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The hearing aid occlusion effect: Measurement devices compared

Hearing aid users frequently complain about the sound quality of their own voices. One of the most common complaints, particularly among new users, is that their voice sounds “hollow” or as if they are “talking in a barrel.” Although such complaints sometimes result from suboptimal hearing aid settings, they also may be associated with significant occlusion created by the hearing aid shell or earmold.1-3 When a person vocalizes, the resulting bone-conducted energy causes vibration of the mandible and the soft tissue located close to the external canal. This causes vibration of the canal’s cartilaginous walls, producing energy that is subsequently transferred to the volume of air within the canal. When the ear canal is occluded, much of this energy is trapped, causing an increase in the sound pressure level delivered to the tympanic membrane and, ultimately, to the cochlea. For some closed vowels, occluding the external ear using a shallow insertion depth can result in levels of 100 dB SPL or more within the canal.4 This energy is centered primarily in the low frequencies, with the peak of the occlusion effect typically occurring in the range of 200 to 500 Hz.5 See Mueller et al.1 and Mueller8 for further discussion. Patient dissatisfaction resulting from the occlusion effect can lead to inconsistent hearing aid use or even rejection.4 The 2001 Knowles MarkeTrak VI report of trends in the hearing instrument market found that only 54% of surveyed hearing aid owners were satisfied with the sound quality of their own amplified voice.6 This was 4% below the satisfaction rate reported in the 1997 MarkeTrak V survey.7 One need only peruse the latest product information from hearing aid manufacturers to realize that occlusion reduction has become a highly marketed feature, although it is questionable that all these approaches are truly effective. As dispensers continue to fit smaller custom instruments that provide limited venting options and to fit patients with milder degrees of hearing loss, they can expect to continue fielding complaints resulting from the occlusion effect.8 The magnitude of the occlusion effect is highly variable among patients.5 Since this effect can decrease user satisfaction, it is critical that clinicians evaluate their patients’ own-voice complaints objectively and treat them systematically. This is because the dispenser must first determine if the source of the problem is the occlusion effect or if it is related to the gain settings of the hearing aid, which is an entirely different problem. If the problem is indeed the occlusion effect, then the dispenser must perform objective measures to monitor treatment—the effects of venting or adjustment of shell/earmold canal length. Traditionally, probe-microphone equipment has been used to measure the occlusion effect objectively. More recently, Etymotic Research introduced a hand-held device, the ER-33 occlusion effect meter. The primary purpose of this study was to compare the results of ER-33 measurements with those obtained with traditional probe-microphone equipment. In addition, we examined the effects of venting, since the current evidence on the effectiveness of this occlusion treatment is conflicting.