US1562165A - Acoustic device - Google Patents

Description

Nov. 17, 192 1,562,165

H.C.HARR$ON v ACOUSTIC DEVICE' I FiledjJuly 17. 1925 v A 00 6 arr/L50,

Patented Nov. 17, 1925.

UNITED STATES PATENT OF-FlCE.

HENRY C. HARRISON, OF PORT WASHINGTON, NEW .YORK, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y.,.A CORPORATION OF NEW YORK.

AcoUs'rIc' nnvron.

Application filed July 17, 1923. Serial No. 652,013.

To all whom it may concern:

Be it known that I, HENRY C'. HARRISON, a citizen of the United States, residing at Port Washington, in the'county of Nassau, State of'New York, have invented certain new and useful Improvements in Acoustic Devices, of which the following is a full,

clear, concise, and exact description.

This invention relates to acoustic devices, the object being to provide an acoustic device capable of faithfully and efficiently reproducing all vibrations in the sound range I and particularly the vibrations of the lower frequencies. I

In general, the inventionprovidesan electro-magnetic device having a vibrating system, with restoring means capable of exert ing a force which varies with the displacement of the vibrating member in substantially the same manner as the magnetic pull of the steady field on the vibrating member varies.

'In one embodiment the invention contemplates a loud speaking receiver of the bal-; anced armature type, in which the armature the magnetic field.

Referring to the drawings:

Fig. lis a view, part in section, of an electromagnetic system for loud speaking receivers embodying the invention;

' Fig. 2 is a cross-sectional view through the armature supporting. means;

- Fig. 3 is a sectional view taken on line 3'-3 of Fig. 1;

Fig. 4 shows comparative curves of operation of present receivers and those embodying theinvention, Y

Fig. 5 shows a loud speaking receiver embodying the invention in a modified form; and

Fig. 6 is a view through section 66 of cies below the resonant frequency of a receiver, or of a :similar electromagnetic re-' producing devic are usually poorly reproduced because 0 the high elastic reactance small and the natural frequency cannot be.

brought 'down to a low audible frequency.

Referring'to the curves-shown in Fig. 4:, A-represents a typical force versus displacement curve for the steady field of a receiver and B the forcewersus displacement'curve of -a restoring elasticity, such as .a reed or a spring supported armature. From the curves A and B it is evident that the force shown bycilrve B atzero separation must be greater than that shown by curve A to prevent freezing of the armature to the pole pieces. armature,- and which determines its natural frequency is the difference between the elasticities shown by curves A and B and is represented by the slope of curve F. A vibratingsystem having anelasticity curve of this character produces distortion in reproductions due to the addition'of harmonics.

. To. avoid these'distortions' it is necessary shown by curve D, or to apply a restoring force having characteristics shown-by curve C, which is a curve of the same order as curve A. Curve 0 is shown plotted on the oppoiste'side of the horizontal axis for the reason that this force opposes that one to the steady magnetic field. For small separations between the armature and the pole pieces of the receiver, the pull on the armature due to the magnetic field varies approximately inversely as the square of the separation. Both curves, A and O, are therefore approximately parabolas. The first solution shown by curves B and D in The net elasticity operative on the volve in general a loss in efficiency asit suitable permanen't. magnet.

would require a substantially large separa tion between the pole pieces to change the magnetic field to have the same characteristies as shown by curve D. Therefore, for the purpose of describing the invention, the structures which have the characteristics shown by curves A and C will be described.

In the embodiment shown in Figs. 1,2. and 3, a core "11, having two arms 12 and 13-}, carries a coil 14, which when connected toa source of electrical energy furnishes a steadymagnetic field. If preferred, the coil 14 and the-core ll may be replaced'by a The core 11 may be supported on a case 15, (only part of which-is shown and which may be of any suitable form) by the studs 16 and the suitable means in the case 15. The arms 24 1 and 25 of the support 22 are provided with recesses 26 and 27 respectively, and the middle arm 28 with a recess 29. The armature 23 extends through the recesses inthese arms and is supported on the arms 24 and 25 by means of resilient. members or springs 30 and 31, respectively. These springs are short "and so designed as to offer, a resistance to the novement of the armature 23, which var es in substantially the same manner as the'magnetic pull on the armature. In this case this resistance varies as-sho-Wn by curve l" or magnetic systems having.

C in Fig. 4-. a maximum movement of .014; inches, springs having a thickness of.()tl2 inche'sa-nd an unsupported length of about .060 inches have i been found. satisfactory. .The armature 23 with respect to the poles.

may be supported intermediate its QXtl'ClIb ities by any suitable means, such as a pin 3 one end of which fits loosely in the armaturc 223 so there will be no initial stress on the springs 3.0 and 31 and the other end may tit snugly in the-arm 28. This pin has pre erably a reduced middle section so as to add no stiffness t0 the vibratin system. Its function is to provide a definite center of oscillation for the armature and may be omitted if the springs 30 and 31 are exactly the same and disposed exactly symmetrical sociated with the armature 23 -hy means of rod 32 is a diaphragm -83 of the usual type,

'which operates" into a horn orid istributes the sound in any well known-'Inanner. The rod 32 is preferably adjusted so there will Operatively as.-

' brating systems.

"be no'stress exerted on the armature by the v I diaphragm at maximum separation.

It will be noted from the curves shown the magnetic field, the armaturewould have zero elasticity and zero natural period for all displacements and would therefore remain infany position in the magnetic field to which-it would bemoved. As the armature would freeze under this condition for zero separation, it is preferable to provide a restoring force greater than the magnetic pull by an amount proportional tothe dis-= placement. One having a low constant elasticity of such a value as to give the vibrating system a low natural frequency of about 50 to'200 cycles per second has been found very satisfactory. This willnot only pre vent freezing at zero separation but will make the device slightly more efficient at the lower frequency range where it is de-.

sirable. For very slight deflections of thesprings 30 and 31 the restoring force is quite small, but as the deflection is increased the force increases rapidly and at substantially the same rate as the pull due to the steady field. A I

The modification shown'inFigs. 5 and 6 only in the manner of supporting the armat'ure. the support 22 in the previous modification, hasa convex bearing surface 41 on its middiffer from the one hereinbefore described A support 40, which'corresponds to i (lle arm, against which the armature, 42 is held by a resilient member 43 having aknifeedge 44 engaging a groovel45 in the armature/12, the bearing surface 41 should have 'a'large radius. For the structure shown a 2" radius has been found to be satisfactory. As the armature 42 vibrates, the distance between the bearing point on the member. 43 and the varies. e 4

The restoring force varies, with this )ivotin' oint on the surface 1-1" 1 s p iii) change in distance and is substahtially proportional thereto. The restoring force also changes with the pressure exerted on the armature by the member 43 which is flexible for vibrations of small amplitudes and acts as a variable load; As the change in the distance. between the supports and the change in the load are both in the same direction the force displacement curve may be made to increase at such a rateas to substantially equal that due to the steady magnetic field or any desired part of it at transmitters, recorders, reproducers or any electromagnetic apparatus employing vi- The invention claimed is: 4

1. In a sound reproducing system, a diaphragm, a magnet, an armature for said magnet operatively connected to the dia- 5-phragm, and means for substantially bal- 3. In an acoustic device, a magnet having a substantially constant magnetic field, a vibrating member disposed in the field of said magnet, and means for balancing the pull of the magnetic field on said member,

said means having a stifiness such that itsrestoring force is slightly greater than the magnetic pull for substantiallyall positions of the vibrating member by an amount proportional to the displacement of the vibrating member from its neutral position.

4. In an acoustic device, a magnet having a substantially constant field, an armature disposed in said field, and resilient supports .for said armature, said supports producing a restoring force which varies with the minute displacement of said armature in substantially the same manner as the magnetic pullon said armature but in the opposite direction.

5. In a magnetic system, a magnet, a vibrating member operatively associated with said magnet, and means for offering a me chan1cal impedance to the armature which varies in the same manner as the mechanical impedance due to the force of the steady magnetic pull exerted thereon.

6. In an acoustic device, a diaphragm having a substantially steady magnetic field, an armature connected to said diaphragm and mechanically associated with said magnet, and means for balancing the armature against the pull of said magnet, said means being of such stifi'ness asto cause a resisting force which varies with the displacement of said armature in substantially the same manner as the pull of the magnetic field. I

7'. In a sound reproducing mechanism, a diaphragm, a magnet having a steady mag netic field, an armature for said magnet responsive to current variations operatively.

connected with the diaphragm, and means offering an impedance to the movement of. the armature substantially op osite in phase.

and equal in magnitude to t e mechanical impedance due to the steady magnetic field 8. In a sound re roducing mechanism, an electromagnet pro ucing a steady magnetic field, an armature, a diaphragm operatively connected with said armature, and means for producinga force in the armature resistto the diaphragm, and a spring connected to netic flux varies with the displacement of ing the magnetic force of the steadyjfield 55 and larger by an amount proportional to thefdisplacement of the armature for substantially all positions.

9. In a'sound reproducing devioe',l' 'g diaphragm, an electromagnet responsive'to'f the current variations, an armature. forthe electromagnet pivotally supported between its ends and operatively connected at one end to the diaphragm, and damping means connected' with the other end of said armature adapted to resist the movement of the. arma I ture in response to the magnetic force thereon and in direct proportion to the magnetic 'force.

10. In a sound reproducing device, a diaphragm, an electromagnet responsiveto current variations, an armature for the electromagnet'pivotally supported between its endsand operatively connected at one end the other end of said armature and so proportioned when mounted that its resistive'force to the movement of the armature in response to the magnetic force is in direct proportion to such force.

11. The method of controlling a vibrating system which consists in applying a steady magnetic field and an opposing resisting force to a vibrating member, the resisting force varying with the displacement of the member in a manner such that thedifierence between the resisting force and the magnetic pull gives a constant elasticity.

12. The method of controlling a vibrating member which consists in applying thereto a steady magnetic field and an opposing resisting force which varies with the displacement of the vibrating member in the same manner as the pull due to the magnetic field varies. 3 i

13. The method of controlling thegvibrating system of a magnetic device which'consists in sustantially counter-balancing the elasticity in' the magnetic field by a second elasticity varying with the displacement of the armature in the same manner as the elasticity of the magnetic field.

14.,The method of controlling the vibrating system of a magnetic device which consists in applying thereto a restoring force which varies with the displacement of the vibrating system in substantially the same manner as the force due to the steady magthe vibrating system. no

15. The method of controlling a vibrating member in' a magnetic system which consists in applying 'a resisting forceto the vibratingmemb'er which varies substantially in-, ver'sely as the square of the displacement'of the vibrating member. *1

16. In a vibratory electromagnetic system responsive to frequencies within the voice frequencies.

range, a magnet, a vibrating armature for range,' a magnet, a vibrating armature for said magnet, and resilient means for plae 1 said magnet, and resilient means for making ing the-"natural frequeney of vibration of the arnlature'highly responsive to the lovver 0 the armature inithe lower range of voice range of voice-frequencies,

, I v In witness whereof, I hereunto subscribe 17." In a Vibratory electromagnetic system"1ny name'th-is 11 day of July A. D.,' 1923.- responsive td fre'queneies Within the voice HENRY C. HARRISON.

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