Instruction manual

103
Technical Notes
Microphone
Measurements of sound pressure level can be carried out with a variety of microphone
types. The precision integral sound pressure level meter NA-27 employs the prepolarized
condenser microphone UC-53A that is compact and delivers stable and reliable response.
Construction and Operation Principle
As shown in the drawing below, a prepolarized condenser microphone consists of four
main parts: diaphragm, backplate, insulator, and housing. The surface of the backplate is
covered by a film holding an electrical charge. When sound pressure is applied to the
diaphragm, the distance between the diaphragm and the backplate changes, thereby alter-
ing the capacitance. Using a load resistor, this change can be turned into a voltage change.
The frequency response as well as the temperature and humidity characteristics of an
prepolarized microphone depend considerably on the type and properties of the materials
used. The frequency range is determined by the resonance frequency of the diaphragm
assembly.