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PRODUCT DATA ¼″ Free-field Microphone — Type 4939 Type 4939 is designed for high-level and highfrequency measurements where a microphone with free-field response is needed. Being externally polarized, Type 4939 must be used with a classical preamplifier. USES • High-level measurements • High-frequency measurements • Model testing FEATURES • Sensitivity: 4 mV/Pa • Frequency: 4 Hz – 100 kHz • Dynamic Range: 28 – 164 dB • Temperature: –40 to +150°C (–40 to +302°F) • Polarization: 200 V external when used in environments with a combination of high humidity and high temperature. At higher frequencies, reflections and diffractions cause a pressure increase in front of the diaphragm. If not corrected for, this would result in an increased output voltage from the microphone. A free-field optimisation means that the frequency response of the microphone has been designed in such a way that the free-field response at 0 degrees incidence is flat. This is only valid when the microphone is used without the protection grid. Free-field microphones are suited for sound measurement in an anechoic chamber or far away from reflecting buildings, etc. Another area for free-field microphones is general electroacoustics purposes like loudspeaker and microphone measurements. Type 4939 is suited for all high-level, high-frequency measurements where a robust and stable free-field microphone is required. Polarization Voltage Type 4939 requires an external polarization voltage and must therefore be used with a classical preamplifier. Externally polarized microphones may be used at higher temperatures without severe changes in sensitivity. TEDS Microphones Type 4939 is available in TEDS combinations with different variants 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. Individual Calibration Data A laser-welded, stainless-steel diaphragm ensures superior long-term stability and mechanical robustness – Type 4939 will withstand the 1 m drop test of IEC 60068–2–32. Each Type 4939 comes with an individual calibration chart including information about the open-circuit sensitivity, the frequency response in a free field as well as the electrostatic actuator response. All Brüel & Kjær Measuring Microphones are assembled in a clean room. This ensures that the microphones maintain their inherent noise floor and high stability, even An enclosed mini-CD contains the individual calibration data at 1/12-octave frequencies plus a wealth of technical information, such as the

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response in different sound fields and much more. Using the CD data and the REq-X feature of PULSE™, a real- time correction for different measurement situations, can increase measurement accuracy. Fig. 1 Typical free-field response of Type 4939 without protection grid. The low-frequency response is valid when the vent is exposed to the sound field dB 5 0 -5 -10 -15 -20 1 Specifications – ¼″ Free-field Microphone Type 4939 (valid from serial number 2496612) IEC 61094–4 Type Designation: WS 3F Polarization Voltage: 200 V Open-circuit Sensitivity (250 Hz)a: 4 mV/Pa, –48 dB ±3 dB re 1 V/Pa 0°...

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