US1976692A - Microphone - Google Patents

Description

J.L.SNOEK Oct. 9, 1934.

MICROPHONE Filed Dec. 17. 1952 2 Sheets-Sheet l INVENTOR- JACOB MSSMEK a. 9, 1934. J L SNOEK 1,976,692

MICROPHONE Filed Dec. 17. 1932 2 Sheets-Sheet 2 102 w m w m m 110 v I30 a: 1. I00 I00 s0 1/ 5 90 u 90 v I M I 00 x s0 5a P00203040 Maze/3040 001010 Y 250,500, 000

INVENTOR- ATTORNEY- Patented Oct. 9, 1934 UNITED STATES PATENT OFFICE MICROPHONE poration of Delaware Application December 17, 1932, Serial No. 647,728 In the Netherlands December 5, 1931 5 Claims. (Cl. 179-423) to simplify and general rule these limited angular directions are within a conehaving an opening angle of about 90 the axis of which is at right angles with the active microphone surface.

All other vibrations reaching the microphone in another direction than those whose axesare right angles to the active surface of the microphones are sensitive only in so far as low frequency vibrations are concerned. In such a case the microphones react very unsatisfactorily to I high frequency vibrations, for instance/those of more than 2000 cycles.

Consequently, microphones having a pronounced directional effect lend themselves as a general rule for satisfactorily picking up of unidirectional sound waves, because there it is possible to choose a favourable position for the microphone.

However, it will be appreciated, that whenever using microphones having a pronounced directional effect in the case of sound waves that are to be picked up which are produced by a plurality of different sound sources, for instance by an orchestra, it is not possible to choose a position which is suitable for each one of the instruments. 1

Insuch a case a {microphone will be required having no, or substantially no. directional effect.

The present invention has for its principal purpose to provide means ,by which it is rendered possible to provide a microphone which may be adjusted in such a manner that it hasa more or less pronounced or even no directional eflect at all, according to whether the circumstances under which the microphone is used require it to be so.

The microphone according to this invention thereupon be. connected together. The pick-up elements may be constructed in accordance with the electrodynamic, electrostatic or electromagnetic principle. Furthermore pick-up elements may be used comprised of separate chambers which contain the electrodes and are filled with carbon granules, the separate chambers being shutoff by a diaphragm. These latter well known form of microphones have a pronounced directional eflect.

The central support body preferably consists of a solid block of a material having the property of damping the vibrations and of being suitable electrically insulating, for instance such material as marble or alabaster may be used. Consequently, according to the invention the pick-up elements of the microphone may be secured to the periphery of the central support block, for instance, in form of a cube.

' However, it is also possible to interconnect the 7 It appears that with a suitable coupling arrangement of the pick-up elements the directional effect of such a microphone is considerably less pronounced than that of each of the pick-up elements separately. However, the pickup elements may also be connected in such a manner that a very strong directional effect is obtained. As stated above, this may be desirable in some cases.

' With reference to obtaining the proper working of the pick-up elements of the microphone they may be properly controlled by placing the microphone in or on a suitable rotary device at a certain distance apart from a stationary sound source, the tone of the stationary sound may be adjusted to a definite frequency. To the microphone terminals there is applied a proper working potential. An indicating instrument is then connected in the microphone line and the deflection of the instrument is measured for difierent positions of the microphone pick-up elements with respect to the constant direction from which the sound arrives. In this manner a polar diagram is obtained, of which some examples will be explained hereinafter with reference to Figs. 4a, 4b and 4c of the drawings.

I have found that it appears from making such a diagram that a microphone according to the invention, in which three or four pick-up elements are provided at the periphery of a central support body with an arrangement of the pick-up elements in such a manner that all pick-up elements behave uniformly with respect to the electric currents, has a considerable supporting bodies.

parallelopipedon at the side faces of which the pick-up elements are arranged. However, it is also possible but less simple from a point of view of manufacture, to provide the pick-up elements located around the periphery of a cylindrical body.

In a preferred form of construction of this invention the adjacent electrodes of the pick-up elements are secured to a common supporting -member and placed in a cavity of the central support body. Consequently, if four pick-up elements are provided there are also provided four In this case the central support body is provided with four perforations for receiving the supporting bodies. By means of suitable screws the electrodes may be secured to the supporting bodies. It is more practical to make the supporting bodies entirely or partly of an electrically conducting material. In this case the supporting bodies may be given such a' size that they will project slightly outward from the central support body, so that they may also serve for connecting suitable conductors to the microphone.

For clamping the diaphragm of the pick-up elements to the central body use is made of frames or frame-like members which are secured to the central body by means of screws or bolts. In one form of construction according to this invention the frames and the electrodes are fixed by the same means to the supporting bodies. In this manner a simple construction of the microphone is obtained.

With microphones according to this invention sound is picked up as follows. When it is consideredwhat properties are required by the re tary method mentioned above with respect to the directional effect the elements are then con: nected in series, in parallel or in series-parallel so that the desired effect is then obtained.

Several further important advantages of this microphone will be set forth by referenceto the several forms of construction represented in' the drawings.

Fig. 1 is a perspective view of a carbon form V of microphone construction according to this invention.

Fig. 2 is a partial cross section of. microphone construction along the line 22 of Fig.1. n Fig. 2a is a section along the line 2a of Fig. 2.

Figs. 3a, 3b and 30 represent several different circuit coupling arrangements of pick-up elements according to this form of microphone construction.

Fig. 4 shows several polar diagrams of the type referred to which are obtained in this manner and which more clearly illustrate the directional effect of the microphone according to the invention. v

Referring now in detail to Fig. 1, 1 denotes a prismatical block consisting of an antivibratory material, such as of marble or alabaster. This PM. These are absolute but relative values.

support body 1 is provided with four perforations extending in parallel with the upstanding ribs and in which four supporting bodies 2 are provided. The four carbon granual chambers 3 are clearly shown in Fig. 2. Each chamber is limited at the side walls by electrodes 4, while at the front side a slight projection is obtained by means of a diaphragm 5 consisting, for instance, of a mica sheet. The diaphragm and the electrodes are clamped as indicated in Fig. 2a between the central body 1 and the securing frames 6 of insulating material by means of screws 7 screwed into the supporting bodies 2.

As indicated,in Fig. 1 the supporting bodies project from the bottom of the central body 1, so that they may serve as a connecting point for conductors. In this case the supporting bodies must consist at least partly of electrically conducting material.

Fig. 3a indicates diagrammatically the manner in which the electric conductors are connected I only at A and B. A, B, C and D denote the junction terminals of the supporting bodies 2. It will be obvious that with this arrangement the branch ADCB is traversed by a weak current only so that the microphone works substantially as the normal or ordinary form of microphone with one pick-up element only. The corresponding polar diagram (Fig. 4a) shows that the microphone has a very strong directional effect with this arrangement.

In the polar diagrams according to Figs. 4a, 4b and 40 it must be imagined that the sound waves always 'come from the direction PM whereas the microphone, which is placed at M is turned over angles of 0 to 180 with respect to this line. variations produced for tones of different frequency are plotted radially as a function of the angle of the microphone with respect to the line In fact, for the sake of convenience the adjustment of the measuring device for difierent frequencies is such that with each manner of connection the sensitivenessof the microphone in the direction PM is the same for all frequencies. Consequently for judging the microphone in the different arrangements only the form of the various curves must be considered. r

The solid lines in the diagrams hold good for frequencies of 4000 and 3000 cycles respectively, the dotted lines for those of 2000 cycles, and the dash and dot lines for vibrations having a frequency of 250, .500 and 1000 cycles respectlvely.

It will be appreciated that in the arrangement shown in Fig. 3a the low frequencies are sufficiently taken up in every position of the microphone. The high frequencies on the contrary are taken up only when the element lying in the plane AB extends entirely or substantially entirely at right angles to the direction PM and if it is turned to the sound direction.

Consequently with this arrangement the microphone is poorly adapted for taking up music The values of the currentcoming from various directions, for instance,

orchestra music. This holds also good for the arrangement shown in Fig. 3b. 'In this arrangement the microphone behaves as if it consisted in this arrangement is still better adapted than in the arrangement shown in Fig. 3a.

A very uniform sensitiveness to different frequencies is obtained, however, when constructing the arrangement as shown in Fig. 3c. This is graphically indicated in Fig. 4b. Consequently in this arrangement the microphone according to the invention is particularly adapted for taking up sound waves not coming from various directions.

However, the microphone according to this invention has the advantage that the arrangement may also be such that there is a distinct directional effect, since by a simple changing over the microphone may be brought into the most favourable condition on one hand for taking up sound waves coming from a single direction and on the other hand for taking up sound waves coming from various directions.

A carbon microphone pick-up element according to the invention contains a particularly large member of active carbon particles, as it is well known that especially carbon microphones have the disagreeable property of producing an annoying buzzing noise.

The cause of this noise which is usually noticed by buzzing of the microphone is believed to be tight packing of.the carbon particles. I have found that the buzzing usually strongly decreases when increasing the number of active carbon particles. Therefore, it isadvisable to give the carbon chamber a constant cross section.

It has been found that the buzzing is inversely proportional to the rootof the number of active carbon particles so that a microphone according to this invention comprising four elements must produce a buzzing which is twice as small as that of a microphone comprising one element only. In fact, experiments have proved that this is approximately the case.

Furthermore, it has been found that the surface or active area of the diaphragm must be large so as to reduce the buzzing.

It will be obvious to those skilled in the art that a carbon microphone according to this invention satisfies all'of these conditions. Consequently the buzzing of such a microphone is materially smaller than that inherent to known forms of construction.

I claim:

1. A microphone comprising a plurality of cated substantially in -each corner of said body,

a plurality of metallic supporting members passing through the apertures in said body, and means on said supporting members for electrical connection of said pick-up elements.

2. A microphone comprising a plurality of pick-up elements having carbon granules located on the side faces of a cubical support body having apertures located substantially in each corner of said body, a plurality of metallic supporting members passing through the apertures in said body, and means on said supporting members for electrical connection of said pick-up elements.

3. A microphone comprising a plurality of pick-up elements located on the side faces of a cubical support body having apertures located substantially in each corner, a plurality of metallic supporting members passing through the apertures in said body, a threaded stud and a binding post on the lower portion of said supporting members for electrical connection of said pick-up elements.

4. A microphone comprising a plurality of pick-up elements, said pick-up elements located on the side faces of a cubical support body having apertures located substantially in eachcorner of said body, said pick-up elements comprising carbon granules retained on four faces of said support body by a frame-like member and a diaphragm, both the said frame-like member and the'said diaphragm being secured to said support body by retaining means joined to a plurality of metallic support. members passing for altering the electrical connection on said pick-up elements to modify the directional effect of said pick-up elements.

JACOB LOUIS SNOEK.

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