Measurement microphone 4138

condenserexternally-polarizedfree-field

Pressure-field microphone designed for very high-frequency measurements in confined spaces with a frequency range of 6.5 Hz to 140 kHz. Type 4138 is designed for high-level and very high-frequency measurements and measurements in confined spaces. Being externally polarized, Type 4138 must be used with a classical preamplifier. USE SCENARIOS • High-level and very high-frequency measurements • Applications which require a high degree of spatial resolution or where space is limited, for example, model testing USE OF PRESSURE-FIELD MICROPHONES Pressure-field microphones should be used for making measurements in small, closed couplers or close to hard, reflective surfaces. Such microphones are optimised to have a flat frequency response in a pressure field. Because of its small size, Type 4138 can also be used for random-incidence measurements at audio frequencies, where its frequency response is less dependent on angle of incidence. POLARIZATION VOLTAGE Type 4138 requires an external polarization voltage and therefore must be used with a classical preamplifier such as Brüel & Kjær Type 2670 together with 1/8" to 1/4" Adaptor UA-0160. CALIBRATION The sensitivity of Type 4138 can be calibrated at 250 Hz using Pistonphone Type 4228, or at 1 kHz using Sound Calibrator Type 4231, in both cases using Adaptor DP-0774. The pressure-field response can be measured using Electrostatic Actuator UA-0033 with Actuator Adaptor DB-0900.