It's clear by the reviews on this site that modern hearing aids are very high tech. The computers inside these tiny devices analyze the world around you in real-time attempting to extract what you want to hear from the noise around you. In most cases, they do a very good job, but as Wiley E. Coyote learned in almost every episode of Roadrunner, physics wins every time.
Understanding speech depends on our ability to hear AND discriminate very specific speech sounds. Human speech spans a frequency range of about 250 Hz to 6000 Hz.1 For those familiar with the piano, this is approximately the B below Middle C extending to the F# four-octave above there.2
We need to take a quick sidebar for a mini physics lesson. Sound is the result of air particles moving in a repetitive pattern called vibration. The amplitude is the amount of movement, and the frequency is how many times the particles move back and forth in a second. The ear and brain sense and interpret these vibrations and create the perceptions of loudness for amplitude and pitch for frequency. Ok. Class dismissed (I told you it would be quick).
When trying to understand speech with a hearing loss, there are a couple of unfortunate realities and a really cruel irony for those with hearing loss. The realities are that high frequencies are very low in amplitude and travel in only one very specific direction. Low frequencies generally have much larger amplitudes and go everywhere (omnidirectional).
The irony of most human speech, specifically English, is that the majority of the energy or “power” of speech is focused in the lower-pitched vowels and “voiced consonants” like “B” “G” and “D”. On the flip side, the majority of the “understandability” of speech rests in the higher-pitched voiceless consonants like “T” “P” and “S.”
The most common hearing loss pattern for folks reading this website is reported as mild sloping to moderate, or pretty good hearing in the low frequencies gradually getting worse throughout the speech range. For many people, the difficulty starts right at the point where those voiceless consonants live. This means that you hear the least important sounds well and struggle to hear the really critical stuff. These significant higher-pitched speech sounds (called phonemes in geek-speak) are incredibly vulnerable to not being understood because of the “realities” above and the fact that distance, reverberation and background noise degrade our ability to understand speech. This is significantly worse for older people with hearing loss.3
3 Hearing Hazards: Distance, Reverberation and Background Noise
The further away a sound is, the quieter it becomes. In fact, distance affects sound amplitude according to the “inverse square law” (sorry, just a bit more physics, then I promise to send you all to recess). This means that when you double the distance from a sound, the amplitude is one-quarter as loud. Conversely, if you cut the distance in half, the sound becomes four times as intense. Because of the very weak energy of those prominent high-frequency phonemes and this reality, the “sweet spot” for conversation regardless of hearing ability is about one meter or a bit more than 3 feet. As a real-life measure, think about shaking someone's hand or if you're hip, giving them a fist-bump to set the maximum “best hearing zone.”
Trying to hear and understand speech at greater distances causes us to miss those high pitched phonemes for two reasons. First, because they are lower in energy, to begin with, they kind of peter out. Even if we had great hearing, they'd be much softer than our brain expected. The second reason is that as I said earlier, most folks with hearing loss have their worst hearing at these high pitches. Hearing aids can help but even they have a finite effective distance. Being very kind to our friends in the industry, I'd say that based on my nearly 30 years at this, 12 feet is about as far as you can really depend on your hearing aids to pick up these most important sounds well enough to really follow the conversation.
When sounds travel across a room, they fade out. When they strike a reflective surface like a wall, floor, or window, the sound bounces off and is amplified due to something called the baffle effect. The more surfaces, the more it is amplified. This bouncing around is called reverberation and is often perceived as an echo or how “live” a room is. In general, reverberation is increased by the type of surface (how hard and smooth it is), how many reflective surfaces there are, and the relationship between the size and shape of the room. We measure reverberation in a unit called RT60 as the number of seconds it takes the sound to reduce in amplitude by 60 dB compared to its initial level. If the RT60 of a room is greater than 0.5 seconds, it is considered sub-optimal for speech understanding.
The sounds we hear around us can either be thought of as signals (things we want or need to hear) and noise (stuff that isn't important). If we subtract the amplitude of each, we can describe the total sound environment's “signal-to-noise ratio” or SNR and report them in deciBels or dB.
Let's imagine a pre-COVID-19 dinner out with friends. You're in a medium-sized chain restaurant in an American city. You're in a group of 6 people having a conversation about home security systems reviewed on senior living.org. There are about 100 people in the room in similar groups and some light jazz music playing in the background. You recently had your hearing tested and purchased advanced-level digital hearing aids from one of the “Big 6” manufacturers. The person who fit you said that these had automatic noise reduction and that you should hear “great” no matter where you go. That's a nice idea, but let's look at the reality.
The documented performance of hearing aids is measured in optimal conditions. The desired sound (signal) is generated at a typical conversational distance of about 3 to 4 feet. Background noise, if any, is generally 6 or more deciBels (dB) LESS than the speech (SNR of +6 dB). A pair of wireless digital hearing aids with two microphones each improve SNR by about 15 dB, and that's being quite generous.
The average conversational speech is about 60 dB. With an SNR loss of 10 dB, you'd need the net background noise at your ear to be not louder than 50 dB (a +10 dB SNR). If your hearing aids reduce background noise by 15 dB, then the dispenser's claim is valid only if the background noise is not louder than 65 dB (50 dB sweet spot + 15 dB reduction). Here's the rub. Restaurants like this have average ambient sound levels between 67 and 83 dB.4 This means that at best, you're really between 2 and 18 dB in the hole in terms of SNR. So while your new hearing aids will likely do great in a small coffee shop off-peak, they fall short in this scenario.
Does this mean you need more expensive “Premium” hearing aids? Actually, no. The hearing aids' limitations in this “hearing hazard” are still there for more advanced hearing aids. What we need to do is improve the SNR beyond what is possible with ear-level devices alone. This next part gets very interesting, so hold onto your HAT (Hearing Assistive Technology).
Accessories Overview (What is HAT, and how do I get it?)
HAT is a term for a group of technologies designed to overcome the limitations of hearing and understanding in non-ideal conditions. The most common HAT tools are within the Assistive Listening Device (ALD) category, but HAT also includes alerting devices. If you've read the recent hearing aid reviews here on senior living.org, you've seen a lot of these ALD products. We'll do an overview of each type with a couple of specific products from major manufacturers. Here we go!
There are a lot of different ALDs out there, but they all accomplish the same three critical functions: Capture. Carry. Couple.
Capture refers to how the hearing aid grabs the sound it amplifies. If you're just using hearing aids, this happens at the microphones on your hearing aids. These are usually spaced about a half-inch apart in an attempt to “zoom in” on specific sounds. This works well in theory, but as the example above shows, the environmental conditions are often such that even though the hearing aids are working as designed, they simply can't extract the signal from the noise.
If, however, we grab the signal very close to the source, the SNR is greatly improved. This can be done with a remote microphone close to the speaker of interest or a hard-wired connection.
Once the signal is captured at an optimal SNR, we need to get it from that acoustic “happy place” to your hearing aids or ears. This can happen via a hard-wired physical connection, electromagnetic inductance, or one of several currently available wireless radio protocols. Well-designed carry systems transmit the sounds without losing any quality or degrading the captured SNR. A bit more on these types of transmission is warranted before we show examples.
- 2.4 GHz – This is a very stable, long-range radio signal that is coded to a specific set of hearing aids. The range is usually 60 to 80 feet depending on the materials in the room. 2.4 GHz is generally pretty resistant to interference, however, some WiFi repeaters can cause these systems to glitch. Most newer WiFi routers allow for a 5 GHz network. Switching to this for your computers and tablets usually resolves the interference. There has been a concerted effort within the hearing aid industry over the last few years to move to a 2.4 GHz platform, and most of the “big 6” have at least a few products in this arena.
- Traditional Bluetooth – The power requirements of traditional Bluetooth prevent its use in most hearing devices directly, however, they can use this transmission protocol with a rebroadcaster, usually a pendant or clip-on device about the size of an old Zippo lighter. The signal goes from the TV streamer to the rebroadcaster via Bluetooth and then is converted to a proprietary near field wireless signal to the hearing aids. This near field system is similar to that used for Apple and Google Pay devices. The range of these devices is 10 meters or a little more than 30 feet to the rebroadcaster and about 10 to 12 inches from the rebroadcaster to the hearing aids.
- Bluetooth LE – Bluetooth LE (Low Energy) has a small enough size and power footprint that it can live directly in a hearing aid. These streamers beam the captured signal directly to hearing aids without the need for a rebroadcaster. The potential range of this technology is 100 meters, but in the hearing aid space, devices usually transmit about 60 feet.
- Infrared – This is the same tech that makes your TV remote(s) work. Invisible light beams travel between transmitters and receivers and require a pretty clear “line of sight” to work. In the TV listening application, the transmitter is hard-wired to the TV, and the receiver is usually worn around the neck. Typically, these systems have earphones or a plug for an inductance neck loop.
- Electromagnetic Inductance – When a loop of wire is connected to a special amplifier, all the audio information in the amplified signal gets converted to an electromagnetic field within the wire. If the hearing aid has a receiver called a Telecoil, you can hear the signal anywhere in the loop as if you're at the source. All cochlear implants and many hearing aids have telecoils that can be set to receive these signals. The range of a loop depends on the power of the amplifier.Telecoils and loops have been around since the 1930s but have recently seen a resurgence in many US cities. It's well worth it to specify that you want a telecoil in your hearing aids and ask for it to be activated and calibrated for hearing loops.5
Once the carry system delivers the optimized signal to you, it has to “handshake” with your hearing system. This can be accomplished using the receiver side of the same carry systems above if you don't yet have hearing aids, some ALDs couple to your ears with earphones or earbuds.
Now that we've got the functional basics down, let's look at some examples. For each, I'll show a picture, then identify the Capture, Carry, and Couple methods, mention suggested uses, and list some specific cases currently available.
Media (TV) Streamer Devices
These devices help overcome the distance and reverberation problem many people experience when watching TV. They also allow for private listening.
- Capture: Hard wired connection from Audio Out (RCA or Optical)
- Carry: Wireless (900 MHz, 2.4 GHz, Bluetooth LE, Bluetooth, Magnetic Inductance, Infrared)
- Couple: Wireless direct hearing aids (900 MHz, 2.4 GHz, Bluetooth LE), Near field from Bluetooth pendant, Telecoil, earphones (infrared)
- Range: 30 feet (Bluetooth) to 60 feet (2.4 GHz)
Phonak TV Link 2
Use Case: Streaming TV or another audio source (laptop, tablet) signal to hearing aids
GN ReSound TV Streamer 2
Notes: Also compatible with Cochlear Americas cochlear implants and bone-anchored implants
These small wireless microphones capture speech very close to the source and beam it to your hearing aids. They significantly improve SNR and help overcome the problems associated with distance, background noise, and reverberation. They have either a fixed directional microphone or a set of mics that can be manually or automatically adjusted to pick up very narrowly or in an omnidirectional fashion.
- Capture: Microphone input. Some multi-function devices also have hard-wired connections and telecoils
- Carry: Wireless (900 MHz, 2.4 GHz, Bluetooth)
- Couple: Wireless direct hearing aids (900 MHz, 2.4 GHz, Bluetooth LE)
- Range: 30 feet (Bluetooth) to 60 feet (2.4 GHz)
Widex ComDex Remote Mic
Phonak Roger Select
All major hearing aid manufacturers offer a few ALD options that are made specifically for their devices. There are also universal ALDs that couple with telecoils or provide earphones. These can be purchased through your hearing care professional, but I've also been very pleased with two online vendors over many years.
Harris Communications6 is a family business run by folks who really get hearing loss and its challenges. They offer personal guidance in selecting the right devices for you and are partners with the Hearing Loss Association of America.
A newer company called Serene Innovations7 has impressed me with their ability to find and repurpose interesting consumer technologies for the hard of hearing. Both are worth a look in addition to the products and care you get from your hearing care team.
Watch the video with SeniorLiving.org Editor-in-Chief, Jeff Hoyt below for a closer look at hearing aid accessories.
A quick, but important note on alerting devices, especially fire and smoke alarms. The typical smoke alarm available today uses a piezo-electric speaker that emits a beep at 3100 Hz. The National Fire Protection Agency says that a smoke alarm must be at least 75 dB at 10 feet.8 Research has found that to wake someone reliably, a sound must be 40 dB louder than their threshold of hearing.9 If we convert from dB sound pressure level (SPL) to the units used in hearing testing (dB HL), you'd need to have hearing better than 35 dB at 3000 Hz to wake up when a standard smoke alarm goes off. If you're wearing hearing aids, it's very likely your hearing at this critical pitch is not that good.
Several alternate systems exist to ensure your safety during a fire. The Deaf community has used visual and tactile signaling systems for decades. These consist of transmitters and receivers that capture the signal of the smoke alarm and then either flash a strobe, trigger a vibrating pad under a pillow, or both. These can be stand-alone systems where the strobe is built into the smoke alarm or integrated systems that also allow for input from telephones, doorbells, and security systems. Harris Communications mentioned above has a great selection of these, and their folks can help you find the one that's right for you.
A really unique device that I like for its designs and thoughtfulness is the LifeTone.10
This alarm “listens” for a standard smoke or carbon monoxide “beep” and then creates a very loud, low frequency “square wave” alert in conjunction with a strobe and optional vibration. The design is based on the waking research above as well as some other studies looking at the best pitch and “shape” of sound to wake up the greatest number of folks. Full disclosure, I did some consulting for them during the development, but I have no financial stake in the product or company.
As you can see, hearing aids, while great, are often not enough. If your hearing isn't what it used to be, not only hearing aids for one-to-one listening but additional devices that work with your hearing aids to allow you to enjoy communication in a much broader range of settings. These devices are often called “accessories” and may be brought up as an afterthought. In almost three decades helping people hear better, I can tell you that these are integral components to systems. In my opinion, buying hearing aids without at least some of the HAT devices in this article is like buying a car without a speedometer that only makes right-hand turns.
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