US1655267A - Sound apparatus for producing and receiving sound waves - Google Patents

Description

Jan. 3, 1928. 1,655,267

W. HAHNEMANN ET AL SOUND APPARATUS FOR PRODUCING AND RECEIVING SOUND WAVES Filed Aug. 7, 1925 In venrdro Wa/fer Habnemana fie/hrx-b Heel?! W W Alfarn 5 Patented Jan. 3, 1928.

UNITED STATES PATENT oF 1,655,267 IHCE.

WALTER HAHNEMANN, OF KITZEBERG, NEAR KIEIVI, AND HEIKBICH HECHT, OF KLEL, GERMANY, ASSIGNORS TQslGNALGEsELLSCHAFT MIT BESCHRANKTER EAFTUNG,

OF KIEL, GERMANY, A FIRM.

SOUND APPARATUS FOR PRODUCING AND RECEIVING" SOUND WAVES.

Application filed August 7, 1925, Seria1 No. 48,822, and in Germany August 11, 1924.

i The invention reters to apparatus for the production and reception of sound waves and moregenerally for the purpose to transfer vibratory mechanical energy from or to 5 the sound propagating medium and to transform mechanical vibratory energy into electrical vibratory energy and vice versa.

It is the problem of the invention toproduce devices of the kind above specified which are adapted to produce and to reproduce sounds of a very broad range of fre- .quencies with, as far as possible, equal efiiciency at all frequencies and with a high degree of efiiciency, and particularly to avold distortion.

A further object vof the invention is to transfer energy with good efiiciency between ifi'erent vibratory structures forming a part of the device, for instance between a diaphra'gm and a' detector (microphone or the like). It is also the object of the invention to produce a device for the reception and reproduction of noises, for instance nolses in water originating from the rotation of ships 4* propellers, and also a device for the reception and reproduction of music and speech.

These several objects areaccomplished by coupling a plurality 'of equally tuned mechanical vibratory structures, forming e16:

ments of the apparatus described, in such a manner that the resonance crests in the resonance curve of the coupled structures of the apparatus are substantially evenly dis tributed over the' desired range of frequencies and that the ordinates of this curve between the resonance crests do not sink below an undesired level, for instance below 30% of the ordinate of the neighboring resonance crests. Another feature of 40 the invention consists in providingat least three vibratory structures coupled in the manner above described. A further feature of the invention consists in inserting a series of such coupled structures between the sound emitting and receiving element (diaphragm) and the energy converting means (detector, microphone) of the apparatus. Another feature of the invention is that the intermediate structures are coupled with one ani other in series; that is, that each structure is coupled with the oneS adjacent to it and with no others.

These particular features of the invention and others may be seen more clearly from Figure 1 shows diagrammatically the structure of Figure 1.

Figure 1 shows a resonance curve such as might be expected from a structure such as shown in Figure 1.

Figure 2 shows a further modification of the invention with a series of coupled resonators, and

Figure 3 shows a modification having a combined system composed of coupled resonators and diaphragms.

In, the art of communication or the like, in many cases it is desirable to operate over a very broadrange of fr uencies with one and the same apparatus, either for the production and reception of sound waves, or for other purposes wherever mechanical or electrical vibrations have to be transferred or 'tran formed. Special examples of this kind are the following:

In submarine signaling'it is often necessary to have'submarine sound transmitters which are particularly adapted to receive water noises. While transmitters for signals covering a very small range of frequencies with high efiiciency are known, real satisfactory solutions of the problem of transmission of noises do not exist, i. e. there are transmitters today which' are capable of picking up and transferring sound over a small range of frequencies, as for instance over a range of 10% to 20%, of the vibrations in the vicinity of the natural frequency a of the transmitter, but transmitters have not been designed to operate successfully over a greater range of frequencies as. for instance one octave or more or from 500 to 1000 cycles.

It is also advantageous to provide a telephone for the reception of such noises efliciently and without distortion. Telephones possessing good receptive properties for single tones and frequencies are known, but the working range over. varying frequencies with good efliciency islimlted to 20%- 3 0% of their resonance frequency (i. e. for instance from 900 to 1200 cycles). Naturally these telephones are not satisfactory for the reception and transformation of electrical 5 fluctuations produced by water noises transmitted from submarine sound receivers where a high efficiency over a broad range of frequencies is desired. This invention 1s applicable therefore for the development of telephones capable of operating over a broad range of frequencies, for exampleover a range'ofone octave. Besides it is very desirable to produce telephones of a high 'efli-' ciency for a broader range of frequencies,

5 especially for the pu-rposeof transforming speech vibrations, in which case it is desirable for avoiding distortlon to have a uniform efficiency over a number of octaves, if

possibleeven more than five octaves.

What has been said'above applies to loud speakers also. Apparatus of this kind has been developed recently which has a good efiiciency for a definite range of frequencies, but even in this case .this range of frequencies was limited from about to of the middle frequency for which the devices were designed. It has been proposed to employ a number of devices of this kind operating to get-her, each of them being tuned to a diiferent range of frequencies so that the whole range of frequencies to be transmitted is covered with equallyetficient devices. However, as the human speech contains frequen-' cies ranging over many octaves (at least five '5 to six) a very great number of such individual devices would'have'to be applied for -covering this whole range wlth a" sat1sfactory degree of eificiency. As it is desirable to dispense with a greater number of devices andto use as few as possible, preferably only one, this invention is particularly useful in this respect. i The invention is based 'upon gouphng a plurality of vibratory structures (three or more) with one another. The invention consists in adjusting in such devices with relation to one another the dan'iping and the degreeof coupling so that the resonance crests in the resonance curve of the coupled system are evenly distributed over the range of frequencies to be transinittedand that tl1c emitted or received energyat all frequencies of this range is a substantial per cent of the maximum energy at the points of thp resonance crests themselves. The even distribution of the resonance crests is obtained ac- The following discussion may elucidate coupling particu'l'arlylmve to be considered.-

If energy travels through a series of coupled systems a resonance diagram results with a plurality of. resonance points. If theefiiciency of the transfer is to be made satisfactory'the individual structures should be tuned to the same natural frequency. The

resonance crests mentioned above in the coupling curve are under such conditions positioned a distance from one another depending upon the degree of coupling between the r individual structures. Broad curves are obtained by coupling the structures closely, each structure forming one crest. Where many structures are coupled.

together the resonance curve hasa number of peaks equal to the number of structures, which peaks become broader the greater the number of structurescoupled togethen As the theory shows for a given natural frequency of the structures-the resonance crests cannot move farther towards the higher frequency than to one and a half times the natural frequency, while towards the lower frequencies crests can exist until to the lowest frequencies. One of the main features of the invention is that in all cases the number of the structures coupled with one another and the degree of coupling between them is so adjusted that the desired range of frequencies is satisfactorily covered. .lVhere ,the-

structures havefslight damping the peaks of the resonant curves are sharp and the amplitudes on both sides of the peaks fall oil very rapidly for changing frequencies. To

1 maintain therefore great amplitudes between peaks of the resonance curve it is .necessary to have the peaks close to each other. Thus a great number of resonant structures are necessary toprovide a. good efliciency "at all points. The damping itself may be caused by radiation of energy or by wasting of. energy. In the mostcnses besides the desired broadresonance curve an initial vibratory structure is already provided, for

. instance in the case of a subn'iarine sound receiver the diaphragm taking up the energ from the water and also the final vibratory structure, the particular detector (microphone, electroi'nagnet or the like). For these elements generally defined vibratory dimensiohs are given, especially the'value of the masses and the elasticity of the elastic members carrying the masses, with regard to the desired properties of the apparatus. a submari'nesound receiver with relatively large damping, generally a relatively large area of the diaphragm is necessary, and consequently a relatively large mass and high For elastic force of the carrying member, while for detectors, especially for. the normal microphone with carbon grantiles, the mass apparently'may be very much smaller than the mass of a large receiving diaphragm. It may easily be understood that it is extreme- 1y difficult to couple two such structures tlghtly together where there are entirely dif-' their mass and elasticity, a tight coupling between these structures may be obtained. This way consists in inserting between the initial structure and the final structure a sufficient number of intermediate vibratory structures which increase in number inversely as the masses decrease. If, for instance, the ratio of the masses of the initial structure and the final structure is 1:100, a casein which for coupling by masses the greatestpossible degree of coupling is by inserting only two additional intermediate structures the individual ratio of masses between neighboring structures may be lowered to 1:5, the coupling being enhanced in this way from 10% in the before mentioned case to and the resonance diagram being broadened accordingly. A further broadening of this diagram arises from the fact that, instead of two crests with 10% distance, now four crests with about i0% distance from one another exist. In this way by the means of the invention i. e. by the interconnection of a plurality of conveniently coupled structures in this case not only a broad resonance diagrain but also the best transfer of energy between the initial structure (diaphragm with great radiation damping) and the final structure (microphone of high sen'sitivenessi. c. with small mass) is obtained.

To explain this feature a little more fully, suppose that the initial structure receiving the sound weighs 100 and the final structure used to transform the sound to electric oscillation weighs 1, both being measured in the same units. 'These two structures may be coupled through a mass structure weighing 10. The result would be a coupling of a rather loose nature. Suppose, however, there were inserted rstructures stepping down from the 100 weight to the 1 in the ratio of 5 or approximately that, then the coupling would be closer and in addition there would also be a broadening and flattening of the resonance curve tending to produce a system capable of, responding over a considerable range of frequency.

In the drawing in which some practical.

examples. of the invention are shown, Figure 1 represents a submarine sound transmitter and receiver, the initial structure of which Is a diaphragm a and the final structure of which is a detector d,-in this case an electromagnetic detector. Diaphragm and detector are coupled with one another by two addi-- tional vibratory structures 6 and a. Each two neighboring structures comprise a, common mass so'that the masses and elastic members are distributed to the structures as follows:

Structure a: masses 1 and 3, elastic mem her 2.

Structure 6: masses 3 and 5, elastic member 4.

Structure 0: masses 5 and 7 elastic 1118111. her 6.

b StSructure d: masses 7 and 9, elastic mem- These structures above are shown analytically'in Figure 1". Themass 1 is coupled to the mass 5 by means of the coupling mass 3, while 5 is coupled to 9 by means of the mass 7. As is shown there are really four oscillatory structures, since all but the outer masses serve as mass elements of two vibratory structures.

s has been stated above each of these oscillatory structures are tuned to the same frequency, each is similar to the other. In F igure 1 it will benoted that the resonance curve of each individual structure a, b, c. d, is illustrated as being the same.

These oscillatory structures are combined together closely coupled so that a considerabl-e amount of energy may be transferred from one to the other. They are combined together by so arranging them in order that the masses are arranged in steps according to their effective magnitude. In this way the coupling becomes very closeand a broad resonance results. The peaks which formerly came together are now separated even though the individual structures have the "same natural frequency.

The result is that a structure is produced.

which is substantially equally responsive over a large range of frequencies. As will be noted the peaks of the structures of Hill smaller weights go towards the higher end of the range while the heavier structures descend below their natural frequency.

The cui've of Figure 1 having the four peaks is the resonance curve of the coupled structure. A loud speaker or the like having a resonance curve-of this nature will resfiond equally well to the low vibrations as to the high ones.- In this case it is not really a question of interposing intermediate structures for the transfer of energy from the m1- tiaLto the final structure but the evolution of a coupled tuned resonant structure which is'capable of responding tosounds of all frequencies. -7

the vibrations, and others responding for In the actual combination all the structures cooperate together, some responding and taking up the burden of operation when their particular structure is most affected by sounds of other frequencies. The idea is to have the sum total of responses 'of all structures about the same at all frequencies. By closely coupling these oscillatory structures together the oscillatory energy is easily transferred from one vibratory structure to the other so that the one which should respond most has the energy andis capable of doing its part inthe whole'operation.

Mass 1 is the outer casing of the appara-,

tus, masses 3, 5 and .7 are metal casings carrying the elastic members 4, 6 and 8 respectively. All elastic members in the example of Figure 1 are diaphragms. They may be replaced by other elastic bodies, as rods, strips or the like. The final structure is i more clearly indicated by Figure 1. It con- The problem in this case is to have the diaphragm cooperate with the telephone and the ear canal efliciently over a broad'range of frequencies. According to this modifica tion a number of coupled resonators b, c, d, are interconnected between the initial structure a and the final structure g. Theinitial 1 structure 02- consists of two masses, the telephone casing 14 together with the field mag- 1 net 15and the armature 16, which are connected with one another by an elastic-diaphragm 17. Similarly, as in Figure 1 the resonators have'common masses so that:

. .Riesonator b embraces; chamber 17 and partly 18.

Resonator cnchamber 18 and partly 19. Resonator d chamber 19 and partly 20 A similar device shows Figure 3 in which the mechanical system h of a loud speaker 18 coupled with radiating funnel i by means'of interconnected resonance chambers 17 1S 18, 19 19, 20; 20, 21-; 21, 22;;these chambers and the openings 23- -27 in the walls be- .tween the chambers bein so adjusted or dimensionedthat a gradua increasing ratio of the masses of neighboring structures exists a and a degree of coupling of suchtightness that a good transfer of energy between it and i is obtained. In this case a very tight coupling must be used onaccount of the very broad range of frequencies (speech-and music) desired to be reproduced and therefore the masses have to decrease verv slowlv from structure to structure. Therefore it is difiicult to obtain a sufiicient tight coupling be-.

tween the first structure (diaphragm 2 with armature. 3) and the cooperating chamber without intermediatestructures. According to the invention in this case' one or more coupled mechanical structures with gradual decreasing masses must be inserted between the initial structure andthe first resonance chamber, as it is shown at 28 in Figure 3.

y In all three examples described above (Figure 1-3), all structures, the mechanical ones and the resonator chambers preferably must be tuned substantially to the same fre quency. I

It maybe understood that the invention is not limited to the examples shown in'the figures. The: invention may be applied generally in' all oasesin which. two definite vibratory structures, an initial structure and a final structure are to operate with one" another over a broad range of frequencies. If this range is excessively broad as for instance for the human voice and'inusic which include vibrations from the highest to the lowest frequencies according .to the invention a large number of vibrator-y structures has to be interconnected between the two end-structures. The closer the coupling between them the better the condition of a broad resonance diagram can be fulfilled with as few interconnectedvibratory structures as possible.

We claim 1. Acoustical vibratory apparatus consisting of a plurality (at least three) vibratory structures built up of separate masses and connecting elastic members coupled with one another in series with the aid of their masses and each elastlc member being held at its rim by one of the said masses and carrying in its middle zone the following mass.

2. Acoustical vibratory apparatus consisting of a plurality (at least three) of equally tuned vibratory structures coupled in series with oneanother, the said apparatus comprising an initial vibratory structure and a final vibratory structure of vibratory magnitudes (mass and elastic force) of different value; the value of the vibratory magnitudes of the intermediate structures decreasing gradually in equal steps towards the struc ture with the smallest vibratory magnitudes.

3. Acoustic vibratory apparatus comprising two end masses and a plurality of intermediatemasses, a plurality of elastic members, each mass bein coupled to the adj'acentanass'by one of said elastic members, said masses being so adjusted with regard to mag. ni'tudethat the resonance crests of the apparatus are evenl distributed over the range of fre ueneies or whichthe apparatusis to be us 4. Acoustic vibratory apparatus comprising two end masses and a plurality of'intermediate mas es, a plurality of elastic members, each mass being coupled to the adjacent mass by one of said elastic members, forming a series of vibratory structures of masses coupled by elastic members, each of the intermediate masses serving as a coupling mass, said masses being'so proportional with" regard to weights and said structures being so damped that the resonance crests of the apparatus are evenly distributed over the range of frequencies for which the apparatus is to be used and the peaks are not more than twice the lowest point of the resonance curve.

5. Acoustic vibratory apparatus comprising a casing, a diaphragm supported by said casing, a mass having a circular flange attached to said diaphragm, a second diaphragm mounted on said circular flange, and a plurality of similar structures, each having a. mass and an elastic member mounted seri- 20 ally on said first elastic member.

6. Acoustic vibratory apparatus comprising a casing, adiaphragrn supported by said casing, a mass having a circular flange attached to said diaphragm, a second diaphragm mounted on said circular flange, and

a plurality of similar structures, each having a mass and an elastic member mounted serially on said first elastic member, said masses being proportioned ,to one another in only gradually diminishing steps.

7. Acoustic vibratory apparatus comprising two end masses and a plurality of intermediate masses, said masses being proportioned to one another successively in gradually diminishing steps, and a plurality of elastic members, each mass being coupled to the adjacent mass by one of said elastic members.

In testimony whereof we aflix our signatures.

WALTER HAHNEMANN- HEINRICH HECHT.

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