US1841658A - Sound amplifier - Google Patents

Description

Jan. 19, 1932. UNDENBERG 1,841,658

SOUND AMPLIFI ER Filed Jan. 19. 1927 3 w a gwoentoz j /wodorc linden!) fly Patented Jan. 19, 1932 PATENT OFFICE THEODORE LINDENBERG, OF COLUMBUS, OHIO SOUND AMPLIFIER Application filed January 19, 1927. Serial No. 162,152.

This invention relates to an improved sound amplifier wherein is provided novel features of acoustics for amplifying or developing sounds produced by vibratory dia-' phragms of the type employed in connection with talking machines, telephone receivers, radio or wireless receiving apparatus and other analogous mechanisms. The principal object of the present invention is the provision of a sound amplifier so constructed as to give forth improved tonal ualities or properties to the recreated soun whereby the natural characteristic of the sounds are developed with great fidelity throughout the 1 entire range of audible sound vibration and the identity of each individual sound or tone property preserved and developed in true proportion to the total volume.

Most of the sound amplifiers or reproducers now in general use have certain inherent characteristic tones which are not favorable toward the complete amplification of sounds of other characteristic tones of vibratory periods. The usual radio sound amplifier comprises either a horn shaped body, or, more recently, a cone sha ed amplifier. It is well known, however, t at practically all of these devices possess a peculiar individual tonal property which while favorable possibly in the amplification of certain sounds, such as the reproduction of violins, piano, various wind instruments or the spoken voice yet these devices, to the best of my knowledge, are incapable of amplifying accurately and faithfully all kinds of sounds, irrespective of its nature nor have such devices overcome the inherent flat, mechanical tone qualities which persist even in the most expensive amplifiers now obtainable 40 on the open market.

To improve this situation and to provide an amplifier formed to provide for a greater degree of naturalness in the developed sounds, together with the minimizing of mechanical defects, the present invention provides an amplifier which consists generally of a casing in which is contained a plurality of simultaneously operable reproducing units, with which are connected individual amplifiers formed to include resonant walls composed of different materials, such as wood, leather, metal, compositionmaterial, paper and the like which, when set into vibration are adapted to sensitively respond to, reproduce and develop sounds corresponding in quality and volume and with great fidelity to the original rendition and to the individual sound notes or properties comprising such renditions, \vhereb is produced a composite blended tone of singularly natural character wherein 'not only the fundamental sounds are reproduced but the overtones and other harmonious shadings are present by which sounds of pleasing and natural qualities are afforded.

The invention herein constitutes an improvement upon or development of the disclosures contained in m prior'applications on sound amplifiers set fibrth in my co-pending application Serial Number 80,917, filed J anuar 13, 1926 and Serial Number 110,560, filed ay 20, 1926. In the former of said applications there has been disclosed a plurality of the horn type amplifiers actuated by individual reproducers and in the last named application a plurality of membranous diaphragms, maintained under tension and also actuated by separate reproducers. In both of said applications, however, the amplifying members are formed from different materials with the primary end in view of improving sound quality. The present invention consists broadly in a structure which comprises a combination of the arrangement set forth in my aforesaid applications, in that in the present invention the amplifier enerally also comprises one or more mem ranous diaph-ragms formed from animal hides or the like and maintained in ataut vibratory condition, and to ether with a plurality of horn type amplifi ers, each of which comprising walls of a single material differing from the materials emplo ed inthe other amplifiers and o rated t rough individual reproducers. owever, I have found that by the combination in the one instrument of both the membranous diaphragms and the horn type amplifiers of different materials, a construction which I consider to be more faithful in sound reproduction and amplification than the other structures and, in addition, a construction which can be produced in commercial quantities at a comparatively low cost. Moreover, by the inclusion in the amplifier as a whole of the membranous diaphragm I have provided a unit which develops most completely sounds having characteristic low periods of vibration to the end of developing the latter to values properly proportioned to the finally emitted sound volume of the amplifier. This membranous diaphragm is used in combination with a plurality of inde endent reproducer units including ampli ers consisting of horns composed of metal, paper and the like which respond faithfully in the development of sounds having relatively higher vibratory periods, whereby through the combination of these interrelated units, the amplifier generally develops composite tones of unusual clarity, proportions and naturalness covering the entire range of reproduced sounds and wherein there is substantially a complete absence of the flat mechanical qualities of ordinary sound amplifiers used in both mechanically and electrically operated talking machines, radio amplifiers and other similar reproducers.

With these and other objects in view, as will appear as the description proceeds, the nvention consists in the novel features of construction, combinations of elements and arrangements of parts hereinafter to be fully described and pointed out in the appended claims.

In the accompanying drawings:

Figure 1 is a front elevation of the sound amplifier comprising the preferred form of the present invention, the front of the amplifier being omitted to disclose the interior structure,

Figure 2 is a vertical transverse sectional view taken on the line 22 of Figure 1,

Figure 3 is a horizontal sectional view on the line 33 of Figure 1,

Figure 4 is a diagrammatic view of the electrical circuit employed in operating the re roducer units of the amplifier.

eferring more particularly to the specific form of the invention herein selected for illustration and description but, which, of course, is subject to modification as explained hereinafter, the numeral 1 designates the cabinet of the amplifier which may be formed to include a base 2, upstanding end walls 3, a top 4, a vertical back Wall 5 and an open front 6. The latter is preferably covered by a grille or screen 7 and to further prevent the muffling of sound within the cabinet the side walls 3 and the back wall 5 may be provided with openings of any description so as to prevent the muffing of tones within the cabinet.

Arranged within the cabinet and toward the back thereof is a membranous diaphragm r unit designated generally by the numeral 8.

This unit comprises a primary diaphragm 9 formed from leather or the like and of any desired thickness. In this instance the diaphragm 9 is of substantiall rectangular form and has its upper an lower edges clamped as at 10 to internally disposed frame strips 11, stationarily mounted within the cabinet 1. The strips 11 also carry adjusting screws 12, having the inner ends thereof swiveled in connection with a tensioning web 13 which engages with the primary diaphragm so that by adjusting the screws 12 the said diaphragm may he placed under any desired degree of tension calculated to produce the best results. The axial portion of the web 13 carries an electrical reproducer unit 14, and the stylus 15 of this unit is connected with the center of the diaphragm 9. It will be observed that by mounting the reproducer unit in connection with the web 13 a proper distance is maintained at all times between the reproducer unit and the diaphragm so as to avoid placing an unnatural stress upon the stylus 15. This enables the stylus to operate to the best advantage irrespective of the degree of adjustment imparted to said diaphragm.

The operation of the unit 8 may be improved by the employment of a secondary diaphragm 16 which, has its upper and lower edges connected with the back wall 5, and the tension thereof may be adjusted by set screws 17 carried by said back wall. The secondary diaphragm is not provided with a reproducer unit but responds to the lower vibratory influence of the primary diaphragm by means of a connecting bar 18, which transversely unites the diaphragms 9 and 16, as shown more particularly in Figure 2. The cooperative action of these two diaphragms results in the creation of sound waves of low amplitude but of sufficient power and definition to form a very essential part of the composite sound volume of the amplifier as a whole. Operated separately and without regard to the remaining units of the amplifier, the diaphragm unit 8 is not individually sufficient to produce the results sought for, but in combination with the remaining units of the amplifier, the diaphragm unit constitutes a very important element, particularly the reproduction of the lower tones.

Arranged on the base 2, within the cabinet 1, and to the front of the diaphragm unit, are a plurality of horn amplifiers 19. Two of such amplifiers have been shown, but it will he understood that this number may be increased if the necessity thereof should be found desirable. Each of the horn amplifiers 19 includes an electrically operated reproducer base 20 with which is connected. above the diaphragm therein, an upright horn 21, which is preferably formed from thin sheet material such as thin gauge brass, and various other metals, wood, paper, or the various moulded composition materials now found in many types of amplifiers. Each of these units has its own reproducer, whereby due to the vibration of the column of air within each of said horns, and the vibration of the material con'iprising the wall of each horn, said units each deliver an individual characteristic tone which, if heard separately, would not be desirable or impressive but erably of nickel and indicated by the numeral 22. This plate responds sympathetically to the sound vibrations created within the amplifier, and is particularly useful in developing more clearly notes characteristic of a piano or like instruments. It may be desirable to dampen the vibration of the outer edges of the diaphragm 9, as at 111, the horns 21, as at 1?), by applying thereto a non-resonant material such as cotton, rubber or fabric in order to prevent the relatively minute and uncontrolled vibration set up in the edges of these amplifying surfaces from interfering with the quality of the amplified sound.

A circuit arrangement has been generally disclosed in Figure 4, wherein the numeral 23 indicates by way of illustration a radio receiving apparatus. The output leads 24 of the apparatus lead to any suitable type of amplifying means for developing the electrical strength of the signal oscillation, as indicated at 25, and from this amplifier leads 26 and 27 extend to the reproducer units 20 of the horns 21, the latter being connected in series by a short conductor 28, in which is located a fixed condenser 29. Shunted across theleads 26 and 27 are conductors 30 and 31 which are also connected with a fixed condenser 32. Other circuit arrangements may of course be employed within the range of the invention but the circuit described has been found to give very satisfactory results and the fixed condensers also contribute toward clarity in tone.

The proportion of the materials may of course be varied. Each of the horns 21 contains preferably seventy-five square inches measured area on one side only. Thus in the present case the horns 21 may provide seventy-five (7 5) square inches of brass and seventy-five (75) square inches of any other material such as soft or hard paper, which vibrates under conditions of low energy and in response to the vibratory air column in the horn. In addition to this each of the diaphragms in the reproducer bases 20 may contain an aluminum disk measuring substantially 4.7 square inches, which vibrate in response to high electric energy. The primary diaphragm 9 also vibrates in response to high electric energy and contains for example one hundred and ninety-six (196) square inches of leather or the like, while the secondary diaphragm 16 contains a like area of leather, wood or other material vibrating under low energy conditions. The metal plate 2 may contain approximately seventy (70) square inches and its vibration is of low energy character." The above areas are calculated for one side only and are given merely to set forth the approximate proportions of the several resonators employed and the material from which they may be constructed, also the nature of their vibrations.

In view of the foregoing it will be seen that the present invention provides an amplifier generally consisting of cooperative individual amplifying units, each of which having its own reproducing unit, and wherein each of said units has been developed in order to amplify completely sounds having certain definite characteristics and properties. I am aware that heretofore amplifiers have been proposed consisting of a plurality of nested conduits formed from different materials but having a common reproducing base, and I therefore do not claim broadly such a structure but have addressed the subjoined claims particularly to the individually and in a sense independently operating units but wherein each unit has a definite place or value in developin the final tone quality of the amplifier consi ered generally.

What is claimed is:

1. In a sound amplifier, a plurality of actuated reproducer units, a membranous diaphragm vibrated by one of said reproducer units, a plurality of resonators carried by the remaining reproducer units, each of said resonators being formed from a material possessing different resonating properties than those of the remaining resonato s, and a member arranged contiguous to said reproducer units and supported to vibrate sympathetically with the sound energy developed y said reproducer units and resonators.

2. In a sound amplifier, a plurality of actuated reproducer units, a membranous diaphragm vibrated by one of said reproducer units, a plurality of resonating horns carried by the remaining of said reproducer units, each of said horns being formed from a material possessing different resonating properties than those of the remaining horns, and a metallic plate arranged contiguous to said reproducer units and supported to vibrate sympathetically with the sound energy developed by said reproducer units and resonators. v

3. In a sound amplifier, a. plurality of actuated reproducer units, a plurality of resonators carried by said units, each of said resonators being formed from a material possessing different resonatlng properties than those of the remaining resonators, and a member arranged contiguous to said reproducer units and positioned to resonate symnttlletically with the sound energy developed hy said reproducer units and resonators.

Iii testimony whereof I affix my signature.

THEODORE LINDEN BERG.

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