G.R.A.S. 47BX 1/4" CCP Flush-mount Microphone Set

Freq range: 4 Hz to 70 kHz
Dyn range: 44 dB(A) to 166 dB
Sensitivity: 1.6 mV/Pa

Typical applications and use

  • Flush mounting in confined spaces
  • Flush mounting in clay models
  • Flush mounting in scale models for wind tunnel tests
  • Ground array measurements
  • General noise measurements


With a height (to the diaphragm) of only 8 mm, 47BX is suitably designed for flush mounting in plates in ground array applications and other applications with size constraints.

The microphone is a prepolarized pressure microphone with a dynamic range from 44 dB to 165 dB and a frequency range from 4 Hz to 70 kHz. The built-in preamplifier is a low noise constant current power (CCP) type, with a built-in TEDS circuit for automatic transducer identification. The set has an integrated 1.5 m cable (G.R.A.S. 47BX-CL with customized length optional) with Microdot connector plus an adapter for BNC cable.

Flush-mounting is ideal where holes can be made in the structure, such as a clay model, to accommodate the front-vented 47BX. A rear-vented version is also available, the 47BX-S1

The 47BX is based on the IEC 61094 standard for measurement microphones.


When leaving the factory, all G.R.A.S. microphones have been calibrated in a controlled laboratory environment using traceable calibration equipment. Depending on the use, measurement environment and internal quality control programs we recommend that the microphone is recalibrated at least once a year.

We offer two kinds of calibration as an optional after-sales service: G.R.A.S. Traceable Calibration and G.R.A.S. Accredited Calibration.

G.R.A.S. Traceable Calibration is a traceable calibration performed by trained personnel under controlled conditions according to established procedures and standards. This is identical to the rigorous calibration that all G.R.A.S. microphones are subjected to as an integral part of our quality assurance.

G.R.A.S. Accredited Calibration is performed by the G.R.A.S. Accredited Calibration Laboratory that has been accredited in accordance with ISO 17025 by DANAK, the Danish Accreditation Fund.

If you want a new microphone set delivered with an accredited calibration in stead of the default factory calibration, specify this when ordering.

Learn more at gras/calib.

Quality and warranty

G.R.A.S. microphone sets are made of components from our proven standard portfolio and are all manufactured of high-quality material and branded parts that were chosen and processed to ensure life-long stability and robustness.

All parts are manufactured and assembled at the factory in Denmark by skilled and dedicated operators in a verified clean-room environment. The microphone diaphragm, body and unique protection grid are made of high-grade stainless steel and make the microphone set resistant to physical damage as well as corrosion caused by aggressive air or gasses.

This, together with the enforced gold-plated microphone terminal guarantees a highly reliable connection. Thanks to the high quality, our warranty against defective materials and workmanship is 5 years.


Should you by mistake damage the diaphragm on a G.R.A.S. microphone we will in most cases be able to exchange it at a very reasonable cost and short turn-around time. This not only protects your investment but also meets your quality assurance department since you do not have to worry about new serial numbers etc.

Frequency range (±1 dB) Hz 10 to 25 k
Frequency range (±2 dB) Hz 4 to 70 k
Dynamic range lower limit (microphone thermal noise) dB(A) 44
Dynamic range upper limit with G.R.A.S. CCP preamplifier dB 166
Set sensitivity @ 250 Hz (±2 dB) mV/Pa 1.6
Polarization voltage V 0
Power supply (Constant Current Power) mA 2 to 10
Microphone venting Front
Output impedance Ω <50
Temperature range, operation °C / °F -30 to 70 / -22 to 158
Temperature range, storage °C / °F -40 to 85 / -40 to 185
Static pressure coefficient @250 Hz dB/kPa -0.008
Humidity range non condensing % RH 0 to 100
Humidity coefficient @250 Hz dB/% RH <0.1
Influence of axial vibration @1 m/s² dB re 20 µPa 66
TEDS UTID (IEEE 1451.4) 27 v. 1.0
Connector type Microdot 10/32
CE/RoHS compliant/WEEE registered Yes/Yes/Yes
Weight g / oz 7.5 / 0.265

Typical frequency response

G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.

All dimensions in mm.

Included items

G.R.A.S. AE0046

Microdot - BNC male adapter


Optional items

G.R.A.S. 12AL

 1-Channel CCP Power Module with A-weighting filter

G.R.A.S. 42AP

Intelligent pistonphone

G.R.A.S. RA0228

Pistonphone Calibration Adapter for 1/4" Flush-mount Microphone Sets

G.R.A.S. RA0302

Removal Tool for 1/2” & 1/4” Flush-mount Microphones

G.R.A.S. RA0502

Mounting Adapter for 1/4” Flush-mount Microphone Set

G.R.A.S. AE0074

BNC male to female adapter

G.R.A.S. AA0035

3 m BNC - BNC Cable

G.R.A.S. AA0037

10 m BNC - BNC Cable

G.R.A.S. AA0039-CL

Customized length BNC - BNC Cable

G.R.A.S. CA0029

Traceable Calibration of Microphone Set

G.R.A.S. CA2301

Accredited Calibration of Microphone Set

G.R.A.S. Sound & Vibration reserves the right to change specifications and accessories without notice.