A silhouette is one type of loop. It is a small loop of wire embedded in a thin hook-shaped piece of plastic with a wire coming out of it that can be plugged into an ALD or ALS receiver, a radio, TV, some computer speakers and some telephones. It is hooked over the ear and nestles beside a BTE hearing aid with a telecoil.
Driven by an ALD, the neckloop generates a weak magnetic signal that can be "heard" by the telecoil and amplified by the hearing aid.
Silhouettes are available in mono (one silhouette) or stereo (two silhouettes) for people with two hearing aids.
Advantages of silhouettes over other loops are that:
- Because they are close to the telecoil, their signal can be relatively low and still much stronger than (and therefore less susceptible to) most EMI (ElectroMagnetic Interference).
- Because they stay aligned relative to the hearing aid, they are less sensitive to head position.
Other types of loops can be used to generate the magnetic signal, too:
Another alternative to a hearing aid's microphone as the input device is the Direct Audio Input (DAI).