US 3342286 A
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COMPLIANCE ACTIVATED MULT I,DIAPHRAGM Filed June 22, 1966 lo 48 44 46 H65 2o- 4s s4 lo-- 1 FIGS INVENTOR BRUNO G. STAFFEN o 200 500 I000 2000 5990 IOOOO 20000 BY QW/M ATTORNEYS United States Patent 3 342,286 COMPLIANCE ACTIVATED MULTI-DIAPI-IRAGM Bruno G. Staffen, Chicago, Ill., assignor to Motorola, Inc., Franklin Park, Ill., a corporation of Illinois Filed June 22, 1966, Ser. No. 559,600 6 Claims. (Cl. 181-32) This invention relates to diaphragms, especially those to be used in audio transducers, such as a speaker, and more particularly to diaphragms capable of having multi- Inode vibrations.
In providing speakers for automobile radios, for example, volumetric requirements are quite important. For meeting such requirements it is desired to provide a speaker diaphragm which has a high aspect ratio and additionally is shallow as measured from the outer edge of the diaphragm to the driving means. In speakers, and other audio transducers having diaphragms, the aspect ratio is the ratio of the diaphragm major axis to its minor axis.
It has been found that in providing speakers having high aspect ratios localized modal vibrations are set up within the diaphragm along the major axis resulting in greatly decreased speaker output. The diaphragm is incoherently flapping rather than vibrating to produce sound. Diaphragms are particularly susceptible to such undesired vibrations at the middle to higher audio frequencies, i.e. above 1000 c.p.s.
Attempts to obivate the above described problem include providing a plurality of spaced-apart corrugations in the speaker diaphragm. Some of such corrugations were made concentric with respect to each other, while others not being perfectly concentric maintained the same aspect ratio of the speaker diaphragm. While improving speaker operations such corrugations did not satisfactorily prevent decreased speaker output in the middle to higher frequencies, especially in those speakers having a low profile. Such diaphragms had sharply varying amplitude responses as the frequency was increased, i.e. so called peaks and valleys in amplitude output response curves measured against frequency.
Therefore, it is an object of this invention to provide a diaphragm for an audio transducer having a high aspect ratio but which operates in a multi-piston mode for providing improved middle-to-high frequency response.
It is another object of this invention to provide a lowprofile diaphragm exhibiting smooth response in the middle-to-higher audio frequencies.
According to this invention a unitary diaphragm is formed to provide substantially independent piston areas each having different aspect ratios and resonant frequencies, such that the coaction between the various piston areas and compliance corrugations smooth and improve the middle-to-high frequency response of the diaphragm.
Referring now to the accompanying drawing:
FIG. 1 is a plan view of a preferred embodiment of the present invention;
FIG. 2 is a partial sectional view of the FIG. 1 preferred embodiment as taken in the direction of the arrows along line 2-2;
FIG. 3 is a partial sectional view of the FIG. 1 embodiment taken in the direction of the arrows along line 33 and which shows a cross-section of the preferred embodiment along its minor axis;
FIG. 4 is a partial-sectional view of the FIG. 1 embodiment taken in the direction of the arrows along line 4-4 showing the cross-sectional characteristics along the major axis, and being approximately the actual size of a diaphragm constructed embodying this invention.
FIG. 5 is a graph illustrating frequency response of the FIG. 1 preferred embodiment and another speaker having the same dimensions but not using the invention; and
FIGS. 6, 7 and 8 are schematic illustrations of alternate embodiments of this invention.
A diaphragm having a high aspect ratio is provided with a plurality of sets of compliant corrugations, some of which cross the major axis in a major piston area. Such crossings provide a second diaphragm portion which acts as an inner piston area and has a different aspect ratio than the diaphragm. The major-axis crossing corrugations effectively and dynamically decouple the second piston area from the major or outer piston area. Both the inner and outer piston areas preferably have the same minor axis.
Referring now more particularly to FIGS. 1-4, inclusive, like numerals indicate like parts and structural features of the illustrated preferred embodiment. The diaphragm 10 consists of pliant paper press-formed or an aqueous slurry deposited on a forming mold formed to the illustrated shape. Diaphragm 10 may be mounted along its outer edges 10F on a frame (not shown) in the usual manner. A voice coil or other electro-mechanical transducers may be affixed to diaphragm 10* adjacent its aperture 10A. Inwardly of outer edge 10F are formed a pair of outer compliant corrugations 12 and 14. A third and innermost outer compliant corrugation is formed by a lift hand portion corrugation 16, a right hand portion corrugation 18 and intermediate corrugation portions 20. Even though the corrugation portions are discontinuous, the four portions cooperate to provide action substantially similar to a continuous corrugation. It is well known that the entire diaphragm 10 will flex between major corrugation 12 and outer edge 10F for providing a first resonant frequency of diaphragm 10.
Inner or minor compliance corrugations are formed by the combination of portions 20, which also form a part of the outer or major corrugation 16-18-20, are combined with corrugation portions 22 to form a minor compliance corrugation 20-22. A second inner or minor corrugation is formed by a left hand portion 24, a right hand portion 25 in combination with corrugation portions 26 of continuous major corrugation 14.
It should be noted that corrugation portions 24 and 26 are discontinuous in the same manner that portions 20 are discontinuous from outer corrugation portions 16 and 18. Such discontinuities do not prevent the described affected corrugation portions from coacting similar to a single continuous corrugation. Therefore, such minor and major corrugations are effectively merged over a part of their respective extents.
The above described compliance corrugations provide, in addition to a major piston area consisting of the entire area inside major corrugations 12, 14, and 1648-20, a minor piston area 28 inside the minor compliance corrugations 20-22 and 24-26 plus the two intermediate piston areas 30 between the corrugation portions 16 and 24 at opposite end portions of diaphragm 10.
Expressed in another way, the major piston area is defined by corrugations 12, 14, 16 and 18 and the minor piston area is defined by corrugations 22, 24 and 25. Along line 33, the corrugations merge so that corrugations 16 and 18 are discontinuous from one another and similarly corrugations 24 and 25 are discontinuous.
The described compliance corrugations also dynamically de-couple minor piston area 28 from the major piston area which is the area within corrugations 12, 14 and 16-1820 to provide an additional resonant frequency by piston area 30 and the minor corrugations. In the illustrated embodiment such effective decoupling is especially noticeable at frequencies above 1,000 cycles per second. Additionally the described intermediate piston areas 30 are effectively decoupled from both the minor and major piston areas, so that they have independent resonant frequencies.
Diaphragm 10 major axis is along line 44 while its minor axis is along line 33. The major axis length is determined by the outer or major compliance corrugations 12, 14 and 16-18-20. Minor piston area 28 has its major and minor axes also disposed along said lines. The minor axes along line 3-3 have the same length for both the minor and major piston areas. The minor piston area 28 major axis is much shorter than the diaphragm major axis, in that its length is determined by minor compliance corrugations 20-22. From inspection of FIG. 1 it is clearly seen that the aspect ratio of the minor piston area 28 is much smaller than that of major piston area inside the major compliance corrugations 12, 14, and 16-18-20. As such, piston area 28 is more eflicient in the middle-to-higher frequency range.
The diaphragm along major axis 44 is also stiffened by minor compliance corrugations 20-22, 24-26 extending across the major axis. In addition to providing above described action such corrugations also serve to inhibit undesired modal vibrations along the major axis.
The profile of diaphragm 10 is quite shallow in that the diaphragm length along line 44 is substantially greater than the diaphragm depth indicated by line 39.
Referring now to FIG. 5, curve 40 shows the frequency response of a speaker having the dimensions shown in FIG. 1, but without minor corrugations 20-22, 24-26, additional piston areas 28 and 30, and the innermost major corrugations 16-18-20 was made continuous. Curve 40 illustrates the frequency response of a FIG. 1 embodiment as used in a speaker. It should be noted that the middle-tohigher frequency response, i.e. above 1,000 cycles, is smoothed in the FIG. 1 embodiment wherein the aspect ratios of various piston areas are different with respect to each other. Also the peak response at 800 c.p.s. is smoothed by the FIG. 1 diaphragm. The narrow clips at 2.5 and 5.0 kc. in curve 40 are critical phasing acoustic effects which are swamped out when radiation is averaged over various angles with respect to the diaphragm axis of vibration.
The frequency response of the FIG. 1 embodiment may be altered by varying the density of the diaphragm in the various piston areas. This can be easily done when the diaphragm is manufactured by pressing compliant paper. For example, piston area 28 may be pressed very hard to make it quite dense, while piston areas 30 may be formed under less pressure and therefore be less dense. Making piston area 30 less dense reduces the sharpness in the upper frequency amplitude response cutoff, tending to smooth the middle frequency response of the diaphragm.
Referring now to FIGS. 6, 7 and 8 the lines therein schematically represent sets of compliance corrugations, such as those illustrated in the FIG. 1 embodiment. Aperture 48 is provided in all FIGS. 6-8 for receiving a driving coil or other audio transducer suitable for use with a diaphragm. In FIG. 6 there is illustrated in outer or major compliance corrugation set 44 in the shape of an elipse and with an inner or minor set of circular corrugations 46. In FIG. 7 the outer corrugation set 50 is circular while the minor corrugation set 52 is elliptical. In this latter modification the major axis 51 is the same for both compliance corrugation sets 50 and 52, while the horizontal minor axes along line 53 are different for corrugations 50 and 52. This difference provides different aspect ratios. In FIG. 8, line 54 represents an outer corrugation set having a somewhat elliptical form while corrugation set 56 is circular. Note in this particular embodiment the aperture 48 is not centered with respect to one set of corrugations. Yet other configurations of multi-piston diaphragms may be formed, an important feature being different aspect ratios of the minor and major piston areas.
It is understood that the described diaphragm in addition to being used in a speaker may also be used in a microphone type of transducer.
What is claimed is:
1. A unitary diaphragm including: an outer set of cOmpliance corrugations the area within which defines a major piston area, an inner set of compliance corrugations formed within said outer set and merging with a limited portion thereof, the area within said inner set defining a minor piston area, at least one intermediate piston area between said inner and outer sets of compliance corrugations, said minor piston area being entirely surrounded by said inner set of compliance corrugations so that it is dynamically decoupled from said major and intermediate piston areas, whereby each of said piston areas has an independent resonant frequency.
2.. The diaphragm of claim 1 wherein said major and minor piston areas each have a first and a second axis, said first axis of each of said major and minor piston areas being coincident with one another, said second axis of said major piston area being aligned with and having a length longer than the length of said second axis of said minor piston area.
3. The diaphragm of claim 2 having a depth dimension relatively short with respect to the length of said second axis of said major piston area.
4. An elliptically shaped unitary diaphragm including: an elliptically shaped outer set of compliance corrugations the area within which defines a major piston area having an elliptical shape, an elliptically shaped inner set of compliance corrugations formed within said outer set and merging with a limited portion thereof, the area Within said inner set defining a minor piston area having an elliptical shape, said major and minor piston areas each having a major and a minor axis, said minor axis of each of said piston areas being coincident with one another, said major axis of said major piston area being aligned with and having a length longer than the length of said major axis of said minor piston area, and two intermediate piston areas formed between said inner and outer sets of compliance corrugations at respective end portions of said major axis of said major piston area, said minor piston area being entirely surrounded by said inner set of compliance corrugations so that it is dynamically decoupled from said major and intermediate piston areas, whereby said piston areas have independent resonant frequencies.
5. The diaphragm of claim 4 having a depth dimension relatively short with respect to the length of said major axis of said major piston area.
6. The diaphragm of claim 4 with said minor piston area and said intermediate piston areas having different densities.
References Cited UNITED STATES PATENTS 1,872,081 8/1932 Hawley 181-32 2,358,823 9/1944 OConnor et al 18131 2,549,139 4/ 1951 Stevens 181-32 2,834,424 5/1958 Badmaieff 18132 2,845,135 7/1958 Cohen et al 18131 2,890,760 6/1959 Bobb 18131 2,962,109 11/ 1960 Haerther 18132 3,095,941 7/1963 Hassan 18132 3,111,189 11/1963 Scholl 181-32 3,166,148 1/1965 Tibbetts 181-32 3,180,945 4/ 1965 Suzuki 1791 15 STEPHEN I. TOMSKY, Primary Examiner.