Title:
Loudspeaker with oscillatory coil
United States Patent 2147605


Abstract:
One of the most difficult problems associated with the construction of dynamic loudspeakers relates to the centering. Despite all attempts heretofore it has not been possible to perform centering in a satisfactory manner. According to the invention, these and other disadvantages are eliminated...



Inventors:
Walter, Lissauer
Application Number:
US75611034A
Publication Date:
02/14/1939
Filing Date:
12/05/1934
Assignee:
Walter, Lissauer
Primary Class:
Other Classes:
381/406
International Classes:
H04R9/04
View Patent Images:



Description:

One of the most difficult problems associated with the construction of dynamic loudspeakers relates to the centering. Despite all attempts heretofore it has not been possible to perform centering in a satisfactory manner.

According to the invention, these and other disadvantages are eliminated by the fact that the disc is secured to the pole plate so as to be free of torsion by means of single, evenly distributed radial projections which are separated from each other by gaps. Irregularities may thus be fully compensated, and the radial projections can assume their natural position corresponding with the tensionless condition. It is 1.5 also possible by means of centering discs mounted in this fashion to guide the oscillatory coil in such a way that on the one hand lateral movements are as far as possible suppressed, and the coil upon its axial movement in the air gap is capable of performing maximum vibration, so that also the lower tones will permit of a good reproduction.

The arrangement according to the invention enables the centering disc to be secured at 12 to 15 or even more points, and the attachment of the centering disc to the pole plate or the diaphragm basket to be performed with three or four screws.

In the case of centering discs secured about the periphery the pressure ring which may possibly be provided is, in accordance with the invention, furnished with recesses corresponding with the radial projections of the disc, so that the pressure ring upon the assembly may be passed in bayonet-like fashion over the centering disc, ;53 which is preliminarily assembled with the diaphragm and the oscillatory coil to form a structural unit, or the centering disc introduced through the pressure ring.

Use has already been made previously of a pressure ring in conjunction with so-called spiders for the mounting of oscillatory coils, the spider being furnished with single arcuate and outwardly extending arms introduced in bent fashion through the pressure ring and then secured by means of the ring. This has nothing in common with the invention. According to the latter it is possible for the first time to secure acoustically correct centering discs by means of a pressure ring so as to be free of tension. An additional advantage of the holding means for oscillatory coils according to the invention resides in the use of a very thin plate for the centering disc or spider. The tensioning method according to the invention enables the centering disc to be furnished with the most favourable form for the generation of the oscillations without consideration to strength. If rendered necessary by the small thickness of the plate employed for the centering disc, for which fibrous substances or materials impregnated with artificial resin are suitable, numerous attachment arms may be provided in order to impart to the centering disc the requisite strength and to secure the same in reliably flat fashion. It is desirable to provide as many radial attachment arms as there are extensions on the outside of the centering disc for tensioning purposes.

The effect according to the invention is also accomplished in substance if the arms of the centering disc are riveted to a rigid ring, or secured thereto in other fashion, and this ring then secured in the proper position.

It will be obvious that the centering disc according to the invention enables perfectly new forms thereof to be developed, which is particularly important as regards the mounting of oscillatory coils of large diameter. A particular advantage associated with the use of large oscillatory coils consists in the fact that the diaphragm, for example a conical diaphragm with inwardly folded double cone, may be placed on the oscillatory coil in self-supporting fashion.

There is also the possibility of covering the spider with a piano-parallel diaphragm, or constructing the same itself as a diaphragm. In this case it is not perforated.

The holding means according to the invention may also be used fundamentally for the inner centering of loudspeakers, which is again to be recommended for oscillatory coils of large diameter. It has been found that inner centering is particularly suitable in those cases in which a holding means is concerned requiring to damp the oscillatory system as little as possible. In this case it is advisable to make the annular portion as narrow as possible to permit of the attachment of the inwardly projecting abutments about the largest possible circumference.

There is also no objection to employing the holding means for the oscillatory coil in accordance with the invention for permanent dynamic loudspeakers. They are also suitable for mounting the oscillatory coils in systems in which the effect of the field excited electromagnetically is amplified by permanent magnets. The method of centering according to the Invention possesses above all particular significance as regards the mounting of oscillatory systems of a novel kind. Thus, for example, according to the invention, a centering disc with elongated 2 2,147 cross-section, for the purpose of supporting an oscillatory system having an acoustic diaphragm of elongated cross-sectional form or a similar outer confinement, may be furnished with projections, and on these projections the centering disc suspended without tension.

Acoustic diaphragms having an elongated cross-sectional form are preferably suited for fitting in the lower part of radio receivers. If, as frequently applies at the present time, the major portion of the front wall of the receiver is reserved for comprehensive station charts, there usually remains for the acoustic diaphragm of the loudspeaker to be fitted merely the lower space of comparatively small height. It is particularly difficult to fit in this limited space a dynamic loudspeaker of high efficiency and excellent quality of tone.

This problem is solved according to the invention by the fact that the attachment curve of the diaphragm on the basket, the cross-section of the oscillatory coil and the centering disc or its inner or outer confinement respectively possess geometrically similar forms, and are thus adapted to each other, and that the outer or inner edge of an elongated centering disc of this nature is secured to the pole plate with radial projections.

In this way there is obtained a high stability of the oscillatory system against tilting and crosssectional oscillations of the oscillatory coil or the acoustic diaphragm.

According to the invention, as already set forth above, provision is made for the parts of the disc secured to the pole plate, which parts are divided by means of gaps into single and separate radial projections, to be held without torsion by means of a continuous pressure ring. Now it has been found that the radial projections on the centering disc may under certain circumstances be secured to the pole plate without tension by means of an adhesive, or secured in other fashion without torsion, so that a special pressure ring is not required. If the radial projections of the centering disc are secured to the pole plate with the assistance of a special supporting ring, the centering disc may be secured by adhesion to the annular edge or between the pole plate and the ring. A supporting ring may also be flanged on to the pole plate in direct fashion, and the radial projections of the centering disc secured thereon by an adhesive.

There is also no objection to furnishing the pole plate with a recess, and securing the extensions of the centering disc by an adhesive to the edge thus formed.

Insofar as the invention refers to elongated centering discs for oscillatory systems, the acoustic diaphragm and oscillatory coils of which possess geometrically similar cross-sectional forms, it is advisable to make the pole plate also of corresponding form. For this purpose, according to an additional feature of the invention, there are provided recesses in the pole plate at the points corresponding with the rounded portions of the oscillatory coil.

The invention will be described more fully with reference to the drawings.

Fig. 1 is a section through an outwardly centered loudspeaker and shows also a section by the centering disc, from which Fig. 2 brings a view.

Fig. 3 is a view of the appertaining pressure ring.

Fig. 4 is a section through a loudspeaker with ,605 an inner centering system, in which the corresponding parts have been furnished with the same designation as in Fig. 1.

Fig. 5 shows an elongated centering disc provided with the projections according to the invention.

Fig. 6 is a variation of Fig. 1 with the centering disc of Fig. 5.

Fig. 7 shows a detail of the loudspeaker of Fig. 6. Fig. 8 shows in front the half of a various oscillating system of a dynamic loudspeaker.

This figure represents a section according to line VIII-VIII of Fig. 9 showing an elevation of the system of Fig. 8.

In the drawings, I is the centering disc, which is firmly connected with the oscillatory coil 2 and the cone 3, preferably in the joint between the same. The centering disc rests on a support 5 having an annular abutment, and is secured firmly thereon and on the magnet system 4 by means of the pressure ring 6 with the assistance of several screws 7.

As shown in Figs. 2 and 3, the pressure ring 6 possesses as many recesses 8 as there are projections 9 to the centering disc i. Upon the assembly the projections 9 of the centering disc may be passed through the recesses 8. The ring or the centering disc and the diaphragm are then slightly rotated and screwed tight in a position such as shown with dotted lines in Fig. 3. Fig. 3 illustrates so, that by means of the pressure ring 6 and by means of screws 7 the projections 9 are secured to the annular abutment 5 of the pole plate 4, whereas the edge 13 is not attached to the pole plate.

Fig. 5 shows an elongated centering disc I for outer centering and attachment to the pole plate 4 with the assistance of the projections 9 on the outer edge. In the case of inner centering the inner edge possesses corresponding inwardly directed projections.

In Fig. 5 is also shown a cross-section of the oscillatory coil 2 attached at the inner edge of the centering disc I.

Further Fig. 5 shows a centering disc comprising a rectangle a., b, c, d the narrow sides of which ac and bd are each rounded off towards the outside by a semi-circle aec and b'd. Therefore according to the invention the cross-sections of the oscillatory coil 2 and the acoustic diaphragm 3 comprise in like manner a rectangle the narrow sides of which are each rounded off towards the outside by a semi-circle. Fig. 6 shows the manner in which the radial projections 9 of a centering disc I for example those in Fig. 1 or of Fig. 5, may be secured to a supporting ring 5 without tension, or without appreciable tension, by attachment with an adhesive.

Fig. 6 shows also how arises over the centering disc an acoustic diaphragm of the cone type being bent outwardly. The boundary curve 14 is a hyperbola. Therefore those parts of the acoustic diaphragm arising over the semi-circles aec and bfd are each a half of a hyperboloid of rotation whilst the connection of each two edges of these hyperboloids of rotation along the longitudinal edges ab and cd then results in each a hyperbolically curved cylindrical surface.

Now from the theory of warped faces it is known that the face of a hyperboloid of rotation may be comprehended as a warped face respectively as a face formed by warped lines, i. e., lines one situated warpedly relatively to a neighboured one.

Further according to the invention acoustic diaphragms of great stability are obtained if those parts forming warped faces are realized by the development of the generatrix warped lines 21 or 23 as rods such as illustrated in Fig. 6. This figure shows also in combination with Fig. 5 the axis 15 and 16 of the both halves of hyperboloids of rotation.

If from the semi-circle there is derived an arc, there is obtained in place of the half of a hyperboloid of revolution the corresponding sector thereof.

If the elongated rectangle is rounded off by a series of arcs having different radii, there is obtained at this point a diaphragm, which is composed of equally as many part surfaces of different hyperboloids of revolution and is realized by a corresponding number of rod systems warped in relation to the axis.

The same applies if the elongated cross-section of the diaphragm is composed of arcs having different radii. With arcs of this nature it is possible in the manner known per se to produce elliptical or other oval cross-sectional forms.

Fig. 7 shows the recesses in the pole plate 4 in conjunction with the oscillatory coil 2 of elongated cross-section according to the invention. These recesses in the pole plate facilitate the centering. There is certainly a slight loss of force of an electrodynamic origin, but this is compensated to a considerable extent by the extremely exact centering in the two straight air gaps and by the greater density of the field in these air gaps.

If for the purpose of reinforcing the oscillatory system there is fitted, for example at the joint between diaphragm and coil, a ring, which then preferably possesses in each case a radially disposed edge at the ends, or a conical edge at the neck of the diaphragm respectively, this ring must naturally also be furnished with the elongated form of the oscillatory coil. The reinforcing effect is increased if the jacket surface of the ring is corrugated. It is important to make the reinforcing ring of such a form that the reinforcement is obtainable with the least possible additional weight. For this purpose there is preferably employed a thin ring composed of light metal (aluminium or aluminium alloys). If the ring is furnished with a U-shaped cross-section, the flange may be widened towards the middle of the longitudinal side.

This is shown in Pig. 8 and Fig. 9. 2 is again the oscillatory coil and 3 the cone. The joint between them is reinforced by the ring 24 having a cylindrical part 24', a conical part 24" and a radially disposed edge 24"'. For this ring preferably is used for a light metal such as aluminium or an aluminium alloy.

For the arrangement of Fig. 8 and Fig. 9 further is essential that the centering disc I is employed in conjunction with centering disc 25 for inner centering. For this purpose the inner edge of the disc 25 is provided with projections 26 which latter are secured at the core of the magnet-system 4 with means of the supporting ring 5' the pressure ring 6' and the screw T', whereas the projections 9 of the centering disc I are secured at the pole plate with means of the supporting ring 5", the pressure ring 6" and the screws 7".

That what I claim is: 1. A loudspeaker of the dynamic type, comprising a magnet system having a pole plate and a pole core arranged to form an air gap, an oscillatory coil disposed in the said air gap, a diaphragm connected with the said coil, means for centering and supporting the oscillatory system of the loudspeaker, the said centering means comprising a plate having symmetrically disposed openings therein and short radial projections on the periphery, a ring holding the said centering plate solely by means of the said projections against the said pole plate, and means for securing the said ring to the said pole plate.

2. A loudspeaker of the dynamic type, comprising a magnet system having a pole plate and a pole core arranged to form an air gap, an oscillatory coil disposed in the said air gap, a diaphragm connected with the said coil, means for centering and supporting the oscillatory system of the loudspeaker, the said centering means comprising a plate having short radial projections on the periphery, an annulus on the said pole plate, a ring holding the said centering plate solely by means of the said projections against the said annulus, the said ring having inner recesses corresponding to the said projections, the said centering plate being secured by passing the said projections through the said recesses to below the said ring and rotating the said centering plate in relation to the said ring, and means for securing the said ring to the said pole plate.

3. A loudspeaker of the dynamic type, comprising a magnet system having a pole plate and a pole core arranged to form an air gap, an oscillatory coil of elongated form disposed in the said air gap, a diaphragm connected with the said coil, means for centering and supporting the oscillatory system of the loudspeaker, the said centering means comprising an elongated plate having short outwardly extending projections on the periphery, an elongated ring holding the said centering plate solely by means of the said projections against the said pole plate, and means for securing the said ring to the said pole plate.

WALTER LISSAUER. 60