So Mr. Beast did a recent video in which he helped a 1,000 people hear again using hearing aids.
He briefly mentioned how technology has shrank and improved the hearing
aid over time. But I figured I can give some additional context.
Electronic hearing aids started out the size of suitcases. Now they are so small we can
put them on our ears. And so functional they are basically computers in their own right.
In this video we are going to talk about how silicon shrank and supercharged the hearing aid.
## Beginnings
The first hearing aids were our hands when we cup them around our ears to hear something better.
This is referred to as the hand reflector and they are basically sound collectors.
They can emphasize sounds in the middle to high frequency ranges.
The first such artificial acoustic prostheses were modeled on these products. For instance,
the "Ellipsis Otica" from 1673 described in an essay by Athanasius Kircher.
In the 1800s, the first known hearing aid company opened in London - Frederick
Rein. These ear trumpets work as you might expect. You insert the
narrow end into your ear and point the broad end at the person talking.
## Telephone
In 1878, Alexander Graham Bell invented the telephone,
unlocking new technologies for your ear.
The technologies for that first telephone were almost immediately
repurposed into tools for the hard of hearing.
It was found that certain individuals could better hear others if through telephones.
A Buffalo Times article in 1897 noted an individual called JC Chester,
who carried a telephone around with him attached to a dry battery. It looked weird,
but it worked and according to him not that uncomfortable.
In 1903, the American inventor Miller Reese Hutchison established
the Hutchison Acoustic Company to produce the Acousticon. It used an
electric current to amplify weak signals by about 20-30 decibels.
The Acousticon was comprised of an earphone much
like a telephone paired with a carbon granule receiver. The receiver captures
surrounding sounds and converts them into electrical signals for amplification.
The whole thing was powered by a large zinc battery. Both of
these had to be worn on the body and their bulk interfered with adoption.
A few years later Siemens separated the amplification function into its own discrete
item. Today's hearing aids largely retain this four-component structure of receiver,
amplifier, microphone, and battery.
## Hearing Aid Structures
I should take a pause to discuss the structure
of a hearing aid. Most share similar working principles.
Sound hits a microphone or receiver which converts this
into a weak electric signal. There are a number of ways to do this.
Carbon microphones for instance generate their signal using carbon granules and a
diaphragm. When sound waves vibrate the diaphragm,
the granules compress or decompress - causing changes in an electrical current.
The signal is then fed into an amplifier. The amplifier then increases the input signal
without significantly changing it. This is done using external energy fed to it from a battery.
Modern hearing aids often also feature digital signal processors which convert
the analog signal for digital processing modifications. We can talk about that later.
Anyway, this boosted audio signal is then piped into the ear using a receiver. These
are microphones in reverse. There are air conduction receivers that
feed the signal to a diaphragm to make sound waves in the air ...
Or bone conduction receivers that put sound vibrations directly into the skin and the skull.
The hearing aid may also include audio controls and custom molds. They can be
placed behind the ear, partially inside the canal, or completely inside the canal.
## Miniaturization
Hearing loss has long been stigmatized.
These unfortunate social implications have pushed
these technologies towards making their hearing aids less noticeable.
Customers very much desired invisibility, even at the cost of effectiveness.
This desire drove their aggressive miniaturization in the electronics age.
In 1920, naval engineer Earl Hanson incorporated vacuum tubes into an amplifier for a hearing aid.
The tube had been invented only a few years prior in 1908 by Lee DeForest.
It worked by applying voltage to amplify electrical signals with little distortion.
Hanson invented the Vactuphone for his mother,
who was deaf. Globe of Boston marketed it with the following line:
> Listen to distortionless speech and hear sounds
that even normal and healthy ears have not heard since the world began
This device amplified sounds far better than
any carbon-granule based system - 70 decibels as compared to carbon's 15.
However, the tubes underlined the need for miniaturization and portability. Tubes were big,
uncomfortably hot, took time to warm up, and used too much power. You didn't wear it but instead
put it on a table. Globe thought to disguise it as a box camera by giving it a dummy lens.
Western Electric and others worked to shrink the technology. Progress
was impressive but still fell short of the ideal.
The "portable" version weighed 35 pounds and had to be carried around in a suitcase.
## Transistors
Thus, hearing aids were some of the first devices to incorporate transistor technology.
The transistor was first invented in 1947 and people marveled over its ability to start,
stop, and even amplify the flow of a current.
In almost every way possible, the transistor was superior to the tube. It generated less heat,
took up less space, and did not need warm-up time. Most critically,
its superior power efficiency allowed for smaller batteries.
An engineer at Raytheon named Norman Krim immediately saw
the benefit. So Raytheon started producing transistorized amplifiers for hearing aids,
becoming one of the first companies to produce a more sturdy "junction transistor".
Raytheon built a factory to produce these amplifiers. The factory was staffed by
people who were hard of hearing, who received the hearing aid product their work went into for free.
In 1953, some 200,000 transistorized hearing aids were sold. Products like the
Microtone Transi-matic rapidly replaced vacuum tube aids in just 18 months.
## Silicon
For a brief period of time, Raytheon was the world's biggest producer
of transistors until they lost the crown to Texas Instruments.
This was because their customers soon realized that the Raytheon transistorized aids had
humidity issues. Early transistors like theirs were made from germanium,
which were quite vulnerable to the outside world.
In 1954, Texas Instruments became the first company to produce a silicon transistor,
far superior to germanium. Their silicon transistors were mostly
used for military applications, but a few soon made their way into hearing aids.
In 1957 Otarion Electronics introduced the
Otarion Listener - the first transistorized hearing aid to incorporate the whole system
into one wearable piece. The aid was discretely blended into the eyeglasses
giving them the name of "hearing glasses" - again emphasizing the concept of invisibility.
The product was widely admired. Lee DeForest - the aforementioned
inventor of the vacuum tube - became a spokesman.
Quite elderly, DeForest had long worn a vacuum tube-based hearing aid. Naturally. He had written
to the aforementioned Norman Krim expressing his dissatisfaction with Raytheon's germanium
transistors. But now, DeForest called the Listener the "finest hearing aid I have ever worn".
## ICs
In 1953, Jack Kilby at Texas Instruments began investigating the concept of integration.
He actually first got into the topic whilst working on improving the
reliability of these germanium hearing aid transistors. Soon,
he realized that one of the transistor's weakpoints was its connections.
So Kilby sought to integrate a circuit's discrete items together to improve their
ruggedness. The integrated circuit was quickly adopted by hearing aid manufacturers.
Zenith came out with the first such device in 1964.
Using integrated circuits and later microprocessors not only allowed
manufacturers to shrink their products even more,
but also give them new capabilities with the power of digital audio processing.
A few years after inventing his integrated circuit, Jack Kilby would need a hearing
aid himself. He first chose to wear the Otarion Listener hearing glasses.
## No Noise
Up until now, all hearing aids were analog.
This means that the signals they handled can vary continuously over time. And so
they can be of any value. Digital signals on the other hand are either 1s and 0s.
Analog hearing aids mostly focused on boosting sound for your ear. But this
also means boosting all the background noise that you didn't really need in your life.
You want to hear people’s speech, not the background noise. There
are a few techniques for taking out the noise. For instance, taking the
sound readings from two microphones and subtracting one from the other.
Or having one omnidirectional microphone listen for background
noise coming from all directions and subtracting that out from the readings
of another microphone. This way turned out to be more practical at the start.
In the same vein, you can enhance the speech experience for people with severe
high-frequency hearing loss by shifting a person’s speech to lower frequencies.
Doing these things is not easily possible with analog
equipment. So thus digital processing is required.
## Going Digital
In the late 1970s Harry Levitt and his colleagues at the City University of
New York's Central Institute of the Deaf started working on a digital hearing aid.
They had previously worked on audio processing using early computers and felt that they could
parallelize the processing of these audio signals to possibly achieve real time performance.
Due to a lack of processing power, the first iterations of these hearing aids were not
fully digital. But were rather digital-analog hybrids - analog equipment controlled digitally.
This sort of worked at first, but eventually it became clear that
they had to go completely digital. So in 1981 they submitted a grant
application for funds to develop a high speed silicon processor for the task.
The device was completed in 1982. And it can do real time audio processing like no
previous device. But it was - to quote the Gen Z kids - "chonk". You had to mount the
thing on a rack with all these antennas and the user had to wear a big set of
FM-enabled microphones on their head. It also had a printer for some reason.
One cheeky doctor quipped:
> It may be a good hearing aid, but you’ll need a friend with a
wheelbarrow behind you to carry the instrument.
## Moore's Law
Quips aside, the main goal of this machine was not to create a commercial product.
But rather to have a platform to explore various digital processing techniques like
noise processing without having to build entirely new sets of hardware.
Throughout the 1980s, scientists experimented with various techniques to improve speech
processing like linear filtering, spectral shaping, spectrum subtraction, and so on.
This research - and the hearing aid industry as a whole - benefitted from continued innovation
in the telecommunications and semiconductor industries.
New faster and smaller chips developed exclusively for digital signal processing
by the telecom and consumer electronics guys replaced older array processors.
Encouraged by a steadily growing market - Ronald Reagan got publicly fitted for
hearing aids in 1983 - manufacturers sought to produce a more wearable digital hearing aid.
There was the Nicolet Corporation with their Project Phoenix in 1984.
Their first hearing aid had a pocket processor you had with you combined
with an earpiece. The processor had three buttons on it for certain audio settings.
A ground breaking product, but it never made it to the market. In
1989 Nicolet withdrew from the hearing aid industry entirely.
Other companies in the space included Resound Corporation, 3M, AT&T, Audiotone, Rion, and so on.
Not to mention Starkey Hearing Technologies, today the largest American player in the market.
However, all of these products retained some analog elements. We did not see our
first truly digital, in-the-ear hearing aid until 1995/1996 with the Widex Senso.
The industry rapidly went digital. Within 10 years,
over 93% of hearing aids sold to the market had some form of DSP technology.
## Packaging
The hearing aid market is highly dependent on technology innovations from other, larger markets.
For instance, those DSP chips from the telecommunications industry. Yet another
big innovation were packaging technologies ported over from the mobile phone industry.
Mobile phone makers have long wanted the smallest, thinnest thing. That not only means the smallest,
thinnest chips, but also the smallest, thinnest packaging for those chips. Such
technologies have been adopted by the hearing aid companies to shrink their products even further.
The core parts in our digital hearing aid is our DSP, memory,
and some capacitors - about 12-16 parts. In the late 1990s and early 2000s,
we packaged these items onto a circuit board made from layers of metal and ceramic.
But at the turn of the century, wireless communications became more of a thing. People
wanted their hearing aids to also connect with their phones and devices via wireless networking.
This increased the number of components inside the hearing aid, which in turn
dramatically increased the amount of interconnects between said components.
In order to stuff all of this into the same small space, the hearing aid industry started
mounting their components on top of more flexible substrates - a process known as "chip-on-flex".
Other new packaging technologies introduced since then include 3D stacking.
As well as even embedding the components right inside
their flexible substrates - or "chip-in-flex".
Packaging technologies tend to be unheralded innovations in miniaturization - and I’m
looking forward to new developments down the line.
## Conclusion
In the 1940s, Eugene McDonald, the founder of the now-forgotten
American electronics-maker Zenith, lost most of his hearing in a car accident.
He bought a pair of hearing aids for $200 and cracked them open only to
find that they were made from radio and telephone parts costing a tenth of that.
This inspired Zenith to eventually produce some of the industry's first transistorized hearing aids.
Recently, the US FDA finalized a rule enabling the sale of hearing aids
over-the-counter to those who have mild to moderate levels of hearing impairment.
As the McDonald story implies, the hearing aid and consumer electronics
fields have long been intertwined. And I have wondered on the significant technology
differences between today's basic hearing aid and a pair of AirPods.
There is a lot of potential here to bring down cost. I am particularly interested
in open source offerings like those from Tympan.
Former hearing aid manufacturers can now focus on new innovations
addressing people feeling discomfort with current hearing aids, those with
more profound cases of hearing loss, or those with cases involving nerve damage.
There are nearly 30 million people in the US and nearly 300 million across
the world with hearing loss. The search for technologies to improve their lives continues.