US2226934A

US2226934A - Acoustic device

Info

Publication number: US2226934A
Application number: US231487A
Authority: US
Inventors: Walter F Kannenberg
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1938-09-24
Filing date: 1938-09-24
Publication date: 1940-12-31
Anticipated expiration: 1957-12-31
Also published as: GB528523A

Description

w. F. KANN ENBERG 2,226,934

ACOUSTIC DEVICE 'Filed Sept. 24. 1958 FIG. 2

INVENTOR 8y WE/(ANNENBERG ATZORNEY Patented Dec. 31,

ACOUSTIC msvrcn Walter F. Kannenberg, Rutherford, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application September 24, 1938, Serial .No. 231,487

17 Claims. (Cl. 179-119) This invention relates to acoustic devices and Fig. 3 is asectional view taken on line 33 of more particularly to acoustic transmitters of the Fi 1; type commonly referred to as ribbon microphones. Fig. 4 is a front elevational view of a ribbon 'Ribbon microphones comprise in general, a -microphone illustrative of another embodiment a light-weight diaphragm in the form of an elecof this invention; v t trically conductive strip or ribbon disposed in a i 5 is a si e ie Pa y n sectidmalon magnetic field of a suitable magnetic structure. e o ig. of the micr ph n W in Vibrations of the ribbon or strip in accordance and with sound waves impinging therein result in the z- 6 is a onal v w t n along lin 66 generation of corresponding electromotive forces of I h m in the ribbon and a circuit of which it forms a Referring w to t e d w in the embodir part. ment of the invention shown in Figs. 1, 2 and 3,

In such microphones, the impedance of the rib- 9 and H (18110139 elongated mbers or polebon diaphragm and the circuit of which it forms pleces of magnetlc matel'lal mounted in Sp H5 a part is quite low and necessitates the use of a parallel relation and extending between and transformer of high step-up ratio for obtaining abutting the Pole-faces of two Permanent a satisfactory matching of the impedance of the nets and of generally horseshoe -U microphone to that of the grid or input circuit The members and g 5 are secured at each of an associated amplifier to which the output to support members M d 55 by i g an of the amplifier is suppliem means such as screws it. The members it and One object of this invention is to facilitate the are of nonfmafgnetic m a and are Prefer attainment of a satisfactory impedance matching ably of electncal msulatwn- E of h sPpport between a transmitter such as a ribbon micromembers and an Integral PRO-196th phone and the input or, grid circuit of an amplior boss n mterfittmg with one of ihevmagnefis 235 fier associated therewith. 12 or IS. The magnets, as shown, areeheld in as Another object of this invention is to improve 3 55 bosfises and g q attracthe structure and performance of ribbon microon mem ers and n If other phones fastening means, such as screws, bolts, clamps or In accordance with one feature of this inven- 1 also be employed between magnets. tion. a ribbon microphone comprises a magnetic ,ggz ig g and i f g g diaphragm vibratile in the field of a magnet th 2 th erye as t 06 structure, andcurrent carrying means, such as g 8 en 2;; edmphragm m'whmn y be a coil or coi1s,'associated with the magnet struc- S up r n of Penna W or qther Sultable i magnetic material and preferably 15 corrugated a time so that vibrations of the diaphragm produce throughout the .major omen of 1 n m variations in the flux linkages of the coil or coils Permanoy may be define? as an auo 1 i whereby an electromotive force is induced therein. nickel to the extent of 30 per cent snore 2 phone comprise a g reat numberof turns of ex-- pro-petty of high initial permeability other matremely fine wire whereby a high impedance temals' 'suchas moiybdgr-mm' may be added to enabling satisfactory impedance matching with b f m gf ggg it g .-'e eerworemoa mm 11. eri on g1$aiglg1t circuit of an associated amplifier, 18 may be the order of one quarter mil in thick ness nd se ur b a The invention and the foregoing and other g' f g asses byvscmws and features thereof will be understood more clearly As shown cleari in E 3 a d fully from the following detailed description y the members Gr s pole-pieces l0 and II have inwardly o ectin witigihreference to the accompany g drawlng in reduced portions 2| and 22, respectivegi. Elon w c gated output or sound current coils 23 and 24 m 1 s a front elevatlonal View of a i b are secured respectively tothe portions 2| and mic op e illustrative of One-embodiment 0f 22by cement or other suitable means.- Each coil this invention; I e has one long side on the face of a pole-piece op- 2 is a side view, pa t y in sec a o posite the edge of the ribbon l8 and slightly line 2-2 of'Fig. 1,, of the ribbon microphone spaced therefrom. 'In other words, these coil shown in Fig. 1; portions occupy the portion of the air-gap adable conductor 25 and to terminals, one of which .is shown at 26, by conductors 21 and 28. The

coils preferably comprise a large number of turns, for example, over one thousand, of very fine wire such as No. 44 B and S gauge, or smaller.

The magnets l2 and I3 have like poles in contact with members If! and II, respectively, as indicated by the letters N and S in Fig. l. The lines of magnetic force in the space between the pole-piece members 2| and 22 are concentratedby the magnetic ribbon l8. v

Sound waves impinging on the diaphragm l8 cause it to vibrate and shift the concentrated lines of force relative to the portions of coils 23 and 24 in the air-gap. A voltage is induced in each of the many conductors of the coil portions in accordance with the diaphragm vibrations. The coils 23 and 24 are so wound and connected that these voltages are additive. In 'view of'the high impedance of the coils 23 and 24 the output may be fed directly to an amplifier, not shown.

7 in Figs. 4, 5 and 6 is generally similar-to that The embodiment of the invention illustrated shown in Figs. 1, 2 and 3. Elements of Figs. 4, 5 and 6, corresponding to those of Figs. 1, 2, and

3 are designated bythe reference character usedin the latter figures, increased by 30. V

The magnetic corrugated, ribbon diaphragm 48 is mounted between the parallel elongated polepieces 40 and 4| and has its end portions secured to blocks 41 of magnetic material,- as by clamping strips and bolts 48. The blocks 41. may be affixed to the non-magnetic, and preferably insulating, support. members ll and 45 by the bolts 49' and provide a path of low reluctance between diaphragm l8 and the the .ends of ,the

ribbon magnets

42 and 43.

An elongated output or sound current coil 53 has its long sides 54' and 55 secured to a face "of each of pole-piece portions BI and 52, respectively,

by cement or other suitable means. Each end of the coil 53 maybe offset as shown'at 5a in Fig. 5

to prevent interference with the ribbon l8. The coil 53 may be connected to suitable terminal I means by conductors?! and, which may be integral extensions of the coil,

One such terminal means is shown at 59. Coil 53, as coils 23 and 24, preferably comprises a large number of turns of very fine wire. V

Itwillbe noted that in the embodiment shown in Figs. 4, 5 and 6, as compared with that of Figs.

1, 2 and 3, but one output coil isprovided and thatthe blocks 41 around which the magnets are fitted, are of magnetic material.

The magnets 42 and 43' are magnetized with like poles at each end and with the opposite pole in the middle as indicated by the letters N and S in Fig. 4. The linesof magneticforce are con-' centrated in the region' occupied

bi coil sides

54 and 55 by the magnetic ribbon 48 andthe polepiece portions SI and 52.' Vibrations of the ribbon in response to sound waves generate additive voltages in the two

coil portions

54 and 55.

It is to be understood thatthe embodiments of the invention shown and described are but illustrative and are-not to be taken as limiting the s p of invention which is defined by. the appended claims only. 1

What is claimed is:

1. An acoustic device comprising a magnetic structure, spaced pole-pieces attached to said, structure, current carrying means having a portion between said pole-pieces, and a ribbon dia- 15 phragm of magnetic material also between the pole-pieces;

2. An acoustic device comprising a structure including magnet means, spaced pole-pieces and support means, sound-current coil means having 10 elongated portions fixed to said pole-pieces, and a ribbon diaphragm of magnetic material attached at its ends to said structure and extending between and in the same direction as the elongated coil portions. .15

3. An acoustic device comprising a magnetic structure having pole-pieces, said pole-pieces having planar, parallel surfaces, coil means havin portions adjacent said surfaces, and a ribbon diaphragm of magnetic material extending between 20 said coil portions.

4. An acoustic transmitter comprising a pair of spaced parallel pole-pieces, magnetic means coupled to said pole-pieces, current carrying means comprising turns of fine wire and having 25 portions thereof fixed to said pole-pieces and located therebetween, and a ribbon diaphragm of magnetic material mounted between the coil portions. A

5. An acoustic transmitter comprising a magnetic structure having spaced parallel pole-pieces, a ribbon diaphragm of magnetic material mounted between said pole-pieces, and coil means having portions thereof fixed to said pole-pieces adjacent the diaphragm, said coil means comprising at least one thousand turns of wire having a cross-sectional area of less than four circular 6. Magnetic circuit means for an acoustic transmitter comprising magnet means, and a ribbon diaphragm of permalloy about 0.25 mil in thickness in cooperative relation with said pole-piece means.

7. An acoustic transmitter comprising a magnetic structure, voice coil means, and a ribbon diaphragm of molybdenum permalloy mounted in operative relation to said structure and *coil means.

8. An acoustic transmitter .comprising spaced parallel pole-pieces defining an air-gap, permanent magnets, connecting means of non-conduct ing, non-magnetic material attached to ends of the pole-pieces an'd positioning the magnets in contact with said ends, current coils one on each pole-piece and each having a "portion thereof fixed on the air-gap bounding. face of a pole-piece, and magnetic field distorting means comprising a sound responsive ribbon of magnetic material attached at its endsto the connecting means and 50 positioned in the air-gap between said portions of said coils.

9. An acoustic transmitter comprising a mag netic structure having spaced parallel pole-pieces,

coil means having portions thereof attached to 65 r th pole-pieces, and a ribbon diaphragm of ma netic material magnetically in circuit with said magnetic structure and mounted for vibration between said pole-pieces.

' pieces to define a magnetic circuit network in- 15 eans, pole-piece cluding elongated air-gaps, and coil means having portions thereof in said air-gaps, said portions being fixed to the pole-pieces.

11. An acoustic transmitter comprising a magnetic structure having spaced parallel pole-pieces, a ribbon diaphragm of molybdenum permalloy attached to the magnetic structure, extending between and parallel to the pole-pieces, and a pair of coils attached to the magnetic structure one on either side of the ribbon, and each having a portion thereof located between the ribbon and the magnetic structure. I

12. An acoustic transmitter comprising a magnetic structure having spaced parallel pole-pieces, coil means having spaced portions thereof between and attached to the pole-pieces, and a diaphragm comprising a thin ribbon ct permalloy attached at each end to the magnetic structure and located in the space between said coil portions.

13. An acoustic transmitter comprising a pair of permanent magnets mounted in spaced relation and having a pair of spaced parallel polepieces therebetween, an elongated coil having spaced parallel sides, one fixed on each pole-piece, and a ribbon diaphragm of magnetic material mounted between the parallel sides of the coil.

14. An acoustic transmitter comprising a pair of spaced parallel pole-pieces, magnet means at tached to said pole-pieces, a'ribbon diaphragm of magnetic material between said pole-pieces and magnetically connected to the magnet means, and

a voice coil having portions thereof fixed to each pole-piece adjacent to, but spaced from the diaphragm, said magnet means being so poled that the pole-pieces are each oi the same magnetic polarity.

15. An acoustic device comprising a pair of magnets having poles of opposite polarity, a pair .of magnetic members magnetically connecting like poles of said magnets, a magnetic diaphragm between said magnetic members, and a coil having a portion in the magnetic field between said diaphragm and one or said magnetic members.

16. An acoustic device comprising a pair of magnets having end portions of like polarity, magnetic members connecting corresponding ends of said magnets, a magnetic diaphragm betweensaid magnetic members, magnetic means'coupling spaced portions of said'diaphragm to said magnets, and a coil having a portion between said 20