- Introduction of Carbon Microphones in the 1900s – The carbon microphone is composed of two plates that are separated by carbon granules. The movement of carbon amplified the electrical current that ultimately leads to the amplification of weak signals.
- Introduction of Vacuum Tubes in the 1920s – The Vacuum tubes consist of a cathode and an anode. The cathode is a filament from where the heat escapes while the anode is the plate that captures the escaped heat. The introduction of a grid between the cathode and anode by DeForest allowed for controlled electron flow resulting in amplification.
- Introduction of the transistors in the 1950s – Transistors control current in a more stable manner than the vacuum tube. There are no filaments and hence the need for a battery is eliminated.
The hearing aid was initially created in the 17th Century while the first electronic hearing aid was only manufactured in 1898. Though there is evidence to suggest that an apparatus like hearing aids existed in the 13th century, it is only from the 17th century onwards, that we can find evidence of more advanced and sophisticated hearing aids. During the thirteenth century, animal horns and seashells were commonly used to amplify sounds, 17th Century witnessed the use of ear trumpets which was known to amplify sounds with a little more efficiency while the 1800s saw the invention of concealable ear trumpets. Ear trumpets were wide at one end to gather sounds while the constricted end-directed amplified sound into the ear. Bone Conduction was also discovered during this period leading to the invention of fan-shaped devices that were placed behind the ear to collect sound waves and transmit them through the bones. It was only in the 1900s when the technology behind telephones and electricity was utilized to invent electric hearing aids. In the 1920s Hearing aids became easily portable due to their vacuum technology and use of batteries. A major advancement in hearing aids happened in the 1950s when transistors were introduced in the hearing aids. Transistors enabled various styles of hearing aids to be evolved such as the Behind the Ear hearing aid and In the ear hearing aid. It was finally in the 1990s when sophisticated features such as noise filtration and amplification were introduced due to the Digital System Processing (DSP). The size of the hearing aid device in the 1900s could progressively shrink due to several factors. Battery Miniaturization reduced the size of the hearing aids significantly while the transistors being manufactured with silicone material also contributed to the size reduction.
Modern Day Hearing Aids: Modern-day Hearing Aids is unlike anything used in the past. They are extremely lightweight, highly concealable, and tremendously efficient at the amplification of sounds. They are known to filter noise effortlessly ensuring that no shadowing of sounds occurs. Most new-age hearing aids consist of a microphone to pick up sound, amplifier circuit to make the sound louder, receiver to deliver the sound to the ear canal, and batteries. Hearing aids can be digital or analog.
- Analog – These hearing aids amplify all sound waves in a similar manner. They are usually programmable for different settings and listening environments. Analog Hearing aids are less commonly used than digital hearing aids.
- Digital – Digital Hearing aids have additional features like conversion of sound waves to digital waves which make them sound exactly like a duplication of the original sound to be amplified. They might also be equipped with advanced features like background sound cancellation or noise cancellation.
- Behind the Ear (BTE) Aids – The parts of this hearing aid are contained inside a minuscule plastic case which is placed behind the ear. The custom earpiece, which is known as an “Earmold” is connected to a tube that transmits enhanced sounds. Advancements in technology have made the BTE hearing aids more discreet and less bulky. This type of hearing aid is the most efficient at sound amplification, but might also amplify noise and background sounds. Most Behind the Ear Hearing aids are programmable and are equipped with volume control options. These are easy to clean and maintain.
- Mini BTE Aids (on the ear) – This is a relatively new type of BTE hearing aid which allows for lesser occlusion and is better for cosmetic purposes.
- In the Ear (ITE) Aids – These hearing aids consist of a shell containing parts of the hearing aid which sit inside the outer ear. Since the receiver sits inside the outer ear canal, it is more susceptible to damage by a buildup of the ear wax over time. Thus, regular cleaning and maintenance are integral to ensure the performance of these hearing aids.
- In the Canal (ITC) and Completely in the canal (CIC) Aids – The parts of these hearing aids are contained in cases which can be partly or completely placed in the ear canal. These are the most compact of all hearing aids available and are usually considerably more expensive.
- Contralateral Routing of Signals (CROS) Hearing Aids – These hearing aids are used to reduce unilateral hearing loss by transmitting the sounds to the ear having poorer hearing capability from the ear with better hearing. In technologically advanced Contralateral Routing of Signals (CROS) Hearing Aids the conduction of the sounds occurs through the bony portion of the skull to the cochlea of the hearing ear. Some CROS hearing aids are also designed to reduce the shadow effect while hearing.