INTEC Acoustics
Hearing protection
Personal hearing protectors are popular for prevention of noise-induced hearing loss because they pr
ovide a practical and relatively low-cost solution. However, they are only effective when noise is sufficiently attenuated during the entire exposure period. This implies that the protectors' attenuation must be adapted to the noise level, but also that they have to be worn correctly and consistently.
Within INTEC, we focus on verification of attenuation and acoustical comfort to enhance the performance of hearing protectors in practice. First, research has clearly demonstrated that the attenuation achieved by an individual user might vary substantially from laboratory measurements. Secondly, people will feel reluctant to wear their protectors if they distort the 
sonic environment or hamper communication; optimised design is needed to improve acoustical comfort.
Our general research approach consists of measurements on a Head And Torso Simulator and human subjects and in-depth acoustical analysis combined with numerical simulations using an in-house developed FDTD model of the outer ear canal.
Performance and MIRE measurements
To apply the Microphone In Real Measurements (MIRE) technique, a microphone is inserted in the ear canal, measuring the sound pressure level behind the hearing protector. In our research project, a custom-ma.jpg)
de earplug with test bore is used so that microphone insertion will not alter the protector's fit. This approach allows quick and reliable sound recordings, but the actual sound pressure level at the eardrum might vary substantial from the microphone's measurement point. To correct for this difference, the possibility to estimate individualised transfer functions between eardrum and microphone is addressed via measurements and numerical simulations. In addition, filters are designed to allow incorporation of these findings in general measurement equipment.
Communication and acoustical comfort under hearing protectors
To improve communication with hearing protectors, earplugs have been equipped with microphone, loudspeaker and signal-processing unit so that the attenuation can be adapted to the incoming noise level. Speech understanding under these augmented protectors is compared to standard earplugs. In addition detailed acoustical analysis is carried out to clarify the obtained speech recognition scores and provide useful guidelines for further design.
References
1 Bockstael, A., Deschrijver, D., Botteldooren, D. et al. (2010). Digital filters for accurately verifying the performance of hearing protectors in use. ACTA ACUSTICA UNITED WITH ACUSTICA, 96(1) 168-178.
2 Bockstael, A., Van Renterghem, T., Botteldooren, D., et al. (2009). Verifying the attenuation of earplugs in situ: Method validation on human subjects including individualized numerical simulations. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 125(3) 1479-1489.
3 Bockstael, A., de Greve, B., Van Renterghem, T., et al. (2008). Verifying the attenuation of earplugs in situ: Method validation using artificial head and numerical simulations. JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA, 124(2) 973-981.