US3536862A - Microphone having a variable unidirectional characteristic - Google Patents

Description

0d. 27, 1970 wgm TN v 3,536,862

MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTER'ISTIC Filed Aug. 9, 196? 4 Sheets-Sheet 1 FIG? Hypercardl'ald FIG. 3

\ ercard/b/d Y INVENTOR Belem/ARI) NElA/GARTMEK ATTORNEYS Oct. 27, 1970 WEINGAR NEFE 3,536,862

MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTERISTIQ Filed Aug. 9, 1967 4 Sheets-Sheet 2 I INVENTOR BiRM/IHKD HEM/641971146? ATTORNEYS L 1970 B. WEINGARTNER 3,536

' MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTERISTIC Filed Aug. 9, 1967 4 Sheets-Sheet 5 INVENTOR H m/ MD Meme/WW5? WQMMM LL ATTORNEYS Oct. 27, 1970 w m 'j- 7 3,536,862

MICROPHONE HAVING A- VARIABLE UNIDIRECTIONAL CHARAOTERISTIC Filed Aug. 9, 1967 4 Sheets-Sheet 4 INVENTOR Beam/m0 we ml 6A3TA167 ATTORNEYS United States Patent 3,536,862 MICROPHONE HAVING A VARIABLE UNIDIRECTIONAL CHARACTERISTIC Bernhard Weingartner, Vienna, Austria, assignor to Akustische u. Kino-Gerate Gesellschaft m.b.H., Vienna,

Austria Filed Aug. 9, 1967, Ser. No. 659,445 Claims priority, application Austria, Aug. 19, 1966, A 7,930/66 Int. Cl. H04r 1/34 US. Cl. 179-121 14 Claims ABSTRACT OF THE DISCLOSURE A microphone having a cardioid directional characteristic, when the sound detour through sound inlet openings communicating with forward and rear diaphragm faces, as measured on the outside of the microphone, has a predetermined length, is provided with a deflecting member mounted on the outside of the microphone between the sound inlet openings and adapted selectively to modify the length of the sound detour.

BACKGROUND OF THE INVENTION There are known microphones which have an omnidirectional (spherical) characteristic, microphones which have a unidirectional (cardioid) characteristic and microphones which have a bidirectional (figure eight-shaped) characteristic. The optimum characteristic for any particular application will depend on the conditions of use. Unidirectional microphones are preferable in most cases. The generation of a unidirectional characteristic can be explained most conveniently by reference to the principle of superposition.

If a microphone having an omnidirectional characteristic and a microphone having a bidirectional characteristic are superposed, for example in a suitable electric circuit, the resulting system will have a unidirectional characteristic. If the contributions of the two microphones are the same (50% omnidirectional charact ristic and 50% bidirectional characteristic) an ideal cardioid directional characteristic will be obtained. If the bidirectional contribution is 75% and the omnidirectional contribution is 25%, a hypercardioid characteristic will be obtained and, a ratio of 63% bidirectional characteristic to 37% Omnidirectional characteristic results in a supercardioid characteristic.

Depending on the conditions of use, each of these three unidirectional characteristics has its special advantages. The pure cardioid characteristic results in a wide useful sound receiving angle, and in a good supression of direct sound which is incident from the rear (180). The hypercardioid characteristic results in a cancelling at an angle 11 of about 110, and in the optimum suppression of diffused sound (reverberation). On the other hand, it results in a narrower receiving angle and a reduced suppression of sound incident fro-m the rear. The supercardioid characteristic is a compromise of the two characteristics just discussed.

Many arrangements have been suggested to provide for a variation of the directional characteristic by a control of the omnidirectional or bidirectional contributions. It is also known that a simple superposition of the acoustic elements of the omnidirectional system or of the bidirectional system enables the generation of a resulting unidirectional characteristic with only one transducer system (one diaphragm).

In a dynamic microphone, the acoustic elements of the pressure-responsive system, having an omnidirectional characteristic, comprise a space which is closed from the Patented Oct. 27, 1970 ice outside air and connected by a frictional resistance to a relatively shallow air chamber behind the diaphragm. On the other hand, the acoustic elements of the bidirectional system consist essentially of a suitably sized opening leading from the air chamber into the free rear sound field. As a result, the diaphragm actuating force of the pressure-responsive system is proportional to the sound pressure in front of the diaphragm, whereas the actuating force generated by the bidirectional system is proportional to the difference between the sound pressure before the diaphragm and the sound pressure behind the diaphragm. This pressure difference is approximately proportional to the distance between the center of the forward side of the diaphragm and the rear sound inlet, provided that this distance is much smaller than the wave length of the sound to be transmitted.

SUMMARY OF THE INVENTION This invention relates to microphones having a pure cardioid characteristic and, more particularly, to such a microphone which can be converted ina simple manner into one having either a supercardiod characteristic or a hypercardioid characteristic.

In accordance with the invention, a microphone having a pure cardioid characteristic, or equal omnidirectional and bidirectional contributions, is provided with means whereby the sound detour is variable, the variation being effected by the provision of deflecting member in the form of a disk or sleeve on the exterior or outside of the microphone. Preferably, the deflecting member is in the form of a frustum of a cone. The deflecting member is located between the sound inlet opening, communicating with the forward face of the diaphragm, and the sound inlet opening communicating with the rear face of the diaphragm.

The deflecting member can be made detachable, adjustable in size, adjustable in shape, or to have any tWo or more of these characteristics.

In one form of the invention, the deflecting member may be formed with openings, apertures, slots or the like, which can be selectively closed by suitable mechanisms, the size of the openings or the like being preferably infinitely adjustable, in the manner of a variable orifice.

An object of the invention is to provide a microphone having a pure cardioid characteristic with means whereby the characteristic may be changed into a supercardioid characteristic or a hypercardioid characteristic, selectively.

Another object of the invention is to provide such a microphone including means for varying the sound detour between the sound inlet opening communicating with the forward face of the diaphragm and the sound inlet opening communicating with the rear face of the diaphragm.

A further object of the invention is to provide such a microphone in which such means comprises a deflecting member in the form of a disk or sleeve and mounted on the exterior or outside of the microphone.

Still another object of the invention is to provide such a deflecting member in the form of a frustum of a cone.

A further object of the invention is to provide such a member which is detachable.

Yet, anotherobject of the invention is to provide such a deflecting member which'is adjustable in size or shape or both.

Yet, another object of the invention is to provide such a deflecting member with openings or other forms of apertures Whose areas are preferably infinitely adjustable or variable by suitable mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS For an understanding of the principles of the invention, reference is made to the following description of typical embodiments thereof as illustrated in the accompanying drawings.

In the drawings:

FIGS. 1, 2 and 3 are graphical representations of, respectively, an ideal cardioid directional characteristic, a hypercardioid directional characteristic and a supercardioid directional characteristic;

FIG. 4 is a sectional view of a microphone embodying the invention and illustrating the basic functioning of the deflecting member;

FIG. 5 is a view, similar to FIG. 4, illustrating the deflecting member as formed with apertures therethrough;

FIG. 6 is a top plan view of FIG. 5; and

FIG. 7 is an elevation view, partly in section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1, 2 and 3, if the contribution of two microphones are the same, that is, 50% omnidirectional characteristic and 50% bidirectional characteristic, an ideal cardioid directional characteristic will be obtained as shown in FIG. 1. If the bidirectional contribution is 75% and the omnidirectional contribution is 25%, a hypercardioid directional characteristic will be obtained as shown in FIG. 2. If the bidirectional contribution is 6 3% and the omnidirectional contribution is 37%, a supercardioid characteristic will be obtained as shown in FIG. 3.

In FIG. 4, a capsule 1 of a dynamic microphone is illustrated as having a forward sound inlet 2 and a rear sound inlet 3. A diaphragm 4 is illustrated in broken lines, and a pressure chamber 5 communicates with the rear of the capsule. The sound detour d representing the external distance between the forward sound inlet 2 and the rear sound inlet 3, determines the magnitude of the actuating pressure difference, and consequently determines the bidirectional contribution. The acoustic elements of the microphone system are so dimensioned that sound detour d results in a cardioid directional characteristic.

When a deflecting disk 6 is applied to the microphone, in accordance with the invention, the sound detour between the forward sound inlet 2 and the rear sound inlet 3 is increased to (1 As a result, the pressure difference and the bidirectional contribution will also increase so that the microphone system, having a cardioid characteristic, is converted by deflecting disk 6 into a microphone having a predominating bidirectional contribution. More particularly, the microphone is converted into one having a supercardioid or hypercardioid characteristic, depending on the size of the disk. To avoid irregularities in the frequency response due to the dynamic pressure eifect or due to diffraction effects of disk 6, the latter is preferably frusto-conical in form.

In the embodiment of the invention shown in FIGS. 5 and 6, the deflecting member 6 is formed with openings 7 whose area is infinitely variable between a fully opened condition and a fully closed condition. Disk 6 is preferably formed of plastic composition material. A closing ring 8 is rotatably mounted in a groove 9 of disk 6', and preferably comprises punched sheet metal. Closing ring 8 is rotatable by adjusting lever '10, and has openings 11, corresponding to opening 7, which enable an infinitely variable opening and closing of openings 7.

The arrangement shown in FIGS. 5 and 6 is capable of providing three different sound detours and three different bidirectional contributions, namely d without the deflecting disk d with the deflecting disk having the openings 7 closed and d with the deflecting disk having the openings 7 open. The detours are dimensioned so that al results in a cardioid characteristic, d in a hypercardioid characteristic and d in a supercardioid characteristic.

A practical form of microphone embodying the invention is illustrated in FIG. 7. In FIG. 7, microphone capsule 1 is incorporated in a housing 12 provided with a cap 13. Sound enters in front through protective screen 14 and enters at the rear through slots 15 in cap 13. Electrical connections are established by cable 16, and the deflecting disk 6, in accordance with the invention, is adapted to be fitted to cap 13.

With a view to a pleasing appearance, the deflecting disk may be provided in different shapes, such as circular, elliptical, or polygonal. Type references and the name of the manufacturer may be provided on the deflecting member 6, which preferably is formed of plastic composition material.

As a further feature of the invention, deflecting member 6 may be used as a foot or the like for supporting the microphone of the table. In this case, it may be desirable to provide a ring 17 of elastic material in a groove formed at the periphery of the deflecting disk, as best seen in FIGS. 7 and 8.

The deflecting member may be flatter than shown in the drawings or may more closely resemble a sleeve. While its contour is preferably circular, elliptical or polygonal, alternatively the deflecting disk may have a star-shaped contour or the like. Also, the size of the deflecting member may be made variable, in the manner of an iris diaphragm such as used in photography, but arranged to vary the outside diameter of the deflecting member.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A microphone, having a variable unidirectional characteristic, comprising, in combination, a capsule containing electro-acoustic transducer means having forward and rear diaphragm faces; means defining forward and rear sound inlet openings communicating with said forward and rear diaphragm faces, respectively; a sound detour representing the external distance between said inlet openings as measured on the outside of said microphone, said microphone having a cardioid directional characteristic in response to sound waves entering through said sound inlet openings when said sound detour has a predetermined length; and a sound path deflecting member mountable on the external periphery of said capsule between said sound inlet openings to modify selectively the length of said sound detour to obtain differently defined unilateral directional characteristics for said microphone.

2. A microphone, as claimed in claim 1, in which the size of said deflecting member is selectable to select the desired length of said sound detour.

3. A microphone, as claimed in claim 1, in which said transducer means comprises a single diaphragm having said forward and rear faces.

4. A microphone, as claimed in claim 1, in which said deflecting member is disengageably mounted on said microphone; said sound detour having said predetermined length When said deflecting member is removed from said microphone, and having a length greater than said predetermined length when said deflecting member is mounted on said microphone.

5. A microphone, as claimed in claim 1, in which the external periphery of said deflecting member is in the form of a closed plane geometric figure, said deflecting member forming a support for said microphone on a base.

6. A microphone, as claimed in claim 1, in which said deflecting member has a form of a flat truncated cone.

'7. A microphone, as claimed in claim 1, in which said deflecting member has a frictional fit on said microphone.

8. A microphone, as claimed in claim 1, in which said deflecting member is formed with sound passage apertures therethrough.

9. A microphone, as claimed in claim 8, in which said deflecting member includes adjusting means selectively operable to vary the areas of said apertures to vary the length of said sound detour.

10. A microphone, as claimed in claim 9, in which said adjusting means is continuously adjustable.

11. A microphone, as claimed in claim 5, in which said deflecting member has an elliptical external periphery.

12. A microphone, as claimed in claim 5, in which said deflecting member has a polygonal external periphery.

13. A microphone, as claimed in claim 5, in which said deflecting member includes a ring of elastic material extending around its external periphery and projecting at least partly from said external periphery.

14. A microphone, as claimed in claim 1, in which said deflecting member is substantially disk-shaped.

References Cited UNITED STATES PATENTS 2,787,671 4/1957 Grosskopf 179-121 10 KATHLEEN H. CLAFFY, Primary Examiner T. L. KUNDERT, Assistant Examiner

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