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March 19, 1963 R. GORIKE 3,082,298 FREQUENCY INDEPENDENT DIRECTIONAL CONDENSER MICROPHONE Filed Feb. 24, 1960 3 Sheets-Sheet 1 H6. 1 DIRECTIONAL PA T7£RN F01? PRIOR ARI’ cwvM/vsm MICROPHONE 160° 100Hz . m5 4\\\\\\\\\\\\ FREQUENCY RESPONSE (URI/E6 F01? PRIOR ART H6 2 comm/W51? MICROPHDNE A7 VAR/0V5 ANGLES 6F sou/v0 INCIDENCE 0” 45" 90’ 150" I55” IN VENTOR ATTORNEY March 19, 1963 3,082,298 R. GORIKE FREQUENCY INDEPENDENT DIRECTIONAL CONDENSER MICROPHONE Filed Feb. 24, 1960 3 Sheets-Sheet 2 2122 H6. 10 H6. 15 INVENTOR Papa/.1" 654’ be‘: I M‘ ATTORNEY March 19, 1963 R. GORIKE 3,082,298 FREQUENCY INDEPENDENT DIRECTIONAL CONDENSER MICROPHONE Filed Feb. 24. 1960 3 Sheets-Sheet 3 ; H6. 15 ¢ na 14 +70 H6‘ 75 3000 H2 135“ 7000 Hz 5000 Hz 100 Hz 90’ \ 00" 10000 Hz 15000 Hz 45" 00 I INVENTOR @ZOl-F 66!!!!‘ BY QM.“ fog-ma; ATTORNEY tt atent time 3,082,298 Patented Mar. 19, 1963 2 1 FIG. 2 shows frequency response curves of the conven tional condenser microphone for various angles of sound 3,082,298 FREQUENCY INDEPENDENT DIRECTIONAL CQNDENSER MIQROPHONE _ Rudolf Giirike, Vienna, Austria, assignor to Akustlsche u. Kino-Gerate Gesellschaft m.b.H., Vienna, Austria, 21 ?rm Filed Feb. 24, 1960, Ser. No. 10,718 Claims priority, application Austria Mar. 4, 1959 13 Claims. ((11. 179-111) incidence, FIG. 3 is an exploded view showing an illustrative embodiment of the invention having a unidirectional pattern, FIG. 4 shows the microphone formed from the parts of FIG. 3 in assembled condition, FIG. 5 shows an illustrative embodiment of the present invention having two diaphragms, The known directional condenser microphones have 10 FIG. 6 shows a microphone according to the invention having a bidirectional pattern, only a small self-capacitance (about 30400 picofarads). To obtain an adequate output voltage it is necessary, there FIG. 7 shows a microphone according to the invention having a prearranged diaphragm for protection against fore, to combine such microphones in a unit with the ?rst ampli?er stage or to connect them only by very short leads moisture, with the associated ampli?er. This results in one case in a 15 FIG. 8 shows a microphone embodying the invention relatively large microphone casing and in the other case which can be changed over from a unidirectional pattern in a reduction of the output voltage if the cable capacitance to an omnidirectional pattern, approaches the self-capacitance of the microphone. An FIG. 9' shows a microphone according to the invention increase of the dimensions of such a microphone button for for stereophonic recording, 20 a directional condenser microphone with the aim of in FIG. 10 shows the directional pattern of the micro creasing the self-capacitance has been opposed by the fact phone illustrated by FIG. 9, that the diameter of the button must be approximately of the order of magnitude of the Wavelength of the highest frequency to be transmitted in order to obtain a directional in FIG. 9, FIG. 12 shows the directional pattern of the micro— pattern which is largely independent of frequency because only in this case is the pressure gradient at the diaphragm linear up to the highest frequency to be transmitted. In ac~ FIG. 11 shows a modi?cation of the microphone shown phone of FIG. 11, FIGS. 13 and 14 show frequency response curves in rectangular coordinates for microphones in accordance with this invention, cordance therewith the usual directional condenser micro_ phones have a button about 1.5-3 centimeters in diameter FIG. 15 is a showing of the frequency response curves 30 and consequently only a low microphone capacitance. in polar coordinates, . On the other hand, condenser microphones have been FIG. 16 shows a microphone in accordance with this disclosed which have a diaphragm area of about 40 square invention having an elongated, narrow diaphragm. centimeters and a capacity of up to about 1000‘ picofarads. FIG. 17 shows the associated directional pattern for Iowever, these microphones designed as pressure trans higher frequencies, and > mitters do not have a frequency-independent directional 35 FIG. 18 shows a microphone embodying the invention pattern. Owing to their high self-capacitance they may in the form of a hexagonal pencil. be arranged at a distance from the ampli?er and may be The subject matter of the invention will be explained connected to the latter by a long cable (up to 10 meters more fully with reference to the above-mentioned ?gures. and more). As has already been stated initially hereinbefore, con As contrasted therewith the invention relates to a direc 40 denser microphones constituting pressure transmitters tional condenser microphone which has a frequency having a large diaphragm are already known. FIG. 1 independent directional pattern as well as a high self shows in polar coordinates, for different frequencies, the capacitance and which for this reason is particularly suit directional pattern of a microphone having a diaphragm able for use with portable tape recorders because, as in size of 4.5 X 9 centimeters. It is apparent that the direc 45 the case of a dynamic microphone, it may be connected tional effect increases with an increase in frequency. to the recording apparatus by a long cable whereas, com FIG. 2 shows the frequency curves of the same micro pared with the dynamic microphone, it has the advantage that sound phenomena taking place at high speed (tran sients) are transduced more accurately. The directional phone for various angles of sound incidence in polar coordinates. ' condenser microphone according to the invention belongs 50 . With such a transmitter the sound character of the sound recording will depend on the distance of the sound to the type in which the diaphragm is exposed to the sound source from the microphone because the ratio of direct to field on both sides and at least one phase shifting member indirect sound becomes dependent on distance. Besides, is provided to provide for directional effect. The micro the sound recordings made with such microphone are un phone according to the invention is characterized in that the diaphragm has an area of at least 10‘ square centi 55 natural owing to an exaggerated reverberation. For this reason it has become generally accepted that the trans meters and that the maximum dimension of the diaphragm, mitter must be small relative to the wavelength of the that is, the largest side of the diaphragm, in the case of a highest frequency to be transmitted in order to obtain a rectangular diaphragm, or the diameter of the diaphragm, in the case of a circular diaphragm, is much larger than frequency-independent directional pattern. the wavelength of the highest frequency of the transmitted 60 The invention discards this opinion because the meas ures according to the invention, which will be described range and that the upper limiting frequency of the phase hereinafter, enable even a condenser microphone having shifting element approximates the frequency at which the a relatively very large diaphragm to be designed for a pressure gradient reaches its highest value. frequency-independent directional pattern. The inven If a bidirectional eifect is desired, frictional acoustic resistance is provided between the diaphragm and electrode 65 tion relates to a-microphone the diaphragm of which is either alone or in combination with frictional acoustic resistance disposed directly on the rear of the cathode. In the drawings which partly illustrate the state of the exposed to the sound ?eld on both sides and which has a su?‘iciently frequency-independent directional pattern in spite of the large area of the diaphragm. For this reason a perfect sound recording can be made even in rooms hav art and partly illustrate embodiments of the invention, FIG. 1 shows the directional pattern of a condenser 70 ing poor acoustic characteristics. It has also been found microphone which is designed as a pressure transmitter that cables having a length of up to 20 meters resulted and has a large diaphragm in accordance with the prior art, in a loss of only about 4 decibels. This does not involve a 3,082,298 3 4 modi?cation of the frequency response, as is known, be cause only a voltage division occurs between the micro the sealing frame 4. The diaphragm 7 is placed on the electrode 5 and stressed by being adhesively connected at its rim. On the side facing away from the electrode the diaphragm is vapor-coated with a metal. The front cover phone capacitance and the cable capacitance. The invention provides further the use of a second dia phragm, which may be electrically effective or ineffective. In the former case different directional patterns can be adjusted in a manner known per se by a change of the polarizing voltage. By the provision of two diaphragms the microphone 8 of the housing with the protective grid 80 or with open ings forms the closure. The cable 9, which may be plas ticeinsulated and have a shielded core and a length of about 1.5 meter or more leads to the ampli?er. In FIG. 4 the microphone of FIG. 3 is diagrammati may be converted to a stereophonic microphone operat 10 cally shown in assembled condition. The diaphragm 7 is supported by the threads 6 and by the rim of the electrode ing on two separate channels. 5. The cavity 13 and the frictional acoustic resistance 2 Besides, the microphone may also be used as a speaker, form the phase-shifting member, which according to the e.g., for dictating apparatus. Owing to the high capacit invention is effective at frequencies below 2000 cycles per ance of the microphone a transformer may be connected second and provides for a unidirectional pattern in this thereto or a transistor ampli?er may be used which is as range. sembled with the microphone to form a unit and which FIG. 5 shows a microphone having two diaphragms 7a may also generate the polarizing voltage and which gen and 7b. One or both of said diaphragms may be elec erates such a high audiofrequency output voltage that the trically effective. It is known that different directional alternating voltage can be transmitted on unshielded lines. It is known that the directional pattern of a pressure 20 patterns can be set by electrical remote control where two electrically conducting diaphragms are provided. A fric transmitter is spherical as long as the wavelength of the tional resistance 1:’) may be arranged between the elec sound is small relative to the dimensions of the trans trodes 5a and 51'). mitter. Beyond this range the pressure builds up to pro A microphone having a bidirectional pattern is shown vide a directional effect which increases with the fre in FIG. 6. The diaphragm 17 of this microphone con~ quency. It is also known that the pressure gradient as a tains only a perforated electrode 18 as an acoustically driving force in a diaphragm exposed to the sound ?eld effective element. The frictional resistance is formed on both sides rises linearly until half the wavelength of the between the diaphragm and the perforated electrode. An sound approximately equals the sound detour around the additional frictional resistance 19 may be provided. For microphone, i.e. the sound path from the center of the front side of the diaphragm to the center of the rear side 30 protection against moisture, a microphone as shown in FIG. 4 may be provided with a slack, thin resilient dia~ of the diaphragm. The two effects described are obtained phragm 20 (FIG. 7). To vary the directional pattern it is almost at the same frequency so that the microphone be possible in accordance with the invention to provide a gins to show a directional effect due to a build-up of pres mechanically actuable slide 21 (FIG. 8). When the sure where the pressure gradient reaches its highest value. openings of the housing 22 are closed the undirectional As the limits are not de?nite, the transition is not strictly pattern is changed to an omnidirectional pattern. The de?ned so that it appears to be more suitable to consider latter pattern, however, has the above-described disad the phenomena which occur considerably above and be vantages of being dependent on frequency, although this low the critical frequency and then to draw conclusions may the desirable for achieving certain acoustic effects. regarding the behavior at the limiting frequency. The mechanism may also serve to obtain the highest At a frequency at which the sound detour corresponds ?delity. approximately to the wavelength the driving force effec The microphone according to FIG. 5 may also be used tive at the diaphragm due to the pressure gradient is for stereophonic recording if the two diaphragms are con theoretically zero. At the same frequency, however, the nected to separate transmission channels I and II, as is build-up of pressure on the front side of the diaphragm is already effective so that the resultant driving force at 45 shown in FIG. 9. En this case the microphone is oriented so that the diaphragm surfaces face the sound source. the diaphragm is larger than zero. Practical experiments The directional pattern is shown in FIG. 10. For stereo have shown that disturbing effects are virtually absent. With a diaphragm having an area of about 40 square phonic recording two individual microphones according to the invention may also be used which are disposed 50 close to each other for intensity recording and for A—B second. stercophonic recording are ‘spaced from each other and As is apparent from FIGS. 1 and 2 a unidirectional arranged at an angle of 90° relative to each other. effect is already obtained above 2000 cycles per second. The diaphragms may be inclined relative to each other. For this reason measures must be taken to provide for a This is an arrangement which has already been provided unidirectional effect below 2000 cycles per second. If the diaphragm has a bidirectional pattern the directional 55 in small microphones (FIG. 11). The patterns will ob viously also be inclined, as is shown in FIG. 12. In FIG. effects are obtained above approximately 2000 cycles 13 the frequency response curves are shown which are per second on both sides of the diaphragm. obtained with the microphones according to the invention In connection with small microphones, it is known to for a sound incidence at 0°, 45°, 90°, 135° and 180°, provide an unidirectional pattern by an RC member and to provide a bidirectional effect by an R member disposed 60 whereas FIG. 14 shows the frequency response curves for a microphone according to the invention having a bidirec in back of the diaphragm. This is also utilized according ' tional pattern for 0°, 90° and 180°. FIG. 15 shows in to the invention but these measures are effective accord polar coordinates the characteristics of a unidirectional ing to the invention only in the frequency range below centimeters the critical frequency is about 2000 cycles per approximately 2000 cycles per second. microphone according to the invention. Without depart trode 5 with parallel spacing threads 6 consisting, e.g., denser microphone in the form of, a hexagonal pencil. A In FIG. 3 a ?rst illustrative embodiment of the inven 65 ing from the invention the diaphragm may have any de sired proportions. For instance, a circular or oval form tion is shown. The ?gure shows the components of may be chosen provided that in accordance with the in a condenser microphone having a unidirectional pattern. vention the area of the diaphragm is suf?cient to ensure a One or more layers of a sheetlike acoustic frictional capacitance of approximately 1500 picofarads or more. resistance 2, e.g., ?lter paper, are inserted in a sheet metal casing 1 having a perforated bottom. A trough 3 consist 70 If the shape according to FIG. 16 is chosen a directional pattern as ‘shown in FIG. 17 is obtained for the higher ing, e.g., of plastic and having also a perforated bottom sound frequencies. This may be desirable for certain is placed on this resistance. An elastic sealing frame 4 applications. FIG. 18 is an enlarged view showing a con of plastic is inserted in the trough. The perforated elec of beads having a thickness of about 20 microns, rests on 75 hexagonal sleeve 21 is perforated on all side faces and 3,082,298 5 serves as an electrode. It is wound with spacing threads 22 and the diaphragm 23- is stretched on the outside over these threads on three adjacent side surfaces. The three side faces opposite to the diaphragm 23 are lined inside the sleeve with ?lter paper 24, a textile insert or the like forming an acoustic resistance. The ends of the sleeve are closed by plugs, not shown. I claim: ‘1. A directional condenser microphone for transmitting 6 7. A directional condenser microphone as in claim 3; wherein said sheet material is textile fabric. 8. A directional condenser microphone as in claim 3; wherein said perforated electrode is in the form of a hol low sleeve having said spacing threads wound thereon, said diaphragm covering a portion of the outer surface of said perforated sleeve, and said sheet material covering another portion of the surface of said sleeve. 9. A directional condenser microphone as in claim 8; a predetermined frequency range; comprising at least one 10 wherein said sleeve is of hexagonal cross-section and has diaphragm having front and rear faces with a minimum six ?at outer surface areas, said diaphragm covering three area of 10 square centimeters and a maximum dimension of said surface areas and said sheet material covering the substantially larger than the wavelength of the highest remaining three of said surface areas. frequency of said range, both of said faces- being exposed 10. A directional condenser microphone as in claim 2; to the action of the sound ?eld; support means carrying 15 wherein said spacing threads are of silk. said diaphragm; means constituting a frictional acoustic 11. A directional condenser microphone as in claim 2; resistance; said support means, said rear face of the dia wherein said spacing threads are of plastic. phragm and said means constituting a frictional acoustic 12. A directional condenser microphone as in claim 1; resistance de?ning a cavity; and said cavity and said fric further comprising an additional diaphragm disposed at tional acoustic resistance being operative as a phase-shift 20 the side of said phase-shifting element remote from the ing element only up to a predetermined frequency in said ?rst mentioned diaphragm. range at which one-half of the wavelength of sound is 13. A directional condenser microphone as in claim 12; less than the effective length of the sound path from the wherein said additional diaphragm is electrically inef center of said front face of the diaphragm around the fective. microphone to the center of said rear face of the dia 25 phragm. References Cited in the ?le of this patent 2. A directional condenser microphone as in claim 1; UNITED STATES PATENTS wherein said support means includes a perforated elec 1,753,137 Seibt _________________ __ Apr. 1, 1930 trode disposed at the rear face of the diaphragm and hav Edelman ____________ __ Sept. 16, 1930 ing spacing threads on the surface of the electrode facing 30 1,776,112 toward said diaphragm, said diaphragm being secured, at the periphery thereof, to said electrode. 2,387,845 2,686,847 Harry ________________ __ Oct. 30, 1945 Aamodt ______________ __ Aug. 17, 1954 3. A directional condenser microphone as in claim 2; wherein said means constituting a frictional acoustic resist ance includes porous sheet material disposed at the side 35 2,787,671 2,852,620 Grosskopf et al _________ __ Apr. 2, 1957 Schoeps et al. ________ __ Sept. 16, 1958 2,920,140 Morgan _______________ __ Jan. 5, 1960 571,870 884,516 920,311 ‘Great Britain _________ __ Sept. 12, 1945 Germany _____________ __ July 27, 1953 Germany ____________ __ Nov. 18, 1954 of said electrode facing away from said diaphragm. FOREIGN PATENTS 4. A directional condenser microphone as in claim 3; wherein said support means further includes means spac~ ing said sheet material from said electrode. 5. A directional condenser microphone as in claim 3; 40 wherein said sheet material is against said side of the electrode facing away from the diaphragm. 6. A directional condenser microphone as in claim 3; wherein said sheet material is ?lter paper. OTHER REFERENCES Acoustics, Beranek, 1954, pp. 149-1150‘.