US1634210A - Diaphragmless microphone - Google Patents

Description

E. REISZ.

DIAPHRAGMLBSS MICROPHO NLv June '28 1927.

Filed. Nov. 'l2'.F 1925 2 Sheets-Sheet 2 EUGEN :QE/sz BY Y.

l ,ATTORNEYS Fetenteai une 2te, we?.

.lleettcn tied Bcvczeter 12, iets', We. w, and in Germany September 1u, 1925.

clay and certain liquids or seits into e piestio mess on which the sound waves ci the eir ect,

These microphones do not hcwever possess any advantage, over the diaphragm micro i0 phones because their sensitiveness over e range of frequencies of from 100 to 7000 vibrations per seccn (such as `is norrneiiy required) is not constant, that is to eey, even in these arrangements denite frequencies accentuated. This isnt is shown by,

'the oiiowing consideration.

'Wien cosi dust is useci without u binciinej ugent the speces between the grains ci coal form a passage for the soun@l waves enti, more especieiiy, for the sound weves with low frequencies, so that the. sensitivencss increases with the irecguenc?,Y and 'then tiecreeses again owingi to the deieterious shunt eiect of the iower eyers. "When :1 binding agent is used, the purticies of coei no ionger osciliete incpendenty. oi each other hut form a coherent osciieting mess which must 'possess resonance points in exectiy the seme we)7 es a carbon diaphragm.

According to the present invention, these disadvantages are overcome hy using a mirture of coarse enci moiecuieriy fine cosi dust as e iiiiing materiel and piiingr this mixture into a. vibration-free receptacie to such e height that the sound waves oi'y the lowest frequency occurringr ure coninieteiy ahsorhec'i in the iiliing. the WhoisA ot the soundtenergyv being thus showed to exert its pressure aetion.

Figure i shows e :iront View of the inicrophone with theinsuiatingg film covering the carbon chambers, the frames supporting; the

l iim and the nridplete remove.

Figure 2 shows a horizontei section of the microphone.

Figure 3 showsin :i conventioneirepresentation, the arrangement or the carbon grains and the two electrodes. m`

Figure i is c. characteristic curr/e showing the proportion of the frequencies of the sound weves to the amount of the change of resistance.

Figure 5 shows a vsimiier curve for varied heights of the piie of cer-hon grains. `--"F:i,g'ure 6 shows :i similar curve for varied size ci' fthe powder.

Figure 7 shows e. curve for e low height of the cerhon powder for Ahigh frequencies.

Before describing e, constructional form of apparatus eccorfiing to 'the present invention, I wiil first explain, with reference to Figures 3 to ci the accompanying drawings, the operation of a fiiayrlhragmless microphone with e Contact powder tilting.

He Vibration-free receptece (see Figure f3) he teken, in which two iixeci electrodes are provide@ for the supply of current and coal dust be spread inthe-chambers between these eiectrocies, s microphone 'will he obtained the grains of the 'eerhon dust or operation of which is grephimilly` represented hy curves es in 1ffigures 4 and 5. For e, `given size of csrhon powder granule and when powder is p'ilefi up in the chamber to u certain height the characteristic curve shown in Figure 4i is obtained. Along the ebscisse erel set out the periodicities of the sound waves which excite the microphone und n rions; the ordinate, thek sensibility veines, that to soy, the magnitudes of the veristions of resistance. If the height to which the 'powder is piieri up he Varied, the dotted series ci curves (see Figure 5) will he ohtniuefi according? to the increase in the thickness of he iep-er ci' granules, while a .fiecrecse such thickness Wiil he represented hy the riot und 'dash curves.

A simiicr fiispizicement of the curves also taires piece, as shownin Figure 6, if' the size ot the freins of the carbon 'powcier he varied enti, with an increased size of grenuie the originai curve i is changed into curve 2.

These phenomene, which are also confirmed h3 exhaustive experiments which the applicant has marie are explained hylgthe fact that the soi'end Waves with the lower frcquencies e great extent through the interstitial speces between the cerhon pow fier granules and, therefore, do not produce :inv Variation of pressure on the grains themseives. 0n the other hsnfhthese interstitial spaces orier a very high resistance the sound waves with the higher frequencies, so that these sound waves are completely absorbed 'even the uppermost ieyers of powder and the iower layers then constitute a deleterious shunt to that port-ion of the carhon powder which is sensitive to changes of resistance. Thus, in the range oi' musical frequencies,

menare lwhich extends to 7000 vibrations per second, 1t 1s evidently necessary that the carbon powder vbe piled into the granule chamber to a very small height only. The obtention 'effected by using material having granules of various diderent sizes, varying say from about 1 mm. down to the very finest pulverulent molecular powder, because it is onlyV with such exceedingly fine material that the l powder c.

interstitial spaces can be completely closed agamst passage of the sound waves. `When `such material is used as Contact powder for the constructional form of the microphone shown in Figure 3, there results a characteristie curve, shown in Figure 7, which runs in a straight line over a sutliciently wide range of frequency.

The same effect could be obtained by the use of very tine powder alone but for the 'fact that such powder has the property of caking together, thus rendering the desired individual oscillation of the separate grains illusory.

'In the constructional form of the microphone shown in Figures l and 2, the layer of carbon is arranged vertically on the front of a fixed vibration free body e. g., a block a of marble. The fixed electrodes of carbon -or of a non-oxidizable metal, which form the connection Vbetween the carbon powder and the conductor wires (not shown) are fixed in two deep troughs 71. in the marble block a, in such a way that their free external surfaces are entirely covered by the contact The attachment is effected for vexample by providing the electrodes b with screws o winch are screwed into heads c of the screw belts-z' which heads are conformed to the shape of the electrodes. These bolts z' pass through the` body a'and are held on the reverse side thereof by nuts Z which Vservie at the same time, to carry the current.

The two lateral deep troughs fr merge at the front of the body a into the granule chamber y, which is exposed to action or the sound waves and is made very fiat, so that the layer of powder may be equally sensitive to variations of pressure for all the various frequencies that occur. The entire chamber is covered in at the front by a thin skin f of rubber, which keeps the powder under a fixed pressure when the chamber is in a vertical position.

The use of a rubber skin for preventing the carbon granules from falling out is known, but in the arrangement herein described it serves a further purpose tor, by

reason of its stretched condition, it increases the pressure under which the contact grains are maintained and makes the mass oi powder perfectly sound proof even when a, very thin layer is used. This rubber skin is held by a grid plate n (of fabric, gauze or the like) provided with a projecting rim m.

It is especially important also that the fixed electrodes shall not be attacked "by the sound waves; otherwise the Velectr-mie rods begin to oscillate. whereby resonance effects are produced in the system.

In the practical constructional form shown in Figure l, there is arranged-above the actual granule chamber, a subsidiary chamber p which can be closed bymeans of a plug g and the purpose of which is to supply the amount of powder required to keep up the constant pressure when the contact powder in the main chamber `settles down with lapse of time.

l claim:

l. In a microphonma vibration free insulating base, a pair of fixed electrodes mounted therein. a layer oi' Contact material extending between and over said fixed elcctrodes, said contact material consisting ot a. mixture ot' coarse grained and fine dust or powder filling 4the inteisticcs lbetween the grains and flexible `means for holding and pressing the grains together withia constant normal pressure.

2. In a microphone, a vibration free insulating base havingla chamber. a .pair of fixed electrodes mounted thcreinnin the base, a layer of `contact material in the chamber and extending o'rer said xed electrodes, Said contact materia/l consisting ot' a mixture of granules and fine dust or powder filling the intcrstices between the granules 'and a flexible stretched skin of an insulating material extending over said layer of contact material and' holding the same in said chamber with a constant normal pressure.

3. ln a microphone, a vibration free insulating base, provided with a chamber having depressions at opposite ends, a pair of elongated fixed electrodes in the depressions of the said base, a layer of Contact matcrial in the chamber and extending between and into said depressions, so as topartially surround said electrodes, said Contact material consisting of a mixture of granules lao'l llating material extending over saidfilling,

and a 'grid secured to the base and securing the skin in position.

5. In a microphone, a vibration-free in'- su'lating base, a granule chamber formed therein, trough-like recesses in the bottom of said granule chamber and extending across opposite ends thereof, elongated electrodes housed in said trough-like recesses, electrical conductin means extending through said base to said fixed electrodes, a layer of contact material filling sa-id granule chamber and extending into said recesses and partly around said hxed' electrodes, a iiexible skin of an insulating material stretched over said granule chamber, and means whereby the chamber is kept filled.

6. In a microphone, a 'vibration-free in sulatingl base, a granule chamber formed therein, trough-like recesses in the bottom' of said granule chamber and extending across opposite ends thereof, elongated electrodes housed in said trough-like recesses, electrical conducting bolts extending through said base and having heads fitting u on and secured to the electrodes, a contact lling in the granule chamber and the trough-like recesses, and

partly surrounding the electrodes, flexible means arranged to close said granule cham ber, and'a grid plate having a rim and secured to the base and securing the exible means in place.

7, In. a microphone, a vibration-free insu.

a granule chamber formed therelating base in, trough-like recesses in the bottomv of said granule'chamber and extending across opposite .ends thereof, fixed electrodes housed in said trough-like recesses,'electricalconducting means extending through said base to said fixed 'electrodes a granular contact fillin for the granule chamber and the troug -likerecesses, said filling consisting of a mass of coarse granules having their interstitial spaces completely filled by molecularly fine powder and iiexible means arn ranged to close said granule chamber and to exert a constant normal pressure on said 'filllng BIn a microphone, a vibration-free insulating base', a granule chamber formed therein, trough-like recesses in the bottom of said granule chamber and extending across opposite ends thereof, fixed electrodes housed in said trough-like recesses, electrical conductin means extending through said base to sai fixed electrodes, a layer of contact powder filling said granule chamber and extendinginto said recesses and'around said fixed electrodes, flexible means arranged to close said granule chamber and to exert a constant normal pressure on said filling,.an

and extending into said recesses and around said iixedelectrodes, iexible means' arranged to close said granule chamber and to exert a constant normal pressure on said filling, an auxiliary contact powder chamber in sai-d insulating base, an opening from said auxiiiary chamber into the granule chamber, an openingl from saidauxiliary chamber to an exterior surface of the base and means` for closing said last named opening.

In testimony whereof I have signed name to this specification. l

vwenn Brisa i

Images