Tools Developed by HearingProTech

CAPA - Measuring the effectiveness of personal hearing protection device

Measure the conformity of a personal Hearing Protection Device and make sure that its wearer is properly protected according to their sound environment.


The CAPA system only takes a few minutes to measure the attenuation of a Personal HPD, to determine its conformity regarding the manufacturer's specifications and to check that its attenuation is properly adapted to the level of sound exposure of its user.

CAPA is a system of measuring the effectiveness of a personal hearing protection device, such as an “earplug”.

How to ensure that a hearing protection device provides effective protection without excessive protection?

Many organizations and studies have highlighted the differences between theoretical attenuation values displayed for hearing protection devices and the actual attenuation values recognized when these protection devices are actually worn.

While Germans impose a systematic efficiency test within six months from the delivery of the customized hearing protection devices, very few customers or manufacturers actually implement these controls.

Two methods exist to measure attenuation, and therefore the efficiency, of a hearing protection device:

  • The MIRE method (objective) measures the attenuation of a hearing protection device adapted for this test using two microphones.
  • The subjective method measures the hearing thresholds of a subject with and without hearing protection. CAPA system is part of this category of measurement.

CAPA uses the preliminary audiometry method of making comparative audiometric measurements on a subject with and without hearing protection devices. An average attenuation is calculated, which is then compared with the attenuation values displayed by the manufacturer, to determine the conformity of the hearing protection device. Once the conformity of the hearing protection device is validated, the CAPA system then verifies the suitability of the hearing protection device with respect to the noise level to which its user is exposed. Residual level at the ear is calculated as described in the European standard EN458 and compared with the recommendations of the EU Noise Directive.

CAPA system currently offers the only universal, reliable, and integrated solution to check the efficiency of intra-type hearing protection devices, at a cost that cannot exceed a few euros per tested protection device.


Additional documents

Difference between an audiometry and a CAPA test (PDF)

INRS study 2013 - Testing of commercially available systems for hearing protector based on individual fit testing (PDF)

Study on defining the minimum attenuation of a personal hearing protection device (PDF)

Study on the impact of ambient noise on the measurements of CAPA system (PDF)

Report on repeatability of measurements of CAPA system (PDF)

Summary of INRS study "Testing of commercially available systems for hearing protector based on individual fit testing" (PDF)

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