1928: Phonophor with microphone amplifier. Lighter and more compact.

After the huge success of the first Phonophor models, Siemens & Halske expanded hearing aid production activities at Berlin’s Wernerwerk plant. The goal of the new models was to allow improved adaptation to different levels of hearing loss. Advances in microphone and speaker technology also made the new devices more convenient for users. New materials and designs made the Phonophor lighter and more compact, while advances in technology improved performance and sound quality. Demand for the Phonophor rose in Germany and beyond, and by the mid-1920s, several thousand units were being sold each year in the U.S. alone.


Phonophor with microphone amplifier

“You don’t have to suffer from hearing problems anymore! Try our Phonophor electric hearing aid, approved for years by many hearing loss patients. Now with an earphone that has been significantly improved after extensive testing and research.” Siemens used this and similar slogans to advertise its hearing aids in newspapers in 1926 and 1927. In fact, Siemens engineers had been hard at work on developing a number of improvements ever since the first Phonophor model was launched. The first earphone was a huge improvement in terms of wearing comfort and a major selling point for Siemens hearing aids, but it did face initial startup difficulties, like many new technologies. The diaphragm was especially problematic, as it expanded under warm conditions, weakening the adhesive bond holding the anchor in place and causing it to loosen or fall out. The designers managed to overcome these initial problems, however, and then went to work on the technology and structural design of the Phonophor. They made great strides, making it possible to add further products to the range and adjust the hearing aids better to reflect individual levels of hearing loss. An optional microphone amplifier was launched in 1924, offering a way to help even those with especially severe hearing impairments. Since sound waves do not merely travel through the air, but also through solid objects, the engineers developed a bone conduction headphone worn behind the ear. This earpiece was especially helpful for those with conductive hearing loss and hearing impairment of the middle ear, both conditions that keep sound waves from passing to the inner ear through the air. Starting in 1928, new materials were used for some models, paving the way for further advances in technology while also enhancing comfort for wearers. The microphone casing was no longer made of metal, but of Bakelite, a new plastic that noticeably reduced the Phonophor’s weight.

Hearing aids were not standard commercially available items like lamps or fans. Even as late as the 1920s, many people with hearing loss still had to be convinced of the benefits of electric hearing aids. Alongside advertising and partnerships with ear specialists, a salesperson’s training was key. Hearing aid salesmen were the predecessors of today’s audiologists, advising people with impaired hearing on how to choose the best model, explaining how to use it, and helping them get used to the device. According to the “Guide to Selling Phonophors” published by Siemens in 1928, sales staff needed to “develop a friendly rapport with the person’s individual characteristics in mind” and “convince customers of the good properties of our Phonophors.”