A custom fit inside the ear.
The idea of a hearing aid placed inside the ear was patented back in 1923, but components were still much too large to build a product based on the patent. Finally, in 1966, Siemens succeeded in putting this idea into practice. The Siretta 339 was the company’s first hearing aid to be worn entirely inside the ear. This in-the-ear (ITE) hearing aid system was made possible by a micro-amplifier designed specifically for it. The Siretta weighed only about 3.5 grams (just over 0.1 ounces) and was designed to fit snugly, without uncomfortable pressure, inside an average-shaped ear. ITE systems became a popular alternative to behind-the-ear (BTE) hearing aids for those with slight-to-moderate hearing loss.
Fine precision is required for assembly, 1966
In the German patent numbered 415944 (dated January 19, 1923) Wilhelm Gramsch, an inventor in the Prussian city of Königsberg (now Kaliningrad, Russia), proposed the construction of a hearing aid with components of such small dimensions that the apparatus can be worn […] in the ear canal, inside the auricle. However, the technology of the time still had a long way to go before an ITE hearing aid would become possible. Advances made over the next 40 years brought hearing aids to the point of being placed behind the ear, but even conventional transistors — a major advance in their time — were too large to allow devices to shrink further.
Siemens developed a new amplifier technology that further reduced the size of transistors for the Siretta. The device’s micro-amplifier was an integrated semiconductor circuit consisting of a single piece. That piece, a tiny silicon plate, was not only significantly smaller and lighter, but also less susceptible to disruptions and interference than conventional amplifiers.
At the same time, other components were shrinking. Almost ten Siretta 339 converters could fit in the same amount of space as a single converter from 1955. And the Siretta did not need much power — a single, tiny battery supplied enough energy for about 60 hours of continuous operation. Users could also choose to power the device with a rechargeable battery that held enough charge for a full day, and then could be recharged at night. To save energy wearers could also turn the Siretta off without having to remove it from the ear.
Today’s state-of-the art hearing aids come in an individually-fitted housing and can be so small they are practically invisible to others. But back when the Siretta came out it was a truly innovative offering.