Twenty years ago, hearing aid selection and fitting procedures were relatively easy. If the hearing loss was severe or profound, a powerful body-type hearing aid was dispensed. The body aid consisted of a cigarette package–sized case containing the battery and all the electronics except the receiver. The receiver, a buttonlike device, snapped into an earmold and was connected to the body-worn device via a 1-foot fine electrical cord. Mild-to-moderate hearing losses were fit with either of two models: a hearing aid built into the temple piece of an eyeglass frame or an aid that hangs behind-the-ear (BTE) and connects to an earmold with soft plastic tubing. The electronics consisted of a linear amplifier, and the maximal output was limited by cutting off voltage peaks in the signal, known as peak clipping. These hearing aids had a narrow frequency response with a harsh, distorted sound.

Today, the eyeglasses hearing aid is no longer made, and the body aid is still available but rarely used. The BTE, still the primary hearing aid for children, has largely been replaced in adults by a new generation of hearing aids in which the entire mechanism is contained in a custom-made shell that fits into the ear canal. The electronics have undergone vast changes and are continuing to do so.

In addition to the improvement of the hearing aid, there have been changes in the hearing aid fitting process. Previously the only objective assessment method available was aided versus unaided sound-field audiometry, which was time-consuming and had problems in reliability. Now, in-situ, real-ear sound measurement of hearing aid performance, made with a small, probe-tube microphone, is the routine standard of practice.

The selection and proper fitting of today's high-technology hearing aids have become complex. Now, in addition to considering the magnitude and configuration of the hearing loss, the audiologist must also consider several patient demographics. This article describes in more detail the current hearing aid selection process. Most of the information is applicable to adults. Fitting and evaluating hearing aids on infants and children present the audiologist with a different and more difficult task and is beyond the scope of this article.