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.
- 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.
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.
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.
- Dynamic range
- – dB
- Frequency range
- – Hz
- Inherent noise
- dB A
- Lower limiting frequency -3dB
- 5 Hz
- Polarization voltages
- Pressure coefficient
- Temperature coefficient
- Temperature range
- – C
- Microphone type
- Pressure Field