Open fittings can help alleviate own voice issues, but at what cost?
Own voice complaints among new hearing aid wearers are caused by two separate phenomena: occlusion and hearing aid amplification. The usual suspect that gets the blame is the occlusion effect. Unfortunately, by opening the fitting to allow low-frequency components of the own voice to escape, amplified sound also escapes rather than being transmitted to the eardrum. This approach also allows ambient sounds (including background noise) to directly enter the ear canal.
By increasing the vent size, or by switching from a closed or double dome to an open dome, we may alleviate the occlusion effect. But at what cost? In terms of gain, as much as 20 dB difference in the low-to-mid frequencies between the open and closed fittings. While most of the loss occurs with low frequencies, a difference also exists in the important mid-to-high frequencies between 1000 Hz and 2500 Hz. According to the prediction of Speech Intelligibility Index (SII), reduced audibility in the mid-frequency bands will significantly impact speech intelligibility (Ricketts, Bentler, & Mueller, 2019).
Hearing aids use ever more advanced signal processing techniques to reduce noise and improve speech intelligibility. But open fittings not only allow processed and amplified sound to flow out of the ear, they also allow unwanted noise in. Because these sounds enter the ear canal directly, bypassing the hearing aid, even the best signal processing schemes provide only partial benefit for open fittings.
Determining the appropriate “openness” of a fitting is a delicate balancing act between the perception of the wearer’s own voice on one hand, and appropriate gain, effective digital signal processing, and feedback stability on the other. As clinicians, if we can tip the balance so the wearer’s own voice is no longer an issue, we have a better chance of providing the amplification required by the wearer, and allowing advanced hearing aid features such as directionality and digital noise reduction to provide more benefit.
By recognizing and optimizing the wearer’s own voice completely independently from all other sounds in the environment, Signia’s Own Voice Processing (OVP) has been clinically proven to improve the acceptance of own voice for 80 percent of dissatisfied wearers (Powers, et. al., 2018).
To learn more about the detrimental effects of fittings that are too open, and how OVP can hep, read the short paper here.
Ricketts, T., Bentler, R. & Mueller G. (2019). Essentials of Modern Hearing Aids Selection, Fitting, and Verification. San Diego: Plural.