US2763730A - Microphone having controllable directional characteristics - Google Patents

Description

Sept. 18. 1956 C. MICROPHONE F PAULL ETAL HAVING CONTROLLABLE DIRECTIONAL CHARACTERISTICS Filed May 51, 1951 Zhwentom .CHARLES F. PAULL MAURICE M. PALO invention is concerned with the design and construction of microphones and more particularly to the art cf pnstruciin andarranging sound pick-up instruments which have controllable directional characteristics. To achieve selective response as regards the direction of "sound propagation in relation to the frontal axis of the pick-up device or microphone it has been heretofore proposed to provide the microphone with multiple acousto-electri'cal transducers coupled with an appro- -'pr'i'ate electrical interconnecting network, or with an auxiliary acoustical chamber to the rear of the diaphragm and having an entrance passage of predetermined acoustic'al impedance, all for the purpose of increasing the electrical response of the instrument when the sound to be transmitted emanates from ajpoiht in front of the instrument. -In this manner directional characteristics of res onse are achieved, making the instrument highly effective in excluding general or background noise in solo woi'k, for example. In other applications, such as in con- "ference work, for example, directionality of response is undesirable, and because of the inability of these prior directional types of microphones to be readily adjusted or converted for non-directional response it is necessary that most pick-up stations provide both types of microphones.

The present invention provides a simply-constructed mechanical arrangement for quickly converting a microphone having inherent directional characteristics into .a microphone of the non-directional type and, further, provides that when the instrument is adjusted for nondirectionalresponse the response will be absolutely uniform from all directions and the frontal'axis of the microphone will be so positioned as to transmit'co'nferences or other group activities or general sound effects with the highest degree of efiiciency.

The abovegeneral objects of the invention are obtained through the invention herein disclosed, by utilizing a cased microphone assembly in which the air path from the front face of the diaphragm back around to the space at the'rear of the diaphrgam is acoustically impeded thereby providing a directionally responsive unit, and'byswivelably mounting this unit in oron a base in suchmaiziner that the said path is entirely obstructed when the unit is tilted to position the frontal axis thereof vertically for non-directional'use. With this general arrangement the assembly may be instantly changed from one type of microphone to another, thereby eliminating'any necessity for 'aplurality of microphones at thepick-up station, and

any decrease in the output level .of the instrument due tothe sealing off of the rear acoustical chamber may be The'a'bove and other objects and advantages of the "invention will become apparent upon consideration of the following detailed specification and the-accompanying drawing'wherein there is 'disclosed certain: preferred "embodiments of the invention.

Un'ted States Patent Cfifice 2,763,730 Patented Sept. 18, 1956 In the drawing:

7 Figures 1 and 2 are side and front elevations, respectively, of a microphone constructed in accordance with the principles of our invention;

Figure 3 is a side elevation, partly in section, of the microphone of Figures 1 and 2;

Figure 4 is a .rear elevation of the microphone of Figures l and 2 but showing the cased diaphragm assembly in forwardly tilted position to expose the air inlets leading to the rear acoustical chamber to thereby effect directional characteristics to the instrument; and

Figure 5 is a front elevation, partly in section, of a modified form of microphone utilizing the principles of our invention.

In the embodiment of our apparatus illustrated in Figures 1 through 4 we provide a base 10 which is preferably of molded construction and which is provided in its upper surface with a spherical-shaped seat 11. As shown in Figure 1, the front and back faces of the base 10 slope toward each other to form, in conjunction with the spherical surface 11 and at .the upper end of the base a pair of transversely spaced ears 12 and 13. The base 10 may be arranged, as shown, to be supported directly on a flat surface, such as a table top, for example, although it should be understood that this space may assume other specific shapes than that shown and be arranged for support on .a vertically adjustable stand, not shown.

A generally spherical-shaped microphone unit having a'semi-spherical case 1415 swivelably mounted in the base 10 by a pair of pintles 15 which are carried by the ears :12 and'13. ,As shown,'the casing 14 isrslightly larger than alhemisphere and is of such dimension that it fits snugly within the seat 11. Closing oif the opening in the casing 14 is a diaphragm 16 and behind the diaphragm is a closure member 17 having an open back which in turnis closed by a porous sintered metal disc 18. Supported on "the disc 18 is a transducer 19 in the form of a piezoelectric crystal which is connected-to the diaphragm 16 in such manner that vibrations of the diaphragm cause the crystal to flex correspondinglythereby generatingtan undulating voltage'the frequency and amplitude of which correspond to the frequencyand amplitude of thesound waves impinging on the diaphragm. The outer face of the diaphragm 16 is protected by a semi-spherical cover member 19 which may either be of open mesh wire cloth or of perforated sheet metal as shown. Casing 14 is formed with'a multiplicity of apertures 20 in that area of the casing 14 which overlies thespherical-shaped seat 11 of'the base ltl'when the frontal axis of the diaphragm 16 is vertical.

It should be understood that the microphone uni-t comprised of the'casing 14*and the parts 16 through 20 has uni-directional characteristics in that the acoustical-impedance offered by'thesintered'metal disc 18 to the impingement of thesound waves'on the rear face of diaphragm 16 operates to shift the phase of the acoustical waves impinging onthe rear surface of the diaphragm Whenthe'waves are 'propagatedin a frontal direction to thereby augment'the driving motion of the diaphragm. The unit may be constructed generally in accordance 'with the disclosure contained in the co-pending application of Alexander L. Dvorsky, Ser. No. 205,349,,fi1ed 'January 10, I951, and'as explained in said co-pending application'theporous disc 18 is "preferably a sintered product made of bronze pellets.

"It should be equally'obvious that directional-response characteristics are achieved in themicrophoneunit'above 'describe'donly :when'the'unit is tilted to expose theaper- "tures'ZOin'theYcasing '14. .Upon the frontal axis of the microphone,nnit'gbeing tilted about-6O degrees fromveriical all the;.apertures ZU-areuncoveredand they remain uncovered, of course, upon further downward tilting movement of this axis. Such tilting'of the frontal axis of the microphone unit toward the horizontal is common practice for solo or localized pick-ups and is, of course, necessary for all types of directionally responsive microphones and it should therefore be apparent that in the normal use of the complete assembly of our invention directional characteristics are automatically created in the assembly through normal manipulation thereof.

Upon the unit comprised of the casing 14 being tilted to position the frontal axis of the diaphragm vertically all directional characteristics of the assembly are automatically abolished and because of the symmetry of the instrument about said vertical axis the response of the instrument in every horizontal direction will be uniform. This provides a superior pick-up unit for translating general sound effects or voices or sounds created by a conference or other group activity.

In the embodiment of the invention shown in Figure 3 the two electrical leads from the crystal 19' may be connected to lugs 21 which are mounted on disc 18 in insulated relation thereto and, as shown, one of the lugs 21 may be grounded through casing 14 and thus through face 10 while the other of the lugs is connected to an insulated contact 22 mounted in an aperture in casing 14 and having sliding connection with an insulated contact strip 22 which in turn is electrically connected to a lead line 23 extending outwardly of the base 10.

In the embodiment of the invention shown in Figure the contact 21 and the arcuate contact strip 22 as shown in Figure 3 are eliminated and the two electrical leads designated generally by reference numeral 24 leading from the crystal 19 are brought out through a hollow pintle pin 25 into a space within the hollow base 16 and thence outwardly through an opening in the side wall thereof. It will be understood that the pintle pin 25 rotatably supports the active microphone unit comprised of the casing 14.

It should now be apparent that we have provided a microphone assembly of exceedingly simple yet rugged construction in which improved controllability as to directional characteristics is effected. Of practical importance is the fact that when the position of the microphone is set in the most natural manner for transmitting general or group sounds emanating from various directions the microphone has no directional characteristics whatever but when the microphone is directed to pick up a localized sound it automatically achieves uni-directional characteristics of output.

The herein disclosed novel method of automatically cutting in or out the directional characteristics of a micro phone as required for the application at hand may be achieved by specific apparatus other than the specific apparatus herein shown and described and reference should therefore be had to the appended claims in determining the scope of the invention.

Having thus described our invention, what we claim is novel and desire to secure by Letters Patent is:

l. A microphone assembly comprising a base having a semi-spherical seat and having a pair of supports at diametrically opposite sides of said seat, a spherically shaped casing having a first semi-spherical portion of open mesh construction and a second semi-spherical portion formed of fluid-impervious material, said second portion of said casing being journaled on said supports for rotation about a common diametrical axis of said casing and of said spherical shaped seat, said second portion of said spherical casing having a plurality of apertures therein diametrically opposed to said open-mesh portion a transducer-driving diaphragm positioned in said casing between said first and second semi-spherical portions in substantially direct acoustical communication with said open mesh portion, means including said apertures for providing an impeded acoustical communication between said diaphragm and the area surrounding said casing, said Iast mentioned means being operative only when said apertures are exposed, and means to selectively cover and expose said apertures comprising said semi-spherical seat, said casing being rotatable on said supports to position said apertures in covered or exposed relation to said seat.

2. A microphone assembly comprising a casing, a transducer-driving diaphragm, an acoustical network comprising apertures formed in the rear portion of said casing to shift the phase of sound waves impinging on said diaphragm along a first axis with respect to sound waves impinging on said diaphragm along a second axis, means pivotally supporting said casing for tilting movement about a horizontal axis from a position in which said second axis is substantially vertical to a position in which said second axis makes a wide angle with respect to the vertical, and means to automatically close off said apertures upon said second axis being vertically disposed and to automatically open said apertures to the atmosphere upon said second axis being inclined with the vertical.

3. A microphone assembly comprising a base which is transversely elongated and formed with inwardly sloping front and back walls, said base being formed with a centrally disposed semi-spherical seat in its upper portion in bisecting relation to said front and back walls and having an upstanding support at each side edge of said base, a spherically-shaped casing journaled on said supports for rotation about a common diametrical axis of said casing and of said seat and nesting within said seat, a transducerdriving diaphragm positioned in said casing, said casing being of open-work construction on one side of said diaphragm and being of fluid-impervious construction on the other side of said diaphragm, said fluid-impervious portion having therein a plurality of apertures adapted to be closed oif by said seat when said casing is rotated into a position in which said open-work portion of said casingis directed vertically upward, and an acoustical network in the fluid-impervious section of said casing and including said apertures to shift the phase of the sound waves reaching said diaphragm through said apertures with respect to the sound waves reaching said diaphragm through said open-work portion, said network being so operative only upon said casing being tilted to uncover said apertures.

4. A microphone assembly comprising a casing, a transducer-driving diaphragm mounted in said casing, means in said casing providing a relatively unimepded acoustical path to said diaphragm in a first direction,

eans in said casing providing a relatively impeded acoustical path to said diaphragm in a direction opposite to said first direction, a base member for supporting said casing in operative positions, said casing being movable with respect to said base between two operative positions, and means associated with said base and casing for auto matically closing said impeded path upon movement of said easing into one of said operative positions, said impeded path being open when said casing is positioned in the other of said operative positions.

'5: Apparatus according to claim 4 further characterized by said first direction being substantially vertically downward when said casing is in said one operative position whereby said assembly is substantially nondirectional in its response characteristics to horizontally traveling sound waves, and by said direction being angularly related to the vertical when said casing is in said other operative position whereby said assembly is substantially unidirectional in its response characteristics to horizontally traveling sound waves.

6. A microphone assembly comprising a casing, a transducer-driving diaphragm mounted in said casing, said casing having means providing acoustical paths to said diaphragm along two divergently related axes, the arrangement being such that when said paths are open said assembly is substantially unidirectional in its response characteristics, a base member for supporting said casing in operative positions, said casing being movable with respect to said base between two operative positions, and means operative automatically when said casing is moved into a first operative position to close one of said acoustical paths to render said assembly substantially nondirectional in its response characteristics, said one path being automatically opened upon said casing being moved to the other of said operative positions.

7. A microphone assembly comprising a base member, a microphone movably supported on said base member, said microphone being of a type adapted for selec tive use for nondirectional or unidirectional operation, said microphone being adapted for movement with respect to said base member between two operative positions, and means associated with said base and said microphone operative automatically upon said microphone being moved into a first of said positions to condition said microphone for substantially unidirectional response and upon said microphone being moved into a econd of said positions to condition said microphone for substantially non-directional response.

8. A microphone assembly comprising a base n1emher having an arcuately shaped upper surface portion and upwardly projecting supports positioned on opposite sides of said surface portion, a microphone casing carried by said supports for pivotal movement about a fixed axis extending through the center of curvature of said arcuately shaped surface portion, said casing having an arcuately shaped outer surface portion adapted to closely overly the arcuately shaped surface portion of said base, said casing having an exposed open portion opposite the arcuately shaped surface thereof, a transducer-driving diaphragm within said casing and in substantially direct acoustical communication with said open end, the arcuately shaped surface portion of said casing having a plurality of apertures therein providing impeded acoustical communication with said diaphragm, the arcuately shaped surface portion of said base constituting means to close off said apertures when said casing is in predetermined rotational orientation with respect to said base.

9. In a microphone assembly the combination of a base, an apertured casing movably mounted on said base, said base having an outer surface portion adapted to cooperate with said apertured casing to control the flow of air into and out of the casing, said casing being movable from a position in which the apertures therein are closed by said surface portion to a position in which said apertures are fully exposed to the atmosphere, a transducer driving diaphragm mounted within said casing, said cas ing having an opening providing substantially direct acoustical communication with one side of said dia phragm, and an acoustical phase shifting network in said casing comprising said apertures, said phase shifting network being operative to provide said assembly with directional characteristics when said casing is moved to expose said apertures and being inoperative to provide said assembly with directional characteristics upon said casing being moved to position said apertures over said surface.

10 Apparatus according to claim 9 further characterized in that said casing is pivotally mounted on said base, said diaphragm being so oriented in said casing that said opening is directed substantially vertically upward upon said casing being tilted to move said apertures into overlying relation to said surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,301,638 Olson Nov. 10, 1942 2,328,941 Anderson Sept. 7, 1943 2,515,031 Black July 11, 1950 2,518,331 Kalin Aug. 8, 1950 2,520,714 Duncan Aug. 29, 1950 2,587,684 Bauer Mar. 4, 1952

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