Comparison of the Passive Sound Attenuation of Custom Ear Molds with Different Hearing Aid Couplings
Hearing aids can amplify sounds to compensate for a hearing loss. Other features such as loudness compression and an output limiter allow for an amplification of soft sounds and a reduction of loud sounds. Therefore, hearing aids can basically also act as hearing protectors. However, the reduction of sounds can only be realized by not amplifying them, since current hearing aids do not provide active noise canceling. Consequently, the passive sound attenuation is crucial for the use as hearing protectors. Closed fittings are required to get high attenuation, and custom ear molds better fit the individual shape of the ear. Nevertheless, the influence of the acoustic coupling between ear mold and hearing aid on the attenuation is not clear. Thus, the passive attenuation of four different custom ear molds is measured with the REAT method (EN ISO 4869-1) for 20 test subjects. The influence of the acoustic coupling is analyzed by comparing the following conditions: (i) closed ear mold, (ii) closed ear mold for behind-the-ear devices with standard and (iii) slim tube, and (iv) closed ear mold for receiver-in-the-canal devices. These results help to define requirements for the certification of hearing aid ear molds as hearing protectors (personal protective equipment).