US2027727A

US2027727A - Sound reproducer

Info

Publication number: US2027727A
Application number: US732795A
Authority: US
Inventors: Ernest W Franck
Original assignee: Individual
Current assignee: Individual
Priority date: 1934-06-28
Filing date: 1934-06-28
Publication date: 1936-01-14
Anticipated expiration: 1953-01-14

Description

Jan. 14, 1936 E. W. FRANCK SOUND REPRODUCER Filed June 28, 195

IN V EN TOR. Ewes! h/fianc/n,

Patented Jan. 14, 1936 STATES PATENT OFFICE A Claims.

This invention relates to new and useful improvements in sound reproducing means and has particular relation to a means for reproducing sound from phonograph records.

Amongst its other objects the invention aims to provide a reproducer which is of simple and economical construction whereby it may be produced at low cost, and which will give a clear and loud reproduction of a record, and which may be light in weight.

Another object of the invention is to provide a sound reproducer which is completely self-contained and which is not dependent on the use of any horn or other air-column as a portion of its dampening means.

Other objects and advantages will become apparent from a consideration of the following detailed description taken in. connection with the accompanying drawing wherein a satisfactory embodiment of the invention is shown. However, it will be understood that the invention is not limited to the details disclosed but includes all such variations and modifications as fall within the spirit of the invention and the scope of the appended claims.

In the drawing:

Fig. 1 is a top plan view of the reproducer;

Fig. 2 is a bottom plan view thereof;

Fig. 3 is an edge view looking from the lower side of Fig. 1;

Fig. 4 is a sectional view taken substantially along the line 4-4 of Fig. 1;

Fig. 5 is a perspective view showing a slightly modified form of diaphragm stretching means employed;

Fig. 6 is a similar view showing a further modified form of said means;

Fig. 7 is a perspective view of a stylus holder; and

Fig. 8 is a detail sectional view showing a slight modification of diaphragm.

In the drawing, my improved reproducer is generally designated Ill and as shown comprises a diaphragm supporting means H in the form of an annulus. A diaphragm disc I2 has its edge portion secured in any suitable manner to the supporting ring or annulus I I and as shown the said diaphragm is of celluloid although any other suitable material may be used. Against any selected portion of one side of the disc I2 there is secured, as by a suitable adhesive, a plate I3 of relatively thin wood. If desired, the plate I3 may be of material other than wood as, for example, it may be of relatively still celluloid or any other material which will stiffen the portion of disc I2 to establish a piston motion when oscillating forces are applied to it by means of a stylus as will later appear.

To the side of the diaphragm opposite the plate I3 there is secured a stylus holder gener- 5 ally designated I4 and which may be bent up from sheet metal. This stylus holder includes base portions I6 and portions I1 and I8 extending at right angles to the base portions It. The base portions I6 are suitably secured as by ce- 1() ment or glue to the central portion of the disc I2 and a stylus I9 is held between the portions I! and I8 of the holder. The said stylus is mounted by inserting its blunt end between the holder portions I1 and I8 and then pinching or 15 squeezing said portions together against the stylus. If desired, a drop of adhesive may be used to further secure the stylus in place and to secure the holder portions .I1 and I8 together.

In the manufacture of the improved repro- 2 ducer the plate I3 may be secured to the central portion of the celluloid disc I2 and thereafter the holder I4 containing the stylus I9 may be secured to either side of the diaphragm. This subassembly may then be secured to the supporting ring II by cementing or clamping the edge of the celluloid disc or diaphragm to one edge of said ring, it being understood that such sub-as- .sembly constitutes a diaphragm with a stiifened or non-flexing center. If desired, the disc I2 :mayfirst be clamped. to the supporting ring and thereafter the stiffening plate and stylus holder may be secured to the said disc.

In mounting the disc I2 on its support it is desirable to follow a method whereby all wrinkles are removed from the disc. Thereafter, the thin celluloid disc I2 is tensioned and this is accomplished by pressing the free edges of the walls '20 of a shallow dish or dome shaped member 2| against one side of said disc. In addition to the 40 ring-like wall 20 the member 2I includes a closed outer wall 22 having a raised rib or bead 23 extending partly across the same and through its central portion. The member 2I is held against the disc I2 by means of a spring clip 24 here shown as comprising a wire or rod extending across the support II and having its end portions bent downwardly and. xthen inwardly as at 25 so as to engage against the lower edge of said support .I I. Intermediate its ends the clip 24 is pressed upwardly as at 26 to provide a slight notch in its lower side. This notch receives a portion of the rib .23 whereby to locate the member 2| in the desired position with respect to the support II and the disc I2 to further locate clip 24 the support 2 may becrimped at diametrically opposite points I 2a to receive the arms of the clip.

It will be understood that the clip 24 being resilient or springy, presses the member 2| against the celluloid disc I 2 whereby the latter is tensioned and its central portion within the wall 20 of the member 2| is in a flat stretched condition and of a diameter desired and in the operation of the diaphragm in the reproduction of a record this stretched central portion covered by disc l3 acts as a piston in the reproduction of vertically cut or hill-and-dale records. When the member 2| is not in place a very poor or low volume and indistinct reproduction may be obtained from a record. However, with the member 2| in place a loud metallic reproduction results and to overcome this I insert a damper 21 in a form of a piece of felt or the like into the member 2|.

This means 21 is of compressible material and normally is of a thickness greater than the depth of the member 2| whereby when it is in said member and the member is clamped against the disc |2 the said damper is slightly compressed and is held against one side of the diaphragm. With means 21 in place highly satisfactory reproduction of the desired volume and clarity is obtained. However, the damping means may be other than that shown and may be in the form of a sheet of suitable material secured to the diaphragm by adhesive or may be held in place by a spring. Also, if desired the damping means may be applied to the diaphragm at the side thereof opposite to that on which the member 2| is located.

When the device is used for the reproduction of lateral cut records as distinguished from hilland-dale records the line or bend 28 of the stylus support l4 represents-a fulcrum to change the direction of the force of the lateral vibrations acting through the stylus with the result that the portions of the diaphragm at opposite sides of this line are rocked vertically in opposite directions as the stylus follows the recorded groove of the laterally cut record. To better adapt the reproducer for reproducing such records a shallow-cup-like member 29 (see Fig. 5) should be substituted for the member 2| of Figs. 1 through 4. This member 29 is in all respects similar to the member 2| with the exception that a partition 30 divides the interior of the member 29 into two parts or chambers and when the member 29 is in use its partition 3|] is aligned with the stylus l9 and is pressing against the diaphragm.

Fig. 6 shows a further modification of a tensioning and damping means holder and in this figure the member generally designated 3| is a shallow cup-like member and differs from the member 2| previously described only in that the member 3| has an opening 32 through its outer or back wall portion 33. When the hole 32 is not overly large satisfactory reproduction may be obtained when using a member as 3|. However, when the hole in the wall 33 is enlarged the quality and volume of reproduction is impaired as the size of the hole increases.

In the design of reproducers of this type considerable control over the performance may be exercised by varying the size and weight of this plate l3. It will be readily seen that if this plate is increased in diameter or size so that its edges approach the wall 20 of disc 2| then the diaphragm stiffness is greatly increased. On the other hand, if the disc is decreased in diameter or size, the diaphragm stiffness will be greatly decreased. Thus, by keeping all other dimensions constant, and varying the size of this plate 3 the effective stiffness of the diaphragm may be changed. It is a well known fact that a stretched diaphragm with a mass disposed at its center or about its center will have its own natural period of resonance. In general this resonance frequency may be increased by the use of stiffer diaphragm material, by increased stretch in the diaphragm, or, as I find it often convenient, by increasing the size of plate I3 as just explained.

The resonance frequency of a weighted and stretched diaphragm may also be controlled to a considerable extent by varying the mass of the central portion. Reducing this mass will result in an increased resonance frequency, and increasing this mass will lower the resonance frequency. In general I find it is advisable to keep the mass of the central portion reasonably small, d

and to control the resonance frequency to give the desired performance by selecting the proper size for disc l3 and adjusting the amount of stretch in the diaphragm.

Whenever a stretched diaphragm with central mass is agitated by a vibromotive force whose frequency is near to the resonant frequency of the stretched diaphragm, there is a tendency for the amplitude of the diaphragm excursions to become excessive and cause a buzzing which is very detrimental to the quality of reproduction. In the conventional reproducer this tendency towards buzzing when excited at frequencies close to resonance is usually counteracted by the dampening efiect provided by the air-column load of a horn, megaphone, or car tubes. Because of this effect, the ordinary type of reproducer is quite unsatisfactory when it is not used in conjunction with its horn or air-column load. Certain types of electro-magnetic load-speakers have been made with a diaphragm having large area and large effective mass. The large effective mass of this type diaphragm, together with the low stiffness of the material used resulted in very low resonance frequency. Besides having a relatively low resonance frequency, this type reproducer also has a large area so that a considerable air load is effective as a dampener although there is no air-column as the term is generally used.

In my device, I control this tendency towards too great freedom at the resonance frequency without the use of the usual air-column load, and without resorting to a diaphragm of low stiffness and/or great area. Thenovel means I use will be understood by refeernce to Figs. 1 through 4 and will be seen most clearly by reference to Fig. 4. Here is shown dome-shaped member 2| with wall 26 held against one face of the diaphragm disc I2. It will be seen that with the damping material 21, held in engagement with one face of the diaphragm |2 as before described the entire area of the diaphragm within the wall 20 which is engaged by the dampening material is effectively uniformly loaded in the sense that each element of area of the diaphragm Within the wall 20 must actually do work on the damping material as it vibrates. I find that the best damping materials for use here are certain kinds of sponge rubber and certain types of woolen fabric.

Fig. 8 shows a modified construction of means for stiffening the central portion of the disc I 2 so as to have such portion function with a pistonlike movement. In the figure a cone shaped sheet metal piece 34 having a relatively large diameter flange 35 is secured to the disc 12. The flange is cemented or otherwise secured to the disc and stiffens the latter and the cone has a stylus 36 secured thereto as shown.

In some forms of my invention I make use of still another form of damping, which, while usually not suflicient in itself to control the diaphragm at resonance, is of distinct benefit when used in combination with the method of diaphragm loading described immediately above. When a closed member as M is employed and the free edge of its wall 28 is pressed tight against the disc 52 a seal is established and any movement of the diaphragm results in compression and expansion of the air in the member 2i and this constitutes a load on the diaphragm. This is true of course only when the cup or member is shallow and closed at its back.

Having thus set forth the nature or" my invention, what I claim is:

1. In a sound reproducer, a supporting means, a diaphragm comprising a sheet supported against said means, an annulus held tight against said sheet to produce a plane radial tension in the diaphragm, a stylus holder connected with said diaphragm, and damping means engaging the diaphragm within said annulus.

2. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm, tensioning means pressing the free edge of said member against the diaphragm to produce a plane radial tension in a central portion thereof, a stylus holder connected with the diaphragm, and damping means within said member against the diaphragm.

3. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow metal cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, tensioning means pressing the free edge of said member against the diaphragm, a stylus holder connected with the diaphragm, and damping means engaging the diaphragm.

4. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow rigid cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly or" said supporting means, tensioning means pressing the free edge of said member against the diaphragm, a stylus holder secured to the diaphragm, and damping means within said member against the diaphragm.

5. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow rigid cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, a spring clip spanning said supporting means and having its intermediate portion pressing against said member to press its free edge against the diaphragm and produce a plane radial tension in the latter, and a stylus holder connected with the diaphragm.

6. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, a spring clip spanning said supporting means and having its intermediate portion pressing against said member to press its free edge against the diaphragm and produce a plane radial tension in the latter, a stylus holder connected with the diaphragm, and a damping means within said member and pressed against the diaphragm thereby.

7. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, a rib on the outer surface of the back of said member, a spring clip spanning said supporting means and clipped thereto and having a notch intermediate its ends receiving a portion of said rib to locate said member with respect to the diaphragm, said clip pressing the free edge of said member against the diaphragm to produce a plane radial tension in the latter, and a stylus holder connected with the diaphragm.

8. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a stifiening member secured to and concentric with said diaphragm, a shallow rigid cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, tensioning means pressing the free edge of said member against the diaphragm to produce a plane radial tension in the latter, a stylus holder connected with the diaphragm, and damping means within said member against the diaphragm.

9. In a sound reproducer, a supporting means, a diaphragm supported at its edge by said means, a stifiening plate secured to the central portion of the diaphragm at one side thereof, a sheet metal stylus holder connected with the central portion of said diaphragm and including a flat portion secured to the opposite side of said diaphragm and a pair of portions projecting outwardly of the diaphragm, and a stylus secured between said outwardly projecting portions by being gripped between them.

10. In a sound reproducer, a supporting means, a diaphragm supported at its edge by said means, a stiffening member secured to the central portion of one side of the diaphragm, a sheet metal stylus holder secured to the central portion of the other side of said diaphragm and including a fiat portion secured to said diaphragm and a pair of portions projecting outwardly 01' the diaphragm, and a stylus secured between said outwardly projecting portions by being gripped between them.

11. In a sound reproducer, a supporting means, a diaphragm supported by said means, an annulus, a spring clip holding said annulus tight against said diaphragm in spaced relation to said supporting means to produce a plane radial tension in the diaphragm, and a stylus holder connected with said diaphragm.

12. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, an annulus held tight against said diaphragm in spaced relation to said supporting means to produce a plane radial tension in the diaphragm, a stylus holder connected with said diaphragm, damping means, and means pressing said damp ing means against the diaphragm.

13. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow rigid cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, 'tensioning means pressing the free edge of said member against the diaphragm and tensioning the latter, a stylus holder connected with the diaphragm, damping means, and means pressing said damping means against the diaphragm.

14. In a sound reproducer, a supporting means, a diaphragm comprising a sheet supported against said means, a rigid annulus held tight against said sheet to tension the diaphragm, a stylus holder connected with said diaphragm, and a damper engaging the diaphragm within said annulus.

15. In a sound reproducer, a supporting means, a diaphragm supported by said means, an annulus having an edge against said diaphragm, a spring clip spanning said supporting means and causing the edge of the annulus to press against the diaphragm and produce a plane radial tension in the latter, and a stylus holder connected with the diaphragm.

16. In a sound reproducer, a supporting means, a diaphragm supported at its edges by said means, a shallow cup-like member disposed with its open side toward the diaphragm and with its free edge against the diaphragm inwardly of said supporting means, tensioning means pressing the free edge of said member against the diaphragm and producing a plane radial tensioning of the latter, a stylus holder connected with the diaphragm, damping means, and said shallow cuplike member pressing said damping means against the diaphragm.

17. In a sound reproducer, a supporting means, a diaphragm supported by said means, a shallow rigid cup-like member completely closed at one side and disposed with its open side toward the diaphragm and with its free edge against the diaphragm, tensioning means pressing the free edge of said member against the diaphragm, and a stylus holder connected with the diaphragm.

18. In a sound reproducer, a supporting means, a diaphragm supported by said means, a rigid member having an edge against said diaphragm, a spring clip spanning said supporting means and causing an edge of the member to press against the diaphragm and tension the latter, and a stylus holder connected with the diaphragm.

19. In a sound reproducer, a supporting means, a diaphragm supported by said means, an annulus having an edge against said diaphragm, spring means causing the edge of the annulus to press against the diaphragm and produce a plane radial tension in the latter, and a stylus holder connected with the diaphragm.

20. In a sound reproducer, a supporting means, a diaphragm supported by said means, a member having an edge against said diaphragm, spring means causing the edge of said member to press against the diaphragm and produce a plane radial tension in it, and a stylus holder connected with the diaphragm.

ERNEST W. FRANCK.