US2453521A

US2453521A - Superimposed duplex loud-speaker

Info

Publication number: US2453521A
Application number: US445179A
Authority: US
Inventors: John F Marquis
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1942-05-30
Filing date: 1942-05-30
Publication date: 1948-11-09
Anticipated expiration: 1965-11-09

Description

NOV. 9, 1948. v J, F, MARQUls v 2,453,521

SUPERIMPOSED DUPLEX LOUDSPEAKER Filed may so. 1942 'Margw ATTQBNEY.

Patented Nov. 9, 1948 UNITED STATE SYPAT SUPERIMPosED DUPLEX Loon-srEAKER` `lohn F. Marquis, Haddonfeld, N. J., ass'ignor to Radio Corporation of "America, a corporation of Delaware Application May 30, 1942, Serial No. 445,179 s This invention relates to signal translating apparatus, and more particularly to a loudspeaker having an extended range of reprodu-ction.

Various loudspeaker constructions have been proposed heretofore wherein two or more diaphragms are provided, each with its own driving constructed, have the disadvantage that the coupling member between the piezoelectric driver and its diaphragm has a fair amount of compliance, and this cuts down the high frequency response. The additional mass introduced into the vibrating system by the aforesaid -coupling mem- 1 Claim; l (C1. 179-109) efficiently at the `lower acoustic frequencies,` and mount a piezoelectric element within the cone in ber also reduces the high frequency response, so

that full advantage cannot be taken of the high frequency range over which the piezoelectric driver is adapted to operate.

The primary object of my present invention is to provide an improved loudspeaker having an extended range of reproduction and which is free from the aforementioned defects. A

More particularly, it is an object of my present invention to provide an improved loudspeaker construction embodying a low frequency unit and a high frequency unit, the latter of which is adapted to operate efciently over a wide range.

Another object of my present invention is to provide an improved loudspeaker as aforesaid in which the moving parts have a minimum mass.

Still another object of my invention isfto provide an improved loudspeaker of the type set forth which ischaracterized by a minimum number of mechanical parts, thereby reducing the cost and greatly facilitating the assembly thereof. It is also an object of my present invention to provide an improved loudspeaker as above described which is highly efficient inuse and which will have a long life under ordinary conditions of use. l

In accordance with my invention, I provide a `unitary loudspeaker construction which comprises a relatively large diaphragm, preferably of the cone type, driven by a suitable electromechanical converter, such as a dynamic or other suitable magnetic driver or motor which operates proximity to its apex end. The piezoelectric element, constituting a second"electromechanical converter, is connected to the-cone at a plurality of spaced points around itsown periphery, with at least one point on its peripheryfreefrom contact with the cone, whereby the last mentioned peripheral point of the element is free to vibrate.

According to onermodication `of my invention, a second, smaller cone diaphragmhas its apex end connected directly to the, aforementioned free, peripheral pointof lthe piezoelectric element` without any intervening coupling devices,` the" piezoelectric element serving as a motor to drive the small cone alone at thehigherfrequcncies. The smaller diaphragm" is also nested within, preferably concentrically with, the largergdia'- phragm and may have it-s periphery or mouth either freely suspended or connected to the body of the large diaphragm by a suitable compliant coupling, as may be found most desirable.

In accordance with another modification of my present invention,` the piezoelectric element may have an area sufficiently large to radiate or` gen` erate acoustic waves directlyupon being energized to vibrate at acoustic frequencies. In either case, the mass of the moving, high frequency systern is extremely smalll and does not appreciably cut down the high frequency response. Also, the

`absence of a compliant coupling between the piezoelectricdriver and its associated small `diaphragm aids greatly in obtaining response over an extended high frequency range. The crystal driver and the dynamic driver may be connected to the same source of audio A.C. power and so adjustedas to increase the `sound output of the unit at frequencies above the normal cut-off frequency of the dynamic portion of the unit alone.

The novel features that I consider `characteristic of my invention are set forthwithparticularity in the appended claims. The invention itself, howeverboth asto its organization and method of operation, as well` as additional objects and advantages thereof,A will best be understood fromthe following description of two embodiments thereof, when read in -connection with the accompanying drawing, in which Figure 1 i-s a central sectional view of one form of loudspeaker constructed in accordance with this invention,

Figure 2 is a fragmentary, plan view thereof,

Figure 3 is a fragmentary, detail, sectional view showing one manner of attaching the piezoelec tric element to the large cone,

ENT N OFFICE Figure 4 is a view similar to Fig. 1 but showing another form of my invention, and

Figure 5 is a fragmentary, plan view of the latter form of my invention.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown, in Figs.1',` 2`and3; a' relativelyflarge, cone vtype diaphragml suitably supported at its mouth or periphery by a pair of rings 3 and having a voice coil form `5 on which is wound a voice coil 1: The voice coil I may be suitably vcentered by a spider 9 in the angular air gap'of Aa suitable magnetic or electromagnetic structure II, all as is well known in the prior art-L may be fed from a suitable audio frequency source through a circuit which includesa coupling transformer I3 and which may be designed to deliver to the voice coil 1 low frequency energy forwhich the relatively large cone' I is particularly suited.

Supported entirely onv and .nested Within the cone ,diaphragm- I in proximity toits apex end is a piezoelectric element I5v of any suitable type, such as a Rochelle salt crystal or the like. The crystal I5 is preferably polygonal inshape (for example, of square shape) and has all but one ofv its corners clamped. between and preferably cementedy to apair of tabs or the like I1 projectinghfro-m aclip or similar holdingl device I9, the basecfwhich is cementedto the large diaphragm I-in proximityv to its apexend, as most clearly shown in Fig. 3.A The piezoelectric crystal element I5 isso disposed on the diaphragm I in the modification of Figs. 1 to 3 that its free corner l-5a-is. substantially on the axis ofthe cone I. A small cone. diaphragm 2|which has a mouth or base'diameter considerably smaller than the mouthdiameter of the cone I-and is particularly suited for operation at the higher frequencies, hasf-its apexcemented. or otherwise suitably secured directly to the free cornerv |511. of the crystal I5 without any interveningv coupling element whichv wouldnormally introduce more or less compliance therebetween. The coner 2| is preferablyfmuch smallerthanthe diaphragm I and itsv mouth or periphery may either befreely suspended, or an compliantl ring or the like 23 may connect the mouth ofv thesmall diaphragm 2| to v the body ofthe large diaphragm I, if` desired.

The crystal I 5maybe connected to the same audio frequency source asthe. voice coil 1, as clearly shown in Fig. 1, by a suitable circuit rwhich may include a capacitor! 25Lvvhich will pass the higher yfrequencies but` filter out the` lower frequencies aswellas any direct current. Atthelower frequencies, the cone I, its voice coil 1, thecrystal I5 anditsdiaphragmZI all move together as a unit. At the higher. frequencies, however, the cone. I is. practically stationary and only the crystal I5 and `its cone` 2|. move.

The. modification of my invention shown in Figs- 4 and`5. is-quite similar to that heretofore described. However, instead of` providing the smallY diaphragm 2|, the crystal or other piezoelectricrelement l5may'bemade sufciently large so; that it will have a vibrating surface which is vcapable of generating acoustical'waves when the Ther voiceV coil 'Il crystal or the like is vibrated at acoustic frequencies. In this case, the piezoelectric element I5 is preferably made considerably larger than the corresponding element of Figs. 1 to 3, and it is mounted on the diaphragm I in the manner heretofore described with one of its corners I5a or some other suitable point or points on its periphery slightly spaced yfrom thecone VI whereby the latter'point or points are freely suspended. As shown in Figs. 4 and 5, this form of crystal is preferably mounted so that it is concentric with the cone I. I-Iere, again, the element I5 vibrates bodily as a unit with the large cone I at the lower frequencies, while atthe higher frequencies, practically all motion is in the element I5 which now vibrates relative to the cone I.

From the foregoing description, it will be apparent to those skilled in the art that I have provided' a novel loudspeaker construction comprised of a minimum number of parts andl capable of reproducing acoustic frequencies over a wide and. extended range. Although lI have shown and described but two embodiments of my invention, it will be apparent to those skilledin the art that many other modifications' thereof are ,possible. It will also be apparent, no doubt, that the construction herein described may also be used as a pick-up device or microphone, as well asa loudspeaker. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior artr and by the spirit of the appended claim.

I claim as my invention:

A loudspeaker comprising a pair of conical diaphragms, a magnetic motor including a movable element connected to al first one ofsad diaphragms for driving said first'diaphragm, and a piezoelectricmotor carried by said first diaphragm, the other of. said diaphragme being connected to said piezoelectric motor and being, adapted to be driven -by said piezoelectric motor, said other diaphragm and said piezoelectric motor being nested within said first diaphragm, said otherdiaphragm having amouth diameter Vwhich is smaller than thatfof said first diaphragm, and the mouthof said other diaphragm having a compliant connection with said rst diaphragm;

J OHN F. MARQUIS.

REFERENCES CITED Ihe following references are of record'in' the file of this patent:

UNITED STATES PATENTS Number Name Date 1,760,198 Hough May 27, 1930 1,839,748 Gruschke Dec. 6, 1932 1,932,461 Deventer Oct. 31, 193,3 2,053,364 Engholm Sept.` 8', 1936 ,60 2,102,668 Ballantinev Dec. 21, '1937 2,269,284: Olson Jan. 6, 1942 2,269,403l Williams' Jan. 6, 1942 FOREIGN PATENTS g Number Country Date' Great Britain Nov. 1o, 192e