G.R.A.S. 45CB Acoustic Test Fixture

ANSI: S12.42


The G.R.A.S. 45CB Acoustic Test Fixture is designed and specified to comply with the ANSI/ASA S12.42 standard. With this test fixture, you can test all types of hearing-protectors in the most realistic way - both in the acoustic lab and in the field.

Compliance with ANSI/ASA S12.42 assures technicians, decision makers, and authorities of repeatable and transparent data when developing and verifying hearing protectors.

The 45CB’s robust design is ideally suited for binaural testing of active and passive earplugs, as well as circumaural hearing protectors. It is designed for portability, which gives you flexibility for your testing setups.

The 45CB directly handles sound pressure levels up to 170 dB and, indirectly (using compasion methods), levels up to 190 dB. The 45CB has a self insertion-loss better than 65 dB, which means you are actually measuring the insertion loss of your hearing protector and not the fixture.

The modified IEC 60318-4 ear simulator (711) with a ¼” microphone extends the frequency range required by the standard (from 80 Hz all the way up to 20 kHz). The 14-mm long ear canal extension is designed to let you also test all types of ear plugs. The silicone-rubber lining of the extension enables leakage-free mounting of both foam plugs and customized molded types.

Another design advantage is the large base plates of the pinna simulators. They can accommodate all types of circumaural ear muffs. The silicone-rubber lining of the plates ensures leakage-free mounting, as well as higher repeatability and reliability.

All the silicone-rubber parts of the 45CB can be heated to body temperature to give the most realistic testing of in-situ performance of ear-plugs. The heating unit of the system is set by default to 37 degrees Celsius.

Calibration is easy with the 45CB. You only need a pistonphone to quickly verify the full measurement chain within minutes and not waste valuable time and resources on a non-calibrated setup.

Typical applications and use

The G.R.A.S. 45CB Acoustic Test Fixture according to ANSI S12.42 is developed for testing of both ear-muffs and ear-plugs.

For testing ear-muffs, special attention was put on those types that are integrated in helmets. The result is head dimensions that reflect the average user of today's available head gear.

For testing ear-plugs, the focus was put on the mounting repeatability and damping as function of the body temperature. The result is a longer, silicone-lined ear-canal that can be heated to body temperature.

Today's use of hearing protectors ranges from construction sites to heavy industries, to civil as well as military aviation and to surveillance activities and combat scenes.

For that reason, the 45CB is designed for tests at very high levels without compromising its self-insertion loss or losing data.

With the newly developed Ear Simulator, you can directly test at levels up to 170 dB and, using comparison methods, indirectly up to 190 dB with both continuous and impulse noise. Noise of this magnitude is typically generated in the field so the 45CB was optimized for outdoor use. To transport and store the acoustic test fixture, a dedicated case, with option for wheels, is included.

Because the 45CB is built to comply with, or exceed, the ANSI S12.42 standard, it can cope with demands such as testing in the field and withstanding high pressure levels like explosions.  It can help manufacturers improve the quality of their products to meet the markets’ and the standards’ growing needs for design, quality assurance, and verified compliance to stricter regulations.

Tests at high sound levels with the 45CB include

  • Measuring the insertion loss and sound pressure levels of
    • Active and passive earplugs
    • Circumaural earmuffs
    • Combined communication and hearing protection devices
  • Testing with continuous or impulsive signals
  • Testing in the laboratory or in the field

Technical Details

  • The pinnae for the 45CB are the same standardized KEMAR pinnae, but with a large base plate to comply with the requirements of the ANSI S12.42 for correct circumaural testing. This large base plate reduces or eliminates the risk of leakage.
  • The ear extension is also based on the original design for the 45BA KEMAR. It has been extended into a 14 mm long and 7.5 mm wide ear canal with a heatable silicone rubber lining. The ear extension can accomodate all sizes of ear plugs, including the deep-insert type.
  • The removable ear simulator is based on the IEC 60318-4 standard (previously known as the 711 coupler) and modified with a ¼” pressure microphone, which makes it possible to test high sound levels and very fast impulse noises.
  • The control unit in the base of the 45CB is for setting and monitoring the temperature during tests. The control unit heats the silicone rubber lining of the ear canal extension to body temperature for realistic measurements of the properties and damping effects of ear plugs.

The 45CB includes two plugs for measuring self insertion loss in a closed ear.

Easy Calibration

We recommend calibration prior to each use to ensure the accuracy of your measurements. The design of the 45CB makes this task very easy. The 42AP Intelligent Pistonphone  or 42AA Pistonphone  are ideally suited for this task.

The Concept Behind the 45CB

At G.R.A.S., we have been working with high-quality measurement testing since the day we began. Our expertise in Manikin based measurements is proven with the 45BA KEMAR manikin and the 45CA hearing-protector test fixture.

It was because of this expertise that ANSI’s American National Standards on Acoustics S12 committee invited us to participate in the development of a new standard for measuring the insertion loss of hearing protection devices in continuous or impulsive noises.

Insertion loss requires testing and measuring both with and without hearing-protection devices and then calculating the difference between the two results. It is crucial for manufacturers to know the insertion loss of their hearing protector devices to achieve and ensure the required protection level and expected performance.

The ANSI S12.42 covers insertion loss testing procedures for both ATF (acoustic test fixtures) and MIRE (microphone-in-real-ear) in laboratory and field setups. At G.R.A.S., we set our focus on the development of the ATF manikin.

The standardized KEMAR design was a good starting point, but the new standard calls for extended ear canals and a higher self insertion loss required for the testing of high sound pressure levels that can be conducted without harm to a human subject. Additional elements were inspired by the 45CA, which conforms to the ISO 4869-3 standard that covers ear muffs, but not ear plugs as required by the new standard.

Based on the broad-reaching and respected acoustic expertise in G.R.A.S. and with the collaboration of the standards committee members, G.R.A.S. has developed a new acoustic test fixture that can meet the need for a commercially available ATF suitable for tests of hearing protectors at very high noise levels - the 45CB. In fact, it meets or exceeds the requirements as defined in ANSI/ASA S12.42.

The sturdy 45CB is built to handle a wide range of noise levels—continuous and impulsive—for testing

  • Earplugs
  • Active and passive ear muffs
  • Ear muffs integrated in work and safety helmets or designed for use under helmets


The 45CB requires a 200 V polarization voltage for its externally polarized microphones.

System verification

For daily verification and check of your measurement setup, we recommend using a calibrator like G.R.A.S. 42AB Sound Level Calibrator.

For proper sensitivity calibration, we recommend using a pistonphone like G.R.A.S. 42AP Intelligent Pistonphone.

Quality and warranty

All G.R.A.S. microphones are made of high-quality materials that will ensure life-long stability and robustness. The microphones are all assembled in verified clean-room environments by skilled and dedicated operators with many years of expertise in this field.

The microphone diaphragm, body, and improved protection grid are made of high-grade stainless steel, which makes the microphone resistant to physical damage, as well as corrosion caused by aggressive air or gasses.

This, combined with the reinforced gold-plated microphone terminal which guarantees a highly reliable connection, enables G.R.A.S. to offer 5 years warranty against defective materials and workmanship.


If you accidentally damage the diaphragm on a G.R.A.S. microphone, we can—in most cases—replace it at a very reasonable cost and with a short turn-around time. This not only protects your investment, but also pleases your quality assurance department because you don’t have to worry about new serial numbers, etc.


Before leaving the factory, all G.R.A.S. microphones are calibrated in a controlled laboratory environment using traceable calibration equipment.

Depending on the use, measurement environment, and internal quality control programs, we recommend recalibrating the microphone at least once a year. 

Connector type 3 m 7-pin LEMO
Theoretical dynamic range lower limit with G.R.A.S. preamplifier dB(A) 39
Theoretical dynamic range upper limit with G.R.A.S. preamplifier @ +120 V / ±60 V power supply dB 181
Set sensitivity @ 250 Hz (±3 dB) mV/Pa 1.5
Set sensitivity @ 250 Hz (±3 dB) dB re 1V/Pa -56.5
Temperature range, operation °C / °F 0 to 39 / 32 to 102
Humidity range non condensing % RH 0 to 100
ANSI standard S12.42
CE/RoHS compliant/WEEE registered Yes/Yes/Yes
Weight g / oz 14750 / 520.29

Self Insertion Loss, Measured with closed ear simulators: 100 Hz – 8 kHz >74 dB

Self Insertion Loss, Measured with closed ear simulators: 80 Hz – 12.5 kHz >65 dB


G.R.A.S. RA0045-S7 Ear Simulators (two), each with an Ear Canal Extension and ¼” pressure microphone
G.R.A.S. GR1407 Plugs (two) for self insertion loss verification
G.R.A.S. 26AS-S3 Preamplifiers (two), each with cable and 7-pin LEMO connector
G.R.A.S. KE0129 Heating control panel, including connectors for the ear simulators and heating elements
G.R.A.S. KB0077 Left pinna for 45CB
G.R.A.S. KB0078 Right pinna for 45CB
G.R.A.S. AB0016 Power supply for the heating system
G.R.A.S. YY0023 Hex key, 2.5 mm
G.R.A.S. KM0082 Flight case with removable wheels
G.R.A.S. LI0052 Manual


G.R.A.S. 12AA 2-Channel LEMO Power Module with gain, filters, and SysCheck generator
G.R.A.S. 12AQ 2-Channel CCP/LEMO Power Module with Signal Conditioning and Computer Interface
G.R.A.S. 42AP Intelligent pistonphone
G.R.A.S. 67SB Blast Probe according to ANSI S12.42
G.R.A.S. RA0157 ½” Calibration adapter for KEMAR pinnae
G.R.A.S. AA0008 3-m LEMO extension cable
G.R.A.S. AA0009 10-m LEMO extension cable
G.R.A.S. AA0012 30-m LEMO extension cable
G.R.A.S. AA0014 100-m LEMO extension cable
G.R.A.S. AA0034 2-m BNC-to-BNC
G.R.A.S. AA0035 3-m BNC-to-BNC
G.R.A.S. AA0036 5-m BNC-to-BNC