US1577254A - Sound reproducer - Google Patents

Description

Patented Mar. 16, 1926. y 1,577,254

UNITED STATES tPATENT OFFICE.

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To all whom t may concern.' subjected to conditions such that it would Be it known that I, HARVEY C. Haras, a be somewhat highly and uniformly damped 55 citizen of the United States, andaresidentpf over its lwhole surface, the reproduction Washington, District of Columbia, have 1n- Would come still nearer to being perfect,

5 vented certain new and useful Improve- 'especially if the diaphragm can be made to ments in a, Sound Reprodueenof, which the have small inertia so that the restoring following is a specification. forces are small. i

My invention relates to a means for trans- An object of this invention is to rovide a y forming electrical energy into sound energy, receiver havin a conical shaped diaphragm and more particularly toa soundv receiver or with uniform y distributed driving and'` reproducer. damp g forces which Will accomplish the In Aorder to transform electrical energy above advantages. p 65 into sound energy without distortion -it be- With this and' other objects in view the comes necessary to furnish some mec anism invention consists in the construction, comcarrying a movable or vibrating member bination and arrangement of parts as will that will be caused to move by the luctuatbe hereinafter described.

ing electrical current, and insuch a way Referring to the accompanying drawing 7 that the pressure uctuations of the air forming part of this specification and in caused by the vibrating movements of this which the ligure illustrates a cross-sectional member will have the same characteristics as view of a sound receiver, 1 indicates a cylinthe current causin this member to move. drical member forming part of a'magnetic This requires that t emovable member shall circuit consisting of magnetic material elebe of such a design or shall be subjected to ments 1, 2, 3, and 4, and having a conedforces in such a way that it will not break shaped upper portion and reduced lower 5 up4 into partial or harmonic vibrations and portion. The reducedportion of this memn shall be so designed or so damped that all ber seats ina ring 2 which is provided with vibrations cease when the current Ailuctuaa passageway for conductors 9. 3 is a cylin- 5 tions stimulatino` the motion cease. .drical outer member connecting the rin 2l These desirable conditions have been apand a conical air-gap between 1 and 4. e proached by the use of conical shaped diamagnetic circuit can be energized by a diphragms and by damping the motion of Hat rect current carried by conductors 9 through diaphragms over those regions where the coil 5 or the metal of the circuit can be made 85 harmonic loops occur, but usually the of magnet steel such that the magnetic method of driving the diaphragm from a flux of the circuit will be maintained after point or small region about its center is so being once established. Coil 6, which is favorable to the establishment of harmonics Wound upon the coned surface of member 1, in the diaphragm that the damping required carries t to eliminate them must be so effective that transferred into sound energy, and which is the motion of the diaphragm as a whole is led to it by wires 8 passing through memgreatly hindered and the device becomes ber 1. A thin conical shaped diaphra very insensitive. preferably made of aluminum, is iexi ly The tendency of a diaphra m to break up suspended between 4 and the coil 6 by a' 95 into harmonic vibrations wou d be almost nil ilange 11 which is secured to the member 4 if the driving force could be uniformly disby screws 10. tributed over the whole surfaceinstead of The principle of operation of the device is being concentrated at a point or small reas follows: gion near its center. It 1s evident, also, if The fluctuating telephonie currents 100 the diaphragm could have the form of a through coil 6 generate substantial eddy curcone so that its rigidit would tend to prerents in the aluminum conical vdiaphragm vent the formation o harmonics by such because of close electrical coupling be`ween small tendency as might` evist, the device thesel elements. These eddy currents circue telephonie current that is to be Vwould come very near to giving true re rolate about the diaphragm in a direction l duction. And if the diaphragm coul be perpendicular to its axis, and are of uniform density throughout the diaphragm 1s-`r if the windings of coil 6 are uniforml tributed over the cone surface of mem er l.

The eddy currents traversing the coned part of the diaphragm pass er endicularly throu h the magnetic held.) ol) the coneshape air-gap, and, according to the well known laws of electro-dynamics, the conductor carrying the current will at allpoints experience a force tending to produce motion along a line perpendicular to both the i field strength substantially uniform throughout the air-gap, and since the current density ic practically uniform throughout the cone of the diaphragm, it follows that the forces tending to urge each particle of the conical `portion of the diaphragm back and forth along an element of the cone may be made substantially uniform throughout the coned portion of the diaphragm. Moreover, the force at any and every point in this part of the diaphragm can be resolved into two componente, one radial to the cone and the other parallel with its axis. The components parallel with the axis are all in one direct1on at any instant, the direction being determined by the direction of the telephonie current in coil 6 at that instant. These forces, therefore, tend to drive the diaphragm back and forth along its axis and the driving force is uniformly distributed over the conical surface of the diaphragm. This force is at all times proportional to the strength of the magnetic lield in the air-gap and to the tele phonic current in coil 6.

Since the diaphragm is both pushed and pulled bv the action of the telephonie current and `does not depend upon restoring forces within itself for its motion,the circular flange rovided for mounting the dtaphragm can e made very light and flexible and under such conditions the natural resonant frequency can be made lower than that `of the sounds which the device is designed to generate. In this way resonance pan be largely eliminated. But even if this were not done the device cannot be highly resonant for the reason that motion of the diaphragm is highly damped. If the diaphra' is made to vibrate either by its own inertla and restoring forces or by some other agency, the coned portion of the diaphragm y will cut across the magnetic .field of the au'- gap with the result that eddy currents will be generated about the cone in such a direction as to oppose its motion. Moreover, this damping effect will be uniformly distributed over the whole conical surface of the diaphragm. This effective damping causes the diaphra m to move at all times in proportion to t e driving current and to stop moving when the driving current sto s.

The forces tendin to move the diaphragm are wholly due to t e reaction of a current passing through a magnetic field and not to a variation in the strength of one or more magnetic poles. This gives the present invention two advanta es: First, since its operation is independent of var ing the strength of the ma etic circuit, the flux of this circuit can be rept saturated and constant and this gives the device a high power factor by confining the flux change through the coil 6 to what it would be if there were no iron resent. This reduces the reactance of the te ephonic circuit to a small value and at the same time practically eliminates the usual losses due to hysteresis. The eddy.

current losses are also greatly reduced for the reason that those set up 1n the moving member are utilized for driving this member. Second, the force driving the diaphragm is always proportional to the current through coil 6, while in most sound reproducing devices of the telephonie class the force is proportional to the magnetic flux linkage between the lixed and movable parts -of the magnetic circuit and this in turn is a somewhat complicated function of the current through the telephonie coils and the relative position of the movable part of the ma etic circuit. As a result, the forces ten ing to move the diaphragm are not proiortional to the current and the character' lstics of the generated sound waves are not strictly proportional to the characteristics of the current.

Having described my invention, I claim:

l. In a device of the character described the combination of a magnetic circuit having a conical air gap, a tele honic current winding uniformly dispose on one side of said gap, and a conductive cone' diaphragm movably suspended between said winding and the second side of said air gap and havin the angularly disposed walls thereof su stantially parallel with said winding.

2. In a device of the character described the combination of a lluxed magnetic circuit having a conical air gap, a current carrying winding uniformly disposed on one side of said gap, and a conductive cone diaphragm vibratorily suspended in said gap and having the angularly disposed walls thereof substantially paralel with said windiv In a device of the character described winding fixed in said gap, and a conductive cone. diaphragm vibratorily suspended in said gap and having the singularly disposed walls thereof substantially parallel with said winding.

4. In a device of the character described means-for creating a conical magnetic gap, a

conductive cone diaphragm vibratorily sus- 10 pended in said gap, :md means for inducing uniformly distributed eddy currents in said diaphragm.

HARVEY c. HAYES.

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