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US1541121A - Insulating medium for transmission of intelligible sounds - Google Patents

Insulating medium for transmission of intelligible sounds Download PDF


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US1541121A US40074120A US1541121A US 1541121 A US1541121 A US 1541121A US 40074120 A US40074120 A US 40074120A US 1541121 A US1541121 A US 1541121A
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Frank C Doble
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Frank C Doble
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    • H04M1/00Substation equipment, e.g. for use by subscribers; Analogous equipment at exchanges
    • H04M1/02Constructional features of telephone sets


June 9, 1925. 1,541,121

, F. c. DOBLE INSULKTING gMEDIUM FOR TRANSMISSION. 0F INTELLIGIBLE SOUNDS Filed Aug- 2, 1920' 2 sheets-sheet 1 s/ 3/ l. 30 e c7@ l /nvenor ZorWe/ys June 9, 1925. 1 1,541,121

F. C. DOBLE INSULATING MEDIUM FOR TRANSMISSION 0F INTBLLIGIBLE SOUNDS Filed Aug- 2. 1920 2 'Sheets-Sheet 2 Patented June 9, 192.5.



Application led August 2, 1920. Serial No. 400,741.v

To all whom it may concern:

Be it known that I, FRANK C. DOBLE, a citizen of the United States, residing at Winchester, in the county of Middlesex and State of Massachusetts, have invented new and useful Improvements 'in Insulating Mediums for Transmission of Intelligible Sounds, of which the followingV is a specilication.

The present invention is concerned with the electrical transmission of speech, 'and other intelligible sounds or audible signals, and with protection for the persons who receive or transmit such sounds and signals from the harmful effects of excessively high electrical potential conditions in the circuits and other electrical conductors employed in electrical sound transmission. Amon the modes of transmitting sounds electrically contemplated in the foregoing statement are included telephonic speech. transmission over metallic circuits, Wireless telephony, wireless telegraphy, and the like. With the ordinary low tension telepho-ne systems possibility, however remote, exists of the line becoming excessively charged, as by lightning discharges, accidental connection with ihigh tension circuits and currents,'etc.; and there are other telephone systems, called high tension systems, of which the line wires are run in close proximity to high potential electric power transmission lines, which are liable to receive high potential charges directly or inductively vfrom the adjacent power transmission line, of a nature and from causes well known vto those acquainted with the art. In the practice of radiotelegraphy the operator receives conventional signals audibly through a telephonie receiver; and in radio telephony he both receives and transmits articulate speech sounds through instruments similar to the receiver and transinitterl of ordinary telephone equipment. In either case electrical stormsAV and lightning discharges are liable to create khigh potentials in the antennae of the radio equipment. All such electrical disturbances are dangerous to persons using theapparatus at the time when they occur, and have on many occasions caused death or serious injury to such persons.

It is the object of the invention to protect the operators of such ksystems andy apparatus (and by the term operator as used in this specification I mean any person who uses the system) from harm from high potential conditions which may occur in the conductors of the system at the time of use,

by an insulating medium which is also' capable of efficiently conveying intelligible sounds; and the invention consists in such a medium, as well as in thecombination thereof with the electrical sound transmission apparatus in connection with which it is used. I have 'discovered that the medium in question causes certain improved effects in the transmission of sound, later explained in detail, and therefore assert that part of the invention or discovery which I desire to protect consists in the hereinafter described means for producing such effects, and all equivalents of such means.

The following specification, in connection with the drawings forming a part thereof, discloses what at resent I consider the best form or embodiment of my invention, and certain illustrative uses thereof, although I have not attempted therein to describe all its possible uses. In the drawings,

Figure 1 is a side elevation of a combined unit apparatus embodying the invention.

Figure 2 is a left hand end view thereof.

Figure 3 is a longitudinal section on an enlarged scale, the terminal fitting being in elevation.

Figure 4 is a cross section of the `box element of the unit containing telephonie apparatus.

Figure 5 is a plan view and partial section of the terminal fitting.

Figures 6 and 7 are perspective views showing different modes of connecting the unit in a telephone line.

Figure 8 is a diagram showing two telephone sets including the novel features of thepresent invention in connection with a telephone line.

Figures 9 and 10 are diagramskillus'trating the use of the invention to protect operators of wireless telegraph and wireless telephone apparatus, respectively.

Figure 11 is a diagram illustrating the use of my invention as a relay for transmission of speech between separate and unconnected telephone lines. v f



, same parts in all ,the

' being lessened by The same reference characters indicate the figures.

I willirst describe the construction and parts of the combined apparatus shown in detail in the drawings, and then explain its uses and principles. 1 represents an elongated sound-transmitting insulating body having two wholly enclosed and separate passages or bores, 2 and 3, extending through it from end to end, and to which at one end is connected a mouth piece 4in exclusive communication with the passage 2 and an ear piece 5 in separate communication with the passage 3. Any material which is at the same time an insulator and a good sound conductor when fashioned in hollow form may be used for making the body l, and of the materials having these characteristics I prefer wood on account of its other useful qualities of strength and light weight. When wood is used it is preferably impregnated with paratin, or otherwise made repellent to water, in order to avoid danger of its insulating property absorption of moisture. This body is the insulating medium referred to in the introductory part of this specification. Structurally it is essentially a tube, and will be for convenience generally referred to as such. in the following descri tion. It may also be considered as a dou le tube or as two tubes combined in o-ne structure, and indeed for many purposes two separate .tubes are equivalent to such double tube; as also is the combination of one or more tubes, which in themselves each inherent stiffness or rigidity, with an extraneous member or structure possessing sufficient stiffness and so asso.- ciated with the tubes as to serve the purposes set forth in this specification.

The mouth piece and ear piece may be arranged at the end of extension tube leading from the bores of the double tube, of such lengths and disposition that said pieces may be placed respectively in front of the. mouth and beside the ear of the operator at one time; and preferably they ,are parts of an integral metal casting, or other formed body suitably connected, detachably or permanently, to the tube 1 and having integral passages. Practically it is necessary that the passageways through the insulating medium to the two terminals, constituted by the mouth pieces and the ear piece respectively, be entirely separate from one another, without intercommunication or any lateral outlet, in `order to avoid confusion of the sound Waves conducted to and from the several terminals, or loss of clearness or loudness of the sound. But I may insert diaphragms at suitable points to exclude moisture, etc. yfrom the passages, since the value of diaphragms for suc-h purposes may offset whatever slight obstruction they may special oppose to sound transmission. 4 and 5a in Fig. 5 indicate such diaphragms in the terminal orifices.

At the opposite end of the tube l from the terminals, the passage 2 is connected to a telephonic transmitter 6, and the passage 3 is connected to a telephonic receiver 7. These last may be identical with any standard transmitter and receiver used in common telephone practice, or they may be of design. For convenience they are secured-in a box or case 8 which is connected to the tube l in a mechanical unit structure. Short tube connections 9 and 10, which may be flexible or rigid, continue the passage 2 exclusively to the sound-admitting aperture of the transmitter, and the passage 3 exclusively to the sound-emitting aperture of the receiver, in order to complete the exelusive sound channels from the transmitter and receiver to the mouth piece and ear piece respectively. The same box preferably contains also a battery, induction coil, conductors, and switch; and also preferably carries protections such as are usually provided in telephone circuits and more particularly those used with. high tension telephone systems, to equalize the potential in both sides of the line. 12 represents the battery, a common dry cell type, and 13 repre- 'Sents the induction coil. The terminals or poles of the battery are in contact with two separated' and insulated contact pieces 14 and 15, from one of which a conductor such as 16 leads to the transmitter and from the other of which a conductor such as 17 leads to one end of the primary winding of the. induction coil. Conductors such as 18 and 19 lead respectively from opposite sides of the switch to the -transmitter and to the outer end of said primary winding. The switch here shown consists of two separated plates 20 and 21 fixedl to the rear wall of the box at opposite sides of a hole 22 in such wall, through which a plug may be inserted to bridge the gap between the plates. But` any other type of switch may be there used. The receiver is connected by a conductor 23 with one terminal of the secondary winding of the coil 13, and by a conductor 24 with an external binding post 25 on one side of the box; and the other terminal of said secondary Winding is connected by a condu-ctor 26 with an external binding post 27 at the opposite side of the box. External conductors 28 and 29 pass from these binding posts and are adapted to be connected directlyor indirectly to the line Wires o f the telephone system. The apparatus just described may be used as a portable set or as a permanent installation and when adapted for portable use, the conductors28 and 29 preferably have substantial strength and are provided at their ends with hooks 30 and 31 whereby they may be CSI hung directly upon the wires of a telephone line (Fig. 6), or like hooks so suspended may be connected with the said binding posts by flexible conductors as shown in Fig. 7. Otherwise, equivalent conductors of any nature may be used. v

The equalizing protection previously referred to is herein illustratively shown as furnished by a -vacuum tube 33 and a horn gap 34 arranged in parallel between the external conductors. The vacuum tube is mounted in any convenient way inside the matically,

box on a side wall thereof, and one end is connected electrically with an external plate 35 in which the binding post 27 is set, while its other end is connected with a conductor 36, conveniently a flat strip of copper, passin around the box to a plate 37 in whicht e binding post 25 is set. The horns of the horn gap are mounted adjustably on the top wall 38 of the box and are connected to conductors 39 and 40 which pass along said wall into contact with the plates 35 and 37. Fig. 8 represents diagramfor greater clearness, the elements of two instruments such as that just described connected in a line; and in said Iigure the same reference' characters distinguish the diagrammatic representation of said elements, while pand s indicate the primary and secondary windingsV of the induction coil. The apparatus thus shown-is essen- 'tially like the ordinary bridging telephone set, but the showing is for illustration only,

, and other telephone connections and means of protection can be used as well, and installed in any suitable way or arrangement, whether that shown in the present drawin s or otherwise without departure from' te central idea of the invention which I desire to protect, as set forth in the' appended claims.

Also the two passages 2 and and .3 are there shown as separate tubes, both for convenience in the diagram and to indicate that two tubes are in `principle .equivalent to a structurally unitary double tube.

In the combination thus described, the tube 1 is a sound conducting and electrically insulating medium enabling the operator to transmit and receive articulate speech and,` lother Sounds through a telephone system without danger.` It protects the operator against passage` through his body to the earth of electrical charges and currents atI high potential from the telephone' line; the degree of protection thus given being al function of the length of the medium. I have found that a length of six feet of properly impregnated wood. is suiiCient, with an ample factor of safety, to protect-the op- 30,000 volts.V

erator against discharge of potentials up to I have found also that'the medium gives improved acoustical effects both in sending both in amplification of the sound trans f mitted in either direction, and in an in-4 crease in the range of vocal pitches possible to be used without production of disagreeable and confusing reverberations or reso-,

nances, when the diameter of the bore and itsl length are in the proper ratio. In other Words, the speech transmission is made both louder and clearer with the aid of this meg., dium` properly proportioned than with the unaided telephone set. Without attempting at the present time to state exact dimen..L sions or proportions, or to formulate a gen1-;- eral law applicable to the subject, I may-"2` state the fact that I have obtained the re-Jfl sults mentioned with tubes having a bore of one-half inch and lengths between three and'ten feet, and also with tubes between ten and twenty feet in length having a bor'eJ of three-fourths of an inch. The values j ust given indicate approximately the correctv` proportions necessary to obtain the im" proved acoustical effects described. The tube or passage having the charFg acteristics substantially as hereinbefore set forth, that is, the tube or passage which extends from the telephonie receiver to the` ear piece, has the veryimportant and valuable effect of diminishing to a safe degree the acoustical shock which occurs WheniX4 a sudden extreme impulse is imparted to the diaphragm by electrical waves of high po'' tential and high frequency on the line. Such waves are Vimposed on the telephone line when an arcing ground or flashing of current aroundan insulator, or analogous accident, occurs in a neighboring high potential electric transmission line; and are also caused by electrical storms and lightning discharges. Electrical waves of the sort here referred to are also called steep front Waves. The effect of such' waves upon the telephonie receiver is to give the diaphragm a sudden violent oscillation which, when the ear of the operator is held inthe ordinary close proximity to the receiver, causes a violent shock upon the ear. In extreme cases this shock may burstthe ear drum; and in any case it causes a nerve shock, and if repeated frequently enough it produces a profound nervous reaction in the operator.

This danger-to operators is so serious that l' danger of harm to the operator from these f causes is avoided and in consequence telephone lines may be continued in operation with the aid of the medium embodying this invention throughout the course of all such disturbances.

So far as I am aware, the use or combination of a sound conducting hollow medium of this nature with an electrical sound transmission instrument for and with the production of such improved effects is a new invention or discovery, for which I claim protection herein. Such mediums adapted for the particular purpose last discussed may be used with telephones of any nature, with or Without the feature of insulation from electrical discharge, but preferably with that feature, all within the scope in whichI claim protection.

The term electrical sound transmission instrument as here used, and likewise such terms as electrical sound converting device, electrical telephonie device, or words of similar import later used in this specification, includ-e any means by which sound waves are transformed into electrical undulations, or vice versa, and specifically include all forms of telephonie transmitters, so-called, and telephonie receivers, so-called. Such instruments are forms of apparatus which are adapted to effect conversion between electrical efi'ects and audible effects;

or in other words to convert an electrical effect into sound, or an audible effect into an electrical efl'ect. So far as concerns the broadest scope in which YI claim patent protection for the invention embodied in the insulating medium I do not limit such protection to so-called telephonie transmitters and receivers, but includes also such medium combined or applied for use with possibly other sorts of apparatus by which conversions'of the characterindilcated may be made.

The combined apparatus with telephone set and sound-transmitting insulating medium may be used in all conceivable relations and positions. It may be carried about and cut in on a telephone line anywhere and lin various ways, someof which are illustrated in the drawings. Ina permanent installation perhaps the most satisfactory way is to mount the telephone on a wall with the insulating tube projecting' horizontally at a convenient height for the operator, and the outer end of the tube with its terminal pieces 'may be enclosed in a booth;'but these arrangements are optional and may be departed from at will.

Somel of the possible other uses of the sound-transmitting insulating medium are shown in the drawings. Fig.v 9 shows its use for protecting a wireless telegraph operator. Such operators receive signals through a pair of receivers held against the ears by a headband. The' receivers of such pair and the headband are designated conventionally as 41, 42, and 43, respectively. During electrical disturbances the operator cannot with safety allow the receivers to remain on his head, and at such times he is, of course, incapable of receiving signals. By connecting insulating sound transmission mediums 44 and 45, having ear pieces, to the receivers, the operator is enabled safely to listen for signals throughout an electrical disturbance. The same thing may be accomplished with wireless telephone apparatus, as shown in Fig. 10 by connecting such a Amedium 46, equipped with a mouth piece 47 to the transmitter 48 of the set, and by connecting the same sort of medium, 49, equipped with an ear piece 50, to the receiver 51. In the latter case the mediums 46 and 49 may be combined in a single unit .tube structure having two bores, like that first described. I have not attempted here to show the complete circuits and equipment of the wireless telegraph and telephone apparatus, for the use of' my sound-transmitting protection therewith does not involve any modification therein. In any other situation where a person is required to listen to sounds emitted from electrical apparatus, protection may be secured by like means in essentially the same way.

Still another use of the invention is that of a relay adapted to connect telephones in different lines acoustically but without electrical connection, and in fact with insulato the other. Fig. 11 shows diagrammatically an installation organized for that purpose, where 52 and 53 are the transmitter and receiver of a telephone set in one line L, and 54, 55 are the transmitter and receiver of a telephone in a different line L. An insulating tube 56, or equivalent sound conductor, passes from the transmitter 52 `of one instrument to the receiver 55 of the other instrument, and a like tube'or medium 57 passes from the receiver 53 of the first telephone to the transmitter 54 of the other. Thus an operator using any second telephone on the line/L can hold a conversation with an operator at any second telephone on the line L; for when electrical undulations'in either line are converted into sound waves in the receiver connected in that line, such sound waves are conducted by the intermediate tube to the transmitterof the telephone in the other line, and are there transformed into electrical undulations which traverse the latter line. Laws or regulations prohibit direct electrical conneci2, tion bein made between certain telephone 0 lines, as or instance'between a low tension public system and a high tension system near a power transmission line, but my invention enables speech to be transmitted between more or less remote stations on the tion preventing current flow from one line 100 `different lines withoutputting either the Ylow tension system or its users in dan er 'from the high potential conditions which are'more liable to occur in the high tension system. In the case last described the sound conduits (56 and 57) may be grounded at a point between their ends, if desired for additional protection. And in any case,

the conduit or tube or equivalent medium verting device (transmitter, receiver, or the like) with which my sound-conveying 1nsulating medium 'may be combined and used. I desire now to state further that Suchmedium is not necessarily requiredl tohbe made as a tube, in the narrowest definition of that word, but that it may have an .form which enables it to conduct soun intelligibly. The-term tube as herein used includes any hollow body or shell having a passage adapted to conduct sound waves vthrough it, whether such shell and passage are regular orfirregular vided always that the medium or tube is additional to the electrical device proper,

' electrical potential.

`tained electrical and (except as to those uses previously described which may be servedwithout insulation)- is an insulating protector capable of preventing flow to ground of high tension To be an insulating within the meaning ofthis specithe medium must be capable of without breaking down a susstress of at least one thouprotector fication, withstanding,

- sand volts pressure (root mean square sine ratus adapted to effect ing an orifice wave value) at any frequency.

What I claim and desire Letters Patent is il e 1.. The combination with an electrical apparatus ada ted to elfect conversion between electrical and audible eEects, of a combined insulating sound conducting medium and barrier including a' channel for to secure by conveyance of sound waves, constructed and arranged to maintain safe separation be. ltween said apparatus and all parts of the personof an operatorusing it.

` 2. The combination with electrical appaconversion between electrical and audible effects, of a structure including a sound conductin channel and rigid supportin material, sai channel ihavesigned to be placed beside in shape and dimensions, pro- .paratus ada the head of the operator, and the .rigid structure .being arranged to maintain said orifice at such a distance from thej electrical apparatus that in the normal use and handling of the 'combined instruments the operator is safely removed from the effects of high voltage at the electrical apparatus; said structure being of insulating material.

'3. The combination with an electrical apparatus adapted to effect conversion between electrical and audible effects, of an insulating sound conducting tube having an orilice' adapted' to be placed besides the head of an operator and being arranged to receivev sound waves from said electrical device; said tube being of a length between the said orifice and said apparatus greater than the length of a normal adult ersons arm, and being further constructe separation between said orificeand the electrical apparatus of a distance greater than the normal reach of an operator when placed with his head beside said orice.

.4. The combination with an electrical de.- vice for converting electrical eifects into sound, of a rigid insulating structure including a channel arranged to conduct sound from said electrical device and having an to maintain a' orifice adapted to be 'placed beside the ear i 4of an operator, arranged and extended from using an electrical telephonieJ instrument;

from the effects of high .potential electric stress in such instrument and in the vicinity thereof, which comprises an insulating structure including a soundI conducting passage having a terminal orifice, of such length and so extended that the orifice is ata greater .distance from the telephonie device than the distance between the ear -of the ,operator using it and the end of his extended arm.

6. The combination with an electrical apparatus adapted to transform sound waves into electrical effects, of an insulating structure having a sound conducting channel with an'orice adapted to be placed in front of the mouth of an operator, said structure having such length and arrangement that said orifice is separatedfrom said electrical device by a distance greater than that to which the operator using it is able to reach speak into said orifice.

7. The combination withan electricalapelectrical e ects, including a channel kfor conduction of ted to convert sound'waves into Y of an insulating medium sounds, Isaid channel leading from the electrical .apparatus and'having Aan orifice, and said insulating medium being further consaid device to such a distance that all parts structed and positioned tomaintain a distance between the orifice and all parts of the person of an operator placed in position to speak into said orifice, sufficient to insulate such operator from the effects of electrical stress at high tension in and adjacent to said apparatus. j

8. A means for making safe the use of telephonic apparatus in the vicinity of high potential electric currents, comprising the combination with an electrical telephonie device adapted to be placed in position to rewalls of which are made of insulating material on which said device is mounted, said holder having a sound-conducting passage through it terminating in sound-receiving proximity to said device, and an ear piece in connection with the end of said passage remote from the telephonic device and adapted to be placed beside the ear of an operator; said holder adapted for manipulatlon to place the telehonic device in position to receive current rom a source of electricity and having a length sufiicient to rotect the user holding it at one end from t e current in a high potential conductor with which its other iend may ,come into contact.

10. A. `mea-ns for making safe useof an electrical apparatus for the conversion of electrical into auditory efi'ects, in the vicinity of hih potential electric currents, comprising t e combination with such an electrical apparatus adapted to be placed in position to receive electrical current or chai-ge, of an insulating holder on which sai ortableand movable by an operator and aving a length and insulating strength suflicient to sa eguard the operator from the effects of high the operator holds said electrical 'apparatus in the vicinityof a conductor of high potential electric current and the holder structure being associated with a sound conducting passage the walls of which are of electrically 5non-conducting material, said passage being in sound-receiving proximity at one end to said apparatus and having an orifice remote from the apparatus through which sound waves may pass.

yof insulating material an apparatus is mounted, said holder beingvl tension electrical stress when,

11. The combination with an electrical telephonie device adapted to convert sound waves into electrical effects of a structure of substantial length made of insulating material, which structure includes strength for supporting and moving the telephonie device and a sound conducting channel leading from said device, and a mouth piece in connection with the end of said channel remote from the telephonie device adapted to be placed in position to receive sound from the mouth of an operator; said holder structure being movable by the operator and having a length sufiicient to protect the operator holding it at one end from the current in a high potential conductor with which its other end may come in contact.

12. The combination with a telephonie apparatus adapted to be used in proximity to conductors of high otential electric current, of a combined holding and assage structure ci) of a length so great that an operator whose head is at the remote end of said structure from the telephonic apparatus is safely distant as to all parts of his person from the effects of an electrical stress at high tension in said apparatus, and said passage being in sound conducting proximity to said apparatus at o ne end andhaving an orifice at the opposite end. i

13. A protective telephonie apparatus comprising a box, a tube projectlng from said box having two se arate channels with distinct terminal ori ces adapted to be placed respectively in front of the .mouth and besidethe ear of an operator, saidtube being of insulating material, an electric telephone apparatus lncluding a recelver and a transmitter in said box, and exclusive tubui lar connections joining the passages in said tube with the transmltter and recelver, respectively. v

14. A telephonie apparatus comprlsmg a receiver and a transmitter, means for holding them adjacent to one another, a tube of insulating material having two separate and exclusive passages, means connectlng one of said passages exclusively to the sald transmitter, means connecting the other of said passages exclusively to said receiver, and terminal fittings in exclusive connection wlth the respective passages.

15. A telephonie apparatus yas set forth 1n claim 14 wherein diaphragms Tor excluding moisture are interposed at suitable points near the respective orifices of said passages.

16.y vAn a paratus as set forth in claim 14 in which a box encloses the telephonie apparatus, and conductors in electrical connection with said apparatus are attached to the box and are provided with hooks enabling them to be hung on the wires of a telephone line.

17. A means for making safe the use of telephonie apparatus in the vicinity of high i potential electric currents, comprising the combination with an electrical telephonic device adapted to be placed in position to receive electrical current or charge, of an insulating medium having an interior soundconducting passage in sound-receiving proximity at one end to said telephonic device and having an orifice remote from said telephonic device through which sound waves, may pass, said medium being so disposed that said orifice is at a distance from said telephonic 'apparatus greater than the reach of an operator when placed with his ear adjacent to such orifice.

18. A means for making safe the use of telephonic apparatus in the vicinity of high potential electric currents, comprising the combination with an electrical telephonic device adapted t0 be placed in position to receive electrical current or char e, of an associated holder and sound con uctin tube made of insulating material, on the older part of which association the telephonic apparatus is mounted and which the tube portion of which association said apparatus is in sound-conducting connection, said holder being operable to place theA apparatus in current-receiving position, and the tube having an orifice remote from said apparatus.

19. The combination with a telephonic receiver of a sound conducting tube extending from said receiver and having an ear piece adapted to be 1placed beside the ear of an operator, saidtu e vhaving a bore of approximately one-half an inch and a length of at least approximately three feet, whereby the contained air column diminishes to a safe'degree the acoustic shock carried by electrical waves of high potential and hig frequency on the line.

20. An electrical apparatus adapted to effect transmission between electrical and audible effects, combined with a tubular sound conductor leadin from said apparatus and adapted to con uct sound waves between the same and a distant orifice; the ratio of the bore of said tube to its length being so small as to damp sound reverberations, and at the same time so large as to conduct sound without substantial diminution of the clearness and loudness of transmitted words; said ratio being within the following named limits, to wit; a bore of approximately one-half inch diameter for tubes between 3 and 10 feet in length; and a bore of approximately three-fourths of an inch in diameter for tubes from 10 to 2() feet in length.

In testimony whereof I have affixed my signature.


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US1774745A US1774745A (en) 1920-08-02 1925-06-06 Insulating telephonic relay

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2573438A (en) * 1946-09-18 1951-10-30 Rca Corp Electroacoustic transducer set
US3993879A (en) * 1975-03-24 1976-11-23 Wallace Keith Larkin Acoustical communications headset
US5613222A (en) * 1994-06-06 1997-03-18 The Creative Solutions Company Cellular telephone headset for hand-free communication
WO2005011326A1 (en) * 2003-07-17 2005-02-03 Siemens Aktiengesellschaft Telephone handset and acoustic converter for one such telephone handset

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2573438A (en) * 1946-09-18 1951-10-30 Rca Corp Electroacoustic transducer set
US3993879A (en) * 1975-03-24 1976-11-23 Wallace Keith Larkin Acoustical communications headset
US5613222A (en) * 1994-06-06 1997-03-18 The Creative Solutions Company Cellular telephone headset for hand-free communication
WO2005011326A1 (en) * 2003-07-17 2005-02-03 Siemens Aktiengesellschaft Telephone handset and acoustic converter for one such telephone handset
US20060210061A1 (en) * 2003-07-17 2006-09-21 Ulrich Hardebusch Telephone handset and acoustic converter for one such telephone handset

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