Feedback is often caused by poorly fitted ear moulds. Feedback can occur spontaneously,
if e.g. the user lifts a telephone receiver to his/her ear or walks closely alongside
a wall. The sound processed by the hearing instrument leaks out of the ear canal
(through the ear mould) and is picked up and amplified again by the microphone,
causing a whistling sound. Most Siemens hearing instruments are equipped with with
effective feedback reduction systems. The new ACURIS, ARTIS and even the CIELO
instrument family come with a sophisticated feedback cancellation system which
eliminates feedback even before it occurs.
