MICROPHONE PLANT WITH SEVERAL MICROPHONES

The invention generally concerns an automatic microphone plant, which is suitable for the use with public-address systems, Schallaufzeichnungen, broadcasting transmissions, teleconferences and such a thing. More in detail the invention concerns a microphone plant with several microphones, which a monitoring circuit is downstream for selective connecting of the output signal of the microphone through over a gate circuit 05 to an exit as a function of the received sound in each case, whereby the practicing mention circuits are connected by a signal line. Regarding the number of the participants or the number of places, where a Schallaufnahme is necessary, several microphones are often used at such opportunities, like in churches, court halls, transmission studio, meetings and legislative bodies, conference halls, and in particular with so-called teleconferences. Will combined the output signals of the microphones thereby usually in a mixer, in order a reinforcement system, a record device or transmission connection to a entfemten place to be then supplied. If with a majority by microphones a conventional Miseher is used, the room noise becomes and the response in the comparison to the sound taken up by only one microphone strengthens taken up; also the inclination to PfeilstiSrungen increases due to Rüekkoppelungserseheinungen, even if only one microphone or two microphones should take up utilizable sound at the respective time. These features are in detail in the article “Direction Sensitive Gating; A new Approach ton of AUTOMATIC Mixing” of Stephen July stream and Thomas Tichy, JAES, VOL. 32, No. 7/8, 1984, July/August described. In recent time automatic Miseher was suggested, which connects through only signals of those microphones selectively (i.e. to the mixture mash course let through), from which an acoustic information signal will receive. The relative effectiveness of these mixers h gt in ers ter line from those means, which are used for the decision whether a microphone is to be connected through. A microphone should be switched rapidly and independently to a valid language input signal over a far Dynamikbereich “on” -. Nontheless it should not address up background noise in the area, and also not on speaking of speakers, whose language should be taken up better by another microphone. Besides a any space loudspeaker, which is present with many telephone conference call systems and sound delivers according to an audio signal of a distant place, should release not the microphone connecting. A connecting through technology, which does not depend on a derived a signal from the microphone output signal, which exceeds a fixed threshold value, been sufficient all these criteria. In the literature different connecting through techniques are suggested, which are practically throughout not satisfying. Thus e.g. dieUS HP suggest 3,814,856 for the improvement of the Durchschaltempfindiichkeit under avoidance of responding on room noise that the threshold value for each microphone signal through-connection of an estimation of the background noise in the area is to follow, with the help of a their own, the noise of taking up microphone, which in a distant place are arranged, or due to an average value of all microphones in the system is made. In the US-PS 3,751,602 a simple telephone conference call system is descriptive, with which a simple microphone in a microphone loudspeaker arrangement is essentially connected through. The noise reference size is received from the only microphone, whereby a representation of the level in a circuit with very slow responding and rapid fading away is processed. Additional circuits prevent a connecting of the microphone through with a sound from the loudspeaker in most room acoustics environments. The US-PS 3,755,625 describes a plant, with which in each case a microphone from several microphones is connected through to a certain time. To this connecting through (and accordingly for the any disconnection of the microphone connected through before) the microphone level must exceed a fixed threshold value, and it must exceed also the level of the microphone connected through before around a selected value, e.g. 3 railways. In the US-PS 4,099,025 is suggested preventing for prevention connecting through of several microphones for individual acoustic source, if a microphone level exceeds a threshold value, triggering all other microphones for a certain length of time plus a short auxiliary time which corresponds approximately to that time, which the sound needs, in order to arrive at the furthest distant microphone the plant. The US-PS 4,090,032 reveals a microphone plant, with which a preselectable fixed threshold value is overridden, as soon as at least from a microphone of the output levels exceeds this Sehwellenwert and is connected through the microphone. The threshold value varies then between a high maximum level and approximately the level of the connected through microphone with the highest level. Connecting through of more than few microphones at the same time even for more (carriage return character) Schallqucllen unite strengstens are prevented. In the US-PS 4,489,442 it is suggested that each “microphone” bcstcht from an arrangement of for example two transducers with Richtungscharaktcristik, which are arranged backs at backs in a common housing, and whose output level is compared with one another. If the level of the front transducer No. 388480 exceeds the level of the rear transducer by a predetermined value, about 9.54 railways, (which means that within a “camera angle” is the acoustic sources), for the signal of the front transducer connecting through is caused. With this well-known system an effective connecting through threshold value is intended in the further, which is to notwen05 digerweise with approximately 5 railways above the ambient noiselevel because of the place of the microphone. Altogether with this training a riehtungsempfindliche connection is received from microphones, which the number of turned on microphones limits with individual acoustic sources, whereby no connection of arbitrary microphones is arranged. In all other respects this system makes a such mounting possible of a telephone conference call system loudspeaker that this does not cause connecting through of any microphone and also not connecting through of Schallsignalen for present speakers substantially handicapped. The FunkUonsprinzip of this well-known system requires however special care during the arrangement of microphone and loudspeaker. Also it is possible to release with only one acoustic source the connection of several microphones which have each other overlapping camera angles. For each microphone in particular two high-quality, to each other suitable transducers are necessary, even if only in each case this pair can be heard. It is of special importance that a normal connecting through by acoustically reflecting articles close of the back of the microphone or by attachment of the microphone at to large distance of an acoustic source, related to which response field in the area can be prevented, whereby by these effects the microphone is prevented from an exact collection of the direction of the acoustic source. The sound, which a microphone in an area “hears”, can simplified as from two parts is existing described: A direct sound, which decreases by a level value from 6 railways with each spacer duplication; and a response field, which comes from all directions, and which essentially remains in the entire area with an even level, if it fades away. This technology of direction-sensitive connecting through functions so long gu to t, as long as the microphone is not too far distant from the acoustic source, so that the response field dominates with the Schallaufnahme of the microphone. In larger areas this is only then the case if the microphone is in a distance from approx. 1.5 m and more from the speaker. With such a distance however the admission would be already hollow, dully/mustily and possibly. incomprehensibly. In smaller areas, as e.g. in office space and many conference rooms, the response field can already dominate with distances from approx. 60 cm or less, whereby a normal connecting through is prevented using the direction-sensitive microphone technology with appropriate distances between speakers and microphone. Contrary to the Verhälmissen in larger areas however the clay/tone photograph quality, sclbst with predominating response, is still understandable and according to the rapid fading time with the response quite acceptable in most these smaller areas. As thus evident, a need at a microphone plant with maximum connecting through sensitivity exists to permit with variable background noise in the area, whereby it is possible to prevent connecting through of several microphones with only one speaker with several Sprechem however simultaneous connecting through of several microphones with small mutual handicap, and all of this in an environment with extemem echo (i.e. e.g. in a small area). Also a sound, which comes from the loudspeaker of a telephone conference call system, should not turn microphones on, whereby desired connecting of a local language through should be not substantially obstructed at the same time, again also in an environment with strong response. It is from there a goal of the invention planning a microphone plant of the initially indicated kind with which in the case of only one speaker in electronic way it is prevented dal several microphones at the same time to the exit to be connected through, but only one microphone, i.e. that one with the strongest output signal, is connected through, against what in the case by several Sprechem for that one by these an associated microphone is to be connected through. During the Sicherstellung of this connecting through behavior likewise is to be considered as the circumstance that when planning a loudspeaker, e.g. with telephone conference call systems, not inadvertently the sound radiated by this loudspeaker causes connecting a microphone through, to which it otherwise in the microphone plant without further precautions to be come could in the consequence also to the variable background noise in the area. All these and further characteristics should be realizable thereby also in areas with extremely strong response, in particular in small areas. In weitercr consequence also the creation of so-called “neutral zones” is to be possible in an area, whereby in these zones acoustic sources present are not to be able to cause connecting any microphone through. The microphone plant according to invention of the initially indicated kind is characterized by it that each monitoring circuit contains with the SignaIleitung connected comparison circuit, to which at the input side No. 388480 further a signal according to the output signal of the associated microphone over a level circuit switchable as a function of connecting the microphone output signal through in the level is put on, whereby of the monitoring circuits to the signal line a signal is put as maximum signal according to the strongest microphone output signal, and that with the comparison circuit one of it is connected triggerable gate signal circuit 05, to which the gate circuit with a S expensive entrance is attached. With such training in simple and reliable way it is reached that, if an accordingly strong output signal of a microphone is present according to triggering the gate signal circuit a gate signal is then set on the gate circuit, in order to cause a connecting of the microphone output signal through. Thus a reliable connecting through of microphones, i.e. microphone output signals, with a maximum sensitivity to speech sound, is reached against what responding look up changing sound according to of background noises in the area one avoids. In the case of only one speaker also reliably only one microphone to course signal is durehgeschaltet, that one, which fulfills the maximum signal criterion. The maximum signal prominent signal line is the only connection between the individual microphone circuits, i.e. the monitoring circuits, and it leads a variable direct current signal equal the maximum of the variable direct current levels of all turned on microphones as also all not turned on microphones, decreased by a firm amount, which is specified e.g. with 6 railways. In order to fulfill this so-called maximum signal criterion, for a microphone the assigned monitoring circuit must “high-hold” at least momentarily the maximum signal signal line (i.e. the maximum signal plan). If this is fulfilled, the associated gate signal attitude is triggered, in which the trigger signal repeats triggerable mono-stable trigger circuit for a “preservation time” e.g. from one is extended, which is specified for example with 0,4 s and is sufficient, in order to bridge gaps with triggering and according to of breaks between words. A subordinate circuit steers the Ansprechund decay rates of the audio signal around attitude, in order to improve the Durchsehaltung. These gate circuits can be trained essentially similarly or equal to those circuits, which are descriptive for similar purposes in the aforementioned US-PS 4,489,442. Although this will not be necessary in many cases, all microphones can be identical and operate to same reinforcement, whereby they differ only in their adjustment and arrangement relative to the different acoustic sources. If a speaker speaks, reached his sound it microphone next arranged (best for the admission of its voice is suitable) before all other microphones and scolded this one, next microphone “on”. This “on” - switched microphone directly e.g. obtains 6 a railway gain compared with the other not turned on microphones, whereby the other microphones are held from the Durchsehaltung for evenly this speaker. Therefore scolded individual speaker only one microphone on, however several speakers can turn normally reliably several microphones on. Normal speech samples have frequent points, a lowering, misfire and breaks, which in the mentioned see to rapidly changing direct current signals are exactly represented. Since several speakers cannot synchronize these changes, frequently possibilities for everyone are given a speaker next convenient microphone “to high-hold” over momentarily the maximum signal signal line, which leads to a gate signal for connecting through, whereby the trigger signal is extended above as beschriebcn. The rapid changes of direct current signal of each voice are normally much larger than the differences the average on average between individual voices. This makes possible also with quieter speaking a turning on it assigned microphone, even if a loud speaker speaks at the same time into another microphone. A favourable further training of the invention is characterized by that by the nmschaltbare level circuit and you are joined in parallel the comparison circuit connected at the outlet side formed S Œ stop circle a Sehwellenwertschaltung with comparator downstream, whereby the comparator is subjected with a signal at the input side deduced by the microphone output signal further, and that the exits of the comparison circuit and the comparator at an AND circuit are put, whereby the associated gate circuit is up-steered only if the microphone output signal achieves a predetermined relationship both for the threshold value of the threshold value circuit and to the maximum signal on the signal line. With this training can be considered to the consideration of the background noise in the area, already addressed, so that the respective microphone not alone then, if its output signal exceeds the Vergleichssignal (maximum signal), but only under simultaneous fulfillment also the condition that a given Sehwellenwertder for the background noise is exceeded representatively actual in appropriate extent, to the exit is connected through. That see normally levels background noise constantly changes, is it here further of special advantage, if threshold value circuit at least control inlet for adjustment their threshold value exhibits and to this control inlet with of Mikrofon_Ausgangssignal deduced signal subjects No. 388480 is, whereby the threshold value is adjustable as a function of the noise level in the area, in which the microphones are. In this way the threshold value mentioned can be adapted automatically at this Geräusehpegel, in order to prevent in such a way that over a certain value of rising noise levels connecting a microphone through releases. For distinction between background noise and utilizable sound (speak) it is further appropriate thereby 05 if the threshold value of the threshold value circuit is rapidly alterable with a raising langsarn, with dropping. A technical circuiting favourable execution form regarding the threshold value adjustment is characterized here by that the Sehwellenwertschaltung contains a reservoir capacitor specifying the threshold value by its load, which is connected with the exit of an amplifier, which is beanfschlagt at an entrance with the signal deduced by the microphone output signal. It is further favorable regarding particularly simple and effective training, if the reservoir capacitor is fed back to another entrance of the amplifier, in order to steer the Aufund unloading of the reservoir capacitor. For the different speeds with the change of the threshold value (slow raising, rapid dropping) it is also favourable, if different Aufladeund of unloading circles, with different time constants, is assigned to the reservoir capacitor. It is also favourable, if the gate signal circuit exhibits a separate gate signal to course, and/or if the gate signal circuit contains a gate signal antiresonant circuit controllable over a mute circuit control inlet. In this way according to invention planned the triggered gate signal circuit can be consulted at the same time as “interface” for further functions, i.e. in order for connecting through the responsible person signal also for other purposes, e.g. mute-scolded a loudspeaker, switching on on of a Videokamem etc., to use and/or over (arbitrarily) the microphone connecting from the outside otherwise released ago to prevent. In order to prevent in the case of an active loudspeaker connecting of a microphone through otherwise taking place, it is favorable, if during planning at least one loudspeaker in the range of the microphones an inhibit signal generator subjected with the loudspeaker signal is intended, whose exit is put to the monitoring circuits for the blockage of the gate signal circuits with the occurrence of a loudspeaker signal. Such an inhibit signal could be used in a direct microphone signal comparison or to the signal line put on, in order to prevent a connecting through with a direct sound from the loudspeaker to the microphone. This would have a minimum effect on desired connecting through for simultaneous local speaking. However sufficiently energy is in the fading away response of the Lautspreeherschalls present, in order to release the Durehschaltung after omission of the inhibit signal in most areas, if the latter is put on in this way. The fading time of the inhibit signal would have to be extended outer f several 10 s and more (for acoustically particularly bad areas), in order to prevent a wrong connecting through. This would bring the rapid change in level in the signal to omission and would make an interruption of an arriving speaker extraordinarily difficult by turning a microphone on. It has sees proven from there as favourable if the exit of the inhibit signal generator is put to a threshold value raising circle of the threshold value circuits of the monitoring circuits. In this way the threshold value can become “high-held”, either by own action or by the inhibit signal, depending on, which is evenly larger. The inhibit signal is measured suitable, in order to prevent according to connecting through the most unfavorable loudspeaker microphone coupling, and short time constants are maintained, in order to reduce the handicap of desired connecting through ffir a good Unterbrechungsmögliehkeit to a minimum. If close, signal again fades away, is not the modified threshold value not equal before the application of the inhibit signal. The modified threshold value follows dern fading away inhibit signal level, until it reaches the level due to the microphone output signal, and away from there it follows the latter level. In absence of a local language the acoustic entrance of the microphone, which follows fading away the inhibit signal directly, is the fading away response of the loudspeaker sound. This does not release Durchsehaltung, since the threshold value criterion is not fulfilled. For desired Durchschaltbzw. Check behavior is of advantage it here also, if the loudspeaker and the microphones are relatively to each other held in firm positions, whereby it is particularly favorable further, if the microphones are laterally outward turned in same distances along a circle arranged and by the center of the circle, against what the loudspeaker is upward attached turned by the Kreismittelpunkt. The acoustic interpretation can be optimized, in order to receive a smooth, bmitbandige Sprachaufnahme and reproduction without Frequenzansprechabweichungen, how they are usually found, if elektroakustisehe transducers are used in close proximity to reflecting surfaces. The loudspeaker distributes all around its sound homogeneously to all Kon more ferenzteilnehmer. The microphones take up the language essentially homogeneously No. 388480 from all sides, with a considerable reduction of the room noise and the response admission, compared to an arrangement with a only one generally arranged microphone. Additionally the arranged microphones Nm the loudspeaker are in such a manner arranged around that the direct loudspeaker sound is not taken up in maximum extent. 05 the descriptive loudspeakers microphone units can be used separately or interlinkedly (“daisy chained”, i.e. under connection to only one bus), in order to achieve a better acoustic collection with longer tables or a majority of tables. A connection is made e.g. by only one multiconductor cable, also the turned on microphone exits, which connects signal lines and the loudspeaker lines. Only dern respective speaker the microphone next present scolded further for its language on. The invention makes thus an optimal connection of microphone possible in telephone conference call systems and/or with combined loudspeaker microphone plants, whereby a rapid and perfectly safe installation, Einstellnng and an adjustment of the system are possible, and whereby an improved Schallaufnahme is obtained also with difficult enviromental conditions. Furthermore is also easy the system to extend. Also several loudspeakers can be intended in a concatenated arrangement. In order to take up furthermore a constant response field with continuous level also at varying number of turned on Mlkrofonen, an automatic gain setting for the microphones can be planned, whereby the microphones can be arranged far from each other far away or however close together. Particularly in the latter case it is appropriate to use direction microphones. With the available microphone plant in particular signal processing circuits are used, which use supplied electrical the signal in the case of a teleconference plant that the respective loudspeaker, which is entzerrt in similar way in the frequency, on details, rapidly changing direct current signals to respond itself, and. Each circuit works on the pertinent direct current signal in a threshold value circuit with slow responding and direct fading away, whereby a threshold value with intoxication adjustment will receive, which after the Hintergrnnd Geräaschpegel existing during short Sprechpausen in the area adjusts itself, which essentially does not react however to SprachschaIlwellen. In order if necessary to then introduce a connecting through, the direct current level must with a microphone the associated - adapted - threshold value around one e.g. with 6 railways specified amount iiberschreiten, which is sufficient straight, around a wrong triggering according to the gate signal circuit coincidental noise level fluctuations too protected. This makes a high connecting through sensitivity possible (low Schweilenwert) when speaking, even if a room noise is present, whereby this high connecting through sensitivity can be further improved by the use of Richlmikrofonen. For example it is possible in a telephone conference call system that no room noise admission with typically 5 to 7 railways, compared to direct language admission, via which microphones takes place. For example does a direct language accordingly become a microphone with approximately the measured ambient noiselevel (measured dumh an generally arranged standard Geräuschmel? turn on, einrichtnng). The invention is still continued to describe below on the basis of remark examples represented in the design. In detail show in the design: Fig. 1 one pattern-fishes, look-figurative regards to a microphone plant in form of a telephone conference call system; Fig. 2 a plan view on a microphone/loudspeaker unit hiefür; Fig. 3 a side view these microphone/Lantsprecher.Einheit in accordance with Fig. 2; Fig. 4 a block diagram of the telephone conference call system in accordance with Fig. 1; Fig. 5 a block diagram the microphone/loudspeaker Sehallkreises of the circuit in accordance with Fig. 4; Fig. 6 a block diagram of one the Mikrofonschaltnngen of the circuit in accordance with Fig. 5; the Fig. 7-13 diagrams of parts of the microphone circuit in accordance with Fig. 6; and Fig. 14 a representation a microphone plant amended by microphone directivity patterns with. In Fig. 1 is schematically a telephone conference call system illustrated, which contains a microphone/loudspeaker unit (11) with a diameter of approximately 30 cm, which are arranged in the center of a Konferenztisehes (13). The microphone/loudspeaker unit (11) is connected with a control unit (15) of the system by a cable (35), which can be moved through in the table bored holes or simply anf the table top side lie. The control unit (15) is connected to connections with a telephone line wall connector (19) by a conventional telephone line (31) for usual “two-wire” -. Further a telephone (17) is attached over a telephone line (33) to the control unit (15). The users can either the telephone (17) or the microphone/loudspeaker unit (11) and the associated circuit in the control unit (15) with the telephone line wall connector (19) connect automatically. Although a connection with a two-wire communication (more combined send/receipt way) is represented, the system can nevertheless also during a four-wire communication (separate send. and receipt way) to be used, No. 388480 those hard-wired or in form of a Funkoder satellite connection be present can. Radio communication can be for example also those of a mobile telephone system. As into the Fig. 2 and 3, contains those is shown microphone/loudspeaker unit (of 11) three direction microphones arranged outward (21.23 and 25) (with kardioidförmiger directional characteristic), which are along the circular over catch 05 of a base (27) in same distances from each other arranged. On the conference table (13) (Fig. 1) a flat, approximately conical form possesses bases (27), which can be set up. In the acoustic center-blaze zero point of the three microphones (21.23 and 25) is arranged a loudspeaker (29), which is upward arranged and flat concisely in the base (27) built. At such an arrangement the microphones (21.23 and 25) work outer rordentlich close of the table surface and with a minimum acoustic lnterferenz according to the base (27). Also the loudspeaker (29) works essentially, as if it would be concisely flat built into a large, even surface. As this is descriptive in the literature, then both the microphones can do (21.23 and 25) and that loudspeaker (29) a smooth, equal förmigen frequency response over the entire Sprechfrcquenzbcrcieh without the usual unfavorable effects by reflections at the table surface to have. In addition the direction measure can do both the microphones (21, 23 and 25) and the loudspeaker (29) by an amount of approximately 3.0 railways (compared to the free area) to be increased, which the purity of the Schallaufnahme and - erzcugung increases. The horizontal distribution of the loudspeaker sound is reached primarily by its small size (cone with approximately 5 cm diameters), whereby a “Riehtstrahl” is avoided to a large extent - effect. Each microphone (21, 23 and 25) reduces an unwanted Schallaufnahme (room noise, response and loudspeaker sound) thereby that it is normally held in one “out” - condition, until it is used. A microphone becomes only then automatically “on” - switched, if it is that microphone, which is next a speech acoustic source different of the loudspeaker. In the case of a noise level in the area or a sound of the loudspeaker none of the microphones (21.23 and 25) is turned on. In absence of a local language the microphones are closed, and it will reassign no echo from LautsprecherschalI to the far end of the communication link. The microphones scolded rapidly and reliably in responding on a Sprachsignal “”, without they cut syllables or words off. According to their Riehtungsempfindlichkeit in connection with the acoustic arrangement of loudspeaker and microphones in the unit (11), as before described, reduce the microphones an acoustic coupling of the loudspeaker and the admission of Raumgeräasch and response in the turned on condition to a minimum. At the conference table (13) several units (11) can be used, which can be switched electrically into chain, as will still more nfiher be described below. In accordance with Fig. those contains 4 microphone/loudspeaker unit (11) a microphone! Loudspeaker circuit (41), and the control unit (15) contains a gate circuit (43). That microphone/Lau tsprecher circuit (41) receives signals from the microphones (21.23 and 25) and gives on that in responding connected through and niehtdurchgeschaltete microphone output signals on the respective lines (45) (for durehgeschaltete microphone output signals) and (47) (for non-connected through microphone output signals) off. The microphone output signals are received from the gate circuit (43), in order to produce a Sendesignal for the transmission for the wall connector mechanism (19). The audio information supplied of the wall connector (19) is used on the other hand by the gate circuit (43) for the delivery of a loudspeaker signal on a line (49). The loudspeaker signal on the line (49) is received from the microphone/loudspeaker circuit (41), in order to head for the loudspeaker (29). The gate circuit (43) can be trained in any suitable, well-known way. It plans a weakening of the loudspeaker signal, if a local language under turning a microphone on interrupts the received language, however takes place this weakening only in such an extent, how it is necessary for the reliable retention of a feedback stability. If the local language is interrupted from the far end, the going out microphone output signal is suppressed, and that loudspeakers is normally heard. The Stcuerschaltung (43) certainly also the necessary change-over sends/EmpfangsRichtung, so that the suppression takes place unobstrusively and in a way aligned to the Konversation. If both ends and/or participant speak at the same time, the interrupting participant is treated with priority, whereby the natural reciprocal effect is maintained. Everyone of the two participants can “come through” always, without having to cry. The combined connected through signals of all turned on microphones are supplied to the gate circuit (43) on the line (45), and sic can be led for example across a usual current expensive amplifier, before they arrive at a conventional hybrid integrated circuit for the forwarding at the telephone line over the plug (19). No. 388480 in accordance with Fig. the MikrofoniLautsprecher circuit (41) contains 5 a Durehschalteanordnung (50), the three microphone circuits (51, 53 and 55) contains, the appropriate microphones (21, 23 and 25) is assigned. A conventional achievement amplifier (59) verse strengthens the loudspeaker signal coming from the gate circuit (43) and supplies it by way of a line (58) with a sufficient Leistungspegel to the loudspeaker (29). The loudspeaker signal transferred on the line (58) keeps 05 a Sperrsignalgenemtor (57) zugeffihrt and produced in responding on that an inhibit signal for each microphone circuit (51, 53 and 55). These microphone circuits (51, 53 and 55) are from similar structure, and accordingly only such a microphone circuit becomes following on the basis the Fig. 6 to 12 more near describes. A signal line (56), below also max bus mentioned, connects the microphone circuits (51, 53 and 55), does not need however not to the gate circuit (43) to be attached, like below with reference to the Fig. to 6 and 11 one will still more near state. In accordance with Fig. 6 the microphone (21) is electrically attached to a preamplifier interface circuit (61). After the preamplification the microphone output signal is put to the line (47) and connected through if necessary over an opto coupler (69), planned as gate circuit, on the line (45). The remaining circuit of Fig. the Aufsteuerung of the opto coupler (69) steers 6 by production of a gate signal on a line (71) to the opto coupler (69). The gate signal on the line (7l) becomes in correspondence (1) the preamplified output signal of of the assigned microphone on a line (73), (2) to in relationship with other microphones the standing the signal, that so-called maximum signal at the max bus (56)” (3) to the loudspeaker signal on the line (58) and (4) to a entwaigen Stummsehaltungslogiksignal on an input line (75) deduced. The microphone output signal on the line (73) arrives at a alignment Kalibirierschaltung (81), which is used, around the associated microphone circuit (51) (Fig. 5) to adjust in such a manner that all three microphone circuits (51, 53 and 55) work same. The microphone output signal is supplied thereafter to a Frequenzentzerrer (“Equalizer”) /Gleichrichterschaltung (83), which accomplishes a Frequenzentzerrung of the audio signal. Lower frequencies and, in smaller extent, high frequencies are reduced compared with the center frequencies in the level. The circuit (83) accomplishes also a precision full-wave rectification of the audio signal and filters the result. Because of the exit thus a GleichspannungssignaI with variable level, which contains information about the amplitude and appearance time of the speech sound as well as the noise level taken up in the area, as by the associated microphone (21, is to the circuit (83)). The exit of the circuit (83) is produced to an intoxication adjustment threshold value circuit (85) put, some threshold value voltage level, which is representative for the noise level in the area in the neighbourhood of the microphone (21). The Sehwellenwertschaltung (85) produces the threshold value by that she follows the mentioned Gleichspannungssignal, whereby she follows directly with an admission very slowly and with fading away. If the direct current signal rises, - as will be still described - a condenser over an RC element with large time constant slowly loaded, and if the direct current signal is then omitted, the condenser with the same speed, how the direct current signal drops, is unloaded. According to the samples when usual speaking the arising tension at the condenser is for the noise level in the area repr'äsentaUv. The threshold value adapts thus to the constant background noise in the area, which does not fall under a besümmten level. Normal speaking will not substantially load the condenser, and the condenser will unload itself constantly at extraordinarily short Sprechpausen to the value according to the noise level in the area. The direct current signal at the exit of the circuit (83) is put also to a reducer circuit (87), where it around 6 railways (according to a factor 2) is weakened. The exit of the reducer circuit (87) and the exit of the threshold value circuit (85) are set on a tension comparator (89). The comparator (89) emits an output signal, which indicates, if rapidly varying speaking exceeds the threshold value representing the kontiniuierliche noise in the area around 6 railways. In this way the exit of the comparator (89) results in an independent decision regarding the microphone, with which speaking arises. As mentioned, the other microphone circuits contain appropriate S chaltkreise, so that at a comparator according to the comparator (89) output signals are present also there, if a Sprachsignal of individual speaker reaches everyone of the microphones (21, 23, 25). Since with individual acoustic source only one microphone is to be turned on, the output signal of the comparator (89) in one becomes together with the descriptive circuits (81.83, 85, 87 and 89) a monitoring circuit for the associated microphone (21) forms - and gate (91) with a second decision signal in accordance with an AND function links, in order to determine whether the associated microphone is to be connected through over the opto coupler (69). In the second decision procedure thereby determined, welchcs the microphones as the first the loudest sound received. No. 388480 the max bus (56) receives thereby signals, which are representative for the other microphone output signals and are meant for use in the second decision procedure. The max bus (56) is connected with a decision circuit (97), effective as comparison circuit, in which of other microphones which are due signals are compared as described with the signal 05 derived from the output signal of the associated microphone (21). The direct current signal coming from the circuit (83) is weakened first into 6 railway reducers (93), before it is supplied to the entrance of the decision circuit (97). The reducer (93) can be switched however over a control line (95) electrically, in order to switch the 6 off railway weakening, if the microphone (21) is turned on and/or connected through, and it forms thus a level circuit switchable in the level. The exit of this level circuit (93) is put to the decision circuit (97), those its output signal with the comparable signals of the other microphone attitudes, which are supplied by way of the max bus (56), compares, in order to specify whether the available signal is momentary stärktste everything of these comparable signals. The signal level at the max bus (56) is steered by the decision circuit (97) and the comparable decision circuits, which are assigned to the other microphones, and from there a maximum signal is always present at the max bus (56). If both the threshold value criterion is fulfilled, i.e. it is spoken and the max bus criterion is fulfilled, i.e. the associated microphone (21) ran loudest speaking take up t, whereby the appropriate signal is modified by the 6 railway weakening of the rule circuit (93) of each microphone circuit settable except function, momen arise at the exit of and gate (91) on a line (98) a signal, around one repeat triggerable mono-stable trigger circuit (99) to triggem. Because of the exit an opto coupler driver (101) is to this mono-stable trigger circuit (99), which forms a gate signal circuit, which heads for the opto coupler (69) together with the trigger circuit (99) over the line (71), whereby the output signal of the associated microphone on the line (45) is connected through. The mono-stable trigger circuit (99) plans 0.4 a circuit time after each triggering. The output signal of the mono-stable trigger circuit (99) is fed back besides to the control inlet of the level circuit (93) over the control line (95). The level circuit (93) off scolded on a high signal of the mono-stable trigger circuit (99) the 6 railway-Abschwäehung. During the descriptive circuit scolded individual speaker only one microphone on, however several normally speaking speakers can turn mehrcre microphones on. The loudspeaker (29) leads naturally to Sprachsignalen at everyone of the microphones (21.23 and 25). In order to prevent a connecting of the microphone output signals through by a Sprachsignal coming from the loudspeaker, the Sperrsignalgenemtor (57) is used. The inhibit signal generator (57) receives the loudspeaker signal on the line (58), in order to emit in at speaking on it an inhibit signal on a line (105). The inhibit signal generator (57) accomplishes a Frequenzentzerrung, a rectification and a filtering of the loudspeaker signal for the production of a direct current signal as inhibit signal on the line (105). The Sperrsigna arising on the line (105)] is supplied to everyone of the microphone circuits (51.53 and 55), it becomes following to a threshold value raising circle of the threshold value circuit (85) for the influence of the threshold value in that in each case on the basis the Fig. 10 way which can be described still more near put on. Connecting through of microphone output signals when loudspeaker sound and its response fading away is thus prevented under minimum handicap of desired connecting through when local speaking. Of course, if two are connected or more microphones/to loudspeaker units (11) in chain network on the conference table, all signal lines and/or max buses (56) are connected; further all loudspeaker Leistungsverstärkereing ge is to be united, with it by the loudspeaker signal by the control unit (15) be addressed ago, and all connecting through lines (45) are united just like all non--connecting through lines (47). The audio muting over the input line (75) can be caused by a suitable logic circuit, in order to prevent a connecting of individual microphone output signal through, whereby the function of the remaining circuit, as so far described, remains unbecinflnBt. Which the Fig. 7-13 concerns, then are naturally all operation amplifiers and comparators and/or difference circuits represented therein as actually admit to an appropriate, regular and filtered, balanced supply voltage by e.g. +15 V put. In accordance with Fig. 7 is the microphone (21) a Elektret Kondensatormikrofon. The Wandlcr is connected to 203) (Sanyo 25K156L) with the preamplifier interface circuit (61), a field-effect transistor impedance buffer (, an attitude resistance (g 1) and Vorspannwiders nde (R2, R3), furthermore preamplifier elements (R4, R5, C2 and C4) and an operation amplifier (207), in an interconnecting as from Fig. 7 evidently contains. The resistance (g 1) is selected in such a way that a same sensitivity for all transducer circuits is obtained. The resistance (R5) stops the reinforcement 9 No. 388480 of the preamplifier and is a precision resistance, so that identical acoustic sensitivities of all microphones for the audio Misehbusse and the Kalibriersehaltkreis (81) are present. The resistances (R7 and R8) are likewise precision resistances. The microphone output signal arrived over the condenser (C5) as well as if necessary more tiber the Fotowider05 stood (for R6) (the one part of the opto coupler (69) is) and the resistance (R7) on the line (45) and/or over the condenser (. C5) and the resistance (R8) on the line (47), and further is transferred it as mentioned over the line (73) for alignment calibration circuit (81), those below in detail with reference to Fig. 8 one will describe. The lines (45 and 47) are opposite earth through resistances of 5,6 kOhm and/or. 1,0 kOhm finally, which are arranged preferably in the gate circuit (43), so that the values do not change, if several microphone/loudspeaker units (11) is connected. These conclusions guarantee that the Hintergrundgeräuseh and the response remain essentially constant with the admission, if the number of used units (11) varies and changes the number of connected through microphones. This technology is actually in the initially mentioned article as well as in the US-PS 4,489,442 descriptive. As from Fig. to 8, contains the Abgleieh Kalibrierschaltung (81) is evident, which the microphone output signal over the line (73) is supplied, an operation amplifier (211), a balancing resistance (R10) as well as thus in Fig. 8 indicated way connected of resistances (R 11 and R12). The alignment calibration circuit (81) serves for adjusting element tolerances, in order to plan comparable signal levels at the exit, on a line (213), for the following Sehaltkreise. In combination with the resistance (g 1) (Fig. 7) and to the use of high-quality Elektretwandlern exactly together can be adapted so the connecting through particularly clinging for all microphones. In Fig. a remark example of the Frequenzentzerrer Gleiehriehterschaltung (83) is represented to 9, which keep the output signal of the alignment calibration circuit (81) supplied by way of the line (213). The circuit (83) raises the language portions of the frequency spectrum and weakens the very high frequencies somewhat and the low frequencies, which lie outside of the speech band, considerably. Also the Entzerrer/Gleichrichtersehahung (83) serves, since in höherfrequcnten portions in the speech band, approximately with “S” - sounds, compared with low-frequency speaking hurrying less energy is present, for the rise of the higher-frequency portions within the frequency band of the language. Altogether thereby breakdown effects are substantially reduced and short filter time constants are made possible. The circuit (83) contains an operation amplifier (215), of resistances (R13-R18) and condensers (C7-C10) as well as a pair operation amplifier (217, 219), those with diodes (Dl-D4), resistance (R19-R22) and condensers (C11, C12) are connected, whereby the verse attitude of the indicated elements in detail from Fig. is evident to 9. A Präzisions Vollweggleichriehtung becomes and - Filternng of the supplied microphone output signal manages. The Ansprechund fading away filter time constants is and amounts to 11 ms. The circuit (83) plans an exact level collection over a broad dynamic range. An operation amplifier (221) buffers the exit of the Entzerrer rectifier switch (83), whereby the Ausgangssi_ arises gnal on a line (223). In Fig. the threshold value circuit (85) is shown 10 more in the detail. The signal arising on the line (223) is a linear amplitude display, i.e. a direct current signal according to the frequenzentzerrten microphone output signal. This direct current signal is compared with a tension, which is present at a condenser (C13) and which noise level in the area represents. The signal arising on the line (223) is set on the nieht inverting entrance of an operation amplifier (225) with field-effect transistor entrance over a resistance (R68). If the signal changes in the non-inverting entrance, the condenser (C13) is loaded and/or unloaded in appropriate way. A low impedance resistance (R27), attached to the condenser, is used, in order to support the stability of the operation amplifier (225). A transistor (Q102) the istzwischen exit and the inverting entrance of the operation amplifier (225) switched and is used as diode with smaller leakage current. If the non-inverting entrance of the operation amplifier (225) leads a higher tension, as the tension at the condenser (C13), holds the operation amplifier (225) amounts to its inverting entrance over the transistor (Q102) on the same tension as at its nieht inverting entrance. Over the resistance (R23) the condenser (C13) is loaded slowly with a Zeitkonstamen by 10 s. If the signal at the non-inverting entrance of the operation amplifier (225) versueht than the tension at the condenser (C13) to become lower, then the operation amplifier (225) unloads, the condenser (C13) over the diode (D5). The operation amplifier (225) draws with a suitable speed in agreement with to the inverting entrance over the resistance (R23) (voltage drop the low input current of the operation amplifier (225) and the low leakage current of the transistor (Q102) has according to a negligible) No. 388480 arising feedback voltage downward. This lets the unloading diode (Dä) appear as precision diode. In this way the threshold value voltage level at the condenser (C13) follows the tension at its control inlet i.e. on the line (223), with one characteristic of slow responding and direct 05 of fading away, whereby it be subordinate to continuous noise level searches. At the condenser (C 13) arising threshold voltage levels by a unit reinforcement operation amplifier (227) with field-effect transistor entrance one buffers. The exit of the operation amplifier (227) plans a signal representing the noise level in the area. As from Fig. furthermore, is composed the reducer circuit 87 of resistances R24, R25 is evident to 10, which plan a signal weakened around 6 railways (in the comparison to the input signal on the line 223) on a line 229. The comparator 89, which is formed with a component LM339 with open Kollektomusgang, receives the buffered output signal of the threshold value circuit 85 at its inverting entrance and the signal at its non-inverting entrance, weakened around 6 railways. A resistance R26 provides for a narrow Hysteresis of the comparator 89 regarding an appropriate switching stability. The exit of the comparator 89 (outlet line 98) is for example high accordingly, if at the associated microphone 21 one speaks. In accordance with Fig. the switchable level circuit 93 of resistances R28, R29, which cause a signal, consists 11, which is weakened in relation to the input signal arising on the line 223 around 6 railways on a line 233. Between the resistance R29 and mass is a field-effect transistor switch 235 (p-channel transistor with so-called “pin CH off” - (screen) stretch ung Vp = 3 V) switched, in order to set the 6 railway weakening except function, if the praying switch is closed 235. During closing the FETs 235 the resistance R29 in the circuit becomes functionless. The signal supplied on the control line 95 arrives over a diode D6 at the gate electrode of the FET switch 235, in order to close it. Between mass and the cathode of the diode D6 a resistance R30 is switched, and a condenser C14 connects the control line 95 with mass. The resistance R30 and the diode D6 help to plan suitable control voltages for the Torlelektrode of the FETs 235. The condenser C14 slows something down the tension fibre course on the control line 95, in order to reduce capacitively coupled intoxication points to a minimum. The decision circuit 97 contains in accordance with Fig. 11 an operation amplifier 237, which is attached with its non-inverting entrance to the exit of the level circuit 93 over the line 233. The inverting entrance of the operation amplifier 237 is over resistances R31 and R32 attached at the Max Bns of 56. The resistance R32 is niedcrohmig and deceives for the stability of the circuit. If the not inveräercnde entrance of the operation amplifier 237 tries, to become higher than the amplitude of the signal of the max bus 56, a diode D7 in forward direction is linked up, and it will high-hold the max bus 56 on a level equal the level at the non-inverting entrance. If the non-inverting entrance of the Operationsverstärkcrs is lower 237 than the tension at the max bus 56, the diode D7 is linked up in reverse. A diode D8 prevents extra large negative tension deviations at the exit of the operation amplifier 237. The pre-loading condition at the diode D7 is produced by a comparator 239 (LM339) supervised, if necessary the logical high signal at its exit on the line 98 if the diode D7 is polarized in forward direction. A resistance R33 plans a Hysteresis for the stabilization of the Kompamtors 239. Further resistances R34 and R35 are as represented attached. At least a resistance R36 should be planned, in order to guarantee under all circumstances a load for the diode D7, which the max bus 56, “highly” - holds, over thereby a reliable collection of the forward pre-loading by the comparator 239 zn to make possible. The exit of the comparator 89 (Fig. 10) is with the line 98 (Fig. 11) connected. The comparator 89 and the comparator 239 serve in such a way for it, a hard-wired AND function (whereby a and gate in Fig. 6 with 91 symbolically shown is to be planned) in the line according to 98 its open collector configuration. If from there both the Schwellenwertkritcrium and the max bus criterion are fulfilled, the mono-stable trigger circuit 99 is triggered. This mono-stable trigger circuit 99 contains an open collector output comparator 241 (LM339), that with resistance R37-R41 in from Fig. l 1 evident way is interconnected. The comparator 241 addresses a condenser C15 on a logical high input signal at its invcrtiercnden entrance, which serves for it, to unload. With resistances a R42-R47 as from Fig. 11 evidently wired comparator 243 (LM339) supervises the tension at the Kondcnsator CI 5 for the production of a logical output signal on the line 95, the control line for the level circuit 93. The condenser C15, the comparator 243 and the associated circuit elements plan 0.4 s-Haltezcit for the output signal arising on the line 95. This --llNr. 388480 0.4 circuit time bridges gaps when triggering. If triggering stops, the condenser begins itself to load C15 again, whereby it lasts 0.4 s, before the condenser C 15 achieves a sufficient tension, in order to change the starting situation of the comparator 243. If triggering arises again, before the length of time of 0,4 s is to end, the condenser C 15 is again unloaded, and the signal on the line 95 does not change. That is put 05 the exit of the mono-stable trigger circuit 99 in Fig to the opto coupler driver 101. 12 is more near illustrated. This driving circuit 101 is used for it, for the opto coupler 69 and/or its light-along-animal-ends to diode (LED) 248 and with it for the change of resistance of the photoresistor R6 (Fig.7) a steered Ansprechund fading time to plan. The driving circuit consists of two operation amplifiers 247, 249, diodes D9, D10, condensers CI 6-CI 8 and resistance R48-R55, whereby these S chaltungselemente as from Fig. 12 is evidently connected. The result is that the audio signal with one 4 ms response time and 0.3 a s-fading time is connected through, which to an inconspicuous scolded without crack noises leads. At S already mentioned tummschalte entrance 75 is turned on over a resistance R69 in as gate signal antiresonant circuit working transistor Ql13, which is switched with its collector emitter distance between the entrance of the driver 101 and mass, in order to mass-short circuit the driver entrance with a mute-scolded with. The resistance R48 separates the short-circuit signal from the remaining circuit. Over a positive tension on S tummschalte input line 75 to put on and thus the transistor Q 113 into the leading condition too scolded, can a suitable, more near not represented logic circuit be used. This special kind of S tummschaltung permits causing of “dead” - to zones, where language and other unwanted sound (Papierrascheln etc.) cannot cause connecting through and cause from there no interruption of a teleconference. In accordance with Fig. 13 takes place in the Sperrsignalgenemtor 57 (see also Fig. 6) a Frequenzentzerrung, a rectification and a filtering on the line 58 anliegendcn loudspeaker signal, in order to produce a direct current output signal as “inhibit signal” on the line 105. This direct current AusgangssignaI is representative for the amplitude level of the sound from the loudspeaker. The Frequenzentzerrungsund filter parameter is essentially identical those the appropriate circuit 83, however the reinforcement for the descriptive purpose is suitably limited. The inhibit signal generator 103 is formed by operation amplifiers 251.253, 255 and 257, diodes D1 I-D14, condensers C19-C24 and resistances R56-R65, whereby these circuit elements as in Fig. 13 is represented connected. In accordance with Fig. 10 becomes on the line 105 (see also Fig. 13) delivered inhibit signal a threshold value raising circle of the threshold value circuit 85, the non-inverting entrance of an operation amplifier 259 for the change of the threshold value voltage level at the condenser C13 supplied. If the voltage level on the line is 105 at earth potential (O V) or is not lower than the tension at the condenser C 13, affects the operation amplifier 259 and the associated circuit elements the enterprise of the threshold value circuit 85. The diode Dl4 prevents extra large negative tension deviations at the exit of the operation amplifier 259, which would arise otherwise according to the positive tension at the condenser CI 3 and their feedback to the inverüerenden entrance of the operation amplifier 259 over the buffer operation amplifier 227 and the resistance R67. If the voltage level on the line 105 tries to exceed the tension at the condenser C 13 then the operation amplifier 259 loads the condenser C 13 over the diode D and the resistance R66 up, in order to hold the two tensions equally large. The signal at the exit of the operation amplifier 259 is supplied also to the non-inverting entrance of the operation amplifier 225 by way of the diode Dl6, in order to override otherwise during the time, while that steers the inhibit signal the tension at the condenser C13, existing the input voltage, in order to prevent a competition for the voltage level at the condenser C13. The direct positive change in the tension at the condenser CI 3, caused by the inhibit signal, would normally arrange the operation amplifier 225 to pull in the opposite direction over the diode D5. By planning the inhibit signal at the non-inverting entrance of the Operationsverstärkers225 with a somewhat higher voltage level than at the condenser C13 this problem is avoided. This slight voltage difference is guaranteed by the resistance R66 and the higher Strompegel in the diode Dl5, compared to the diode Dl6. If the inhibit signal on the line 105 decreases from its peak value, the condenser C13 is unloaded of 259 over the diode Dl6 exactly in the form of steps by the operation amplifier 225 over the diode D5 under control by the operation amplifier. The tension at the condenser C13 and the exit of the Paffer operation amplifier 227 follow accurately the voltage level and the rapid Anund fading times of the inhibit signal on the line 105, until it falls under the voltage level on the line 223, whereby here the normal threshold value adjustment is again taken up. At this time the direct current signal will probably show the fading away NachhaU of the Lautsprecherschallcs, which the tension at the condenser C13 if will desired follow. No. 388480 05 for the descriptive circuit elements can be selected for example the following values: Resistance value would resist R2, R46 8.2 K. ('2 R3 9.1 K_Q R4, R27 200. (2 R5 470 K 3 " 2 R7 5,1K _C). R-S, Rll 11K R31, R67, R50, R51, R52, R48 100 K. C) - R12, R55, R40 30 K R13, R56 2.7 K R14, R57 1K _ (“2 R15, R16, R20, R22, R47, R58, R59 51 K C2 R17, Rl! 3, R60, R61 510 R! 9, R21, R32, R66, R62, R64 100 f”! R24, R25, R45, R69 10 K R23, R44 2.2 M R26, R49, R42 1.5 M R28, R29, R34, R35, R68 20 K _ (“2 R30, R33, R36 1 M D”) R37, R38 15 K A " 2 R39 1,5. O_ R41 750. {3. R43 27 K R53 680. D. R54 390 D). R63, R65 24 K R! Nominal reconditions 12 K. (9. R10! 00 K I'2 alignment potentiometer R6 photoelectric cell on: Resistance 500. (2 photoelectric cell out: Resistance! 0 M. {'2 condensers capacities C2 0.33 UF C4 10 pF C5, C 13,4.7 jaF C 7, C9, C10, C 19, C 21, C 22 0.15 aF C 8, C 20 0.068 UF C ll, C 12, C 15, C! 7 0.22 F C 14 0.01 jIF C 16,0.1 jaF C 18 0.047 jaF C23, C 24 0.47 jlF No. 388480 actually can be used also Mikrofonein separate housings, whereby also microphones with other directivity patterns than a one-sided characteristic can be used. Furthermore a plant with several microphones is however possible without loudspeakers. In this case became, with reference to the Fig. and 10, the achievement amplifier 59, inhibit signal generator 57 and the loudspeaker 29 are omitted. Likewise 05 became the operation amplifier 259, which is not needed diodes Dl4, DL 5 and D 16 and the resistances the R66, R67 and R68, whereby the resistance would have to replace R68 by a simple connection. With reference to Fig. 11 it is also evidently that the logical control signal on the line could be used of 95 for example functions standing for the controlling other in connection, as for instance to the audio muting in the height attached of a loudspeaker, to the automatic scolded a video camera or by speaker indicator lights. In order to be able to access this logical control signal (the gate signal), a separate exit 94 is intended. As the further variation direction microphones in an arrangement extremely close can be used together. For example this could be an arrangement of two, three or four arranged microphones (with kardioidförmigen directivity pattern), which are operated with identical reinforcement and in the same level under angles planned in same distances outward are arranged. In this case the maximum signal decisions for individual switching source are primarily supported by relative microphone amplitudes instead of on relative times, when the speech sound reaches the respective microphone. The directivity pattern in the horizontal level is ffir an arrangement of three such arranged microphones in Polarkoordninatenform in Fig. 14 shown. The curves 401.403 and 405 represent - by the distance of the respective lines from the center 411 - relative sensitivities of the three microphones regarding a sound arriving from all sides to the microphones. The curve 407 represents the directivity pattern of the combination or sum of the curves 401 and 403. Similar diagrams can be received for the sum of the other two pairs. The relative sensitivity of the curve 407 is limited, in order to maintain the same total sensitivity, compared to a sensitivity of individual Kardioid microphone, regarding background noise in the area and response, which arrives and/or in equally from all directions. The directivity pattern can be regarded as Weitwinkelkardioide. The curve 409 represents the sum of the curve 401.403 and 405, wie&um under a calculation for preservation the same sensitivity in relation to room noise and response. This directivity pattern is a Alkichtungsdiagramm. In the case of symmetry arrangements with two or four microphones, under combination of opposite pairs of Kardioidlinien or under combination of all microphones would likewise result in, an all direction diagram. In the arrangement with four microphones the combination of two or three neighbouring microphones will result in different wide angle Kardioiddiagramme. The diversity of the directivity patterns and adjustments, as just now described, becomes under use of the Durchsehalttechnik in accordance with the available invention receipt EFF, if differently many speakers at different places speak approximately around the arrangements in different combinations. A microphone or several microphones in an arrangement can be mute-switched, in order to receive a direction-sensitive connecting through similarly to that one as into the US-PS 4,489,442 descriptive, whereby however relatively few disturbances arise by close reflections and NachhalI. It is generally desired to maintain in an automatic microphone plant a constant admission of the noise in the area and the response if the number of the connected through microphones changes. This eliminates audible Hintergrundgeräusch-Anschwellund of AbschweII effects and keeps the Rückkoppelungsschleifenverstärknng constant, on the assumption that the microphones are in the response field of the loudspeaker. Usually, also in the preferential execution form of the available microphone plant, the microphones are sufficiently far from each other arranged, in order to be able to accept a coincidental phase relationship in their responding to noise and response in the area. In order to maintain a constant Schallaufnahme, the reinforcement should be weakened in accordance with the following relationship, which became standard practice: Weakening = 10 logs I ON whereby the weakening - n railways is present and to N the number of the connected through microphones indicates. This is equal an additional 3 railway weakening for each duplication of the number N. The necessary weakening law differs from those with close together intended microphones. Around in Fig. 14 Bcmessungscharakteristik shown for an arrangement with three microphones to receive, are necessary the following relative weakenings: 1 microphone at 0 railways of 2 microphones at -5,12 railways of 3 microphones at -8,29 railways No. 388480 around a constant sewing resounding sound admission in an arrangement with four microphones to maintain, whereby the two-microphone arrangement represents a Untergamitur, the following relative weakenings are necessary: 1 microphone 0 railways of 2 opposite microphones at -4,77 railways of 05 2 neighbouring microphones at -5,44 railways of 3 microphones at -8,45 railways of 4 microphones at -10,79 railways with reference to Fig. 7 can be used, approximated these weakening values with grol3er approach using a similar mixture bus arrangement, as already during the connecting through line 45. If the bus with a resistance is final, whose resistance value is as large as the sum of the resistance of the photoresistor R6 in the Ein-Zustand and the resistance R7 four times, then the following relative weakening values result: 1 microphone at 0 railways of 2 microphones at -5,11 railways of 3 microphones at -8,30 railways of 4 microphones at -10,63 railways in this case would have (not represented) B usabschlußwiderstand a resistance value of 22 kOhm instead of kOhm. A group can be used for itself alone or in combination with other microphones or microphone units, which are intended in distance from it. In these cases is separated the bus locked with that 22 kOhm resistance locally within an arrangement by a buffer, which feeds the overall system mixture bus for the connected through microphones over another opto coupler. The associated resistance values are indicated as original for this bus. This additional opto coupler is up-steered, as soon as any microphone in the associated arrangement is turned on. The option described above permits the creation of “microphones” with automatically variable directional characteristic and automatically variable adjustment and its installation into the automatic connecting through system, which of special importance is. The choice is not evidently on on one side arranged microphones (with Kardioidrichtcharakteristik) or to microphones aligned in the same level limits.