US2205670A - Sound translating device - Google Patents

Description

June 25, 1940.

H. c. PYE 2,205,670

SOUND TRANSLATING DEVICE Fiied July 22, 1938 2 Sheets-Sheet 1 u 1 1. ll 40111111111511!!! umnnull/11111111111!!! IN VENTOR.

, Harald]: F e BYMMIMW ATTORNE Y5.

Patented June 25, 1940 UNITED STATES PATENT OFFICE SOUND TRAN SLATING DEVICE Application July 22,

7 Claims.

1938, Serial No. 220,759

The present invention relates to sound transfree vibration, together with means associated lating devices and more particularly to improvements in diaphragm assemblies for telephone receivers.

In the conventional telephone receiver, a diaphragm is provided which forms a part of the magnetic circuit of the associated field structure and vibrates in response to variations in the flux traversing the field structure and occasioned by signal currents flowing through the voice coils wound on the pole pieces of the field structure. Usually the diaphragm is mounted for substantially free vibration by clamping its outer edge between two of the field structure housing members. As thus mounted, the diaphragm has a frequency-response characteristic over the operating range which peaks at frequencies in the vicinity of the natural frequency of vibration of the diaphragm and falls off at the higher frequencies of the operating range due to the mechanical inertia of the diaphragm. For the purpose of flattening the resonance peak in the response characteristic of the diaphragm, various forms of friction damping means and damping chambers have been used. In some cases it has also been the practice to use resonating chambers for the purpose of enhancing the response of the diaphragm at the high frequency end of the operating range.

It is an object of the present invention to provide an improved assembly for the moving system of a sound translating device which is so arranged that an improved and relatively flat response characteristic is obtained throughout the operating frequency range.

It is another and rmare specific object of the invention to provide in a device of the character described an improved and exceedingly simple arrangement of the parts whereby a damping effect is exerted on one side of the diaphragm or vibratory member and a resonating chamber for enhancing the response of the diaphragm at the high frequency end of the operating frequency range is provided on the other side of the diaphragm.

It is a further object of the invention to provide a simple, rugged, compact and economical assembly arrangement for the vibratory member of "a sound translating device.

attained by providing, in a sound translating device, a moving system which comprises a ,vi-

bratory member having a predetermined response characteristic over :an operating fre- 55 quency range when arranged for substantially In general, the objectsas set forth above arewith one side of the vibratory member for altering the response of the moving system over one band of frequencies within the operating range-and means associated with the other side of the vibratory member for altering the response of the moving system over a diflerent band of frequencies within the operating frequency range. More particularly, the diaphragm or vibratory member of the device is mounted within 10 the housing of the device, together with an inner plate which is displaced from the diaphragm to provide a damping chamber adjacent the inner side of the diaphragm. A structure comprising a second plate mounted upon the inner plate in 1 spaced-apart relation is provided for defining a passage communicating with the chamber, the dimensions of the passage being such that the response of the diaphragm is substantially reduced at frequencies approaching the natural frequency of vibration of the diaphragm. The housing for the device is also provided with a cover portion which is displaced from the diaphragm to define a second chamber adjacent the outer side of the diaphragm. The cover portion of the housing is provided with a passage extending therethrough and communicating with the second chamber, the dimensions of this passage being so proportioned that the response of the diaphragm is substantially increased at the upper end of the operating frequency range. Further features of the invention pertain to the particular arrangement of the assembly whereby the two chambers described above are provided.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figure 1 is a side sectional view illustrating a sound translating device having incorporated therein the features of the invention as outlined above, Fig. 2 is an elevational view of the device shown in Fig. 1 with the diaphragm assembly removed therefrom, Fig. 3 is an exploded view illustrating .the method of assembling the device shown in Fig. 1, Figs. 4 and 5 are detail views of certain of the elements shown in Figs. 1 and 3, Figs. 6 and 7 are detail views of modifications of certain of the elements embodied in the device, and Figs, 8 and 9 are graphs illustrating the effect of providing the two' chambers on the two sides of the diaphragm in the manner referred to above.

Referring now more particularly to Fig. 1 of the drawings, there is illustrated a sound translating device in the form of a telephone receiver of the cell type mounted within the cup-shaped portion 1 of a hand set handle. The cell is supported between the rim of the cupshaped opening and the inner wall of a cupshaped ear piece 8 which is adapted to be screws; on the threaded portion of the portion 1 in the manner illustrated. The ear piece is provided with eight sound transmission holes 9 in the bottom wall thereof and also with a cutaway portion which forms a chamber adjacent the cover member of the cell. The receiver cell comprises a cup-shaped housing l constructed of non-magnetic conductive material, such, for example, as an aluminum alloy, and having mounted thereon the magnetic field structurematerial, such, for example, as silicon steel,

having a high A. C. permeability. The magnetic field structure of the device comprises a pair of pole pieces l4 and I5, upon which the voice coils l6 and ll of the receiver are wound, and a permanent magnet 18 of the bar type which, in conjunction with the diaphragm l3 and the pole pieces l4 and I5, forms a substantially closed magnetic c'rcuit interrupted only by the narrow air gaps extending between the pole faces of the pi Cos l4 and I5 and the diaphragm i3. More p;:.rticularly, the pole pieces 04 and I5 are re specai' ly provided with offset extensions '43. and '55, which extend through snugly engaging spaced pfart openings l9 and 20 cut in the bottom of the cup-shaped housing member Ill and are arranged to receive a magnet member I8 therebetween. For the purpose of retaining the magnet bar l8 within the pole piece extensions I45 and 15s, the upper corners, and more particularly the edges, of the magnet bar are beveled as indicated at '89. and lab, and the upstanding corner portions of the pole piece extensions He and 15;. are bent over to engage the beveled edges the magnet bar in the manner best illustrated in Fig. 5. Preferably, the length of the bar is just slightly greater than the spacing between the pole piece extensions I411 and I5; so that the oppositely disposed bases of the pole piece etr'iensions Ma and I5& firmly engage the adjacent faces of the magnet bar to provide a low reluctance connection between the pole pieces and the magnet bar. It will be noted that the mounting arrangement just described serves to restrain the magnet bar 18 against movement in any direction and, thus, this bar is rigidly held in place when the assembly of the device is completed.

The magnet bar I8 is preferably formed of an alloy consisting of nickel, aluminum and iron, such, for example, as the alloy known as Alnic; while the pole pieces I4 and 15 are formed of an alloy comprising approximately 45 per cent nickel and 55 per cent iron, such, for example, as the alloy known as Allegheny electric meta The magnet winding I6 is wound upon the pole piece l4 between winding heads 2| and 22 constructed of insulating material and is insulated aaoacvo from the pole piece M by a layer of insulating material 23 which may, for example, comprise varnished cambric or Empire cloth. The ends of the windings l6 are brought out through slots provided in the inner side walls of the winding heads 2| and 22 to anchoring studs 2'3, and 22a formed integrally with the winding heads 2| and 22, respectively, and projecting therefrom. In a similar manner, the winding I1 is wound upon the pole piece l5 between winding heads 24 and 25 and is insulated from the pole piece l5 by a layer of insulating material 26. The ends of the last-mentioned winding are brought out through slots provided in the inner side walls of the winding heads 24 and 25 to anchor studs 24a and 258. formed integrally withand projecting from the winding heads 24 and 25, respectively. In accordance with conventional practice, the two windings l6 and H are connected in series by soldering together the ends of the windings terminating at the anchor studs 22a and 24a. The remaining two winding terminals are brought out and connected to the connecting terminals of the device which, in the arrangement illustrated, comprises the conductive housing l0 and a U-shaped contact member 21 having its legs straddling the magnet member l8 and secured to the housing [0. More specifically, the ends of the legs of the contact member 21 are bent over and provided with holes, 28a and 28]: therein which register with holes 299. and 29b formed in the housing In. The contact member 21 is mounted upon the housing In by rivets 30a and 30b extending through the openings 28a, 29a, and 28b, 29b, respectively, and is insulated from the housing It] by insulating washers 3'11, 31 32a and 32b in the manner illustrated.

As indicated above, the housing l0 through which the pole piece extensions 4a, and I5; extend is closely coupled with the magnetic circuit of the field structure and effectively constitutes a short-circuited conductor encircling each of the two pole pieces l4 and I5. The close inductive coupling between the housing and the magnetic circuit of the field structure results from the fact that the side walls of the openings l9 and 20 closely embrace the pole piece extensions I48 and I5. to provide support for the field structure and to prevent the entrance of dirt and moisture within the housing l0. With this arrangement, alternating or undulating flux traversing the pole pieces l4 and I5 and the magnet bar l8 necessarily caused induced voltages to be set up in the conductive housing In, so that a portion of the alternating current energy producing the alternating flux is dissipated as hysteresis and eddy current losses in the housing. In order to prevent alternating flux developed during operation of the device from linking with the housing In, there is provided within the housing an auxiliary flux path extending between the two pole pieces. This auxiliary flux path comprises projections I41, and l5s formed integrally with the pole pieces l4 and I5, respectively, and extending toward each other. The adjacent ends of the projections Mn and lit are separated by an air gap 33 which is so proportioned that the magnet bar I8 is not effectively short-circuited and a substantial amount of the steady state flux produced by the magnet I8 is caused to traverse the diaphragm l3. Preferably, this air gap is of the order of .0625 inch. These pole pieces I4 and I5 are stamped from flat stock and during the stamping operation there are cut in the projecting portions Nb and I51 thereof a plurality of openings 34 and 35, which are utilized in securing the pole pieces to the housing I0. More particularly, the pole pieces I4 and I5 are mounted upon the housing III by means of rivets or bolts 35 and 31 extending through the openings 34 and 35, respectively, and through openings 38 and 39 formed in the bottom portion of the housing I and spaced to register with the openings 34 and 35.

The diaphragm assembly comprises, in addition to the diaphragm I3, an inner plate 40, a cover member 4|, an annular supporting and spacing ring 42, and an assembly ring 43. In accordance with one feature of the present invention, the innerplate 40, in conjunction with the diaphragm I3 and the annular ring I2, defines a damping chamber adjacent the inner surface of the diaphragm I3, while the cover member H, in conjunction with the diaphragm I3 and the ear piece 8, defines a resonating chamber adjacent the outer surface of the diaphragm. The dimensions of the damping chamber and of the restricted passages communicating therewith are so proportioned that the peak in the response characteristic of the device caused by the natural period of vibration of the diaphragm I3 is substantially reduced to flatten the over-all frequency response characteristic of the device. More particularly, the inner plate 40, which is constructed of non-magnetic material, such, for example, as aluminum, is provided with six openings 44 and has mounted thereon in spacedapart relation a fiat annular ring 45 which defines a realtively long, narrow, restricted and annular passage 45 communicating between the interior of the housing I0 and the chamber formed between the plate 40 and the diaphragm I3. By suitably proportioning the size of the holes 44, and the length and width of the restricted passage 45, there is achieved the desired damping effect over the band of frequencies within which the natural period of vibration of the diaphragm I3 is most effective to cause distortion of the over-all response characteristic. Also, the layer of air in this chamber serves artificially to enhance the stiffness of the diaphragm I3, thereby to improve the fidelity of reproduction of the device. Although given by way of example only, the following specifications for the parts defining the dimensions of the damping chamber and the passages communicating therewith have been found to be highly satisfactory in practice:

Inches Diameter of chamber 1.683 Depth of chamber 0.030 Diameter of holes 44 0.076 Depth of passage 45 0.0030 to 0.0040 Width of ring 45 0.319 Outer diameter of ring 45 1.444

As best shown in Fig. 4, the annular ring or plate 45 is separated from the inner plate 40 by means of thin washers 41 and is mounted upon the plate 40 by means of rivets 48 extending through the washers and registering with openings 49 and 50 respectively provided in the plate 40 and the ring 45. As best shown in Fig. 3, the openings 49 and 50 through which the mounting rivets 48 extend are staggered so that the assembly comprising the plate 40 and the ring 45 is prevented from buckling. The plate 40 has formed therein a pair of slots 0a. and 40b through which the pole face ends of the pole pieces I4 and I extend. A cross-slot 40c connecting the two slots 40. and 40b is also provided for preventing the circulation of eddy currents in the plate 40. The dimensions of the slots 40B. and 40s are substantially greater than the cross-sectional dimensions of the pole face ends of the pole pieces I4 and I5 so that relatively large air gaps are provided between the adjacent surfaces of the pole pieces and the plate 40. By virtue of this arrangement, the coupling between the magnetic circuit of the magnetic field structure and the plate 40 is extremely loose and theproduction of eddy currents in the plate is substantially prevented.

An alternative arrangement for providing the restricted passage communicating with the damping chamber is illustrated in Fig. 6. In this arrangement a plurality of annular plates or rings 45a, 45b and 45c are provided which are mounted in spaced-apart and stacked relation upon the inner plate 40 to define a plurality of narrow annular passages connected by staggered openings 54 cut in the enumerated rings. The annular passages are closed at the sides by annular supporting rings 55 and 55 which serve to support the plates 59., 45b and 45c in spaced-apart relation. Rivets indicated at 51 are utilized to secure the stacked assembly to the inner plate 40. The holes 44 provided in the plate 40 register with the restricted passages defined by the stacked plates 55., 45b and 45.: and the spacing between the plates is so proportioned that the response of the diaphragm I3 is substantially re duced at frequencies approaching the natural frequency of vibration of the diaphragm.

Another arrangement for providing the restricted passage communicating with the damping chamber is illustrated in Fig. 7. In this arrangement a plurality of annular plates 58 and 585 are provided which are mounted in spacedapart stacked relation upon the inner plate 40 to define a relatively long' narrow sinuous passage. More particularly, the inner ring 55 is mounted upon the plate 40 by means comprising a spacing ring 59 and rivets 50, and the outer ring 58a is mounted upon the plate 40 by means comprising a spacing ring 5| and rivets 52. The openings 44 provided in the plate 40 register with the sinuous passage thus formed, and the spacing between the rings is so proportioned that the response of the diaphragm I3 is substantially reduced at frequencies in the vicinity of the natural frequency of vibration of the diaphragm.

It will be observed that, in each of the three arrangements respectively illustrated in Figs. 1, 6 and '7 for defining the passage communicating with the damping chamber, the passages are formed parallel with the diaphragm I3. By virtue of this arrangement, only a small amount of space is required to form a passage of any desired length. Moreover, the depth of the passage is easily controlled by using spacing washers or rings of the appropriate thickness to provide the correct depth.

The cover member M, which, in conjunction with the diaphragm I3, defines a resonating .chamber adjacent the outer surface of the diaphragm, is provided with a centrally disposed opening 5I through which sound waves are transmitted from the resonating chamber to the exterior of the device. The cover member H is also provided with a projecting annular portion 52 having a smooth upper surface which is adapted to cooperate with the oppositely disposed lower surface of the annular ring portion I2 of the housing I 0 to clamp the peripheral edge of the diaphragm I3 therebetween. The clamping surfaces of the two annular portions I2 and 52 are so formed that the peripheral edge of the diaphragm i3 is clamped therebetween with uniform pressure at all points around the outer circumference of the diaphragm. The effect of the resonating chamber upon the response of the diaphragm I3 is determined to a certain extent by the narrow chamber formed between the inner bottom wall of the ear piece 8 and the outer surface of the cover member 4i. Actually this second chamber may be considered as a part of the resonating chamber. Preferably, the dimensions of the resonating chamber and of the passage 5| are so proportioned that the natural period of vibration of the chamber occurs at approximately 2700 cycles per second, whereby the response of the moving system is materially enhanced at frequencies lying within the band extending from 2400 to 2800 cycles per second. To achieve this greater response in the frequency band indicated, it has been found that the following dimensions for the resonating chamber and the passages 5| and 9 are satisfactory:

Inches Outer diameter of chamber adjacent diaphragm 1.688 Maximum depth of chamber 0.033 Diameter of passage 5! 0.250 Depth of passage 5| 0.051 Diameter of passage 9 a- 0.1015 Diameter of chamber adjacent ear piece 0.750 Depth of chamber adjacent ear piece 0.062

In constructing the device described above, the terminal member 21 is first mounted upon the housing ID in the manner explained previously, and the extensions Ma and l5a of the pole pieces 14 and I5 are inserted through the openings l9 and 20, respectively. The last-mentioned operation is performed with the windings l6 and I! fully assembled on the pole pieces l4 and I5. After the pole piece extensions '43. and '53, have been inserted through the openings l9 and 20, the magnet member I8, which is at this time demagnetized, is forced between the adjacent opposite side surfaces of the pole piece extensions, and the extensions are pressed toward each other to bring the inner surfaces thereof into firm engagement with the pole faces of the magnet member l8. Simultaneously, the projections Nb and l5b of the pole pieces 14 and i5 are pressed against the bottom wall of the housing l0. While the above-mentioned forces are acting upon the pole pieces l4 and 15, the rivets 36 and 31 are inserted through the openings provided in the housing l and the pole pieces, and the ends thereof are flattened in the usual manner, thereby rigidly to mount the field structure upon the housing In. Also, while the above-mentioned forces are being exerted upon the pole pieces l4 and I5, the upstanding corner portion of the pole piece extensions [49, and I55 are bent over against the beveled corners I89. and I8b of the magnet member l8. After the field structure assembly is completed in the manner just described, the diaphragm assembly is mounted upon the rim of the cup-shaped housing ii). To this end, the inner plate 40 is forced within the snugly engaging side walls of the annular ring H! to abut against the ledge formed by the lower surface of the housing flange II. This operation is performed with the flat annular ring 45 mounted upon the plate 40, and during the performance thereof the pole face ends of the pole pieces l4 and I pass through the slots 40a and it provided in the plate 40. The inner plate 40 is rigaaoaevo idly held within the annular portion ll! of the housing 10 by staking the inner surface of the ring portion 12 at spaced points around the circumference thereof in a well-known manner. Also, a sealed joint is provided between the plate 40 and the pole face ends of the pole pieces l4 and I5 by pouring an insulating compound, such, for example, as Bakelite cement, through the spaces between the side walls of the slots 08. and 40s and the side surfaces of the pole pieces l4 and I5, thereby to insure that the damping chamber shall only be connected with the interior of the housing ill by way of the restricted passage 46 described above. The next step in the construction of the device is to clamp the diaphragm l3 between the clamping surfaces of the two ring portions l2 and 52 projecting respectively from the housing l0 and the cover member 4|. While the diaphragm is clamped in position, the assembly ring 43 with the annular ring 42 inserted or telescoped therein is telescoped over the cover member 4| until the flanged portion 433, thereof engages the tapered surface of the cover member 4|, following which the rim of the retaining ring 43 is bent over as indicated at 43b to engage the underside of the flanged portion ll of the housing I 0. The final step in the construction of the device is that of magnetizing the magnet member l8 by positioning this member in a strong direct magnetic field. After the device is fully constructed it may be mounted within the opening of the cup-shaped member I in an obvious manner.

In the operation of the device constructed and arranged in the manner set forth above, an attractive force is normally exerted upon the diaphragm l3 by virtue of the flux produced in the magnetic field structure by the magnet member l8. Due to the length of the air gap 33, t! magnet member I8 is not short-circuited and a substantial portion of the flux traverses the diaphragm l3. When incoming signal currents traverse the voice coil windings I6 and H, the

steady state flux is increased and decreased in the usual manner in accordance with the undulations of the signa currents. The change in the flux traversing the pole pieces l4 and I5 causes induced voltages to be developed in the closely coupled conductive housing ill. The resulting circulatory currents cause back electromotive forces to be developed which oppose the flux changes in the usual manner. Thus, the reluctance of the portion of the magnetic circuit comprising the permanent magnet l8 and the pole piece extensions 4a and '53. is effectively increased so that the greater portion of the alternating components of the flux traverse the auxiliary path described above and comprising the pole piece projections Mb and I5b and do not link with the housing l0. As a result, only a small portion of the signal current energy is dissipated as hysteresis and eddy current losses in the housing Ill. The variations in the flux traversing the diaphragm l3 cause this diaphragm to vibrate in the usual manner so that sound waves are transmitted by way of the opening 5| to the exterior of the ear piece 8. The provision of the inner damping chamber defined by the plate 40 prevents an excessive response of the diaphragm l3 at frequencies approaching the natural frequency of vibration of the diaphragm. Also, the provision of the resonating chamber defined by the ear piece 8 enhances the response of the moving system at frequencies in the upper portion of the operating range. Thus, a substantially fiat response characteristic typifying good fidelity of reproduction is obtained.

The effect of providing the two chambers on opposite sides of the diaphragm l3 and of varying the dimensions of the passages respectively extending thereto is well illustrated by the graphs shown in Figs. 8 and 9, wherein the response of a typical receiver, measured in decibels above one bar pressure is plotted as a function of frequency. In Fig. 8 the curve A represents the response characteristic of a receiver cell provided with a damping chamber adjacent the inner side thereof and a resonating chamber of the form just described adjacent the outer side thereof; a passage 5| having a diameter of .346 inch being provided in the cover member 4|. It will be noted from an inspection of this curve that the response of the diaphragm drops off appreciably at frequencies above 2200 cycles per second. This decreased response at the high frequency end of the band is due to the stiffness or mechanical inertia of the diaphragm and becomes even more pronounced when the passage 5| is made of larger diameter further to decrease the effect of the chamber resonance on the vibration of the diaphragm. The curve B is the response characteristic of the same receiver provided with a passage 5| havinga diameter of .255 inch rather than a diameter of .346 inch. In the latter case the effect of resonance on the diaphragm is enhanced, so that the response of the diaphragm over the band of frequencies extending from 2200 to 2800 cycles is substantially increased. This increase in response at the high frequency end of the band is accompanied by a slight decrease in response at frequencies within the mid portion of the operating frequency range, but the loss of response at the mid-range frequencies is of no practical importance. The increased pressure output at the high frequency end of the frequency range, however, results in a marked improvement in the fidelity of reproduction of the receiver.

Referring now to Fig. 9, the curves there reproduced illustrate the effect of providing the damping chamber adjacent the inner side of the diaphragm and of varying the dimensions of the restricted passage communicating with this chamber. More particularly, the curve C depicts the response characteristic of the diaphragm when provided with a resonating chamber adjacent the front or outer side of the diaphragm and no damping chamber is provided adjacent the inner side of the diaphragm. Due to the resonant response of the diaphragm at frequencies approaching the natural frequency of vibration of the diaphragm this response curve peaks sharply at approximately 1175 cycles per second. This sharp peak is indicative of distortion in the reproduced output of the receiver. The curves D, E and F depict the response characteristic of the same receiver when provided with a damping chamber adjacent the inner side thereof and constructed in the manner shown in Fig. 1. The differences in the three last-mentioned curves represent the change in the response of the diaphragm effected when the dimensions of the passage communicating with the damping chamber and defined by the plates 40 and 45 are changed. Thus, the curve D depicts the response characteristic of the receiver when a passage 46 having a depth of .004 inch is used; the curve E represents the response of the receiver when a passage 46 having a depth of .003 inch is used; and the curve F illustrates the response of the receiver when a passage 46 having a preferred depth of .0035 inch is used. It will be observed that the provision of the damping chamber having a passage 46 communicating therewith materially reduces the response of the diaphragm at frequencies in the low frequency end of the range and approaching the natural frequency of vibration of the diaphragm. Moreover, by properly proportioning the dimensions of the passage 46 the response characteristic is rendered substantially fiat over the major portion of the operating frequency range. This flattening of the response characteristic represents a marked improvement in the-fidelity of reproduction of the device.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a sound translating device, a moving system comprising a vibratory diaphragm and having a predetermined response characteristic over an operating frequency range when arranged for substantially free vibration, means defining a first chamber adjacent the inner side of said diaphragm having a passage communicating therewith, the dimensions of said passage being so proportioned that said first chamber acts substantially entirely as a damping chamber effective substantially to decrease the response of said moving system at frequencies within a band of frequencies extending toward the low frequency end of said range, and means defining a second chamber adjacent the outer side of said member having a passage communicating therewith, the dimensions of said last-mentioned passage being so proportioned that said second chamber acts substantially entirely as a resonating chamber effective substantially to increase the response of said moving system at frequencies within a band of frequencies extending toward the high frequency end of said range.

2. In.a sound translating device, a housing, a diaphragm mounted within said housing, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted within said housing for substantially free vibration, said diaphragm having a natural frequency of vibration such that said response characteristic peaks at frequencies within the low frequency end of said range, means defining a first chamber adjacent the inner side of said diaphragm having a passage communicating therewith, the dimensions of said passage being so proportioned that said first chamber acts substantially entirely as a damping chamber effective to remove said peak from the response characteristic of said diaphragm and substantially to decrease the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 1500 cycles per second toward the low frequency end of said range, means defining a second chamber adjacent the outer side of said diaphragm having a passage communicating therewith, the. dimensions of said last-mentioned passage being so proportioned that said second chamber acts substantially entirely as a resonating chamber effective substantially to increase the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 2000 cycles per second toward the high frequency end of said range.

3. In a sound translating device, a housing, a diaphragm mounted within said housing, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted within said housing for substantially free vibration, said diaphragm having a natural frequency of vibration such that said response characteristic peaks at frequencies in the low frequency end of said range, an inner plate mounted within said housing and displaced from said diaphragm to define a first chamber adjacent the inner side of said diaphragm, means comprising a second plate mounted upon said inner plate in spaced apart relation for defining a passage communicating with said first chamber, the spacing between said plates being so proportioned that said first chamber acts substantially entirely as a damping chamber effective to remove said peak from the response characteristic of said diaphragm and substantially to decrease the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 1500 cycles per second toward the low frequency end of said range, means defining a second chamber adjacent the outer side of said diaphragm having a passage communicating therewith, the dimensions of said last-mentioned passage being so proportioned that said second chamber acts substantially as a resonating chamber effective substantially to increase the response of said diaphragm at frequencies within a band of frequencies extending from a frequency of the order of 2000 cycles per second toward the high frequency end of said range.

4. In a sound translating device, a cup-shaped housing member having an outwardly extending ledge displaced inwardly from its rim along the inner wall thereof, a diaphragm having its outer edge clamped to the rim of said housing member, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted upon said housing member for substantially free vibration, an inner plate mounted upon said ledge within said housing and displaced from said diaphragm to define a chamber adjacent the inner side of said diaphragm, and means comprising a second plate mounted upon said inner plate in spaced apart relation for defining a passage communicating with said chamber, the spacing. between said plates being so proportioned that the response of said diaphragm is substantially altered in one sense over a band of frequencies within said range.

5. In a sound translating device, a cup-shaped housing member having an outwardly extending ledge displaced inwardly from its rim along the inner wall thereof, a diaphragm having its outer edge clamped to the rim of said housing member, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted upon said housing member for substantially free vibration, an inner plate mounted upon said ledge within said housing and aaoaevo displaced from diaphragm t0 define a chamber adjacent the inner side of said diapm'agm, said plate having a plurality of spaced apart openings therein, and means con'orising a flat annular plate overlying said :pening and mounted upon said inner plate in spaced apart relation for defining a passage communicating with said chamber, the spacing between said plates being so proportioned that the response of said diaphragm is substantially altered in one sense over a band of frequencies Within said range.

6. In a sound translating device, a housing, a diaphragm mounted within said housing, said diaphragm having a predetermined response characteristic over an operating frequency range when mounted within said housing for substantially free vibration, an inner plate mounted within said housing and displaced from said diaphragm to define a chamber adjacent the inner side of said diaphragm, said inner plate being constructed of non-magnetic condui iive material and being provided with a pair of spaced apart openings connected by a cross-slot, a field structure 'at least partially enclosed by said housing and including pole pieces projecting through said openings out of contact with the walls thereof, insulating material closing said cross-slot and the space between said pole pieces and the walls of said openings, and means comprising a second plate mounted upon said inner plate in spaced apart relation for defining a passage communicating with said chamber, the spacing between said plates being so proportioned that the response of said diaphragm is substantially altered in one sense over a band of frequenries within said range.

7. In a sound translating device, a cap-shaped housing member having an outwardly xtending flanged portion carrying an annular rim a diaphragm adapted to have its outer edge clamped to said rim, said diaphragm having a predetermined response characteristic over an operating frequency range when clamped to said rim for substantially free vibration, a cover member provided with an annular surface for clamping the edge of said diaphragm to said rim and having a portion displaced from said diaphragm to define a chamber adjacent the outer side of said diaphragm, said cover member being provided with a passage communicating with said chamber, the dimensions of said passage being so proportioned that the response of said diaphragm is substantially altered over a band of frequencies within said range, means comprising an assembly ring having a flange engaging the outer side of said cover member and adapted to have its side walls bent over to engage the flanged portion of said housing member for clamping said cover member and said diaphragm to said rim, and a supporting ring telescoped within said assembly ring and surrounding said annular rim and the outer edge of said cover member.

HAROLD C. PYE.

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