GRAS 46BC 1/4" CCP Multifield Microphone Set, High Sensitivity
Acoustic challenges in a car cabin
The constant evolution of motor vehicles is a never-ending source of new acoustic challenges. The transition from internal combustion engines (ICEs) to electric vehicles (EVs) is a lot more than just swapping power sources.
New challenges
Added to the vehicle noise itself come the audio and infotainment system assessment challenges. Efforts to increase efficiency and extend the range between charging go beyond the technological improvements in battery and motor efficiency. Lighter materials are being incorporated into the vehicle structures and interiors. This introduces a range of new challenges for assessing the quality of in-cabin audio:
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Lighter materials with their own dampening characteristics
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Highly reflective elements like instrumentation panels, windows, and even panoramic glass that may or may not be exposed on the interior ceiling.
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The combination of the above.
This results in a combination of sound fields where noise can come to the occupants from multiple angles, with a range of dampening effects for different frequencies. If not evaluated properly, occupants could experience muddled audio for some frequencies or reverberant dissonance for other frequencies.
Beyond the capability of traditional testing
The new challenges have pushed audio testing needs beyond the capabilities of ½″ microphones.
Can the 46BC match ½″ microphones on the low end?
The noise floor of traditional ¼″ microphones was once a primary limitation for use in automotive NVH testing. However, the 46BC has the lowest noise floor of any ¼″ microphone on the market, making it uniquely suited to replace the ½″ microphones in current use, enabling improved high-frequency accuracy, while maintaining low noise floors.
Benefits of 46BC at a glance:
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Only multifield microphone on the market.
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Optimized for Free-field measurement.
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Lowest ¼″ noise floor.
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Reduced influence of the angle of incidence.
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Meets the requirements of the AES Acoustics Measurements recommendation.
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Well-suited for high-frequency measurements.
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Reduced influence on measurement environment due to their small size.
Why is a ¼″ microphone better?
The actual physical size of ¼″ microphones provides many benefits for in-cabin acoustic testing. The size-related properties (blog post) reduce the pressure build-up effect on the diaphragm and minimizes error when measuring in a non-free-field environment, such as in-cabin. This enables improved accuracy at higher-frequency ranges. 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
The cabin is a complex sound field, consisting of multiple source contributions that can change due to factors that depend on velocity, such as road noise, wind noise, braking noise, etc. This environment is a prime example of a multifield environment, and it can only be measured accurately with ¼″ or smaller microphones.
According to the Acoustic Engineer Society (AES) In-car Acoustics Measurements recommendation, microphones that match the characteristics of 46BL-1 and the 46BC are ideally suited for these types of measurements.
Freq range: 4 Hz to 20 kHz
Dyn range: 24 dB(A) to 145 dB
Sensitivity: 20 mV/Pa
Technology
GRAS 46BC multifield microphone
46BC is a true multifield microphone for use in pressure, free-field, or random-incidence environments or any scenarios where the sound field is ill-defined or changing. The design of this microphone takes advantage of the microphone's small dimensions and slightly enhances the high-frequency content, which results in the perfect microphone for in-cabin measurements or any scenarios where measuring in a random incidence environment is needed.
Sound fields have historically been defined in microphone standards as pressure, free field, or random incidence. Multifield microphones can accurately measure in any field or in any combination of the defined fields.
In all situations, sound fields, and angles of incidence, 46BC is compliant with IEC 61672 Limits.
46BC protection grid
Unlike other ¼″ microphones, 46BC is optimized for use with the protection grid. This feature ensures protection during in-cabin measurements.
NOTE: The protection grid creates a resonance that will occur around 35 kHz. This resonance is in the order of magnitude of + 6 dB.
Microphone set concept
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 users, data safety translates directly into tools that allow for easier microphone selection, simple system configuration, and reduction of measurement errors.
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 small size and optimized frequency response make 46BC ideally suited for applications where the sound field is ill-defined or changing. This is due to the combination of size and optimization, which reduces the influence of angle of incidence of source positions and reflections. The result is a reduction in measurement uncertainty in applications such as in-cabin noise, architectural acoustics, and outdoor measurements. GRAS 46BC is also well suited for general acoustic measurements where high sensitivity and low noise are required.
In-car acoustic measurements
Find more information on the RA0399 array and the typical use according to EAS whitepaper in this instruction manual: RA0399 H-shaped holder for 6-unit microphone array
NOTES:
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To achieve optimal performances 46BC must be powered on for at least two minutes before starting a measurement.
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Unlike other CCP microphones, a positive pressure on the 46BC diaphragm generates a negative output voltage.
Compatibility
To perform as specified, the GRAS 46BC microphone set requires a constant current input module that can deliver 3.5 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 46BC is IEEE 1451.4 TEDS v. 1.0 compliant. If your measurement platform supports Transducer Electronic Data Sheets (TEDS), 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.
Calibration
46BC has a diaphragm that is slightly larger in diameter than is standard for ¼″ microphones. This does not affect sensitivity calibration, but for frequency calibration, you need a RA0236 Adapter.
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, specify this when ordering.
Learn more at calibration.
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 five years.
Service
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.
Specifications
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Dynamic range lower limit with GRAS preamplifier |
dB(A) | Max 24 Typical 23.5 |
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Dynamic range upper limit with GRAS CCP preamplifier |
dB | 142 RMS 145 Peak level |
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Dynamic range |
dB | 120 |
Typical frequency response (with protection grid)
Free-field and Random-incidence corrections
⅓-octave noise curve, linear
⅓-octave noise curve, A-weighted
Narrow-band FFT (1 Hz bandwidth)
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
Dimensions
Weight (g / oz)
8 / 0.282
Dimensions in mm
Length: 53
Height: 7
Ordering info
Optional items
| GRAS AA0070 |
3 m Microdot - BNC Cable |
| GRAS AL0029 |
¼″ Microphone Holder, POM |
| GRAS AL0013 |
¼″ Microphone Holder, Stainless Steel |
| GRAS AL0005 |
Swivel head |
| GRAS AL0006 |
Tripod |
| GRAS AM0071 |
Windscreen for ¼″ Microphones |
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1-channel CCP Power Module with A-weighting filter |
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| GRAS 12BA, BB, and BE |
1-, 4- and 2-channel CCP Power Modules |
| GRAS 12AQ |
2-channel Universal Power Module with signal conditioning and PC interface |
| GRAS 42AG |
Multifunction Sound Calibrator, Class 1 |
| GRAS 42AP |
Intelligent Pistonphone, Class 0 |
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GRAS RA0236 |
Adapter for frequency calibration of 46BL (also fits 46BL-1, and 46BC) |
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GRAS CA0029 |
Traceable Calibration of Microphone Set |
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GRAS CA2301 |
Accredited Calibration of Microphone Set |
GRAS Sound & Vibration reserves the right to change specifications and accessories without notice.
