The microphone capsule of the U 67 microphone is a pressure-gradient device. It is composed of two identical cardioid systems arranged back to back. By switching of the polarizing voltage these two cardioid patterns can also be combined as to produce the three directional characteristics cardioid, omni-directional, and figure-8. Selection of these patterns is accomplished by a switch located at the front of the microphone directly beneath the wire cage. The symbol of the characteristic selected appears in a window directly above the switch. Two additional switches are located at the rear of the microphone. One switch provides for a sensitivity reduction of appr. 10 dB ahead of the amplifier section permitting transmission of the highest sound pressure levels without danger of overloading the amplifier. The second switch produces a roll-off at the low frequency end beginning at 200 cps. This permits compensation of the normally occurring low frequency rise when a pressure - gradient microphone is addressed at close range. This position further serves to suppress low frequency mechanical interference. These two switches like wise have windows in which their position is indicated. When the sensitivity reduction is effective, the window shows "-10 dB", and when the low frequencies are attenuated, the window shows a horizontal line with its left end bent downward. (These symbols are described as viewed when the microphone is on a stand with its connector end facing the floor.)
A special circuit within the amplifier distinctly attenuated all frequencies below 30 cps, while those above 40 cps are reproduced linearly. The microphone amplifier's response may be extended to below 20 cps flat by opening the jumper "S-2" in the amplifier itself.
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