US1815987A - Conical diaphragm for loud speakers - Google Patents

Description

y 1931- c. w. PETERSON CONICAL DIAPHRAGM FOR LOUD SPEAKERS Filed Feb. 13, 1929 2 Sheets-Sheet l 'INVENTOR.

July 28, 1931. c. w. PETERSON 1,815,987

CONICAL DIAPHRAGM FOR LOUD SPEAKERS Filed Feb. 13, 1929 2 Sheets-Sheet 2 FiglX.

INVENTOR.

Patented July 28, 1931 PATENr orFIcE CHARLES W. PETERSON, OF CINCINNATI, OHIO CONICAL DIAPHRAGM FOR LOUD SPEAKERS Application filed February 13, 1929.

This invention relates to conical diaphragms for loud speakers of the type which have a large diaphragm freely exposed to non-confined air.

The object of my invention is to provide a cone of large enough area to reproduce the low bass notes and yet of such a flexible and aperiodic nature that the high notes may be reproduced in the light central part of the cone without disturbing or producing interfering vibrations in the outer heavy parts of the cone.

This invention is an outgrowth of the invention disclosed in my application Serial No. 755,056, filed Dec. 10, 1924.

The novel means by which I accomplish the objects of my invention will be clearly understood from the following description, taken in connection with the accompanying drawings which form part of this specification.

Figures I and II show plan and sectional views respectively of one of the simplest forms of this invention. Figures III, IV and V show the mode of operation on low, medium and high frequencies respectively of a little more complicated form of cone containing my improvements. Figures VI to IX inclusive show how my invention may be applied to diaphragms of various construetions and of various modifications of conical shape. The construction, operation and clifferences from the past art are as follows:

The cones used up to the present time have been made of one piece of rigid material or of several pieces of material rigidily connected or cemented together. One of these cones will move as a whole, i. e. with true piston action, when vibrated at low frequencies by a loud speaker driving motor, similar to the 7 this last case the vibration of the cone is broken up into variously shaped patterns of nodes, depending upon the frequency being reproduced and the speed of the vibration wave in the material of the cone. The central portion only of the cone is vibrating in Serial No. 339,557.

phase with the motion of the driving motor, and the other sections of the cone are vibrating, some in phase,and some out of phase with the center. This condition makes exact reproduction impossible and gives the speaker a muflled, barrel like or hashy sound as compared to the original sound being reproduced.

To get exact reproduction, the whole vibrating part of the cone must be vibrating in phase with that of the driving motor. My new method of cone construction herein disclosed gives cones which approach, within practical limits, this ideal of operation.

This new principle of cone construction may be clearly understood by referring to Fig. I. The cone material in this case is divided into two zones 1 and 2. These two zones are separated by a small gap at which is bridged by a ring of soft aperiodic mate rial 6 such as felt, cloth, rubber, leather, etc. This felt or other soft material is shown attached to the cone by stagger stitch sewing 9. A ring 8 of felt or the like is shown around the outer-edge of the cone to allow the cone to move as a whole without rattling against the case of the speaker and to absorb extraneous vibrations the edge of the cone the same as is described in my application Serial No. 755,056 filed Dec. 10, 192-1.

The operation of these cones may be clearly understood by reference to Figs. III, IV and V which show a cone of similar construction to that of Figs. I and II except that it has three zones 1, 2 and 3 instead of two.

W hen a low frequency vibration from the driving motor acts on the cone center, the

cone moves as a whole as shown in Fig. III by dotted positions 1, 2, 3 and 1, 2, 3 imparting vibrations to an area of air the size of the whole cone. At low frequencies the weight of the cone does not offer much in ertia, neither does the air offer much re sistance to being moved. The felt rings 6 and 7 offer enough resistance to being bent that 0 they transmit the cone motion from zone 1 to zone 2 and from zone 2 to zone 3. Hence the whole cone vibrates the same as an ordinary undivided cone.

lVhen a medium frequency force though acts on the center of the cone as in Fig. IV, the inertia of the cone and air is greater, and the outer zone 3, which is the heaviest and acts on the largest area of air, offers more inertia to being moved than felt ring oli'ers resistance to being bent: hence outer zone remains stationary as shown at 3. Zone 2 though does not have as much inertia as zone 3, and belt 6 offers enough resistance to being bent to transmit some of vibration 11 of zone 1 to zone 2 as shown by dotted portions 22.

At high frequencies, Fig. V shows that even zone 2 offers more inertia to being moved than felt ring 6 offers resistance to be ing bent, so the Vibration 1-1 of zone 1 is not transmitted to zone 2 but ends in felt 6. Thus at high frequencies only central portion 1 of the cone vibrates and imparts sound waves to the air.

A much smaller diameter of cone is reqnired to transmit the high pitch vibrations to the air than the low pitch vibrations and this area regulation according to pitch is automatically obtained in this invention as has just been explained. IVhen frequencies other than the low, medium and high are reproduced, the movement of the zones is not as definitely bounded as shown in III, IV and V but is an average. Thus when a frequency between low and medium is reproduced, zone 3 will not be vibrating as far as is shown at 3 8 in Fig. III, but will not be stationary as shown at 3 in Fig. IV.

From above description of the action of the zones and the resistantly flexible connecting rings, it may be seen that if a cone is designed with the distance from the cone center to the outside edge of any zone less than one half the wave length of the shortest wave length of the vibrations to be reproduced in that portion of the cone, and the soft connecting material is selected for the proper resisting force; that no portion of the cone will be vibrating in reverse phase to that of the driving motor and the action of the cone will approach ideal piston action at all frequencies for which it has been designed. Li e in the cones of my application Serial No. 755,056, filed Dec. 10, 19241 there is a very small amount of interfering vibrations in the new cones herein described, due to the reflection of the vibration waves from the edge of the cone back toward the center, for the felt or other soft material at the edge of the cone and end of each zone is aperiodical- 1y resistant in nature and the energy reaching the edge of the zone or cone, not transmitted to an outer zone, is absorbed in the soft resistant material.

The manner of connecting the different zones of the cone together by the soft resistant material may be varied considerably. In Fig. VI it is shown as a pad 6 between the zones 1 and 2. In this case the diameter of the inner zone 1 is greater than the diameter of the hole in zone 2. Pad 6 may be cemented, or fastened in any other way, to both zones 1 and 2, or may be fastened to only one zone and merely press against the other zone, which pressure may be made possible, for instance, by loud speaker case 10 pressing against soft material 8 at edge of cone, or any other method.

My improvements are applicable to diaphragms which are not of a true conical shape as for instance those shown in Figs. VII,'VIII and IX.

Fig. VII is an edge view of a diaphragm of concave conical shape for a moving coil type speaker, which cone is made of cloth stiffened with varnish or similar material. My improvements are easily applied to these stiffened cloth cones by simply leaving the stiffening out of a narrow band as shown at G. This unstitfened band acts the same as the felt or other soft resistant material shown in the first figures.

My flerzible connection between zones makes a handy way to combine zones of various kinds or thicknesses of material or zones of various angles or of complicated curves such shown at 1 and 2 Fig. VIII.

In some cases it is adtnntageous to bead over or reinforce the edges of the zones where they join the ring of soft material as is shown at 11 in Figs. VII and VIII.

Fig. IX shows a plan view of a diaphragm with my improvements, which is oval in shape instead of circular. ther sha es also can be used.

By varying the number, width, angle and curvature of zones; kind and thickness of zone material; kind and size of soft resistant connector material, etc., the acoustical performance of a speaker can be varied over very wide limits.

Having thus described my invention, what I claim as new and wish to protect by Letters Patent is:

1. A diaphragm made up of a central rigid zone, a larger rigid zone and connection between the zones made of less rigid material than that of the zones. 7

2. In a loud speaker of the type having a. large diaphragm freely exposed to non-confined air, a conically shaped diaphragm, divided up into a plurality of circular bands, said bands being connected to each other through bands of flexibly resistant material.

CHARLES IV. PE'IERSON.

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