Open-canal fittings

Abstract

Fitting hearing aids involves innovation and compromise. This is especially true in deciding the tightness of the fit, whether of an earmold or a custom product. Tight-fitting instruments are good for obtaining high levels of gain and output, especially in the lower frequencies, and for minimizing feedback problems. However, they often are uncomfortable, sometimes create an unacceptable occlusion effect, and can give the patient a “plugged up” sensation. If the patient has normal or near-normal hearing in the lower frequencies, it is common practice to move toward a more open fitting to alleviate occlusion and let low frequencies into the ear naturally. In this case, the compromise is reduced gain and output, and a greater chance of unwanted acoustic feedback. There is little documentation of the first open-canal (OC) fittings, but we know they received considerable attention immediately after the CROS-type hearing aid was introduced.1 It was quickly discovered that the open earpieces (or tubing only) used for the CROS hearing aid also could be used for ipsilateral high-frequency amplification (hence, the term IROS [ipsilateral routing of signals], referring to a large vent). In the late 1960s, researchers showed that OC fittings could provide useful high-frequency amplification.2-4 In the ensuing decades, there wasn’t much excitement about open fittings, though there was some renewed interest during the Libby horn’s peak of popularity5 and on other occasions when a product designed specifically for high-frequency hearing loss was introduced.6 The ho-hum attitude toward OC fittings that persisted for more than 30 years was stirred up considerably a few years ago when five key aspects were combined in a single OC product: a small “cute” BTE casing, multichannel compression and gain adjustments, a thin tube channeling the sound from the hearing aid to the ear, a comfortable nonoccluding eartip, and, most importantly, effective feedbackreduction algorithms. As reviewed by Mueller,7 these five factors combine to offer a wide range of potential patient benefits, and OC products have rapidly taken over a sizable share of the total hearing aid market. While the peer-reviewed journals have published little about these modern OC fittings, several articles about this style have appeared in the trade journals, and the OC product is a hot topic at hearing aid workshops and seminars. However, there are still some key issues related to these products that need further clarification, and maybe even a couple areas where misconceptions exist. In this paper, we’ll provide some tips on OC fittings, which we hope will clarify more than they confuse.