First evidence for people trying to improve hearing with an external device. The early hearing aids were simply horn shaped objects. These devices collect the voices on their wide side and lead them through a narrowing tube to the narrow side which was located right next to the ear. Those early devices were made of animals’ horns and later out of wood and all sorts of metal.
Due to industrial revolution, the hearing aids are more spread. In addition, the mid class is rising, and more people are capable of having the relative expensive hearing aids. The main technology leap is related to the invention of the carbon microphone (1877). The basic ability of the carbon microphone is to translate sounds and voices into electrical signals. This enabled the usage of electronics to amplify the sounds before they are transmitted to the ear. Carbon based microphone pushed the hearing aids a big push forward. Towards the end of the 19th century, you could buy an expensive, portable hearing aid. Typically, it had to be placed on the table and wouldn't help severe hearing loss.
Two inventors claimed to invent the first carbon microphone. Both Thomas Alva Edison (1847 – 1931) and Emile Berliner (1851 – August 3, 1929) handed their patent application for carbon microphone somewhere in 1877. Eventually court ruled in favor of Edison as the inventor. Another great inventor who straggled with hearing improvements is Alexander Graham Bell (1847 – 1922), highly due to his wife hearing loss. Among all of his inventions (the telephone is the most famous) he contributed great dill to audiology technology progress.
Miller Reese Hutchinson (1876 - 1944), is considered by many to invent the first electronic hearing aid (his partner and he named it Akoulathon). It was available on 1899, you have to place it on a table in order to use it and it was sold for about 400$.
Have a look on one of the early patents by Thomas Edison that pushed the amazing hearing aids’ history on this link.