To amplify sound, imagine putting a horn in your ear or even hauling around clunky batteries for your hearing aids. Well, those options were once the only ones for hearing better. But hearing aids have gone through dramatic transformations over the last century. Features, size, and battery power are stunningly revolutionary, now versus then. Now, wearers have many options, including devices that are hardly noticeable to virtually invisible.
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Bigger does not mean better for hearing aids

1954: Phonophor Epsilon
Lighter than a tennis ball, as small as a matchbox.

Shortly after the first pocket hearing aids were introduced, Siemens added a new model to its product range; one that was even smaller and only weighed about one-fourth as much. The Phonophor Epsilon weighed only about 50 grams (less than two ounces), including the batteries, and was the size of a matchbox. This was made possible by a discovery just a short time before that has gone on to become a fixture of our everyday lives — transistor technology. Along with reducing the size and weight of hearing aids, the shift from sub-miniature tubes to transistors brought many other advantages. These new developments helped push the Epsilon, which was designed especially for moderate hearing loss, into becoming the top-selling Siemens hearing aid in Germany and abroad within a short time.


Phonophor Epsilon, 1959
Sub-miniature tubes represented an important step towards ever-smaller hearing aids. But few years would go by before they were replaced by a revolutionary new technology: the transistor. Development began on the transistor in the 1920s by many different researchers, most of them working independently. Transistors were ready for series production in 1954. Used as amplifiers, transistors offered advantages similar to those of sub-miniature tubes, while outperforming them in many respects.
Siemens developed the Phonophor Epsilon, a fully transistor-based hearing aid distinct from others of its kind, starting with outward appearance. The Epsilon was much smaller than devices that used sub-miniature tubes. Its light weight was immediately apparent when held — it was lighter than a tennis ball and weighed noticeably less than earlier hearing aids. This leap was made possible primarily because of transistors’ low power needs. Older hearing aids had to devote about half their size to a battery, but the Phonophor Epsilon managed with just a button cell. Transistors not only made the Phonophor Epsilon compact and energy-efficient they also further enhanced sound quality, especially in the upper frequency range.
A newly-developed microphone contributed to this. Unlike older crystal microphones, the new model from Siemens was also based on a transistor, one that absorbed sound and converted it electromagnetically. The transistors brought with them a practically unlimited lifespan. They were impact-resistant and they did not have any cathodes that could age, or filaments that could burn out. The Epsilon even stood up to extreme temperature fluctuations — from high temperatures in the summer to bitter cold in the winter — better than older pocket hearing aids. For areas with especially hot climates, Siemens developed an even more rugged version, the Phonophor Epsilon Tropic, which delivered the same excellent performance at temperatures of up to 50 degrees Celsius (122 degrees Fahrenheit).

The power of electrons – right in your vest pocket.

Better performance with lower use of power, less noise, and no distortion at high frequencies. As early as the 1920s, great strides were made in amplifier technology, and the many advantages electron tubes had over conventional electrical sound amplification became clear. Even with these advances, the engineers of the time had not yet invented a way to manufacture small, portable tubes that could be used for hearing aids. It was not until World War II and the postwar period that sub-miniature tubes were developed, allowing for lightweight, compact hearing aids that encapsulated the benefits of the new technology in a form small enough to fit in a vest pocket. Siemens made this giant leap in hearing aid technology with the Fortiphon and Phonophor Alpha pocket hearing aids.

Electric hearing aids based on telephone technology began to reach their limits, especially when greater amplification was needed. High frequencies are hugely important for voice transmission, but they presented particular limits for the existing technology. Higher amplification was especially an issue when conventional carbon microphones were used — voices sounded louder, but they were distorted. The combination of sub-miniature tubes and crystal microphones solved this problem while also making it possible to build smaller and more powerful hearing aids. In the late 1940s, Siemens was the distributor for the Fortiphon, a pocket hearing aid based on this technology. The company then developed the similarly designed but even more powerful Phonophor Alpha.
Before World War II, a company named Fortiphone was responsible for selling Siemens hearing aids in the UK. Starting in 1949, the roles were reversed for a short time. With Siemens selling the Fortiphon — a pocket hearing aid with sub-miniature tubes and a crystal microphone — on the German market. The sub-miniature tubes developed in the U.S. and in England were not yet available in postwar Germany. Not long afterward, in 1951, Siemens launched its own first hearing aid of this type: the Phonophor Alpha.
Both hearing aids benefited from the advantages of the new technology. The three powerful electron tubes used as amplifiers were each about half the length of a wooden matchstick. Equipped with a crystal microphone, these devices delivered significantly clearer sound quality. This was especially apparent at high frequencies, which are key to faithful reproduction of consonants and whole syllables. The Phonophor Alpha had more than 250 parts, but still weighed in at just 175 grams (a little over six ounces) including batteries, and it was almost as small as a pack of cigarettes. Dubbed “pocket hearing aids,” the Alpha and the similarly compact Fortiphon slipped easily into a vest pocket and could even be worn under clothing.
Another factor that helped make these hearing aids more discreet was their skin-tone earpieces, which were connected to the unit via a cord in the same color. Various sizes of earphones were available. If the wearer’s ear canal varied greatly from the average form, an impression could be taken in order to produce a custom-fitted earpiece. The Phonophor Alpha was also specifically designed to be easy to use. A tiny dial was used to turn the device on and off and adjust the volume, and a flat slider on the side of the housing could be used to adjust the two frequency responses to the desired tone.

Siemens expanded hearing aid production after the huge success of the first Phonophor models.  The aids were produced at Berlin’s Wernerwerk plant. New speaker and microphone technology made the new instruments easier to use and sound better.  The new Phonophor was also smaller and lighter.  Demand increased beyond Germany and several thousand units were being sold annually in the U.S. alone.

In 1924, an optional microphone amplifier was launched for those with especially severe hearing impairments.  Starting in 1928, the metal microphone casing was replaced with a new type of plastic, called Bakelite, that reduced the weight.  Siemens hearing aid consultants of the time had many of the same responsibilities as today's hearing aid providers.  They helped consumers choose the right model, get used to hearing well again,  and explained how to use it.