingswood, N. J. (assignee: Radio Corporation of America)
Abstract: My invention relates to the art of propagating sound and in particular to means and a method for so converting electrical vibrations into sound waves as to control the low frequency response of a loud speaker.
   Devices of one sort or another have heretofore been used for the purpose of giving proper emphasis to the sound waves within different frequency bands. Among the various systems that have been resorted to are those which employ a plurality of diaphragms suitably mounted in a single cabinet. In some cases it has been proposed to actuate each of these diaphragms from its own driving mechanism. In other cases it has been proposed to utilize additional diaphragms which are vibrated only by their own resonant characteristics. An example of the last mentioned type of construction was disclosed by W. D. La Rue in his Patent No. 1,787,946 dated January 6, 1931. La Rue has a loud speaker comprising a cabinet with cone diaphragms mounted in openings of the cabinet structure. One of these cones is directly driven by an electromagnetic device; the other cone vibrates freely in response to sound vibrations set up by the driven cone. This disclosure, however, does not teach anything with regard to the problem of increasing the low frequency response of a loud speaker.
   An object of the present invention is to provide a loud speaker and a method of operating the same whereby the low frequency response thereof may be increased.
   Another object of my invention is to develop a dependable method for lowering the cutoff point of the low frequency response in a loud speaker.
   A further object is to increase the faithfulness of reproduction of. sound in accordance with the original production thereof.

*U.S. Patent No. 2,007,748 , 07/09/1935 [DjVu182KB]
Acoustic Device
Olson, Harry F. (assignee Radio Corporation of America)[DjVu182KB]
This invention relates to improvements in translating apparatus of the electrodynamic or moving coil type. More particularly, the invention relates to improvements in the moving coil of such apparatus and to improvements in the elements associated with the moving coil. The invention is especially applicable to acoustic apparatus and in the following specification it is specifically described and illustrated as applied to loudspeakers. The invention is also applicable to microphones and to other types of translating and energy converting apparatus.

*U.S. Patent No. 2,084,160 , 06/15/1937 [DjVu112KB]
Filter System for Loudspeakers
Minton, John Preston and Ringel, Abraham S. (assignee Radio Corporation of America)

     The invention refers to improved loud speaker construction and has for its principal object to provide a device in which different bands of frequencies resulting from a composite or complex sound are separately amplified and thereafter blended to give a true intensified reproduction of the original sound.

*U.S. Patent No. 2,113,393 , 04/05/1938 [DjVu88KB]
Audio Frequency Amplifier
Bierwirth, Rudalph A. (assignee Radio Corporation of America)
     The present invention relates to audio-frequency amplifiers. More particularly, the present invention relates to tone filter systems for amplifiers of that character, and has for one object the provision of a simplified and inexpensive combined tone filter and output transformer for an audio-frequency amplifier.
     A further object of the present invention is to provide an improved and simplified tone control system for an audio-frequency amplifier.
     A still further object of the invention is to provide an improved audio-frequency amplifier wherein undesirable high audio-frequency interference and higher audio-frequency harmonics generated in the amplifier devices, may be filtered
from the output of the amplifier following the power amplifier devices or tubes.

*U.S. Patent No. 2,121,008 , 06/21/1938 (app. 07/16/1936) [DjVu106KB]
ACOUSTIC TRANSLATING DEVICE (class: 181/31)
Bilhuber, Paul H.
Abstract: This invention relates to mountings for sound reproducing equipment, as for instance, loudspeakers. One. object of the invention is to provide means for improving the low frequency response. Another object of the invention is to provide means for increasing the clarity of the response. Still another object of the invention is to provide means for reinforcing the output of the loudspeaker unit. Another object of the invention is to provide for yieldingly supporting the outer end of the conical diaphragm of a loudspeaker, said support being in the nature of a vibratory continuance of the diaphragm., responsive to said diaphragm. Another object of the invention is to induce and locate the resonant frequency at some desired portion of the low frequency spectrum. For this purpose, the invention consists in an improved baffle under pressure or tension, so arranged and combined with a housing and a diaphragm of a loud-speaker mechanism as to carry out the foregoing objects. In a pre-stressed 25 panel made in accordance with my invention, considerably less absorption or vibromotive impulses occur than in the panels heretofore used.

*U.S. Patent No. 2,182,328 , 12/05/1939 [DjVu103KB]
Band Width and Tone Control Circuit
Weinberger, Juilus (assignee Radio Corporation of America)
     My present invention relates to tone control circuits for radio receivers, and more particularly to combined band width and tone control circuits for radio receivers of the high fidelity type.