Lesson 3/Learning Event 1
Figure 32. Connection and construction
of a singlebutton carbon microphone
(1) The output voltage from a carbon or pressure microphone is
proportional to the displacement of the diaphragm.
(2) Figure 31 (1) shows the field pattern is omnidirectional.
(3) One of the principle disadvantages of the carbon microphone is that
it has continuous high frequency hiss caused by the changing resistance between the
carbon granules. In addition, the frequency is limited and the distortion is
rather high.
6. What is a double button carbon microphone? The doublebutton employs two
carbon buttons similar to those used in a single button microphone. One button is
mounted on each side of the diaphragm. Pressure waves (or sound waves) striking
the surface of the stretched diaphragm cause it to move, (or oscillate) disturbing
the contact resistance of the carbon granules in the buttons similar to the action
that happens within a single button carbon microphone.
a. As the diaphragm moves, the contact resistance in the granules of
the button mounted on the pressure wave side is reduced, while the resistance of
the button on the opposite side is increased.
b. When the pressure wave reverses itself, the reverse action takes
place in the carbon buttons.
c. The current through the buttons corresponds to each half of the
pressure wave at the diaphragm. This action is some what similar to the action of
a pushpull amplifier stage. Figure 33 shows the circuit connections and
construction.
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