Hearing aid technology has dramatically improved throughout the last 30 years. The devices have become smaller, more powerful and more technologically advanced. Today a hearing aid can restore multiple types of hearing loss for people of all ages, and perform many feats that engineers only dreamed of achieving in the 1970’s and 1980’s. By all accounts, early hearing aids are primitive when compared to today’s devices. To learn more about how hearing aids have evolved we chatted with Denis Carpenter, who has worked with Rayovac for 37 years and is now the director of technology and OEM liaison.
Analog Aids Turn Digital
When Denis began working on hearing aid technology, hearing aids were designed as analog devices. An analog device has the technical capability to perform one main purpose, which for older hearing aids is to take in sound and made it louder. The major downside of this raw amplification method is that the user gets flooded with extraneous background noise which drowns out what the person is trying to hear.
But in the last two decades, Denis says he has seen digital hearing aids transform the entire industry. A digital aid receives a sound wave and then an onboard computer processes that sound into bits, which is a digital format that the device can manipulate to achieve certain results. It’s essentially computerizing sound. There are some analog ways to do accomplish this, but they are very limited in scope and effectiveness.
Denis says the biggest game changer during his tenure is the capability for digital hearing aids to change any incoming sound. Because of this, what signals go in the devices aren't necessarily what gets transmitted to the ear.
Let’s say a woman is hearing impaired and a sound wave enters her ear. The sound is quiet and it needs to be made louder so she can hear it. Analog devices could do this, but the aids were indiscriminate toward loud sounds, too, which mean that it’s extra painful to encounter loud sounds. It’s the equivalent of somebody whispering or shouting through a megaphone. The tool amplifies the sound at the same intensity, but one is much more painful to hear than the other.
To counter this, engineers began eliminating excess background noise and figuring out how to make important sounds forefront. As the devices became more digital they can do more things, and that advancement goes right in line with chip technology. When they first started including computer chips, the technology could only perform so many processes per minute. Consequently, the original digital aids were quite crude. But every year the technology improved, and the tools got more sophisticated because they performed more processes per minute.
Improving the processing power within the aids was a crucial task because, unlike other sound-oriented devices, hearing aids must provide immediate feedback. Otherwise, the aid won’t help people keep up with a conversation.
This need for accurate, instantaneous feedback, coupled with faster and more powerful processors, meant that engineers began experimenting with how the hearing aid reacted to receiving sound from different angles, Denis says. The result of these tests is directional microphones.
So let's say you’re talking in a dinner conversation and you want to hear what somebody has to say. Because of background noise, even people with normal hearing can struggle with this. To counteract the ambient feedback, engineers placed directional microphones into the hearing aids. These are microphones that point toward the object you want to hear, and then 90 degrees away from the object you want to hear. Using input from the various angles, the microphones allow aids to amplify where you're pointing, and cancel out stuff on the side.
Denis says as engineers made more headway with directional microphones, they began developing devices that could isolate, amplify and dampen sounds from any direction. Originally the devices could only adequately handle sounds in front of your head, and you had to point your head toward the person you wanted to talk to. But if someone on the side says something to you, then you'd miss that.
Nowadays the device is able to change the focus of what you're able to hear by itself, and do it nearly instantly.
Directional microphones altered how people hear, but the biggest hearing aid innovation in the last five years is wireless connectivity. And it’s changed the lifestyle for hearing aid users.
The wireless connectivity that’s becoming more common allows hearing aids to connect to smartphones, cars and other electronics via a 2.4 gigahertz spectrum. This lets people essentially stream phone conversations, music or the TV directly to their aid.
The other method is called near field connectivity. And the near field method is based around magnetic induction. What happens is an intermediary device, which is a meter or half-a-meter away from your ear, communicates between the hearing aid and the device it’s streaming from.
More Powerful Hearing Aid Batteries
Although Rayovac isn’t an expert on hearing aid devices, Denis and his team work closely with device manufacturers to develop hearing aid batteries that meet the required power consumption of these new innovations.
The fully wireless 2.4 GHz system added several superb lifestyle features for hearing aid users, but those features also doubled the device’s electrical current draw. When a normal hearing aid is functioning it may run at about two milliamps. When it's running in the streaming mode with a 2.4 GHz system, the power draw goes up to about four to five mA with the additive that that power draw is consistent.
In the past you'd get short duration pulses of that power requirement, but now it's a sustained requirement. Denis says Rayovac engineers had to design a new zinc air hearing aid battery that is more powerful and more efficient under those conditions. This task came about when the company was shifting to a zero mercury battery as well, which made it quite a challenge. The zero mercury products originally had less power than mercury-containing batteries.
The Rayovac team solved the power issue, but the battery lifespan has fallen. Denis says that the batteries don't last as long in new digital devices as they did in analog devices.
When Denis talked with engineers 15 years ago, the size 10 battery, which is Rayovac’s smallest hearing aid battery, was being developed in coordination with Starkey to fit for an ear canal hearing aid. At the time that battery could deliver 59 mA hours. Denis says his engineers wanted the per-battery lifespan to last seven days. Today a size 10 battery delivers twice as much energy, but when you talk with engineers they want it to last three days.
Although Rayovac has doubled the energy that battery can deliver, he problem is that the batteries don't last like they used to. And that's not because the battery is poor. The root cause is that the hearing aid technology is more advanced and requires a lot more consistent power. As manufacturers add more features, the devices require more power. Once you design a battery with more power, the device engineers add more features. So it’s a lifecycle.
The Future of Batteries
The current top-of-the-line option for hearing aid batteries is the zinc air system, which is a very high energy density platform, Denis says. There are not many other systems that have more energy per size.
If you think about a watch battery, the anode and the cathode are both inside the battery itself. The zinc in the cell determines how much energy the battery can deliver. By taking the cathode and putting it on the outside of the battery, engineers can then take more zinc and put it on the inside. This method lets the zinc air system last two to three times longer than a button cell battery.
Rechargeable batteries are supposedly the next big milestone for hearing aid technology. Denis says one of the challenges engineers are facing with rechargeable batteries is making the battery small enough while still giving it enough energy to make it last a day. He says there is product that is market viable, but it’s still right on the edge, and the dilemma around size continues to be prevalent. Denis says the battery needs to be a little bit bigger than engineers really want it to be. Right now the 312 size is the number one battery being made because it's a shorter battery and manufacturers can make a thinner hearing aid with it. So designers really want to have a rechargeable battery as a 312 size. He says that rechargeable products will work pretty easily with a 13 size, but it gets very tenuous around a 312 size. Denis says he’s confident the product will come to fruition, but it still might be a while before the technology is perfected.