GRAS 147EB CCP X-Rugged Microphone Set

GRAS 147EB Microphone

Prolonged on-road testing on all surfaces, in all climate zones and weather conditions

Silent brakes are important to car owners and noisy brakes quickly translate into costly after-sales service for the manufacturer. This is why brake noise testing is so important to auto manufacturers and subsuppliers of brake components. Testing of brakes is not complete without comprehensive road testing. The countless different conditions that arise during real-life use need to be investigated. This is why we have developed the GRAS 147EB, a new rugged microphone that can withstand prolonged exposure to extreme temperature variations, water, salt, dust, snow and impacts from gravel. These conditionas are all verified during our Highly Accelerated Lifetime Test (HALT). Watch the video about HALT test here.

The GRAS 147EB is a free-field microphone set optimized for automotive brake noise testing. It is optimized to withstand the challenging conditions found close to the wheels. This has been achieved by combining the basic ruggedness of the new generation of GRAS automotive microphones for noise, vibration and harshness (NVH) with addtional protection of the diaphragm.


Due to the rough environment, recording of brake noise in the wheelhouse during on-road testing is very demanding. When mounted close to the wheel, in real-life driving tests on public roads, the microphone is subjected to harsh conditions that will decrease the performance and shorten the lifetime of any ordinary measurement microphone:
bullet pointVibrations Dirt
bullet pointDust and impacts from gravel
bullet pointExtreme temperatures
bullet pointRain, salt, snow and ice

The use of traditional ½” microphone sets mounted in the wheelhouse has major drawbacks leading to low-quality measurements in addition to damaged microphones, which must be replaced often.


Bright Blue V The ruggedness of the microphone set makes it resistant to shock and vibration, extreme temperatures, salt, water and oil.
Bright Blue V Two grids with built-in filters and an optional windscreen protect the diaphragm against moisture and particles, e.g. impacts from gravel.
Bright Blue V The microphone set is certified according to IP67
Bright Blue V Online calibration data with correction factors for the protection grid. 

Explore the benefits


Can safely be used in wet and splashy conditions - the microphone-preamplifier housing is certified watertight according to IP67.

Shock-absorbing Design

Innovative design ensures accurate data even during rough testing, e.g. on proving grounds or public roads.

Extreme Temperature Performance

Optimized for extreme temperatures without compromising sensitivity. It is the most temperaturestable CCP microphone on the market.


A customized and easily replaceable windscreen constitutes the outer layer of protection and guards against rain, snow and impacts from gravel, etc.

GRAS 147EB Microphone

Water, Oil and Dust-resistant and Replaceable Grid

Two grids – fitted simultaneously – with built-in filters ensure that it can be used in heavily contaminated environments with dust, dirt, water, snow and ice. Easy replacement.

Waterproof Connection

Can safely be used in wet and splashy conditions. A rubber-sleeved connection ensures data integrity and survivability during outdoor tests in all types of weather.

Protected Venting

Dual, protected venting prevents moisture from blocking the venting and ruining your measurements.

Online Calibration Data

Calibration data for each specific microphone can be accessed at

Thorough protection

In addition to the basic ruggedness of the 147EB, we have furnished the diaphragm with three layers of protection. A ½” protective grid with a built-in filter that protects the diaphragm from water, oil, dust and high-velocity particles constitutes the first layer. On top of this, sits a 1” protective grid adding another layer of protection. This grid also has a built-in filter.

Both filters are made from a fabric that is water and oil repellent. If the filters become clogged, the grids can easily be exchanged, reducing downtime and costs. Corrections for the acoustic influence of the filters are included.

A large windscreen completes the third layer of protection. It will reduce the influence of windinduced turbulence, but it also provides a further layer of protection against water, dirt, particles and stones, e.g. impacts from gravel. To ensure watertight connection, the BNC connector is protected by a large rubber sleeve.

GRAS 147EB Microphone1/2" grid with filter - inside 1" grid with filter

Windscreen to GRAS 147EBLarge, custom-designed windscreen

Rubber-sleeved watertight cableRubber-sleeved, watertight cable


Provided the grids and windscreen are cleaned or replaced at appropiate intervals, they ensure problem-free testing for prolonged periods of time. Learn about how to calibrate your 147EB with GRAS 42AG multifunction sound calibrator and discover all our technical support videos for our NVH microphones when performing technical maintenance.

If you need further assistance, visit our Global Support section.  

Freq range: 3.15 Hz to 20 kHz
Dyn range: 18 dB(A) to 133 dB
Sensitivity: 50 mV/Pa
Temperature: -40 to +125°C
Humidity: 0 – 90%
IEC 61672 class 2

GRAS 147EB CCP X-Rugged Microphone Set



147EB is a free-field microphone optimized for wheelhouse brake noise testing in the automotive industry. It is designed to withstand the conditions in the wheelhouse during prolonged testing on public roads in all types of climate and weather. A rugged design that withstands shock and vibrations combined with a three-layer protection system for the diaphragm enables it to be used for realistic testing of brakes on proving grounds and public roads. The two protective grids and the customized windscreen are easily replaceable consumables. With the 147EB it is now no longer necessary to use sub-standard microphones and cumbersome customized protection for acoustic road testing of brakes - it is now possible to measure without compromising data quality using a high-quality IEC 61672 class 2 microphone.


Like other members of the GRAS family of microphones for automotive NVH testing, the 147EB is designed to perform optimally under the rough conditions encountered in automobile NVH testing. The most important design features to accomplish this are:

Effective protection

The microphone-preamplifier assembly is effectively sealed against moisture and is IP67 rated. Special protective water and oil repellent coating adds further protection and makes it easy to clean. The microphone diaphragm is protected by two grids, a 1/2" grid inside a 1" grid. Each has a comprehensive multi-layer filtering system that ensures good protection against high-velocity particles and prevents dirt and dust from polluting the microphone. The filter in the 1/2" grid is acoustically transparent. The filter in the 1" grid is the same filter as that in the 1/2" grid supplemented by a layer of foam. The influence of the 1" grid can be compensated for with the transfer function that is included with the factory calibration. The calibration data and transfer function can be accessed online. Provided the filters are replaced at appropriate intervals this system ensures that the microphone will function properly even in very dirty conditions. The filter also protects the diaphragm against water splashes and oil mists.

GS0883 D

Exploded view of the two-grid protection system. Both grids are furnished with filters for protection of the diaphragm.

A customized windscreen is available. Even if turbulence is not a problem it must be used as the first layer of protection and thus protect the next layer of protection against early contamination.

147EB B2

 A large, customized windscreen takes care of turbulence but is also a very important part of the protection against moisture and dirt.

 147EB B4

A plastic ring inside the windscreen locks the windscreen onto the microphone.


The 147EB can withstand the effects of handling, including the occasional drop. A new design of the preamplifier and other internal parts makes it resilient to shock and vibrations.  It functions well under conditions with vibrations and g-forces from uneven road surfaces and other sudden directional shifts as encountered in real-life driving tests.

Even though the microphone will be firmly attached to a vibrating structure and subjected to frequent directional shifts, this fact will not interfere significantly with the measurements.  If the effects of vibrations are considered to result in noise, it retains a very good signal-to-noise ratio even in vibration-rich conditions.

The most vulnerable part of any condenser microphone is the diaphragm. In the 147EB a more robust type is used. It can be replaced during repair, keeping maintenance costs at a minimum.

Watertight connection

When mounted in the wheelhouse, the connection between the microphone set and cable will be located very close to the road. This is why special water and heat resistant cable, AA0121, is available. The BNC connector in the microphone set end is located inside a long rubber sleeve that fits tightly around the preamplifier housing. In this way, a waterproof connection is ensured.

The cable is 5 meters long and would be a good choice for a permanent installation. Disconnecting the microphone from the cable is fairly easy.

Resists temperature changes

The microphone set works properly up to temperatures of 125°C/257°F and down to -40°C/-40°F. The cable is a high-temperature type. This means that the 147EB can be mounted close to the road and used in all types of climate and seasons.


The comprehensive precautions taken to make the 147EB immune to adverse test conditions result in a number of benefits that all translate into shorter development times and lower costs of ownership.

  • The same microphone set can remain mounted in a test configuration for extended periods of time or remounted very quickly.

  • The protection grids with their protective filters can easily be replaced, for example when dirt and oil mists are clogging the meshes.

  • The concept with easily replaceable protection makes maintenance easy and reduces downtime.

  • The CCP (Constant Current Power) technology allows for a low cost per measurement channel.

  • The total life span of the microphone set will be many times that of a conventional microphone set that must be discarded due to damage from dirt, moisture, shock, and vibrations.

These advantages mean that the 147EB not only ensures a low cost of ownership for your microphones but will also contribute to speeding up the development process by improving the quality of your measurements and reducing set-up time.


The 147EB requires a constant current of typically 2 mA and is terminated with a BNC connector.

Ready to use standard coax cable assemblies of various types and lengths are available. Waterproof, heat and chemical resistant cables are also available.

The 147EB is IEEE 1451.4 TEDS v. 1.0 compliant. If your measurement platform supports Transducer Electronic Data Sheets you will be able to read and write data like properties and calibration data.


For daily verification and check of your measurement setup, we recommend using a sound source like the GRAS 42AG Multifunction Sound Calibrator.

Calibration data for each individual microphone set can be accessed online via the serial number. In this way, you can easily download and configure your analyzer with calibration data.

Accessible on-line are also correction data for the protective grid in a format that your analyzer can read at


When our R&D team develops a measurement microphone, it must undergo the most demanding tests to prove that it can withstand our customers' daily test conditions. Using a series of Highly Accelerated Lifetime Tests (HALT) we ensure that our microphones live up to the high quality and precision that our customers have come to expect and trust. Our HALT tests actively accelerate the lifetime of a microphone by simulating the handling and use it is exposed to in real-life situations. By stress testing to the limits, we have been able to optimize the design for robustness and stability.

Service, warranty and repair

When leaving the factory, all GRAS 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: GRAS Traceable Calibration and GRAS Accredited Calibration.

GRAS 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 GRAS microphones are subjected to as an integral part of our quality assurance. GRAS Accredited Calibration is performed by the GRAS 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 instead of the default factory calibration, please specify this when ordering.

All parts are manufactured and assembled in Denmark by skilled and dedicated operators in a verified clean-room environment. Our warranty against defective materials and workmanship is 5 years, the windscreen and the protective grids are consumables covered by a 6-month warranty.

The warranty does not cover damages to the protection grids caused by their intended use in the challenging conditions in the wheelhouse.
GRAS offers a complete overhaul including calibration at a reasonable price.


Frequency range (±2 dB) (IEC 61672 class 2)
3.15 to 20 k*
0 V / CCP
Frequency range (±1 dB)
5 to 5 k*
Dynamic range lower limit with GRAS preamplifier
Dynamic range lower limit, linear
Dynamic range upper limit
Set sensitivity @ 250 Hz (±2 dB)
Set sensitivity @ 250 Hz (±2 dB)
dB re 1V/Pa
Output impedance
< 50
Power supply min. to max.
2 to 20
Output Voltage Swing, min. @ 28 V CCP voltage supply
DC bias voltage, typ.
Microphone venting
Temperature range, operation
°C / °F
-40 to +125/-40 to 257
IEC 61672 compliance
Class 2
Temperature range, storage
°C / °F
-40 to 85/-40 to 185
Temperature coefficient @250 Hz
dB/°C / dB/°F
0.015 / 0.009 (typically)
Static pressure coefficient @250 Hz
Humidity coefficient @250 Hz
dB/25-90 % RH
< -1
Humidity range non condensing
% RH
25 to 90
Influence of axial vibration @1 m/s²
dB re 20 µPa
Connector type
CE/RoHS compliant/WEEE registered
g / oz
61.5 / 2.17

  * when corrected for the influence of the 1" grid.


  GRAS HALT Test Parameters**  

Humidity 90%


48 hours

Drop - horizontal orientation of microphone, attached to 2 kg load



Drop - vertical, grid downwards, attached to 2 kg load



Drop - tumbling 1 meter



Vibration - horizontal and vertical


60 hours

Salt mist, IEC 60068-2-52:1996

5% NaCl, pH 6.5-7.2

3 cycles, 3 days

IP rating, IEC 60529:2013***



**For a short introduction to HALT, see the section "GRAS HALT" above
***International Protection Marking, IEC standard 60529.
****IP67: Totally protected against dust, protected against the effect of water of up to 1 m of submersion.

IP67 and salt mist tests performed by DELTA - a part of FORCE Technology, Denmark.

Correction curve

 Typical frequency response.
The blue curve is the free-field response with 1/2" grid, the dotted orange curve is with 1" grid.
This curve can be made equal to the blue curve with the transfer function for the 1" grid.


Noise floor curve

Typical noise floor, linear and A-weighted.

 GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.






 Dim til PI



Ordering info

Included items

GRAS 147EB CCP X-Rugged Microphone Set
GRAS AM0387-1 Windscreen for 147EB, 1 pc.

Optional items

GRAS RA0360  1/2" protection grid, dust, oil, and water resistant
 GRAS RA0355  1" protection grid, dust, oil, and water resistant
GRAS AM0387-1 Windscreen for 147EB, 1 pc
GRAS AM0387-4 Windscreen for 147EB, 20 pcs.
GRAS AA0102 3 m  waterproof BNC-BNC cable
GRAS AA0103 10 m waterproof BNC-BNC cable
GRAS AA0107 1 m waterproof high-temperature BNC-BNC cable
GRAS AA0108 3 m waterproof high-temperature BNC-BNC cable
GRAS AA0121  5 m waterproof high-temperature BNC-BNC cable with sleeve
GRAS AA0122 7 m waterproof high-temperature BNC-BNC cable with sleeve
GRAS AA0109 10 m waterproof high-temperature BNC-BNC cable
GRAS AA0110 30 m waterproof BNC-BNC cable
GRAS RA0341 Calibration adapter
GRAS CA2300 Accredited Calibration

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