Microphone Cartridges

4178 1/4-Inch Sound Intensity Microphone Pair

4178 1/4-Inch Sound Intensity Microphone Pair

Type 4178 consists of a pair of selected Type 4939 1/4″ microphones, whose phase responses are matched between 100 Hz and 20 kHz.


  • Measurement of sound intensity using two-microphone technique, in accordance with IEC 61043 Class 1
  • Sound power measurements in accordance with ISO 9614-1, ISO 9614-2, ECMA 160 and ANSI S12.12, using sound intensity probes
  • Measurement of particle velocity of sound sources


  • Broadband matching of phase responses
  • Phase calibrated in 1/3-octave frequency bands from 100 Hz – 20 kHz

The Type 4939 microphones are specially designed for high level and high frequency measurements. By using stainless steel diaphragm and protection grid, the microphone is optimised to withstand rough environments and is capable of working at high temperatures – up to 150°C (302°F). The microphones are mainly used in Sound Intensity Probes to measure sound intensity and can also be used for particle velocity measurements.

Other uses include measuring the volume velocity of a sound source, using, for example, Brüel & Kjær’s Volume Velocity Adaptor Type 4299 fitted to the OmniSource™ Omnidirectional Sound Source Type 4295.

Type 4178 is supplied with 6 mm and 12 mm spacers, along with calibration charts giving the individually measured free-field frequency response for each microphone and a Phase Response Comparison Calibration (100 Hz – 20 kHz).


Phase calibration of 1/4″ microphone pair Type 4178 is done at Brüel & Kjær by subjecting the two microphones to the same sound signal in a pressure coupler. This individual phase calibration can be used to derive the Pressure-Residual Intensity Index for the microphone pair.

Sound intensity measurement systems containing a sound intensity probe set can be conveniently calibrated using a Sound Intensity Calibrator Type 3541.

This permits simultaneous sensitivity adjustment of both channels of the processor (in pressure, particle velocity or intensity modes) and allows determination of the 20 Hz – 5 kHz Pressure-Residual Intensity Index of the probe and processor combinations.

Capacitance: 6.1 pF
Diameter: ¼
Dynamic range: 28 – 164 dB
Frequency range: 4 – 100000 Hz
Inherent noise: 28 dB A
Lower limiting frequency -3dB: 3 Hz
Polarization: Ext polarized
Polarization voltages: 200 V
Pressure coefficient: -0.007 dB/kPa
Sensitivity: 4 mV/Pa
Temperature coefficient: 0.003 db/ºC
Temperature range: -40 – 150 C
Venting: Side
Weight: gram
Sound field: Free-field
Input type: Classic