GRAS 46BD 1/4" CCP Pressure Standard Microphone Set

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The Industry Leaders—GRAS 46BD has the lowest noise floor of any ¼″ pressure-field microphone

Why is high-frequency measurement needed?

Acoustic quality requirements for telecom, audio, PCs and tablets are ever increasing, with a constant trend towards tighter production tolerances and the need to include higher frequencies in testing. The physical properties of smaller microphones not only make them a great solution for meeting those requirements and minimizing error in the data measured on the production line, they are more easily placed on the lines, where a small footprint is critical—smaller microphones can be fitted in smaller test setups.

Is smaller better?

There is no magic microphone that is perfect for all possible measurement scenarios, but the actual physical size of ¼″ microphones provides many benefits. The size-related properties reduce the pressure build-up effect on the diaphragm, but also significantly minimize error when when the sound wave is not 0° incidence and can inherently enable measurements at higher-frequency ranges and pressure levels. And when accounting for real-world conditions and measuring where there are many reflections and disturbances, such as in-cabin, the physical advantages of a ¼″ microphone can greatly increase accuracy and simplify post-processing data. For example, at 20 kHz, a ½″ free-field (FF) mic underrepresents the sound power of a 90° incidence wave by ca. 10 dB—a ¼″ FF mic, only by approx. 3 dB. This results in more accurate data in environments with random angles of incidence where corrections are difficult or impossible to estimate.

Benefits at a glance

  • Reduced influence of the angle of incidence.
  • Well-suited for high-frequency measurements.
  • Minimal footprint for easy placement on a production line.
  • Small diaphragms enable the possibility for testing miniature microphones, such as MEMS.
  • Reduced influence on measurement environment due to their small size.
  • Lowest noise in the industry for high sensitivity, pressure and free field.
  • Enables extreme SPL measurement.
  • Competitive pricing.

Freq range: 5 Hz to 70 kHz
Dyn range: 44 dB(A) to 166 dB
Sensitivity: 1.45 mV/Pa

GRAS 46BD 1/4" CCP Pressure Standard Microphone Set



Through a close cooperation with our customers, we know that data-safety is highly important because the costs related to unsuited and unreliable sensors may determine whether your project turns into a success or not.

For our users, data safety translates directly into requests for easier microphone selection, simple system configuration and reduction of measurement errors.

To meet these requirements, we invented the microphone set concept. It is simple, reliable and robust and consists of a microphone cartridge and preamplifier combination, which is calibrated as one unit. This eliminates errors because there is only one sensitivity value to account for and the risk of contaminating the interface is eliminated. Combine this with our unique and proven design and you have the most reliable measurement microphone sets available in the industry today.

Typical applications and use

The 40BD is ideal for sound pressure measurements, as well as high frequency and high level pressure measurements. It is suitable for general purpose acoustic measurements in couplers and at boundaries.

Regarding temperature range, see the Specifications. Should higher temperature limits be required, we recommend considering  the GRAS probe microphones where the microphone and preamplifier can be isolated from the hot source.


The GRAS 46BD is a high-performance standard microphone set. In our clean-room environment the set is assembled and sealed with a label. However, the microphone set can be dismounted, if you wish to use the components separately.

The microphone cartridge is the high-quality IEC  61094 WS3P standardized GRAS 40BD 1/4" Prepolarized Pressure Microphone, designed for long-term reliability in multiple environments.

The preamplifier is the GRAS 26CB Preamplifier which is inclusive TEDS and based on our well-known circuit board substrates. In the industry these are famous for their low self-noise, wide frequency and excellent slew rate performance.

46BD is rear-vented. A front-vented version is available, GRAS 46BD-fv.


To perform as specified the GRAS 46BD microphone set requires a constant current input module that can deliver 4 mA and 24 V unloaded CCP voltage supply. If the constant current supply is lower, the capability of driving long cables is reduced and consequently the upper frequency is reduced. If the voltage supply is lower it will influence the upper dynamic range.

The microphone set is terminated with a 10/32 Microdot female connector. Ready to use coax cable assemblies of various types and lengths are available in standard as well as customized lengths.

The 46BD 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.

System verification

The functionality of TEDS is very useful to determine which microphone is connected to which input channel. However, it is not a check of whether the microphone is within specifications or not. For daily verification and check of your measurement setup, we therefore recommend using a sound source like the GRAS 42AG Sound Calibrator.

For proper sensitivity calibration we recommend using a reference sound source like the GRAS 42AP Intelligent Pistonphone.


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 in stead of the default factory calibration, specify this when ordering.

Learn more at gras/calib.


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.

For more about HALT, see

Quality and warranty

GRAS 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 GRAS 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.


0 V / CCP
Frequency range (±1 dB)
10 to 25 k
Frequency range (±2 dB)
5 to 70 k
Dynamic range lower limit with GRAS preamplifier
Dynamic range upper limit with GRAS CCP preamplifier
Set sensitivity @ 250 Hz (±3 dB)
Set sensitivity @ 250 Hz (±3 dB)
dB re 1V/Pa
Output impedance
Output Voltage Swing, min. @ 24-28 V CCP voltage supply
Power supply min. to max.
2 to 20
Power supply min. to max. (single/balanced)
DC bias voltage, typ.
Microphone venting
Rear (Front on request)
IEC 61094-4 Designation
Temperature range, operation
°C / °F
-30 to 85 / -22 to 185
Temperature range, storage
°C / °F
-40 to 85 / -40 to 185
Temperature coefficient @250 Hz
dB/°C / dB/°F
-0.01 / -0.006
Static pressure coefficient @250 Hz
Humidity range non condensing
% RH
0 to 90
Humidity coefficient @250 Hz
dB/% RH
Influence of axial vibration @1 m/s²
dB re 20 µPa
27 v. 1.0
Connector type
Microdot 10/32
CE/RoHS compliant/WEEE registered
Yes / Yes/Yes
g / oz
8 / 0.282


Typical frequency response (without protection grid)


Free-field corrections for different angles of incidence


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


Ordering info

Optional items


1/4" CCP Pressure Standard Microphone Set, Front-vented


3 m Microdot - BNC Cable


1/4" Microphone Holder, POM


1/4" Microphone Holder, Stainless Steel


Swivel head




1/4" Nosecone


Windscreen for 1/4" Microphones


Rain-protection cap for 1/4” microphones


1-Channel CCP Power Module with A-weighting filter


2-Channel Universal Power Module with signal conditioning and PC interface


Multifunction Sound Calibrator, Class 1


Intelligent Pistonphone, Class 0


Traceable Calibration of Microphone Se


Accredited Calibration of Microphone Set

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

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