US2734591A

US2734591A - Loudspeaker structure

Info

Publication number: US2734591A
Authority: US
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

Feb. 14, 1956 H. F. OLSON EI'AL 2,734,591

LOUDSPEAKER STRUCTURE Filed March 2, 1953 2 Sheets-Sheet l INIENTOR.

Harry 1701/0114 c/a/zn PZEJ'ZLOIZ ATTORNEY Feb. 14, 1956 H. F. OLSON ETAL 2,734,591

' LOUDSPEAKER STRUCTURE Filed March 2, 1955 2 Sheets-Sheet 2 H W 5 M a? INVENTORJ m fi'rry F 0/4004 Q Jab]? Prarfazz l ATTORNEY United States Patent LOUDSPEAKER STRUCTURE Han-y F. Olson, Princeton, and John Preston, Metede conk, N. 1., assignors to Radio Corporation of America, a con poration of Delaware Application March 2, 1953, Serial No. 339,810

3 Claims. (Ci. 181-31) This invention relates to acoustics and more particularly to loudspeakers.

There has been developed and marketed a wide frequency range loudspeaker which is characterized in that the single speaker has a low frequency cone and a high frequency cone. The low frequency cone is truncated. The high frequency cone is arranged centrally of the larger, low frequency cone, constituting substantially a continuation of the conic surface of the larger cone. An example of such a speaker is known, commercially, as the RCA Duo-Cone. Although the speakers of the type give excellent results and have found wide acceptance on the market, it has been found that the response of the speaker in the range of 2500 to 8000 cycles/sec. was somewhat low. Signals in that frequency range are supplied by the high frequency or smaller cone. The output of a direct radiator loudspeaker can be increased by reducing the solid angle into which the speaker radiates. However, a symmetrical reduction of the solid angle, in the case of speakers of the type under consideration, would mean a reduction of the angle of the low frequency cone. Such an expedient would, obviously, impair the broad directivity pattern of the low frequency cone.

It is, accordingly, an object of the present invention to provide means for improving the output of the high frequency cone of a double-cone speaker without impairing the output of the low frequency cone.

It is another object of the present invention to provide an improved double cone, wide frequency range loudspeaker which is characterized in that the output of the high frequency cone is improved without impairing the output of the low frequency cone.

It has also been noticed that slight dips occur as certain frequencies along the axis of the speaker. These dips, it was determined by the present inventors, are caused, at least in part, by sound waves from the small, highfrequency speaker being reflected by the surface of the larger, low frequency speaker.

It is a further object of this invention to provide an improved double cone loudspeaker in which the foregoing difiiculty is overcome.

A still further object of this invention is to provide an improved speaker as set forth in which the reflecting surface of the low frequency cone is broken up.

A further irregularity in the output of the speakers was noted with respect to the low frequency cone. The outer periphery of the large cone is supported by a corrugated annulus which provides a flexible connection between the cone and the usual fixed support. This corrugated annulus resonates at certain frequencies of operation of the large cone. Sometimes this resonant vibration is out of phase with the large cone and sometimes it is in phase with the vibration of the large cone. Such operation re sults in irregularities in the response characteristic of the speaker.

Yet another object of the present invention is to provide an improved loudspeaker in which the foregoing difiiculty is overcome.

Still another object of the present invention is to provide an improved loudspeaker as set forth wherein means are provided which prevent the suspension annulus from I being substantially a continuation of the conic surface of the larger cone. A number of small cones are secured to the front face of the conic surface of the large cone.

These small cones are arranged in a non-symmetricalarray with respect to the axis of the speaker and with their vertices directed toward the front of the speaker. In addition, a soft foam rubber or sponge annulus is secured in energy absorbing relation to the surface of a corrugated annulus supporting the periphery of the larger cone.

A better understanding of the present invention may be had from the following detailed description when read in connection with the accompanying drawing in which:

Figure l is an elevational view of the loudspeaker constructed in accordance with the present invention,

Figure 2 is an end view partly broken away of one of the diffusing cones secured to the speaker cone,

Figure 3 is a side view of cones shown in Figure 2,

Figure 4 is a crosssectional view taken along the line 4-4 of Figure 1.

Referring now to the drawing in more detail, there is shown a loudspeaker of the type having a high frequency sound radiating cone 2 and a low frequency sound radiating cone 4. The low frequency cone 4 is secured at its periphery to compliant member 6 which is in turn sup-,

ported by a rigid cone supporting member 8, commonly referred to as a dishpan. The compliant member may be integral with the cone member and constitute an annulus having a plurality of concentric corrugations 10. The inner end of the low frequency cone is supported by a substantially similar compliant member 12 which is secured to a supporting ring 14 carried by the aforesaid dishpan 8. The high frequency cone 2 is supported at its periphery by a compliant member 16 which is carried by a supporting ring 18.

A motor unit for this type loudspeaker is shown and claimed in copending application Ser. No. 51,962, filed September 30, 1948 in the name of the present inventors. That motor consists of a permanent magnetic member 20 mounted in an outer magnetic shell 22. A pole cap 24 and members 26 and 28 define a pair of cylindrical annular air gaps in which the voice coils 30 and 32, respectively, operate.

It may be seen from an examination of the drawings, particularly reference to Figure 4, that the high frequency cone 2 is mounted coaxially with the low frequency cone and constitutes substantially a continuation of the conic surface of the low frequency cone. Thus the high frequency cone defines the solid angle into which the high frequency cone radiates. In order to reduce that solid angle without appreciably altering the radiation characteristic of the low frequency cone a plurality of small conical members 34 are secured to the concave surface of the low frequency cone. It may be seen that these conical members substantially reduce the solid angle into which a high frequency cone radiates. However, since the low frequency cone operates as a piston the conical members do not appreciably affect the radiation characteristics of the low frequency cone.

As has been previously pointed out, when the high frequency cone is operating, reflections of the sound waves generated thereby are reflected from the surface of the low frequency cone. Since the two cones are mounted coaxially the low frequency cone is symmetrical about the high frequency cone. Therefore, the reflections from the 3 low frequency cone will be uniform and will meet at a point on' the axis on the cones. If the conical members 34 are symmetrically arrayed about the axis of the cone, the reflections from the low frequency cone may be somewhat diffused butthere will be interference patterns set up. Consequently, to more effectively diffuse the reflections from the low frequency cone the conical members are arrayed asymmetrically with respect to the axis of the cone. The conical members, shown more clearly in Figures 2 and 3 are made of substantially the same material as the loudspeaker cone. It may be noticed from the drawings that the periphery 36 of the conical members is shaped to conform to the concave surface of the large low frequency cone. Thus the conical members may be placed on the surface of the cone and cemented. The slightly added mass due to the conical members does not have a deleterious effect upon the response characteristic of the low frequency cone. Alternatively, the smaller conical members may be protuberances formed in the surface of the speaker cone while it is being molded.

It was also previously indicated that when the large cone is supported from the periphery by a compliant member such as the corrugated annulus 6, the compliant member resonates and produces spurious response characteristics. To overcome such resonant vibrations of the compliant support member, an annulus of sponge or foam rubber 38 is employed to absorb the acoustical energy of the compliant member. The energy absorbing annulus 38 may be rectangular in cross section as shown in Figure 4 or it may be round or the like. Whatever the cross sectional configuration may be the dimension is such that when the annulus is placed in one of the corrugations, of the compliant member 6 it does not fit into the bottom of the corrugation but leaves an air space between the bottom of the corrugation and the surface of the annulus. Thus the annulus is mounted in the corrugation in bridging relation thereto. The points of contact between the annulus and'the compliant member are cemented together. Thus arranged the annulus absorbs acoustical energy coupled to the compliant member and accordingly prevents the compliant member from resonating within the audible range.

Thus it may be seen that there has been provided in accordance with the present invention an improved loudspeaker wherein the irregularities and response characteristics are substantially improved.

What is claimed is:

l. In a loudspeaker assembly including a sound radiating cone, a rigid support means for supporting the periphery of said cone and a compliant coupling member con-' nected between the periphery of said cone and said support member, said coupling member comprising an annulus having a plurality of concentric corrugations therein, the improvement comprising an acoustical energy absorbing member secured to said coupling member in bridging relation to one of said corrugations.

2. In a loudspeaker assembly including a sound radiating cone, a rigid support means for supporting the periphery of said cone and a compliant coupling member con: ncctcd between the periphery of said cone and said support means, said coupling member comprising an annulus having a plurality of concentric corrugations therein, the improvement comprising an acoustical energy absorbing member secured to said coupling member in bridging re lation to one of said corrugations, said absorbing member being an annulus of foam rubber.

3. A loudspeaker comprising a sound radiating cone, a supporting member, a compliant member having a plurality of concentric corrugations integral with said cone connected between the periphery of said cone and said supporting member, and a rubber annulus mounted in one of said corrugations in bridging relation thereto whereby an air space between the bottom of the corrugation and the surface of said annulus is provided.

References Cited in the file of this patent UNITED STATES PATENTS 1,616,553 Rupinski Feb. 8, 1927 1,904,538 Round et al Apr. 18, 1933 2,549,091 Hopkins Apr. 17, 1951 yan