US1715344A - Arrangement for eliminating disturbances in sound signaling - Google Patents

Description

June 1929. w. HAHNEMANN El AL ARRANGEMENT FOR ELIMINATING DISTURBANCES IN SOUND SIGNALING Filed Feb. 4, 1921 2 Sheets-Sheet l June 1929. w. HAHNEMANN ET AL ARRANGEMENT FOR ELIMINATING DISTURBANCES IN SOUND SIGNALING z Sheets-Shet 2 Filed Feb. 4, 1921 Patented June 4, 1929.

PATENT OFFICE.

WALTER HAHNEMANN AND LEONID ADELMANN, OF'KITZEIBERG NEAR KIEL, AND

HUGO LICHTE, OF KIEL, GERMANY, ASSIGNORS TO THE FIRM SIGNAL GESELL- SGHAF'I. M. B. H., OF KIEL, GERMANY.

ARRANGEMENT FOR IELI'JtIINA'II?ING' DISTURBANGES IN SOUND SIGNALING.

Application filed February 4, 1921, Serial No. 442,589, and in Germany January 25, 1917.

The devices used for the reception of sound signals usually comprise a sound collecting or absorbing member, such as a diaphragm that responds to sound vibrations, and a member that serves to receive the absorbed sound energy, such as a microphone. In such devices the latter member may be associated with a v1- bratory body or structure, such as a tuning fork or the like.

Receiving apparatus of this kind are usually tuned as a. whole to the frequency used for signaling. Although the tuning increases the sensitiveness of the receiver, it is accompanied by the disadvantage that whenever the apparatus is excited by shocks, due to mechanical or acoustic disturbances, sounds are heard in the apparatus that correspond to the frequency for which the apparatus is tuned, so that its receiving function is seriously interfer-ed with. If the expedient of tuning is entirely dispensed with, or if the receiving apparatus as a whole is tuned to a frequency that differs very much from the signaling frequency, the sensitiveness of the apparatus to the sound signals employed will be considerably impaired.

The object of the invention is to provide a receiving apparatus of this kind which is sufficiently sensitive to sounds whose rate of v1- bration corresponds to the actual signaling frequency, but which is afiected by disturbing sounds or noises to the smallest possible extent.

The invention relates more particularly to receiving apparatus which comprise a system consisting of two or more vibratory structures or bodies coupled to each other, and in which one of the structures or members of the system, which structure or member may consist of a diaphragm, a piston, the hull of a ship, or the like, assumes the function of collecting or taking in energy that arrives through the propagating medium (water, air), while another member of the system that acts as the receiver proper, and may take the form of a microphone or an electromagnetic detector, assumes the function of converting the sound energy into electrical energy that may be made erceptible by the human ear with the aid o an instrument such as a telephone receiver.

The invention consists in general in so tuning the various vibratory bodies or structures of which the apparatus is composed that after due allowance is made for the .eifect produced on each vibratory body by its being coupled to another, any one of the plurality of frequencies of resonance which the composite vibratory apparatus will with the frequency used or signaling, barring the particular frequency which corresponds to that of the vibratory receiving structure proper, i. e. that of the microphone or the like.

The purport of this will be explained by the following description with reference to the accompanying drawings in which Fig. 1 shows the resonance curves obtained from a diaphragm alone, a microphone alone and the resultant curve when the diaphragm and microphone are coupled together;

Fig. 2 shows the resonance curve of a coupled system in which the diaphragm is more highly damped than the microphone;

Fig. 3 shows the resonance curve of a coupled system in which the resonance peak cor responding to the natural frequency of the diaphragm coincides with the signaling frequency and the peak corresponding to the natural frequency of the microphone is so far removed from the signaling frequency as to have little effect on the functioning of the coupled system; and

Fig. 4 shows a sectional view of a practical example of a sound receiver constructed ac cording to the invention.

If in a composite vibratory apparatus or system comprising two vibratory structures coupled to each other, each individual structure has its own frequency of resonance, the behaviour of the system when subjected to vibrations will be such that each'of the individual vibratory structures will exhibit two frequencies of resonance and these two frequencies will be the same in each structure. One of them will, however, be lower and the other higher than the frequencies of resonance of the individual structures when separated from each other, and the effect produced in each structure will be greatest at the particular frequency of resonance that belongs to its own natural rate of vibration.

Hence in accordance with the invention, in receiving apparatus comprising a collecting member that takes in the energy and an energy transferring or converting member, these vibratory members are so tuned and coupled as to bring about a coincidence between the particular post-coupling frequency ossess, will coincide of resonance (i. e, the frequenc fat which resonance is obtainedafter the ifierent vi-' bratory structures are coupled to each other) that belongs to the natural rate of vibration of the collecting member and the frequency used for signaling, but not between the signaling frequency and the post-coupling frequency of resonance that corresponds to the natural rate of vibration ofthe said transferrin member. I

In ig. 1, in which the abscissa: designate the frequencies while the ordinates designate the amplitudes, the solid graph represents a coupled vibratory structures are indicated by a broken line and a dash and dot line, the fre uency of resonance of the microphone by itse f lying at 11. and that of the diaphragm by itself lying at n In accordance with the invention N is the frequency that must beselected for signaling with this'system. Disturbances which chiefly arise from shocks or vibrations that are practically non-periodic will be transformed in a system of this kind principally into periodical vibrations whose frequency is N,, so-

that signals with a-frequency of N will be clearly distinguishable from the disturbing noises. By coupling the two vibratory structures more or less closely the crests of the resonance curves may be shifted more or less apart. This can also be done by making the individual natural'rates of vibration of the coupled vibratory structures of the system differ from each other more or less widely.

It will be obvious that this expedient of altering the difference between'the post-cou pling frequencies of resonance is in itself a very effective means of eliminating disturbances. In accordance with the inventionthe freedom from disturbances can be considerably enhanced by damping the vibrations of the diaphragm more than the vibrations of the microphone' The resonance curve of a system damped in this way is shown in Fig. 2, in which the same signs of referenceare used as in Fig. 1.

Thus-in vibratory apparatus comprising a diaphragm coupled with a microphone the post-coupling frequency of resonance of the diaphragm is caused to coincide with the frequency of the sound used for signaling. This Is also done in an apparatus comprising a diaphragm, a special vibratory structure and microphone contacts attached to the vibratory structure. The post-coupling frequency of resonance of the microphone or of the vibratory structure withits attached microphone, may be made either higher or lower than the signaling frequency. In Figs. 1 and 2, the natural frequency. of the microphone, to-

ether with its corresponding post-coupling requency, are below' the natural frequency of the'diaphragm and the corresponding postcoupling frequency thereof used as the signaling frequency. But a preferred arrangement, particularly in cases of receiving apparatus in which the detector used is a microphone, is one in which the natural note of the microphone is so chosen that the post coupling frequency corresponding to it is higher thanthe signaling frequency.

' a For receivers consisting of a rigid casing,

a receiving diaphragm, and a microphone coupled to this latter, it is to be considered as characteristic of the invention that the natural rate of the diaphragm is lower than that of the microphone, so that in the whole apparatus the post-coupling frequency belonging to the diaphra m coincides with the signaling frequency.- referably the vibratory structures are so tuned that the natural period of the microphone lies above the signaling frequency about twice the amount that the natural period of the diaphragm lies above this frequency, (in practice 20% and 40%). Then the coupling between the two parts is to be so chosen, for example, by suitably distributing the masses over the two parts coupled together, that-the post-coupling frequency corresponding to the diaphragm coincides with the signaling frequency. In this way at the same time, a degree of coupling especially advantageous for the efliciency o the receiver may be obtained.

Naturally, it is not absolutely necessary to make coincide with the signaling frequency the post-coupling frequency belonging to the fundamental vibration of the diaphragm, but it is also possible to choose a suitable harmonic of a diaphragm of an essentially lower fundamental vibration.

In Fig. 3 of the accompanying drawings the most favourable relations of tuning for a receiver (casing with diaphragm and microphone) treated according to the invention are represented by the resonance curves of the particular structures of the apparatus. The natural vibration of the diaphragm which, in this case, is identical with its fundamental-vibration, is J, the natural vibration of the microphone is Z. By acoustically coupling these vibratory structures together the vibrations are displaced into J and Z re-- spectively, which are the frequencies of resonance of the coupled system, J coinciding with the signaling frequency 'X A special advantage obtained by this tuning is that the inconstancy of the natural note of the microphone ceases to be a factor that greatly affects the efliciency of the receiver. I

Figure 4 presents a sectlonal view of a practical construction of a sound receiver according to the principle previously explained. 1 represents the casing to WhlCl'l the resonant diaphra m 2 is clamped by the rivets 5, 5. Mounte on the diaphragm 2 and therefore acoustically coupled with it 1s the microphone 3 in its usual form. The diaphragm 4 of the microphone is coupled to the diaphragm 2 by means of the clamplng nut 7. The diaphragm 4 carries one electrode 8 while the casing 6 carries the second electrode 9 between which electrodes are the carbon granules 10. The diaphragm 2 is tuned to the desired resonant frequency by proper dimensions of size, thickness and material of the diaphragm. The microphone is also suitably tuned to the desired frequency as explamed above.

In order to obviate the necessity of using a microphone, bi-resonant .or multi-resonant electro-magnetic contrivances may be used which may be made to act both as sending means or receiving means. In accordance with the invention the frequency of the sound signals employed when receiving with an arrangement of this kind would be one that does not belong to the receiving device proper (energy-converter) In producing multi-resonant apparatus of this kind each individual vibratory body or structure is referably tuned by itself to a frequency of resonance which, when it is changed by the effect of the various coupled strut'ures, results in the desired post-coupling frequency of resonance. This is done by using the degree of coupling that has been determined by experiment or calculation to be the proper one. When once the amount b which the frequency of resonance is clzanged through the influence of the coupling has been ascertained in a trial apparatus, the preferable procedure in tuning each indi-' vidual vibratory structure will be to substitute the amount of the mass of the cooperating parts to be coupled thereto, that affects its tuning, by attaching a weight of corresponding size to it. In doing this it must be remembered that the vibratory structure that takes in the sound energy from the propagating medium upon which it abuts is also affected by a certain amountof the mass of this medium. In the cases of heavy mediumssuch as liquids this amount is considerable.

The term sound radiating member is used in the claims to define generically a member which takes up vibrations from or imparts vibrations to the sound propagating medium; while the term energy-converting means is used to designate generically a device which convertssound energy into another form of energy, for example, into electrical energy, or Vlce versa.

We claim:

' 1. In sound signal apparatus, an individ' ually tuned vibratory structure, and an individually tuned energ -converting means, means for coupling said vibratory structure and said energy-converting means together acousticallg, and the frequencies of resonance of t e coupled system being such that the resonance frequency corresponding to the energy-converting means is substantially different from the sound signal frequenc 2. In sound signal apparatus, an in ivid' ually tuned sound radiating member, and an individually tuned energy-converting means, means for coupling said sound radiating member and said energy-converting means together acoustically, and the fre uencies of resonance of the coupled system eing such that the resonance frequency corresponding to the energy-converting means is substantially different from the sound signal frequency- 3. In sound signal apparatus, an individually tuned vibratory structure, and an individually tuned microphone, means for coupling said vibratory structure and said microphone together acoustically, and the frequencies of resonance of the coupled system being such that the resonance frequenc corresponding to the microphone is substantially different from the sound signal frequency.

4. In sound signal apparatus, an individually tuned vibratory structure, and an individually tuned energy-converting means, means for coupling said vibratory structure and said energy-converting means together acoustically, and the frequencies of resonance of the coupled system being such that the resonance frequency corresponding to the energy-converting means is substantially higher than the sound signal frequency.

5. In sound signal apparatus, an individually tuned vibratory structure, and an individually tuned energy-converting means, means for coupling said vibratory structure and said energy converting means together acoustically, and the frequencies of resonance of the coupled system being such that the resonance frequency corresponding to the energy-converting means is substantially different from the sound signal frequency while the resonance frequency corresponding to the vibratorv structure substantially coincides with the sound signal frequency.

6. In sound signal apparatus, an individually tuned vibratory structure, and an individually tuned energy-converting means, means for coupling said vibratory structure and said energy-converting means together acoustically, the frequencies of resonance of the coupled system being such that the resonance frequency corresponding to the energy-convertingmeans is substantially different from the sound signal frequency, and

comprising. a tuned sound radiatin phragm, means for coupling said diap ragm greater; vertin f 7. ulti-resonant the darn of the vibratory-structure being anthdi damping o the energy-consound signal apparatus,

dia-

toa tuned sound detector, the tunings and coupling bein such that the frequency of resonance of t e coupled system corresponding to the said sound detector is substan-' tially difierent from the sound signal frek quency.

- 8. Multi-resonant sound signal apparatus, comprising a tuned sound radiatin diaphragm, means for coupling said dlap ragm 'to a'tuned sound detector, the tunings and the couplin being such that the frequency of resonance 0 the coupled system corresgondstanin to the said sound detector is su tia y different from the soundsignal frequency and that the frequency of resonance of the coupled system corresponding to the about twice as great as the said diaphragm substantially coincides with the sound signal frequency. f

9. In sound signal apparatus, a vibratory structure indivi ually tuned to certain frequency higher than the sound signal fre-' quenc an energy-converting means indiferent from the sound si 'nal frequency.

In testimony whereof we afiix our signatures.

- LEONID ADEL'MANN.

WALTER HAHN EMANN. HUGO LIGHTE.

ifierence be .vidua y tuned to a frequency higher than ed 'system'corresponding to the energy-converting means is substantially di15- 7

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