TYPE 4178

1/4" Sound Intensity Microphone Pair, Ext. Polarized

Sound Intensity Microphones specially designed for high level and high frequency measurements over a frequency range of 4 Hz to 100 kHz,  with broadband matching of phase responses.

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


  • Measurement of sound intensity using the two-microphone technique, following IEC 61043 Class 1
  • Sound power measurements following 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

Type 4939 microphones are specially designed for high-level and high-frequency measurements. By using stainless steel diaphragm and protection grid, the microphone is optimized 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 for sound power and intensity measurements, and can also be used for particle velocity measurements.

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-inch 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
Sound Intensity Calibrator Type 3541-A. 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.

6.1 pF
Dyn. range
28 – 164 dB
Freq. range
2.6 – 180000 Hz
Inherent noise
28 dB A
Lower limiting frequency -3dB
3 Hz
Sound Intensity
Ext polarized
Polarization voltages
200 V
Pressure coefficient
-0.007 dB/kPa
4 mV/Pa
Temperature coefficient
0.003 db/ºC
Temperature range
-40 – 150 C
Sound field
Input type
Microphone type
Sound Intensity