US3870820A

US3870820A - Microphone with different directional modes

Info

Publication number: US3870820A
Application number: US374870A
Authority: US
Inventors: Tomohide Suzuki; Toshio Aoki
Original assignee: Victor Company of Japan Ltd
Current assignee: Victor Company of Japan Ltd
Priority date: 1972-06-30
Filing date: 1973-06-29
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11

Abstract

A built-in microphone for a tape recorder, comprising a diaphragm responsive to sound waves and sensing means behind it in the microphone case. The microphone case has at least one opening to admit the sound waves to impinge on the inner surface of the diaphragm so as to counteract the effect of the sound waves impinging on the outer surface of the diaphragm for unidirectional mode of operation. The openings can be closed for nondirectional mode of operation.

Description

United States Patent [191 0 Suzuki et al.

[111 3,870,820 [451 Mar. 11, 1975 1 MICROPHONE WITH DIFFERENT DIRECTIONAL MODES [75] inventors: Tomohide Suzuki; Toshio Aoki, both of Yokohama, Japan [73] Assignee: Victor Company of Japan, Limited, Yokohama, Japan [22] Filed: June 29, 1973 [21] Appl. No.: 374,870

[30] Foreign Application Priority Data June 30, 1972 Japan 47-77450 June 30, 1972 Japan 47-77451 June 30, 1972 Japan 47-77452 [52] US. Cl. 179/1 DM, 179/121 D, 179/179 [51] Int. Cl H04! l/38 [58] Field of Search.... 179/121 D, 1 DM, 178, 179, l79/1llR, 121R [56] 7 References Cited- UNITED STATES PATENTS 2,787,671 4/1957 Grosskopf et a1 179/121 D TAPE RECOHDI NG HOUSING I l l 2,862,070 11/1958 Bonnatfous 179/121R 3,141,070 7/1964 Schenkel et al. 179/121 D FOREIGN PATENTS OR APPLICATIONS 1,129,540 5/1962 Germany 179/179 1,117,647 11/1961 Germany 179/121 D Primary Examiner-Kathleen H. Claffy Assistant Examiner-George G. Stellar Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato; Bruce L. Adams [57] ABSTRACT 2 Claims, 10 Drawing Figures SOUND WAVES SOUND WAVES SL1 DABLE CLOSURE PATENT-El] MRI 1 I975 SHEET 1 0i: 3

PATENTEU H975 I 3870.820

' sum 2 o 3 ROTATABLE CLOSURE MEMBER 4+ SLIDABLE CLOSURE PATENTEDIARI 1 1 I 3,870,820

sum 3 9f 3 \ANGLE OF DIRECTION OF SOUND WAVES MICROPHONE WITH DIFFERENT DIRECTIONAL MODES This invention relates generally to microphones, and particularly to a microphone whichcan be switched from nondirectional to unidirectional reception and vice versa.

The general tendency is toward incorporating the microphone into a small-sized cassette tape recorder. Al-

' though this built-in arrangement affords an advantage in that there is no need for the user to carry a separate microphone with its long connecting cord, he has to bring the recorder near his mouth whenever he wishes to eliminate ambient noise from being recorded together with his voice. It is therefore convenient for the user to be able to choose between nondirectional and unidirectional microphone receptions as desired.

Directional reception switching may be obtained, according to one prior art teaching, by providing an additional chamber behind the diaphragm of the microphone. This, however, requires high precision work and the microphone becomes bulky, making it unsuitable for incorporation in small-size tape recorders.

It is accordingly an object of the present invention to provide a compact microphone having an inexpensive directional reception switching facility.v The features and advantages of the present invention will'be better understood from the following description when taken in conjunction with the accompanying drawings, in which:

FIG. la is a partly cutaway view in elevation of a microphone in accordance with the present invention;

FIG. lb is a cross-sectional view of the FIG. la microphone taken along the line l-1 of FIG. la;

FIG. 2a is a plan view of a first preferred'form of a microphone in accordance with the invention, shown installed in an end wall of a tape recorder;

FIG. 2b is a cross-sectional view of the FIG. 2a microphone taken along the line 22 of FIG. 2a;

FIG. 3a is a plan view of a microphone of a second preferred form according to the invention, shown installed in an end wall of a tape recorder;

FIG. 3b is a cross-sectional view of the FIG. 3a microphone taken'along the line 33 of FIG. 3a;

FIGS. 4a to 4c illustrate still another form of an embodiment of a microphone in accordance with the present invention; and

FIG. 5 is a graph illustrating directional pattern of a microphone in accordance with the invention in a unidirectional mode of operation.

Reference is now made to FIG. 1 wherein the operating principle of a microphone in accordance with the present invention is schematically shown. The microphone generally indicated at reference numeral is of an electrostatic (condenser) type and comprises a diaphragm 11, a backplate 12 spaced inwardly therefrom and a housing 13 constructed in a conventional manner. The diaphragm and'backplate form a condenser and the outer surface of the diaphragm 11 is exposed to the signal producing sound waves. Impinging sound waves cause vibrations of the diaphragm and corresponding variations in capacitance. Under these conditions, the electrical output across the condenser corresponds to the motion of the diaphragm. In accordance with the invention, the backplate 12 is provided with a plurality of apertures 12a arranged in a circle about its center. It is to be understood that the backplate is dispensed with if a sensor such as a crystal detector or an electromagnet is operatively coupled to the diaphragm. The housing 13 has a larger diameter portion 13a enclosing the backplate and the diaphragm, a smaller diameter portion 13b and a shoulder 13c formed therebetween. Small openings l3d are provided in the housing portion 13b to provide communication between the environment and the interspace between the diaphragm and backplate through the apertures 12a. This arrangement allows sound waves to .impinge not only on the outer surface of the diaphragm, but on its inner surface as well. Since the sound wave impinging on the inner surface has a phase angle substantially opposite to that impinging on the outer surface, the resultant output is reduced. If the two sound waves impinging on the diaphragm in opposite directions are equal in sound pressure, no output signal results. Since the sound pressure on the diaphragm depends largely on the surface area of the diaphragm exposed to the impinging sound wave, the sound wave impinging directly from the front side on the outer surface causes a greater motion of the diaphragm than that caused by the sound wave impinging from behind on the inner surface. As previously described, the magnitude of the resultant output signal depends on the difference in sound pressure between the outer and inner surfaces. Therefore, the maximum output is obtained with the sound wave impinging from the front side on the diaphragm. The magnitude of the output varies as the angle of incidence of the impinging sound wave varies. In the extreme case, the minimum output results when the sound wave impinges on the diaphragm also from behind because the minimum difference exists between the sound pressures on the inner and outer surfaces. As is apparent from the foregoing, a microphone constructed in accordance with the present invention has a directional sensitivity to impinging sound waves.

However, it is desirable that such a directional reception may be varied when the need arises, e.g., when the microphone is used in a noisy environment it may be switched to the unidirectional mode, while, when a group of people is seated around a table in a meeting, the microphone may be switched to operate in the nondirectional mode.

FIGS. 2a and 2b show a first preferred form of an embodiment of the invention to provide switching between nondirectional and unidirectional receptions by the microphone. The microphone 10 is shown inserted into a receiving opening 14 of the tape recorder 15. An annular packing 16 of a flexible material is inserted into the smaller diameter portion 13b of the housing 13 to absorb possible vibrations caused by the driving motor of the tape recorder to prevent transmission thereof to the microphone. An opening 17 is provided on one surface of the tape recorder in alignment with the opening 13d of the microphone housing 13. A closure member 18 of a flat plate having a pair of inwardly flared portions 18a is slidably engaged with a pair of slots 19 provided on the surface of the recorder. When the closure member. is shifted to the right in FIG. 2a, the opening '17 is closed to prevent the intrusion of sound wave an alternative to the closure member 18, an annular member 20 of a flexible material has its opening 20b rotatably fitted into the smaller diameter portion of the housing 13. The annular member has a pair of openings 20b in diametrical relation to each other which are brought into alignment with a pair of openings 13d of the housing 13. When the annular member 20 is manually rotated about its axis about 45, the

openings

13d and 20b are brought into disalignment with each other, closing the passage for the sound wave impinging on the inner surface of the diaphragm 11.

A third form of the embodiment of the invention is shown in FIGS 4a to 40. The microphone is constructed in the same manner as previously described with reference to FIGS. 1 through 3, except that the openings 13d are provided on the shoulder 13c of the microphone housing 13. In FIG. 4b the microphone housing is slidably inserted into the receiving opening 14 of the tape recorder 15. Under this condition only sound wave impinging from in front of the diaphragm 11 is allowed to cause a motion of the diaphragm and the openings 13d are closed by an annular flexible member 21 fixedly attached to the tape recorder. Therefore, the microphone is brought into the nondirectional mode of operation. When the microphone is pulled a small distance away from the end wall of the tape recorder 15, the openings 13d are opened to allow sound waves to be admitted thereinto and the microphone is switched to the unidirectional mode as previously described.

FIG. 5 shows graphically the result of a test conducted on a microphone in accordance with the present invention. As will be apparent from the graph, the microphone has its minimum gain of 21 dB at 1,000 Hz with respect to sound waves impinging from behind the microphone 180 from the reference angle) and its maximum gain of 0 dB with respect to sound source placed directly in front of the microphone (0).

While the foregoing description has been concerned with an electrostatic (condensor) type microphone having a sensor operatively coupled with the diaphragm for generating signals in response to the sound waves(s), it is to be understood that the present invention is not limited to it, but includes any other microphone type. It is further to be understood that the important feature of the invention is to provide at least one opening in the microphone housing to admit sound waves to impinge on the inner surface of the diaphragm to counteract sound vibrations caused by impingement on the outer surface of the diaphragm.

The foregoing description shows only preferred forms of an embodiment of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the forms shown and described are only illustrative, not restrictive.

What is claimed is:

1. In combination, a recording apparatus having a casing and a microphone having a housing with a larger diameter portion and a smaller diameter portion defining a shoulder portion therebetween, said apparatus casing having an opening receiving said smaller diameter portion slidably movable with respect to said casing, said shoulder portion having at least a first opening therein, a diaphragm mounted in said larger diameter portion of said housing and having a first major surface exposed to frontal soundwaves and a backside second major surface opposite to said first major surface, a sensor operatively coupled to said diaphragm, a backplate mounted in said larger diameter portion spaced from said second surface of said diaphragm and defining a space between it and said shoulder, said backplate having therein at least a second opening communicating with said first opening through said space, whereby upon slidable movement of said smaller diameter portion away from said apparatus casing said second opening is uncovered and soundwaves impinge on said second surface through said first and second openings.

2. A microphone as claimed in claim 1, including an annular shaped flexible member disposed on and inner edge of said receiving opening of said apparatus, said annular shaped flexible member having means closing said first opening when said smaller diameter portion of said microphone is slidably inserted into said opening and said shoulder is disposed against said annular flexi-