M49-history电路图.pdf

neumann.berlin the microphone company M 49 The First Remote Controllable An important step forward in microphone technology was made with the model U 47. Its dual diaphragm capsule M 7, active on both sides, made possible the first condens- er microphone with switchable polar patterns. The ques- tion arose, whether it could be possible to change the char- acteristic during recording. The relevant patent of Dr. Grosskopf reads: “Thus. the influence of exaggerated re- verberation can be dimin- ished . the recording dis- tance . can be increased without getting a vague tim- bre . It is therefore an ur- gent need for the recording technique to easily exchange microphones with different polar patterns .” The objec- tive was to avoid an exchange of microphones or capsules and to remotely control the microphones directional pickup pattern. For this pur- pose it is important that the output of the microphone remain fairly constant and independent of the selected pat- tern. The only switchable pattern microphone existing at that time, the Neumann U 47, exhibits an increase in the output by 5 dB when switched from omni to cardioid. In the cardioid position the rear half of the capsule in the U 47 was simply electrically disconnected. As a consequence, the output of the rear capsule and the attenuation of the front via the fixed parallel capacitance of the rear were avoided. “Comfortable” pattern con- trol for the new M 49 micro- phone was achieved by keep- ing both capsule halves con- nected to the impedance converter with regard to the signal, however, insulated from each other with regard to the DC bias. The front di- aphragm is polarized with a constant voltage of 60 Vdc, while the bias for the rear di- aphragm is adjustable from 0 Vdc to 120 Vdc. This al- lows the polar pattern to be- come variable between omni through cardioid to figure-8 maintaining a practically constant sensitivity. The power supplies for the model M 49 microphones included a po- tentiometer with a pointer knob and a corresponding scale. Available were portable and rack mounted versions of the power supplies. Due to the many supply voltages the M 49 microphone was equipped with an 8-pole connector. As tube, in the early versions, a directly heated triode MSC 2 made by Hiller was employed, which later was succeeded by the Telefunken AC 701 (k). The mechanical construc- tion provided means for the suppression of structure born noise. The amplifier was mounted on a solid rubber disk, mechanically isolating the amplifier from the housing. In addition, the microphone capsule was mechanically decou- pled by means of a swing-metal shock mount. This meth- od was incorporated later in most of the succeeding Neu- mann microphones. The M 49 was introduced to the German Radio Broad- casters in 1952. Because of its unprecedented versatility it conquered the international recording studios rather quick- ly. Due to the innovative feature “remote pattern control” it found widespread application as the important main mi- crophone above large orchestras. Other applications were as a spot microphone for wind and string instruments, for piano and as the favorite announcers microphone. RadioFans.CN 收音机爱 好者资料库