Abstract
We conducted studies regarding sensitivity changes of Electret Condenser Microphones (ECMs) that were stored in a laboratory for 18 years, and using the results, estimated the working lifetime of an ECM. The average sensitivity change of the ECMs stored at room temperature for 18 years was unexpectedly small-only about 0.3dB. We estimated the main factor that determines the lifetime of an ECM-surface charge decreases of electret foil-over a period of time, using a heat acceleration test and the results of our long-term sensitivity change studies. The results of our estimate showed that a sensitivity decrease of 3dB in ECMs stored at room temperature may be found in 60 years, and a 6 dB decrease, which is the limit of microphone performance, may be found after 200 years. In this paper, we propose a form of expression for the decrease pattern of electret surface charges, over a period of time, and temperature as a three dimensional form.
