There is a new head in town that will help you improve and document your hearing protectorsí acoustic capabilities

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

The new standard is unique because it approaches testing of both ear-muffs and ear-plugs - all with the same fixture properties and testing parameters. This makes comparison straight forward, and no questions are asked when it comes to the reliability of your test data.

*Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise Using Microphone-in-Real Ear or Acoustic Test Fixture Procedures (2010)

  • Compliance with ANSI/ASA S12.42 - As with all standardized procedures and equipment, this assures technicians, decision makers, and authorities of repeatability and transparent data when developing and verifying hearing protectors.
  • Design that directly handles sound pressure levels up to 174 dB and, indirectly, levels up to 190 dB - This enables in-situ testing where not only the self-insertion loss, but also the effects of head-band tension and positioning can be verified.
  • High self insertion-loss better than 65 dB - One of the vital main criteria of an acoustic test fixture that ensures you are actually measuring the insertion loss of your hearing protector and not the fixture.
  • Extended frequency range from 80 Hz to 20 kHz - The standard is defined up to 12.5 kHz, but the use of a modified IEC 60318-4 ear simulator (711) with a ¼" microphone extends the frequency range further and allows for testing not only hearing protectors, but also earphones.
  • Large base plates of the pinna simulators accommodate all types of circumaural ear muffs - This ensures leakage-free mounting and higher repeatability and reliability.
  • Long (14 mm) ear canal extension lined with silicone rubber for accommodating all types of ear plugs - This enables leakage-free mounting of both foam plugs and customized molded types.
  • Control unit for heating the ear canal extensions and pinnae to body temperature - For the most realistic testing of in-situ performance of ear-plugs, the system is, by default, set to heating the ear canals to 37 degrees Celsius.
  • Easy calibration - The test fixture can be calibrated without use of any additional tools other than a pistonphone. This enables the user to quickly verify the full measurement chain within minutes and not waste valuable time and resources on a non-calibrated setup.

Application Examples

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 to test 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 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.

Read more about G.R.A.S. 45CB Acoustic Test Fixture or download the manual.

Read more about G.R.A.S. 67SB Blast Probe Microphone or download the manual.


The new standard, ANSI S12.42 (2010), 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.

The ANSI 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 the G.R.A.S. 45CA Hearing-protector Test Fixture, 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 much appreciated collaboration of the standards committee members, we have 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.

About G.R.A.S.

Since the company's beginning in 1994 we have been 100% dedicated to developing and manufacturing high-quality measurement microphones and related acoustic equipment.

G.R.A.S. Sound & Vibration is therefore capable of offering you the right acoustical solutions within the fields of aerospace, automotive, audiology, consumer electronics, noise monitoring, building acoustics, telecommunications and naturally; microphone calibration.

The company is located in Denmark and founded by the Danish acoustics pioneer, Gunnar Rasmussen who for more than half a century has contributed to the world of sound and vibration with his unique ideas and designs. Mr. Rasmussen's special understanding of acoustics, electronics, metallurgy and physics has during the years lead to many innovations in acoustic instrumentation and measurement techniques. From the first commercially available series of 1" measurement microphones to intensity probes and techniques, artificial ear simulators and hundreds of customized applications, focus has always been on the users' needs and on the highest possible product quality.

This tradition of aptitude and working excellence is spun off and worked into every solution from G.R.A.S. Sound & Vibration for the benefit and satisfaction of our users. Our R&D Team is continuously improving our well-known solutions as well as developing new products to meet the industry's demands and the recommendations of various, international standardization boards.

G.R.A.S. is represented worldwide in more than 40 countries by subsidiaries and distributors. Whether you are searching for a multi-channel solution or just a replacement microphone for your sound level meter your local G.R.A.S. distributor will in close corporation with us be able to help solve your measurement needs.