Understanding Binaural Hearing Aids: Benefits and Technology

If you're a new hearing aid user or considering using hearing aids, you might wonder if you need one or two devices. The answer often lies in the concept of binaural hearing - the ability to hear with both ears. For most individuals with bilateral hearing impairment, the body of evidence collected across decades of research has also found that the provision of two compared with one hearing aid yields significant benefit for the user. This article briefly summarizes the major advantages of binaural compared with monaural hearing, followed by a detailed description of the related technological advances in modern hearing aids.

Binaural hearing allows us to hear sounds in three dimensions. Our brain uses the subtle differences in the sounds each ear hears to help us locate the origin of a sound. Hearing loss often occurs in both ears, a condition known as bilateral hearing loss. In these cases, wearing two hearing aids can be beneficial as it aligns with the natural binaural hearing process.

Binaural hearing aids are hearing devices worn in both ears, rather than just one. They are designed to work together as a pair, helping your brain process sound from both sides more naturally. This setup more closely matches how people with typical hearing experience the world, where both ears pick up sound and send information to the brain for interpretation. Clinicians have understood the advantages of listening with two ears compared with one. In addition to improved speech intelligibility in quiet, noisy, and reverberant environments, binaural versus monaural listening improves perceived sound quality and decreases the effort listeners must expend to understand a target voice of interest or to monitor a multitude of potential target voices.

Therefore, the challenge for an ideal, technically assisted binaural hearing rehabilitation is twofold: (1) provide acoustic cues to the impaired auditory system in such a way that the individual mental spatial map can be created and maintained and (2) allow attention to focus on single acoustic sources if needed. Achieving both perceptual goals at the same time is not always possible, depending on the degree of hearing loss and the acoustic coupling of the hearing aid to the ear.

Binaural Hearing Aids: How They Work and Their Benefits

Benefits of Binaural Hearing Aids

One of the most important benefits of binaural hearing aids is improved speech understanding, especially in noisy environments. Just as stereo sound is more enjoyable than mono, hearing with two aids usually provides a richer, more natural sound experience. Binaural hearing aids can help you better understand speech in noisy environments. When you’re surrounded by background noise, it can be challenging to focus on a specific conversation. With the improved sound localization that binaural hearing aids provide, you’re able to pick out voices from other sounds, reducing the need to strain or ask people to repeat themselves.

Listening with one ear can be more tiring than listening with two. With two hearing aids, the listening effort is shared between both ears, reducing fatigue. With less effort needed to understand speech and background sounds, you may feel less tired at the end of the day.

Using a hearing aid in only one ear could potentially lead to auditory deprivation in the non-aided ear. Over time, the unaided ear might lose its ability to understand speech.

Binaural hearing aids can greatly enhance your ability to engage in conversations by making it easier to pick up on subtle cues in your environment. With two hearing aids working together, you can hear sounds coming from different directions, which helps you focus on the speaker without constantly having to turn your head.

Choosing binaural hearing aids can offer a more balanced and natural hearing experience. Wearing just one hearing aid can sometimes cause you to miss important details or feel off-balance, especially in group settings or busy environments.

Binaural hearing aids can make a big difference when it comes to situational awareness. When you wear a hearing aid in each ear, your brain receives sound from both sides. This helps you notice what’s happening around you more clearly. These hearing aids also help your brain figure out where sounds are coming from. For example, if someone calls your name or a car horn in the distance, binaural hearing aids make it easier to tell the direction of the sound. This can be especially helpful in situations where quick decisions are needed, like crossing the street or reacting to something unexpected.

Improved situational awareness doesn’t just help with safety - it also helps you feel more connected. When you can tell where voices and sounds are coming from, conversations feel more natural. You won’t have to turn your head constantly or ask people to repeat themselves as often.

When both ears receive sound, your brain can process information more clearly and help you notice where sounds are coming from. Wearing only one hearing aid may cause sounds to feel unbalanced or make it harder to follow conversations.

With its sensitivity to acoustic information arriving from any location around the listener, the sense of hearing is especially helpful for guiding the sense of vision, and, by that, body posture in a direction potentially worth focusing more attention. The sense of hearing is “always on,” thereby allowing it to create a basic mental representation of the physical world in relation to the human body even when a person sleeps or when visual information is unavailable. This representation consists of characteristic information about the surrounding space and the location of acoustic objects.

The capability of the senses in combination with the abstraction power of the brain to create and maintain a reliable mental map of the ever-changing environment in relation to the position of the human body is essential for a person to reach a certain level of “peace of mind” or to focus attention on a single acoustic object. People with hearing loss might fall short of creating such a reliable map under all circumstances.

Listening can be enhanced by comparing differences between the two ears for the same sound. Some differences arise because a sound originating from a particular location in space will arrive earlier at one ear (ipsilateral ear) relative to the other (contralateral ear) and will be louder at the ear closer to the sound source relative to the far ear.

Fig. Interaural time differences (ITDs) in the low frequencies (red) can be used for localization, but ITDs for higher frequencies might be ambiguous (blue).

Interaural time differences

Fig. : Low-frequency sound waves are not affected by the presence of the head (red), while high frequencies (blue) are attenuated by the head shadow.

Frequency dependency

Proposed the duplex theory of hearing whereby the auditory system uses the ITDs below approximately 2 kHz and the ILDs above. At low frequencies, the neurons in the auditory system can follow the sound waveform and therefore detect ITDs very well. In contrast, at high frequencies, ITDs can be detected only in the envelope of the signals but not in the fine structure (which is no longer resolved by the neurons) of the transmitted signals.

For low-frequency pure tones and noise, human psychophysical experiments show that ITDs as low as 10 to 20 μs can be resolved, which corresponds to an angular accuracy of 1 degree for sound arriving from the front. The healthy auditory system seamlessly uses redundant ITD and ILD information, for example, when the low- or high-frequency parts of speech are masked by noise. For normal-hearing listeners, a low-frequency noise masking the ITD cues of the target signal can be easily compensated by the high-frequency ILD/IED cues. However, hearing-impaired listeners cannot usually make as much use of this redundancy.

In most hearing aid fittings, an individual user's residual hearing capabilities are unknown, so the fittings are based on group averages, which assume a gradual decline in binaural hearing capabilities with increasing hearing threshold. Most often, hearing aid selection and adjustment is a compromise between comfort (especially, own voice quality) and achievable audibility in the mid- to high-frequency region.

Restoring audibility for softer signal parts independently (i.e., employing wide dynamic range compression) in the two ears will, on average, lead to smaller ILDs reaching the eardrums of the user compared with the original ILDs. Reducing the ILDs might not seem optimal for spatial perception, but providing audibility to both ears is essential for the binaural system to utilize the ITD and ILD information. For example, ensuring audibility allows the user to exploit the high-frequency IED information even if the absolute ILD information is altered.

The position of the hearing aid microphones is another source of altered ITD and ILD cues. Binaural cues are altered the most when the microphone is positioned behind the ear. Binaural cues are altered to a lesser extent when the microphone is positioned in the ear.

Typically, sound traveling from the free field to the eardrum must first pass the human torso, head, and pinnae, which together induce a series of direction-dependent acoustic transformations that help listeners localize auditory objects. Hearing loss per se does not affect a listener's HRTFs because they relate to the listener's anatomical characteristics. However, when a hearing-impaired listener uses hearing aids, the perceived HRTFs will change as a function of the microphones' position. For example, in the case of in-the-ear (ITE) hearing aids, the microphones are placed at the ear canal entrance; therefore, the perceived HRTFs are more similar to the original ones. In contrast, for fully occluded fittings and with a single microphone placed behind the user's ear, the perceived HRTFs are very different from the original individual HRTFs.

Consequently, manufacturers offer a function to approximate the average directionality of a pinna when hearing aids are fit with the microphones placed behind the ear. Usually, this is accomplished by applying a weak type of beamformer for frequencies above 1.5 kHz.

The accuracy of sound localization improves when listeners move their heads while the sound is being presented. Have also shown that dynamic ITDs, rather than ILDs, provide a strong cue for front/back hemifield detection. Showed that dynamic ITDs could compensate for the disruption of monaural spectral cues when tubes are inserted into the ear canals. Together, these results suggest that dynamic ITDs associated with head movement can help resolve ambiguities and improve localization performance.

When target and masker signals are produced from different locations, there is a resulting signal-to-noise ratio (SNR) advantage at one ear relative to the other. This SNR advantage is based on the fact that the head acts as an acoustic barrier that produces a level difference between the ears (i.e., head diffraction effects). As aforementioned, this is more prominent at higher frequencies, typically above 2 kHz, because low-frequency wavelengths are substantially larger than the head dimensions and therefore do not “see” an obstacle. The benefit provided by better-ear-glimpsing is limited in hearing-impaired listeners by reduced audibility at high frequencies.

Binaural redundancy is the advantage obtained when identical information about the signal is received in both ears. When listening with one instead of two ears, there is only one opportunity for the auditory system to capture the available information in a signal. This process is particularly relevant for listeners with asymmetrical hearing losses because the auditory cues available in a signal may be more readily accessible for one ear than for the other.

Binaural loudness summation can be advantageous for the perception of sounds whose level is close to the hearing threshold. Showed that hearing-impaired listeners demonstrate binaural summation to the same extent as normal-hearing listeners. This finding suggests that a listener with bilaterally symmetrical sensorineural hearing loss may benefit from binaural loudness summation. As discussed in the previous section, it is evident that hearing aids should preserve-and potentially enhance-the benefits associated with two-eared listening.

Technology Behind Binaural Hearing Aids

As discussed in the previous section, it is evident that hearing aids should preserve-and potentially enhance-the benefits associated with two-eared listening. Binaural hearing implies a synergistic exchange of information from the left and right ears in the central auditory system. While bilateral fittings, which entail independent processing in the left and right hearing aids, may promote activation of binaural hearing mechanisms, they do not guarantee it.

Similarly, to achieve binaural hearing aid fittings, some data exchange is required between the left and right hearing aids. The rate and amount of data exchange impact the power consumption of the hearing aids and possibly the hearing aid size due to the need for a bigger battery and/or wireless antenna. Therefore, binaural processing might not be available in all form factors (e.g., completely-in-the-canal hearing aids).

Current technology for wireless binaural data exchange uses either near-field magnetic induction (NFMI) or 2.4 GHz wireless technology. Both approaches are robust and reliable. The NFMI approach can be optimized for low power consumption, but it is restricted in transmission bandwidth and increases the design complexity and size of the hearing aids. In contrast, 2.4 GHz technology offers more bandwidth and reduces design complexity because it can integrate with standard Bluetooth wireless transmission protocols using a single antenna.

Therefore, the activation of binaural signal processing should be strategically adjusted to the targeted perceptual benefits for the individual hearing aid user, which will depend on their auditory needs and residual hearing capabilities. The chosen acoustic coupling and the listening environment also play a significant role in the achievable real-world benefit.

Fig. ) Monaural processing with binaural synchronization. ) True binaural processing. P: parameters of left (L) and right (R) algorithm. Dashed lines show wireless data exchange. Each hearing aid processes the audio signals received from its own microphones (solid lines), then exchanges information (i.e., parameter data) with the other hearing aid (dashed lines) to synchronize filter parameters or program settings, for example.

Binaural processing

Depending on the rate and amount of data exchange between the hearing aids, binaural synchronization can offer substantial advantages for the user. The most basic synchronization is “event-triggered.” For example, changing the volume control on one hearing aid can simultaneously change the volume control on the other hearing aid. Likewise, information about the classification of the listening environment can be exchanged between the hearing aids. Using this information, the joint operation of the two hearing aids can be optimized to maximize the user's benefit.

With higher investments in the data exchange rate, data volume, and power consumption, a higher degree of synchronized binaural system behavior can be achieved. Whether the high-rate synchronization of a specific signal-processing algorithm (e.g., noise canceller, beam-former, gain model, and limiting system) is beneficial for a user will depend on the details of its implementation and parametrization. For example, while increasing the effectiveness of a noise-canceling algorithm might improve the SNR, this will likely degrade binaural ITD/ILD cues if the algorithm is implemented independently.

Hearing aids work by taking in sound from your surroundings and shaping it into something clearer and easier to understand. This processor analyzes what it receives and adjusts the signal based on your hearing needs, which are programmed by an audiologist. Modern hearing aids also respond to changes in your environment. Many devices learn from your listening habits and automatically adjust settings, so you do not have to constantly make manual changes.

Binaural hearing aid processing refers to technology that allows two hearing aids to communicate and respond together rather than acting independently. This helps create clearer speech, smoother volume balance and a listening experience that feels closer to natural hearing.

A key part of binaural processing is the wireless connection between your hearing aids. For example, if one hearing aid detects loud noise on one side, both devices can work together to lower the volume or reduce background noise.

Binaural processing helps your brain figure out where sounds are coming from by using both ears together. This process makes it easier to tell if a sound is coming from the left, right or straight ahead. Many people feel frustrated when they cannot tell where voices or noises are coming from, especially in busy places. When both hearing aids work together, your brain receives a smoother and more balanced sound.

Consulting with an Audiologist

While there are clear benefits to wearing two hearing aids, the decision is best made in consultation with your audiologist. Adjusting to binaural hearing aids might take some time. Be patient with the process and communicate with your audiologist about any concerns or difficulties you may have. Wearing two hearing aids can bring us closer to the natural hearing experience and provide many advantages, especially for those with bilateral hearing loss. But, remember, each person’s hearing loss journey is unique. Your audiologist is there to guide you through this process, ensuring that you get the most out of your hearing aids and improving your communication and participation in life’s beautiful symphony of sounds.

Before deciding on which hearing aids are right for you, talk with your audiologist. They can guide you towards better hearing and improved quality of life.

An audiologist can help you decide if binaural hearing aids are right for you. They will test your hearing, explain your results and recommend hearing aids based on your specific needs. If hearing loss is present in both ears, audiologists suggest wearing two hearing aids to achieve the best results. Once your devices are selected, there may be a short adjustment period. Your audiologist can fine-tune the settings to make sure both hearing aids work together smoothly. You may notice small changes at first, like hearing conversations more clearly or feeling more aware of what’s going on around you.

To get the best results from binaural hearing aid features, make sure you use both devices together every day. Trying out different listening situations, like talking with friends in a busy cafe or relaxing at home, can help you notice how your devices adjust to different sounds. Using both hearing aids together allows your devices to share information and work as a team, making everyday listening easier and less tiring.

If you are interested in learning more about binaural processing or want to discuss options for your hearing care, schedule an appointment with an audiologist.

Benefit	Description
Improved Speech Understanding	Enhances clarity, especially in noisy environments.
Reduced Listening Effort	Distributes the workload between both ears, minimizing fatigue.
Prevention of Auditory Deprivation	Maintains hearing ability in both ears.
Enhanced Sound Localization	Improves the ability to identify the direction of sounds.
Better Situational Awareness	Increases awareness of surroundings for safety and connection.