HALT - Highly Accelerated Lifetime Tests

Whether during storage or operation, microphones may be subjected to extreme temperatures. In the former case, the temperature is typically constant while in the latter case the temperature may vary greatly. Based on differing coefficients of thermal expansion, extreme temperatures may cause microphones to structurally distort thus altering their frequency response. Deviations from room temperatures may equally influence the polarization of CCP microphones, changing their sensitivity.

Humidity varies greatly with geography as does it with the quality of HVAC systems. It may severely affect the internal damping of a microphone. Moreover, long-term exposure to humid weather may lead to corrosion. GRAS microphones are specified to withstand levels of relative humidity ranging from 0% to 95%, both during storage and operation. In this humidity stress test, the microphone sets are sequentially stored for 48 hours at 90% relative humidity at a temperature of 50 °C.

Microphones may be vibrated during both transportation and operation. Prolonged exposure to severe vibrations may unsettle the critical elements making up a measurement microphone, the important components being: the diaphragm, the back plate, the insulator, the outer casing and the output contact.

Impulse stresses may accidentally be imparted to a microphone set during transportation and handling, often as a consequence of the microphone set or its container being dropped. However, impulse stresses may similarly occur during operation, if mounted on vehicles that undergo significant accelerations. A mechanical impulse may affect the internal workings of a microphone in a similar manner to that of vibrations, though with the additional possibility of large dents to the structure.