With the improvement of living standards and the popularization of health awareness, the incidence of conductive hearing loss in China has been decreasing year by year. The development of audiology has allowed the majority of conductive hearing loss cases to be treated through medication or surgery, preserving or improving hearing to some extent. However, for patients with sensorineural hearing loss, there are currently no clear and reliable medical or surgical treatments available. They can only rely on hearing aids, cochlear implants, and other assistive devices to help individuals with hearing impairments achieve hearing compensation or reconstruction.
Hearing aids are small amplification devices designed to compensate for hearing loss and are currently widely used and relatively affordable assistive devices. The development of hearing aids has undergone five eras: the Primitive Acoustic Amplification Era, the Carbon Element Era, the Vacuum Tube Era, the Transistor and Integrated Circuit Era, and the Digital Hearing Aid Era.

Primitive Acoustic Amplification Era

Looking back at the history of hearing aids, in ancient times, if people had hearing impairments, the only thing they could do was cup one hand behind the ear to amplify sounds. The initial appearance of hearing aids was inspired by this hand cupping method and included devices like "ear trumpets," wooden "hearing boards," "hearing tubes," "hearing hats," "hearing bottles," "ear fan wings," and even long "speaking tubes" resembling stethoscopes. These simple mechanical hearing devices were used for centuries until the 19th century when they were gradually replaced by carbon element hearing aids.

Carbon Element Era

In 1892, the first patented telephone-type hearing aid appeared. It was a carbon-element hearing aid that used the principle of electrical amplification, powered by batteries, and comprised a carbon-element transmitter and a magnetic earphone. Due to the limited gain of carbon-element hearing aids, along with significant noise and distortion, and their susceptibility to humidity, they were eventually replaced by vacuum tube hearing aids after a short period of use.

Vacuum Tube Era

In 1907, the vacuum tube hearing aid was introduced, and the first electronic tube hearing aid was produced in the UK in 1921. It had greater amplification and improved clarity. Initially, these tube hearing aids were large and required heavy batteries, making portable use nearly impossible. Over time, the size of tubes and batteries decreased. In 1938, the miniaturization of tubes was a turning point in the development of hearing aids. The advent of mercury batteries significantly reduced the size of hearing aids, allowing batteries and hearing aids to be integrated. This period also saw the emergence of small crystal earphones, making the production of portable box-type hearing aids possible.

Transistor and Integrated Circuit Era

With the emergence of various new technologies and materials during World War II, the integration of hearing aids became significantly smaller. During this period, eyeglass-style and spectacle-style hearing aids appeared. The introduction of transistors in the 1950s replaced vacuum tubes, making hearing aids smaller, less prone to breakage, and with extended lifespan.

In 1964, integrated circuit hearing aids were introduced, featuring smaller size, lower power consumption, and better stability. Integrated circuits revolutionized electronic products. As integrated circuits advanced, the appearance of hearing aids also underwent various changes. From the early transistor era with clip-on and eyeglass styles to behind-the-ear styles introduced during the integrated circuit era, and in the 1980s, the emergence of in-the-ear styles. In the 1990s, the birth of completely in-the-canal styles made hearing aids almost invisible in appearance.

Digital Hearing Aid Era

In the mid-to-late 1980s, digital signal processing (DSP) chips were applied, marking the era of "programmable" hearing aids. DSP chips have storage and computing functions, storing hearing data and various parameters determined after selection. They dynamically analyze different external input signals and determine the working processes of other analog components in the circuit.

In the mid-1990s, the functions of digital signal processing chips became more powerful and their size continued to shrink. In 1996, Widex and Oticon almost simultaneously launched Senso and Digifocus, the earliest fully digital hearing aids. Apart from their tiny size (completely fitting into the ear canal in the case of Completely-in-Canal or CIC styles), they were based on a hardware-based dedicated DSP closed-loop platform, implemented entirely through digital circuitry hardware. The software is fully embedded in the hardware circuitry, with no redundant parts in the structure, resulting in high processing speed (performing millions of operations in less than 1 second without perceptible delay).

Today's hearing aids use tiny chips, completely replacing the bulky bodies of 100 years ago. Technological progress has not only changed the quality but is also evident in continuous breakthroughs in design. From tube hearing aids, vacuum tube hearing aids, integrated hearing aids, transistor hearing aids, programmable hearing aids, to today's fully digital hearing aids, they have become smaller and more stylish. At the same time, most modern fully digital hearing aids use dedicated DSP chips with processing speeds of over 100 million operations per second. By utilizing digital technology's low noise and small distortion characteristics, many hearing aid manufacturers have developed "artificial intelligence" processors based on the human ear's auditory perception model, introducing new concepts in selection methods.

Mr. Ernst, Chairman of the European Hearing Aid Industry Association, stated in 2006, 'As we all know, today's hearing aids, apart from the name, are no longer comparable to the complex hearing systems of the past.' Today's hearing systems not only differ significantly from traditional hearing aids in hardware but more importantly, they have made breakthrough progress in functionality and usage scope. The powerful functions of software have played a revolutionary role in the re-creation of hearing aids.

Current Advanced Hearing Technologies

Real Ear Measurement (REM): This involves testing the actual hearing threshold after a patient wears a hearing aid. In pure-tone audiometry, headsets are commonly used for testing, without considering the effects of external ear canal blockage and microphone positioning after wearing the hearing aid. Therefore, REM accurately obtains the actual hearing threshold after wearing a hearing aid, making subsequent hearing aid adjustments more accurate.

High Precision Localization System: This is an upgraded version of directional technology. Improving speech resolution in noisy environments has always been a goal of hearing aid technology development. Directional microphone technology has always been a focus in the field of hearing aids, as it is the only technology repeatedly proven to help improve the signal-to-noise ratio and assist hearing aid wearers in enhancing speech recognition rates. The high precision localization system enhances traditional directional technology by real-time differentiating noise positions in different frequency bands, making real-time directional changes more effective in improving the overall signal-to-noise ratio in noisy environments and facilitating easy listening to sounds behind.

Noise Reduction - SII Speech Enhancement: Noise reduction technology separates noise from the signal of speech with noise, a technique that is used to remove noise. In the field of hearing aids, how to make hearing aids better handle sound in noisy environments to help hearing aid users obtain clearer speech signals has always been a concern for clinical audiologists and hearing aid users. This is because high-quality noise reduction is one of the essential reasons hearing aid wearers find hearing aids more acceptable and useful, as the most significant problem for users during hearing aid use is understanding language in various noise environments. Traditional noise reduction methods involve reducing the gain compensation of hearing aids in noisy environments, which may affect the pickup of speech. Therefore, the current trend is to use new calculation methods that compensate for the shortcomings of the original calculation method by calculating the Speech Intelligibility Index (SII). This new noise reduction method is referred to by manufacturers as speech enhancement noise reduction. SII speech enhancement noise reduction technology uses different gain reduction amounts for users with different degrees of hearing loss, helping various hearing loss users achieve the best speech intelligibility and further enhancing their speech understanding.

Frequency Shifting Technology: This refers to the transfer of important high-frequency speech signals that hearing aid wearers with no residual high-frequency hearing or poor residual high-frequency hearing cannot hear with regular hearing aids to the mid-low-frequency range where they still have good residual hearing. Current hearing aid frequency shifting technology can be roughly divided into linear frequency shifting technology and nonlinear compression frequency shifting technology, depending on different signal compression processing modes. Linear frequency shifting technology, also known as audible frequency expansion technology, is a linear frequency shifting hearing aid technology that mainly moves high-frequency sounds with no residual or poor residual high-frequency hearing to the mid-low-frequency region where they still have some residual hearing. Nonlinear compression frequency shifting technology compresses high-frequency sounds with no residual or poor residual high-frequency hearing to adjacent lower-frequency regions.

Intelligent Wind Noise Processing Technology: In windy environments, wind can create vortices at the hearing aid microphone, directly striking the microphone and causing the hearing aid wearer to perceive an impact noise greater than the actual wind noise. The impact of wind noise is a continuous problem that the hearing aid industry is exploring solutions for. Currently, commonly used solutions involve reducing low-frequency gain and changing the hearing aid's directionality to omnidirectional, improving the impact of wind noise. Alternatively, sound transmission technology can be used to transfer high-side sound to the low-side sound in terms of signal-to-noise ratio, but this requires wearing hearing aids on both ears, and different signal-to-noise ratios for different binaural hearing aids limit the effectiveness of reducing wind noise. At the same time, there is a new intelligent wind noise processing technology that detects wind noise through dual microphones, classifies the relevance of microphone input signals through classifiers, and detects speech or wind noise. This achieves an improved signal-to-noise ratio in windy noise environments, providing users with better speech recognition in windy noise environments, whether they are wearing hearing aids on one ear or riding in the wind, ensuring clear listening.

Sound Classification Technology: This allows hearing aids to automatically adjust functions in different environments, reducing the need for hearing aid users to switch programs in different environments. It intelligently processes sounds, allowing hearing aid wearers to better adapt to hearing aids and various environments.

Tinnitus Treatment Solutions: Currently, the incidence of tinnitus is constantly increasing, with an average of 3 tinnitus patients among every 20 people. Treatment methods for tinnitus include sound therapy, masking therapy, and habituation therapy. Many hearing aid manufacturers have added tinnitus masking or habituation methods to their hearing aids, and there are even specialized tinnitus treatment programs to help alleviate the impact of tinnitus on users.

MFi Wireless Direct Connection Technology: MFi refers to the ability of hearing aids to directly transmit signals (including voice signals such as phone calls and audio signals like music/videos) from an iPhone through low-power 2.4G Bluetooth transmission technology directly to the hearing aid without the need for any other auxiliary devices. At the same time, hearing aid wearers can use a mobile app to personalize adjustments to the sound, achieving convenience, personalization, and intelligence.

Rechargeable Technology: Hearing aid wearers no longer need to worry about replacing batteries. Rechargeable technology allows hearing aids to be charged directly through a charging dock, similar to a mobile phone. Currently, rechargeable batteries can be fully charged in 3 to 4 hours for all-day use without worrying about battery depletion. In the future, fuel cells that can be charged in a matter of seconds will also be introduced. Additionally, there will be hearing aids with 2.4 GHz wireless direct connectivity and rechargeable capabilities, providing hearing aid wearers with more advanced, intelligent, and convenient choices.

The Future of Hearing Aids

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