US3403235A

US3403235A - Wide-range loudspeaker

Info

Publication number: US3403235A
Application number: US440373A
Authority: US
Inventors: Bishop Nathaniel
Original assignee: NEWMARKETS Inc
Current assignee: NEWMARKETS Inc
Priority date: 1965-03-17
Filing date: 1965-03-17
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24

Description

Sept. 24, 1968 N. BISHOP 3,4 5

WIDE-RANGE LOUDSPEAKER Filed marh'l v, 1965 2 Sheets-Sheet 1 INVENTOR. 7157 c? NATHANIEL BISHOP Sept. 24, 1968 N. BISHOP 3,

WIDE-RANGE LOUDSPEAKER Filed March '17, 1965 2 Sheets-Sheet 2 INVENTOR. NATHANIEL BISHOP ATTOR/VEVI United States Patent 3,403,235 WIDE-RANGE LO'UDSPEAKER Nathaniel Bishop, Fairfield, Conn., assiguor to Newmarkets, Inc., Fairfield, Conn., a corporation of Connecticut Filed Mar. 17, 1965, Ser. No. 440,373 Claims. (Cl. 179115.5)

ABSTRACT OF THE DISCLOSURE A loudspeaker capable of reproducing a wide range of audible frequencies and having a low deviation from level response is disclosed. The loudspeaker of the invention can be effectively operated in an enclosing structure only slightly larger than the loudspeaker itself. The disclosed loudspeaker includes a member, associated with the speaker cone suspension means, extending over and covering the larger end of the speaker cone. This covering member is transparent to sound emanating from the speaker cone and, advantageously, has friction loss damping characteristics and can, if desired provide a low frequency barrier between the front and back of the speaker cone.

The present invention relates to loudspeakers and is directed more specifically to improvements in the construction of loudspeakers whereby the frequency response of a loudspeaker of given size may be effectively extended on the low frequency end of the range and the smoothness of response throughout the attainable range is increased.

In conventional sound reproduction systems it is customary to utilize a plurality of speaker units, usually including a high frequency tweeter unit and low frequency woofer unit. The use of two speaker units naturally increases the size and cost, and at least the woofer unit typically is of relatively large size, such that a complete woofer-tweeter unit may represent a physically bulky and unsightly item of household furniture. In addition, the typical, conventional system, consisting of more than one speaker unit for a given channel, may represent a significant item of expense in a reproduction system.

Although it may be desirable to utilize relatively large size speaker units for achieving high power levels of bass response, it is more often the case of a typical household hi-fi reproduction system that separate tweeter and woofer speaker units are required because of the relative inability of a single speaker to deliver with flat response over the entire hi-fi frequency ranges. It is thus one of the basic objectives of the present invention to provide a novel and improved speaker system, incorporating a single speaker unit, which is so constructed as to deliver a very flat response over an extended range of frequencies. With the speaker of the invention, a hi-fi system of adequate household level can be achieved using a single 3 /2 or 4 /2 inch speaker, and because of the advantages realized by the novel design of the invention, the speaker can, if desired, be housed in a small cubic closure. Among other things, this enables individual hi-fi speaker systems to be manufactured in such small sizes as to be readily concealable, or at least able to be unobtrusively placed, in the room.

I have been able to confirm that a remarkably level response characteristic is obtainable over a range of frequencies far in excess of conventional design standards if certain design parameters are followed. To some degree, these design parameters are known in theory, but their realization in a single unit speaker of practical, economical design has been elusive. Primarily, a flat response speaker must incorporate a minimum movable mass, represented by a rigid speaker cone and voice coil, in conjunction with a supporting means for the mass of high enough compliance in the direction of movement of the cone. In addition, I have established that, to attain the desired compliance and low free space resonance in a small and light cone-voice coil structure, the suspension means must be limited to one plane at right angles to the axis to the cone and voice coil, preferably at the outer periphery of the cone. The material or arrangement of materials utilized for suspension should be increasingly absorptive of cone surface vibrations with increasing frequencies and, when taken together with the speaker cone and voice coil, must have a free space resonance well below the lower limit of the desired response range. The structure must provide for opacity to low frequency pressure differences between the front and rear surfaces of the speaker cone. If the cone is suspended from an annular margin outward to the frame, the necessary opacity may be derived from the suspension material itself. But if the cone is suspended from an annular margin inward to the cone axis, in accordance with another aspect of the invention, then the suspension material must, of course, be transparent to pressure differences.

In addition to having the characteristics mentioned above, a practical, economical single unit speaker system must utilize components available on an economical basis and must be capable of controlled production and assembly. To this end, the speaker of the invention incorporates many speaker components of essentially conventional design and construction. By way of example, in the practice of the invention it is feasible to utilize a speaker substantially in accordance with the Model P5V3 speaker manufactured by Jensen Manufacturing Company, making modifications therein with respect to the suspension of the speaker cone. The advantageous results of the invention may be achieved, using such conventional speaker components, by eliminating altogether the customary suspension facilities for the small end of the cone and reconstructing the suspension facilities for the large end of the cone in accordance with the principles of the invention. In particular, the outer edge of the otherwise relatively soft, pliable paper cone is rigidified by means of a light, annular reinforcing element, and the reinforced cone edge is connected to the speaker frame, surrounding or within the cone, by high compliance sus-. pension elements having the characteristics mentioned above. Reinforcement of the suspension plane of the cone is important, inasmuch as, according to the invention, both the speaker cone and the compliant suspension elements are of a distortable nature, and the reinforcement serves to isolate the cone itself from the distorting forces applied by the suspension elements and vice versa, and thereby prevent distortion of the cone and of the voice coil carried thereby.

Pursuant to one aspect of the invention, suspension arrangements are provided for the speaker cone which, in addition to affording superior axial compliance, serve to introduce friction-loss damping of nodal vibrations within the cone, which tends to occur at higher frequencies and normally causes sharp changes in response. This combination provides maximum flatness of response over the operative range of the system.

In one specific physical embodiment of the invention, the speaker is supported by compliant means extending radially outward to the cone from a fixed support within the cone envelope. This arrangement is advantageous for the reason, among others, that a relatively large suspension radius is available in a speaker of small size. The suspension material is relatively transparent to the pressure variations produced by cone vibration, but includes friction-loss damping characteristics for improving flatness of response.

For a better understanding of the invention, reference should be made to the following detailed description and to the .accompanying drawing, in which:

FIG. 1 is a front perspective view of a speaker system incorporating principles of the invention;

FIG. 2 is a cross-sectional view, taken generally along line 2-2 of FIG. 1;

FIG. 3 is an enlarged, fragmentary, cross-sectional view taken generally along line 3-3 of FIG. 1;

FIG. 4 is an enlarged, fragmentary, cross-sectional view of a second modified form of theinvention;

FIG. 5 is a fragmentary, cross-sectional view of a third modified form of the invention; and

FIG. 6 is a fragmentary, cross-sectional view of a fourth modified form of the invention.

Referring now to the drawing, and initially to FIGS. 1-3 thereof, the reference numeral 10 designates a housing or enclosure for the speaker unit, which may be of cubic form. In keeping with the objective of minimizing the physical bulk of the system, the housing 10 is designed to have minim-um dimensions in relation to the electromechanical characteristics of the speaker unit itself. As shown in FIG. 2, the front of the housing 10 is open and receives a speaker unit, generally designated by the reference numeral 1.1, of a type incorporating features of the invention.

The speaker unit 11 includes a flat mounting flange 12, which is somewhat greater in its principal dimensions than the size of the front opening of the housing 10 and is arranged to be secured to the housing as by means of screws 13. A speaker frame 14, of more or less conical configuration, is adjustably or permanently secured to the back surface of the mounting flange 12, by suitable fasteners 15. Typically, the fasteners 15 may provide a permanent connection between the flange 12 and the frame 14, although it may be desirable in some cases to provide for limited adjustment of the frame .14, in the plane of the flange 12, for optimizing alignment between relatively movable parts of the speaker, as will appear.

In accordance with conventional speaker construction, the back portion 16 of the speaker frame mounts an annular permanent magnet 17 and an axially projecting pole piece 18 disposed concentrically within the magnet 17. The magnet 17 and pole piece 18 form a narrow cylindrical air gap 19, as indicated in FIG. 2.

In a low cost speaker of conventional construction, it is customary to provide a speaker cone 20, formed of a light paper material. conventionally, the cone 20 is suitably suspended from the speaker flange 12 by an integral cone flange formed of the paper material of the cone itself and joined to the main body of the cone by an annular flexible region. In addition, conventional constructions usually include means for supporting the inner or small end of the cone. In accordance with the invention, however, these conventional suspension facilities have been replaced by advantageous and improved arrangements according to the invention, to be described.

At the center of the speaker cone 20 there is mounted, in accordance with conventional practice, a cylindrical element 21, which projects rearward of the speaker cone and concentrically into the annular air gap 19. Adjacent its rearward end, the cylindrical element 21 mounts a small coil 22, referred to as a voice coil, which is more or less centrally positioned with respect to the axial end limits of the air gap.

As is well known, actuation of the speaker, to produce audible sounds, is effected by electrical energization of the voice coil 22 with audio frequency currents in such a way as to cause the speaker cone 20 to move axially in a direction determined by the direction of current flow in the voice coil. For energization of the coil 22, suitable lead-in conductors 23 connect the voice coil 22 with a terminal block 24 on the speaker frame.

In order to achieve faithful conversion or transduction of audio frequency electrical signals into audible sounds,

however, it is necessary that the speaker cone 20 respond faithfully to the energizations of the voice coil 22. In accordance with the present state of the art, it is not yet known how to achieve wide-range, faithful audio reproduction in a single cone speaker unit, and in a typical high fidelity system it is conventional to employ at least two and sometimes a larger number of speaker cones, each optimized to .a given frequency range. The construction of the present invention, however, enables the faithful response range of a given speaker assembly to be significantly increased and affords more uniform speaker response within the limits of the increased range, such that, in any case, speaker performance is significantly improved and, for at least some non-professional high fidelity reproduction systems, it may be feasible to utilize a single speaker cone according to the invention in place of the customary plurality of speaker cones without noticeable reduction in the quality of sound reproduction. It should be realized, however, that the advantages of the unique loudspeaker design outlined herein are not limited to use in a small single speaker system but may be applied to advantage in speakers of larger size or smaller size for use in a wide-range loudspeaker system suitable for high acoustic level usage.

The improved performance characteristics of the speaker of the invention .are realized by observing the following conditions in the specific design of the speaker structure: First, the combined mass of the paper cone and voice coil assembly must be maintained as low as is compatible with minimum required cone rigidity; second, the suspension of the paper cone and voice coil assembly must be limited to one plane of suspension at right angles to the axis of the voice coil, .and in the smaller size cones this plane is preferably the plane of the outer edge of the cone; third, provision must be made for rigidifying the pliable cone material in the plane of suspension; fourth, the material used for cone suspension must have such compliance characteristics that, when resonated with the mass of the cone and voice coil assembly, it provides a free space resonance substantially lower than the lower limit of the desired range of acoustical response; finally, the suspension system, or, if the cone is suspended from within its envelope, other facilities, must be so arranged in relation to the frame and housing elements as to provide opacity to low-frequency pressure differences between the front and rear surfaces of the paper cone as well as to provide for absorption characteristics with respect to nodal cone vibrations at increasing frequencies.

In accordance with the above conditions, the illustrated speaker assembly of the invention omits the customary small end cone suspension and provides for supporting of the paper cone 20 solely by its outer flange. A compliant cone supporting material, which I have found to be very advantageous in satisfying the above-mentioned conditions, is a soft chamois, felt, or pliable plastic foam material. In accordance with one specific aspect of the invention, arcuate segments 27 of the suspension material disposed in a circumferential array about the outer edge of the speaker cone 20. The outer edges of the segments 27 are secured to the front surface of the mounting flange 12, by suitable cement or by clamping means, and the inner portions of the segment project radially inward into overlying relation with and are secured, through a reinforcing ring element to be described, to the outermost extremities of the paper speaker COne 20. The suspension elements 27, which may be on the order of 20 mils in thickness, have particularly desirable compliance characteristics with respect to movement of the free inner ends of the element in the direction of the speaker cone axis while, on the other hand, the compliance in the plane of the mounting flange 12 is very low, so that the speaker cone and voice coil assembly can be supported and positioned within the air gap 19 in a reliably precise manner.

In accordance with one of the specific aspects of the invention, the paper cone 20 may be formed of conventional coneforming paper materials, which are relatively soft and distortable. Accordingly, in order to support and precisely locate the voice coil 22, the outer edge flange 28 of the paper cone is reinforced and rigidified, advantageously by being cemented to a reinforcing ring 29 formed of a light, stiff material, such as kraft paper or the like, which serves to rigidify the circular outline of the flange 28 and retain its fiat, planar condition under service conditions. Alternatively, such reinforcement can become a specification of cone fabrication wherein the normal complaint annular ring of thin paper deposit would be supplanted by a thick deposit providing the desired rigidity. The suspension elements 27 have their projecting inner ends cemented to the reinforcing ring 29, substantially as shown in FIGS. 2 and 3, so that the soft, flexible paper cone 20' is isolated from suspension forces which might otherwise tend to distort the configuration of the cone, particularly in view of the cantilever suspension thereof.

As shown in FIGS. 1 and 2, the arrangement and disposition of the chamois suspension elements 27 is such as to form a relatively complete barrier between the front and back sides of the cone 20, to provide for relative opacity to low frequency pressures. In addition, the soft, pliable, absorbent nature of the chamois is such that it serves to absorb vibrations in the higher frequency ranges, with increasing effectiveness as the frequency increases, to provide for a more level response over the operative range of the speaker.

It should be clearly understood, of course, that material other than chamois may be used in the formation of the suspension elements 27, although chamois has been found to be a particularly advantageous material to satisfy the various conditions heretofore mentioned with respect to extremely high compliance in the axial speaker direction, sound opacity and high frequency absorption characteristics, etc. Felt and styrofoam are examples of other advantageous materials which may be substituted for chamois.v

In accordance with the invention, high frequency absorption or damping is obtained by friction loss, so that high frequency energy at specific frequencies which ordinarily cause peaks in the response of the loudspeaker is actually partly dissipated as heat. If the principal material used for cone suspension does not have suitable friction-loss damping characteristics, then special friction-loss material must be utilized in addition to the principal suspension material.

A speaker constructed in accordance with the principles described, and as illustrated in FIGS. 1-3, exhibits superior response characteristics with respect to an otherwise conventional speaker of similar construction, incorporating conventional suspension means adjacent the voice coil and at the outer edge of the cone. Not only is the range of the speaker extended, but it exhibits superior flatness of response with its operative range, such that the undesirable distortions of mid-range peaking and the like are significantly minimized. The advantages are such that an acceptable high fidelity reproduction system may be provided using a single, relatively small diameter (3.5 inch cone) speaker unit, which is light in weight and can be inconspicuously housed and located. While the power limitations inherent in any small diameter speaker impose practical limits on the audibility of very low frequencies, the speaker according to the present invention, in addition to having an extended low frequency range to begin with, has characteristics, probably stemming from its particularly flat response over its operative range, which impart a desirable and advantageous impression of low frequency reproduction through clear reproduction of higher harmonics of the low frequencies, which of course requires an ability to move at the low frequency fundamental.

It is well known in the art of acoustics that the nonlinear characteristics of the human ear will recreate a low frequency if harmonics of this low frequency impinge upon the eardrum. If the harmonics of a pure low frequency tone, say 30' cycles, are not created by distortion in the amplifier, they will not be created by the loudspeaker unless the cone is able to respond or move significantly at the fundamental frequency itself. In the speaker of the invention, even though the fundamental sound pressure reproduced may be low, at low frequencies, the action of the cone serves to produce acoustic harmonics which will beat in the ear and thereby recreate the fundamental tone.

Referring now to FIG. 4, there is shown a modified form of the invention wherein the compliant suspension arrangements for the speaker cone may be provided by a material which, while having the necessary high compliance, does not necessarily have adequate friction-loss damping characteristics. In such case, it is contemplated by the invention that separate friction-loss damping means will be provided in, or in direct association with, the suspension arrangements.

In the FIG. 4 modification, the speaker cone 50, suspended only at its outer edge, may be provided more or less along conventional lines, with an integral annular bellows portion 51, which is designed and/or treated to be highly compliant and permit axial vibratory movements of the cone relative to a rigid mounting flange 52. In accordance with one aspect of the invention, the outer edge portion of the cone 50, just inside its integral connection to the compliant bellows portion 51, is rigidified to provide a stitf cone rim portion 53 of substantially fixed circular configuration and planar form. The necessary rigidity may be imparted by suitable impregnation or other treatment of the rim or by other means, such as cementing thereto a light, stiff reinforcing ring 54. However the reinforcement of the cone rim area is carried out, it must be consistent with maintaining the mass of the cone and its rim as low as practicable.

In order to provide desired damping of high frequency vibrations, the outer flange 55 of the cone suspension portion is secured to the mounting flange 52 through a friction-loss damping element 56, which may be a ring of a material such as felt, Styrofoam, or the like, which will dissipate vibratory movements as heat, to an increasing extent with increasing frequencies. This energy absorption minimizes resonant peaks which otherwise would result from nodal vibrations of the speaker cone and serves to flatten the response of the speaker over its operative range. It will be understood, of course, that separate friction-loss damping means are not required where the compliant suspension means inherently has friction-loss damping characteristics, as in the case of felt, chamois, or like suspension materials.

In the modification of FIG. 5, the suspension means for the speaker extend radially outward to the speaker rim, from a point within the speaker cone envelope, instead of radially inward from a point outside the envelope as in the case of more conventional constructions. In the arrangement of FIG. 5, a mounting flange is secured to the enclosure 10 and supports a frame 61 carrying an annular magnet 62 and pole piece 63. A supporting rod 64 projects axially forward from the pole piece 63 and is secured at its forward end, by means of a mounting plate 65 and suitable fastening nuts 66 to a suspension element 67 which extends radially outward to the rim of the speaker cone 68. Within the purview of the invention, the suspension element 67 may be in the form of a solid disk, substantially closing off the open end of the speaker cone, or it may be of spoked configuration. In any event, either by configuration or by the composition of the material from which it is made, the supporting element 67 is transparent to sound vibrations emanating from the speaker cone 68. Felt or styrofoam are suitable materials for the purpose, and have additional advantages in that In accordance with the invention, the cone 68 of the FIG. 5 modification has its rim portion 69 rigidified, as by a reinforcing ring 70, and the suspension element 67 is secured to the reinforced rim under sufiicient radial tension to support the speaker cone with its voice coil 71 accurately aligned in the air gap. The necessary opacity to low frequency vibration, between the front and back sides of the speaker cone, may be provided by means of a limp annular sealing element 72, of felt or the like, which is connected to the flange 60 and the cone edge but does not perform a support function or otherwise affect the action of the cone 68. Alternatively, the seal may be formed by establishing a close fitting relationship between the outer edge of the suspension element 67 and the inner edge of the flange 60 or by providing an obstructing lip (not shown) in line with the gap between the suspension element and the mounting flange 60.

The modification of FIG. 6 is similar in principle to the modification of FIG. 5, except that a suspension element 80 illustrated to be formed of felt, is mounted on the axis of the speaker cone 81 by a mounting bracket 82 secured to the front of th mounting flange 83. The mounting bracket 82 may be of relatively small dimensions, viewed from the front of the speaker, so as to be relatively non-obstructive to pressure source propagation from the speaker.

In the modification of FIG. 6, the felt suspension element 80 is secured by a short bolt 84, extending into the cone envelope from the mounting bracket 82. The supporting element extends radially outward into secured relation with the reinforced outer rim of the speaker cone, substantially as described in connection with FIG. 5. The bolt 84 may have a shoulder, where it meets the coneside surface of the bracket 82, and a threaded extension beyond the opposite face of the bracket, engaged by a nut 85. The bracket 82 may have an oversize hole permitting adjustment and locking if required in production. The entire assembly also could be welded where manufacturing tolerances permit. If the structure is s'ufliciently rigid, an inward extension of the bolt 84 could be used to support the pole piece within the magnet.

The modifications of FIGS. 5 and 6 incorporate the various inventive principles described with reference to the forms of the invention described in FIGS. l-3 and have, in addition, certain relative advantages with decreasing speaker sizes. In this respect, it is advantageous to prO- vide a relatively long suspension radius between the point of rigid attachment of the suspension means and the point of its attachment to the rim of the speaker cone. Where the suspension is fixed along the speaker axis, the effective length of the suspension means approximates the maximum radius of the speaker cone, in an overall installation which need not be much larger than the speaker itself. To achieve a corresponding effective suspension length in a system in which the suspension means is radially outward of the speaker cone, the overall installation would have to be approximately twice the maximum moving mass, rigidified cone edge, and high comof center-outward cone suspension is the ability of such a structure to give the designer wide latitude in the choice of suspension material, radial length of material used for suspension, and of other design parameters, so as to permit a wide designer control over free space resonance of complete cone and suspension assembly to suit the design requirements.

Speakers of any of the before-described forms are characterized by wide range of response and flatness of response over their operative ranges, while at the same time being of low cost construction. This optimum result is achieved in part by imparting extremely high axial compliance to the speaker suspension without sacrificing its other operating characteristics. By a combination of minimum moving mass, rigidified cone edge, and highly compliance suspension in one plane (that of the rigidified cone edge) speaker cone response has been significantly extended and low frequency resonance reduced well below the lower limit of desired audible response. Although power output of a small speaker is inherently limited at low frequencies, the ability of speakers according to the invention to move efliciently and faithfully in response to low frequency energizing inputs enables the speaker to respond well and with reasonable output power at harmonics of the low frequency fundamentals. This causes or enables the ear to respond to an effective illusion of actually hearing the fundamental lows at a reasonable level.

In conjunction with the foregoing, the speaker of the invention incorporates friction-loss damping means as part of or in conjunction with the complaint suspension arrangements, whereby nodal vibrations are partly dissipated. This provides a built-in mechanical compensation for the normal tendency of a speaker to peak at certain frequencies within the normal range.

A specific feature of the present invention resides in the provision of means, operating in conjunction with highly compliant, single plane speaker cone suspension, for rigidifying the outer edge of the speaker cone without adding unduly to its mass. This may be accomplished, while utilizing a speaker cone of conventional pliable paper material, by providing an annular rigidifying ring, for example, which is cemented or otherwise incorporated with the outer edge of the cone. This arrangement, under service conditions, eliminates dimensional and shape distortion of the cone and hence the voice coil when subjected to the forces involved in movement of the cone in normal operation. With a rigidified low-mass cone, it is possible to utilize suspension arrangements of extremely high compliance, arranged solely about the outer edge of the cone, while still maintaining proper clearances in the air gap in which the voice coil operates.

While the inventive features described 'herein are applicable to advantage with large diameter speakers, the more outstanding results are realized in connection with relatively small diameter speakers, whose range may be extended with significant improvement in the smoothness of response.

Speakers according to the invention exhibit a flatness of response which is characteristic only of more costly and sophisticated speaker systems incorporating conventional principles of construction. In addition, the effective range of response has been extended, particularly at the low end.

It should be understood that the specific forms of the invention herein illustrated and described are intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

I claim:

1. A loudspeaker characterized by a low deviation from level response, which comprises (a) a speaker cone having larger and smaller ends,

(b) a voice coil mounted at the smaller end of the cone,

(c) a supporting frame structure positioned in spaced relation to the speaker cone,

(d) means serving to rigidify an annular area at the larger end of said speaker cone,

(e) radially disposed compliant suspension means connecting said rigidified annular area with said frame structure,

(f) means forming a relatively sound-opaque barrier between the front and back of the speaker cone,

(g) friction-loss damping means associated with said speaker cone, and

(h) said suspension means including a highly compliant solid disk-like suspension element covering the large end of said speaker cone,

(i) said suspension element being transparent to sound vibrations emanating from said speaker cone.

2. The loudspeaker of claim 1 wherein (a) said suspension element forms a sound barrier between the front and back of said speaker cone that is relatively opaque to low frequency vibration.

3. The loudspeaker of claim 1 further characterized by (a) said suspension element having friction loss damping characteristics thereby minimizing resonant peaks and flattening the response of the speaker cone over its operative range.

4. A loudspeaker characterized by a low deviation from level response comprising (a) a speaker cone having larger and smaller ends,

(b) means forming a relatively rigid flange area at the larger end of said cone,

(c) a voice coil mounted at the smaller end of the cone,

(d) a voice coil magnet mounted in fixed relation to said voice coil, and

(e) a highly compliant disk-like suspension element secured to said rigid flange area and substantially covering the larger end of said speaker cone,

(f) said suspension element being transparent to sound emanating from said speaker cone and having fric tion loss damping characteristics thereby minimizing resonant peaks and flattening the response of the speaker cone over its operative range.

5. The loudspeaker of claim 4 wherein (a) said suspension element forms a barrier between the front and back surfaces of the speaker cone, and

(b) said barrier is substantially opaque to low frequency vibrations.

References Cited UNITED STATES PATENTS 1,861,222 5/1932 Minton 181-31 1,877,294 9/1932 George 181-31 1,967,223 7/ 1934 Bostwick 181-31 1,982,443 11/1934 Messick 181-31 2,014,621 9/1935 Jensen 181-31 2,234,833 3/1941 Preston 181-31 2,897,292 7/1959 Van Den Bosch 179-115.5 3,138,667 6/1964 Avedon 181-31 KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, 0.0. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,403,235 September 24, 1968 Nathaniel Bishop It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 59, after "terial" insert are Column 5, line 3, "coneforming" should read cone-forming line 58, "with" should read within Column 7, line 59, "moving mass, rigidified cone edge, and high com" should read diameter of the speaker cone. A unique advantage line 74, "highly" should read high Column 8, line 14, "complaint" should read compliant Signed and sealed this 9th day of June 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. E.

Attesting Officer Commissioner of Patents