TYPE 4138

1/8-inch pressure-field microphone, 6.5 Hz to 140 kHz, 200V polarization

Designed for very high-frequency measurements in confined spaces.

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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.

Capacitance
pF
Diameter
1/8
Dynamic range
– dB
Frequency range
– Hz
Inherent noise
dB A
Lower limiting frequency -3dB
5 Hz
Polarization voltages
V
Pressure coefficient
dB/kPa
Sensitivity
mV/Pa
Temperature coefficient
db/ºC
Temperature range
– C
Weight
gram
Microphone type
Pressure Field

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