1/4" Free-field Microphone, Ext. Polarized

Using stainless steel diaphragm and protection grid, Type 4939 Microphone is built to withstand rough environments and can be used in high-temperature measurements up to 150°C (302°F). 

The microphone requires an external polarization voltage and must therefore be used with a classical preamplifier. Externally polarized microphones can be used at higher temperatures without severe changes in measurement sensitivity. 

USE SCENARIOS

• High-level measurements
• High-frequency measurements
• Model work

MICROPHONE BUILD AND STABILITY

A laser-welded, stainless-steel diaphragm ensures superior long-term stability and mechanical robustness. Type 4939 will withstand the 1 m drop test required by IEC 60068-2-32.

The microphone is assembled in a clean room, ensuring that the microphones maintain their inherent noise floor and high stability, even when used in environments with a combination of high humidity and high temperature.

TEDS Microphones

Type 4939 is available in a TEDS Microphone set with different variants of classical preamplifiers. The TEDS microphone is considered one unit and has been sealed in a clean environment.

The TEDS is programmed with the loaded sensitivity of the actual cartridge and the data is therefore readily available in the transducer. The default TEDS template is according to IEEE P1451.4 but TEDS to IEEE 1451.4 is available on request.

CALIBRATION

The sensitivity can be calibrated at 250 Hz by using Pistonphone Type 4228 with ¼-inch Adaptor DP 0775. The actuator response can be measured using Actuator UA 0033 with Adaptor DB 0264.

The free-field response can be obtained by adding the type-specific, free-field correction to the actuator response.