A Closer Look at How Hearing Aids Work

Hearing aids are designed to help a person hear by making sounds louder. The basic design for a hearing aid consists of a microphone, amplifier, battery, and speaker. The microphone picks up the sounds from the person’s immediate environment, the amplifier converts the sound wave into electrical signals that are adjusted based upon the unique needs and preferences of the wearer, and then the amplified and altered signals are converted back into sound waves and delivered to the ear through the speaker.

Unfortunately, one of the shortcomings of hearing aids that regularly frustrates the people who use them is their struggle to filter out extraneous noise. Hearing aids lack the ear’s natural ability to identify the signals that a person wants to focus on and dismiss background noise. A hearing aid amplifies all the noise it detects in the surrounding area, both the important signals and the ambient ones, and that creates a lot of different noises for a person with hearing loss to wade through. As a result, a person wearing a hearing aid will still miss key parts of a lecture, directions, or other important information because the hearing aid detects and amplifies those signals as well as the conversation occurring a few feet away, the footfalls on the concrete, the rustling bag of chips, and the whirring of the HVAC unit.

Background noise and distance from the speaker often create barriers to comprehension for people with hearing loss, even if they are wearing a hearing aid or have a cochlear implant. Even with making all the noises louder, people with hearing loss can still have significant problems understanding speech, exert high levels of effort to comprehend and decipher what they are hearing, and experience poor or unnatural sound quality. “The ability to understand speech in the presence of noise is often degraded in people with hearing loss,” explains Andrew King, auditory neuroscientist at the University of Oxford in England. “It’s the single biggest challenge of someone with a cochlear implant.”¹

In order to help people with hearing loss more easily comprehend and participate in what is going on around them, they need to increase the signal-to-noise ratio (SNR) in their environment. SNR compares the level of signal strength to the level of background noise. It is generally expressed in dB. Higher SNR values indicate that the audio signal is louder than the surrounding noise, meaning the signal will be clearer and easier to understand.

In the article “Hearing Loops: The Preferred Assistive Listening Technology” published in the Journal of the Audio Engineering Society in April 2015, the authors wrote, “Research has indicated that hard-of-hearing listeners may require an increase in signal-to-noise ratio of more than 10 dB, some as high as 25 dB, to achieve the same word recognition as a normal-hearing person in the same situation. A decline in the signal-to-noise ratio makes it more difficult for people with hearing loss to effectively discern speech from what would be considered a mild background noise to listeners with hearing within the normal range. The result is that users of even the most advanced digital hearing instruments or cochlear implant processors frequently report that they are able to hear but not fully comprehend spoken information.”

Introducing Assistive Listening Systems

Assistive listening systems are designed to turn up the strength of the signal of interest, improving the SNR and making it easier for a person with hearing loss to accurately decipher what is being said.

These systems typically feature three components: a microphone, a transmitter, and a receiver. The microphone picks up the signal (the speech, music, or combination of the two) and sends it to a transmitter, where it is converted into an electronic signal and sent to the receiver, which is attached to the person with hearing loss.

While there are a growing number of assistive listening systems, the three most common types are a frequency modulation/radio frequency (FM/RF) system, an infrared (IR) system, and an audio frequency induction loop, also referred to as a hearing loop. Each of these systems differs in the way they transmit the signal to the receiver and the type of receiver they require, which impacts the level of convenience and the quality of the sound signal they provide.

Audio Frequency Induction Loop/Hearing Loop

Hearing loops are an assistive listening solution that are unique in their ability to send the enhanced audio signal directly to a person’s hearing aid or cochlear implant, without requiring the person with hearing loss to wear a separate receiver, headphones, or a neckloop. The key difference is that these systems utilize the telecoil technology that already exists inside a hearing aid or cochlear implant as the receiver.

Hearing loops send the audio signal directly to a person’s hearing aid, allowing attendees with hearing loss to hear a speaker more clearly without wearing additional equipment.

Here’s how a hearing loop works. A copper wire is installed throughout an assembly area, in either the floor or the ceiling. A hearing loop driver, the system’s amplifier, connects to the microphone or sound system at the site and the cooper wire. A current is driven through the copper wire, creating an electromagnetic field within the audience. When the speaker talks into the microphone, the audio signal is transmitted over the electromagnetic field and received by the telecoil in the hearing aid or cochlear implant of the person with hearing loss. The person receives the signal he or she is interested in, without all of the background noise competing with it. The improved SNR allows the listener to hear and understand the words being spoken with greater clarity and ease.

Today, it is estimated that virtually all behind-the-ear hearing aids and cochlear implants, along with most in-the-ear devices, are equipped with this telecoil technology. This means that most people with hearing loss who use a hearing device are equipped to receive the clearer signal transmitted by the hearing loop system. In order for a hearing aid or cochlear implant with a telecoil to detect the signal sent over the electromagnetic field, the telecoil must be activated. The wearer activates the telecoil by turning the t-switch in the hearing aid on, which is often done with the push of a button. When the t-switch is on, the microphone in the hearing aid that picks up the local environmental sounds is deactivated, and the person with hearing loss only hears the sounds being transmitted by the hearing loop. This dramatically improves the SNR of the speech, presentation, or play that the person is attending.

Those with hearing loss who do not have a hearing aid with a telecoil can also benefit from the clarity offered by the hearing loop. A venue with a hearing loop will often offer portable hearing loop receivers that come with earbuds or headphones. A person simply wears the receiver and the available earbuds or headphones to receive the enhanced audio signal being sent over the assistive listening system.

FM/RF System

FM/RF systems transmit the sound signal to the receiving device wirelessly through radio waves. While there are FM accessories that can be purchased for hearing aids that would allow an FM/RF system to transmit the wireless signal directly to a person’s hearing aid, these are quite costly and have not been widely adopted. This means that, for most people, if a venue offers an FM/RF assistive listening system, the people with hearing loss will need to find and wear additional pieces of equipment to be able to access the signal. Those additional components include a receiver and the headphones or ear buds that accompany it.

A neckloop is a necklace-sized loop of wire that is plugged into the FM/RF receiver. The neckloop converts the sound signal from the FM/RF receiver into electromagnetic waves and radiates them so that they can be received by the activated telecoil in the person’s hearing aid.

IR System

IR systems transmit the sound signal through a transmitter and receiver with infrared light, the same IR technology that is often found in television remotes. Just like the FM/RF system, an IR assistive listening system also requires a direct line of sight between the transmitter and receiver. The person with hearing loss wears a receiver and headphones to hear the presentation with greater clarity and without the distraction of the background noise.

These systems often include multiple IR transmitters (also called IR radiators) to provide the necessary line-of-sight coverage throughout the assembly area. However, it can still be difficult to achieve an unobstructed connection around the perimeter of the room.