There are basically two types of hearing aids: in-the ear systems and behind-the-ear devices. About two thirds of hearing aids fitted in Germany are behind-the-ear systems. They consist of the device itself behind the ear and a bent tube which passes over the ear to a mould which fits in the outer ear or in the ear channel. Whereas cosmetic reasons are usually given for preferring in-the-ear devices, behind the ear hearing aids are easier to wear, easier to switch on and off, and battery changing is also less of a problem. In addition, the mould separates easily from the appliance, so that it can be cleaned regularly. And, an audio link can only be used with behind the ear system. This allows wearers to hear speech without disturbing background sound, or to connect up to sound systems.

Open fitting - advantages with sound quality and comfort
Behind the ear systems can be fitted open or closed. The latter have a fitted ear mould which more or less completely closes the outer ear and ear channel. By modifying the ear mould with drilled holes, the acoustician can alter the sound quality and the wearing comfort of the hearing aid and adapt it to the specific requirements of the wearer. Generally, the more open the mould, the more comfortable the hearing aid is to wear. An open system ensures that the ear is ventilated and helps to avoid overheating or the collection of moisture in the ear. It also helps to avoid distortion of the wearer's own voice, and the unnatural amplification of swallowing and chewing noises. (This is similar to the effect produced by talking or chewing with a finger in the ear.) The wearer experiences a more natural sound because the sound propagation to the ear drum and the directional function of the outer ear and the ear channel are maintained. Finally, there is optimal amplification in particular in the high frequency range.