FM systems for hearing aid users

FM systems and modern wireless transmission systems can significantly improve speech intelligibility for hearing aid users, particularly in acoustically challenging environments. The wireless technology transmits speech directly from the speaker to the hearing aid, bypassing disruptive background noise, long distances and reverberation. From school and the workplace to leisure activities, these systems open up new possibilities for clear communication. Choosing between analogue FM and digital DM technology, as well as ensuring the correct connection to the hearing aid, are key considerations.

Basic principle and technical definition

FM systems, also known as radio transmission systems, are hearing-assistance technologies for the wireless transmission of audio signals via radio waves. They represent an important addition to hearing aids or cochlear implants and serve the purpose of ensuring clear communication in acoustically challenging environments. The basic principle is based on routing the speech signal directly from the speaker to the listener, thereby bypassing the acoustic problems of the room.

The term ‘FM system’ has evolved over time and derives from frequency modulation, which was used in older analogue systems. However, modern systems are increasingly utilising digital transmission methods as well. The aim of all systems is to create the impression that the speaker is standing right next to the user. This can significantly improve the quality of life for people with hearing loss and enables more active participation in social life.

Acoustic challenges in difficult listening environments

Despite advanced hearing systems, speech comprehension remains problematic for people with hearing loss in certain environments. The greatest challenges are background noise, the distance from the speaker and reverberation in the room. Hearing aids tend to amplify not only speech but also ambient noise, leading to an unfavourable signal-to-noise ratio. This describes the relationship between the desired speech signal and the distracting background noise.

As the distance increases, the voice loses intensity whilst the noise level remains constant. This makes understanding even more difficult and leads to increased listening fatigue. In rooms with poor acoustics, reverberation further exacerbates the problem, as reflected sound waves interfere with the direct transmission of speech. FM systems can minimise or eliminate these disruptive factors by transmitting the voice clearly and directly to the hearing aid. The technology fully compensates for the attenuation of the voice over greater distances.

Structure and operation of wireless transmission

A wireless transmission system essentially consists of two main elements: a transmitter with an integrated microphone and one or more receivers. The microphone picks up the speaker’s speech signals, whereupon the transmitter converts these into modulated radio signals and transmits them. The receiver, worn by the hearing aid user, picks up the radio signal and converts it back into an analogue audio signal, which is fed directly into the hearing aid.

The speaker usually wears the microphone close to their mouth, either clipped to their clothing or held in their hand. This proximity to the mouth is crucial for the quality of the transmission, as it ensures the voice is picked up at an optimal volume whilst ambient noise remains significantly quieter. The distance between the mouth and the microphone should ideally be no more than 15 to 20 centimetres to achieve the best results.

Analogue versus digital transmission technology

The original term ‘FM system’ derives from frequency modulation, which was used in older analogue radio systems. With this technology, the carrier frequency is modulated in accordance with the audio signal. Modern systems increasingly use digital modulation (DM), often in the 2.4 GHz or DECT frequency range. These digital systems generally offer clearer sound quality and are better at avoiding interference that can occur with analogue FM signals.

An important technical aspect is latency, i.e. the delay between the spoken word and its reproduction in the hearing aid. Analogue systems have virtually no latency, whilst digital systems may exhibit a minimal, system-related delay. However, this is typically in the range of a few milliseconds and is not perceived as disruptive by most users. The advantages of digital technology in terms of sound quality and resistance to interference outweigh the disadvantages in most cases.

Improvement in signal-to-noise ratio in the far field

The key advantage of wireless transmission is the dramatic improvement in the signal-to-noise ratio, particularly in the so-called far field, i.e. at a considerable distance from the speaker. Through the direct transmission of speech and the reduction of ambient noise, a dynamic gain of between 15 and 25 dB is achieved compared to using a hearing aid alone. This improvement can make the difference between understanding and not understanding.

The systems enable the user to understand speech better, even when the speaker is far away, in some cases over distances of up to 30 metres or more. This is particularly important in large spaces such as lecture theatres, conference rooms or theatres. The technology ensures that the speaker’s voice always arrives at the same volume and clarity, regardless of their position in the room.

Compatibility and connection to hearing aids

Wireless systems can be connected to almost all standard hearing aids and cochlear implants, provided they have a suitable interface. The audio signal is transmitted to the hearing aid in various ways. The traditional method is direct connection via an audio shoe with a Euro socket on the hearing aid. This is attached to the lower part of the behind-the-ear device and establishes a mechanical and electrical connection to the receiver.

Another tried-and-tested option is wireless transmission via a neck loop worn around the neck. This requires an activated T-coil (telephone coil) in the hearing aid. The induction loop generates an electromagnetic field, which is received by the T-coil and converted into an audio signal. The advantage of this method is that no direct mechanical connection to the hearing aid is required.

Modern Bluetooth integration

Modern hearing aids with Bluetooth technology can often receive the radio signal via an intermediate accessory device or directly. These streamers act as a bridge between the FM transmitter and the Bluetooth-enabled hearing aid. The advantage of this solution lies in the wireless connection and the often simpler handling. Some manufacturers offer integrated solutions where the FM receiver is built directly into the hearing aid accessory.

Compatibility between different manufacturers can vary, which is why expert advice on assistive devices and technology is important. Hearing care professionals can assess which connection option is best suited to the existing hearing aid and make the necessary adjustments. The initial configuration is crucial for optimal performance and should not be carried out without specialist knowledge.

A variety of microphones for different communication situations

There are different designs of transmitter microphones, each optimised for specific situations. Lapel microphones, also known as clip-on microphones, are ideal for one-to-one communication. They are ideally attached to clothing at chest height, approximately 15 to 20 centimetres from the mouth. This position ensures clear voice pickup whilst minimising susceptibility to background noise.

Table microphones or omnidirectional microphones are designed for meetings or small groups. They pick up voices from all directions around the table, enabling participation in group discussions. Handheld microphones can be passed around in larger groups, which encourages speakers to speak clearly and ensures speech intelligibility for the user. With digital systems, it is often possible to connect several microphones together in a network.

MultiTalker function for complex situations

This networking capability allows access to different speakers in large meetings or in the classroom. Modern systems such as Phonak’s Roger technology enable multiple microphones to be active simultaneously, with the receiver intelligently switching between speakers. This is particularly valuable in classroom settings where both the teacher and individual pupils may be speaking.

Head-worn microphones, which are worn on the head with a headband, maintain a constant position relative to the mouth and are particularly suitable for teachers or lecturers who move around a lot. Choosing the right type of microphone depends on the specific application and should be done carefully to achieve optimal results.

Application in paediatric audiology and the school environment

FM systems are an indispensable aid for pupils with hearing loss. Classrooms often have high noise levels averaging 60 dB, whilst values of 35 dB or less are recommended for optimal speech understanding. In addition, room acoustics in many school buildings are problematic, with significant reverberation and poor sound insulation. Under these conditions, speech understanding can be significantly impaired even with well-fitted hearing aids.

With the help of a wireless system, children can pick up to 42 per cent more speech during lessons. The teacher’s voice always sounds the same volume, regardless of where they are in the classroom. This significantly reduces listening effort and enables pupils to concentrate better on the lesson content. The use of such systems is generally always beneficial for children and young people with severe hearing loss, but can also offer significant advantages for those with milder hearing loss.

Cost coverage and legal basis

In Germany, FM systems for children and young people can be obtained through the assistive devices guidelines of the statutory health insurance scheme. Costs are usually covered if the need is certified by a doctor and confirmed by a paediatric audiologist. Provision often requires close cooperation between the school, parents, hearing care professionals and the health insurance provider.

The systems are considered a basic necessity for meeting the need for improved speech and hearing development, as well as for reducing fatigue caused by listening strain. Nurseries and pre-schools can also benefit from the technology, particularly for children with severely impaired speech comprehension in noisy environments.

Use in auditory processing disorders

FM systems are also of great benefit to children and young people without conventional hearing loss if they suffer from auditory processing and perception disorders (APPD) or attention disorders such as ADHD or autism spectrum disorders. In AVPD, those affected have difficulty distinguishing the target signal from background noise, even though the peripheral hearing organ is intact. The central processing of acoustic information in the brain is impaired.

The FM system provides clear and direct access to the speaker’s voice by significantly elevating the signal above background noise. This can significantly improve speech intelligibility and attention. For this group, there are special receivers that are worn directly behind the ear and do not require hearing aids. These so-called behind-the-ear receivers are connected to headphones and can be worn discreetly under the hair.

The provision of FM systems for AVWS often requires a paediatric audiological diagnosis and may be covered by health insurance in cases of severely impaired speech comprehension in the presence of background noise. However, the decision is made on a case-by-case basis and requires careful documentation of the hearing problems and their impact on academic performance.

Applications in adult life

FM systems support adults in a wide range of professional situations. At meetings, conferences or presentations, they reduce background noise and amplify speech. Particularly in open-plan offices or at events with many participants, the technology can make the difference between active understanding and frustrating guesswork. This makes professional participation despite hearing loss considerably easier.

In private life, FM systems improve communication in acoustically challenging situations such as noisy restaurants, family gatherings or church services. The systems can also be used at concerts, theatre performances or cultural events, provided the organiser supplies the appropriate transmission equipment. Mobile transmitters can also be connected to external audio sources such as televisions, computers or telephones to stream sound directly to the hearing aid in optimal quality.

Connection to media devices

For watching television at home, many manufacturers offer special TV adapters that are connected between the television and the FM transmitter. The sound is then transmitted wirelessly to the hearing aid without disturbing other people in the room. The volume can be adjusted individually whilst the television plays at a normal room volume. This can prevent arguments between partners and make watching television together enjoyable again.

FM systems can also be helpful for telephone calls. By connecting a telephone adapter, the conversation is transmitted directly to both hearing aids, which improves intelligibility and allows for hands-free calling. Modern smartphones with Bluetooth can often be connected directly to hearing aids equipped with the relevant technology, making additional adapters unnecessary.

Stationary and mobile system solutions

Wireless transmission systems are available in two basic designs. Stationary systems are designed for fixed, larger spaces, such as conference rooms, theatres, lecture theatres or classrooms. They feature a permanently installed transmitter to which multiple audio sources can be connected. The range is designed for larger events and can extend up to 100 metres or more, depending on the system and frequency range.

Mobile, portable systems are intended for personal use. They can be easily taken to different locations and serve as a personal aid. The devices are compact, lightweight and often fit in a jacket pocket. They are suitable for spontaneous situations such as doctor’s appointments, lectures, guided tours or excursions. The range of mobile systems is typically 15 to 30 metres, which is sufficient for most everyday situations.

Soundfield systems as a collective solution

Soundfield systems represent a special type of transmission system and are primarily used to improve the general room acoustics. They consist of a wireless microphone for the speaker and one or more loudspeakers installed in the room. The voice is slightly amplified and distributed evenly throughout the room. Unlike FM systems, the sound is not played back in individual hearing aids, but via room loudspeakers.

This system benefits everyone present, including those with normal hearing, people with attention difficulties or non-native speakers. In classrooms, a soundfield system can improve the learning environment for all pupils and reduce listener fatigue. Teachers need to strain their voices less, which also benefits their vocal health in the long term. However, a soundfield system does not replace the benefits of an individual FM system for children with hearing loss.

Practical use and maintenance

The day-to-day use of FM systems is usually straightforward once users have got used to them. The transmitter must be connected to the supplied charger regularly after use. Modern devices feature lithium-ion batteries, which cannot be overcharged. Charging typically takes two to three hours, and the operating time ranges from eight to twelve hours, depending on the model.

The receiver is either powered directly by the hearing aid or draws its energy from the hearing aid’s batteries or rechargeable cells. This significantly increases the hearing aid’s power consumption. When using an FM system, care should therefore be taken to ensure that the rechargeable cells are sufficiently charged or that fresh batteries are used. Some systems have their own rechargeable cell in the receiver, which must be charged separately.

Optimal microphone positioning and avoiding errors

The speaker should ensure that the microphone is not covered by clothing such as scarves, ties or necklaces, as this causes disruptive friction noises. For clip-on microphones, a position on the outside of the clothing is ideal. The microphone should point upwards towards the mouth and not be covered by hair or scarves. If the speaker has long hair, it may be advisable to tie it back or position the microphone in a less hairy area.

In the event of a fault such as a lack of sound, hissing or dropouts, a systematic troubleshooting process should be carried out. First, check the rechargeable or standard batteries in the transmitter and receiver. Then check that all plugs and connections are correctly positioned. In systems with multiple channels, interference with other radio systems may occur. In this case, a different channel should be selected. The user manual usually contains a detailed troubleshooting checklist.

Security against eavesdropping and social aspects

As radio waves, unlike infrared systems, are not blocked by walls, there is theoretically a risk that third parties outside the room may be able to eavesdrop. Modern digital systems often counter this risk through encryption methods. With analogue FM systems, transmission is generally unencrypted, which should be taken into account in sensitive areas such as medical consultations or legal advice. In such situations, digital systems with encryption may be the better choice.

Another, more social aspect is the fact that the use of external receivers clearly identifies people with hearing loss as such. In practice, this can lead to adults in particular, in professional or academic settings, hesitating to use or request these devices, as they wish to avoid stigmatisation. Modern, compact designs and integration into Bluetooth headsets can help to lower this barrier.

Acceptance and awareness

The acceptance of FM systems depends heavily on education and support within the social environment. In schools, it is important that teachers and classmates are informed about the technology and understand its benefits. If a teacher forgets to switch on the microphone or accidentally leaves it switched on whilst going to the toilet, this can lead to awkward situations. Good training for everyone involved is therefore essential.

In the workplace, it can be helpful to inform colleagues and managers about the necessity and functioning of the technology. This promotes understanding and facilitates integration into meetings and discussions. Open communication about one’s own hearing situation can break down barriers and improve collaboration.

Cost considerations and financing

The cost of FM systems can vary considerably depending on the model and manufacturer. Simple portable systems start at around €1,500, whilst high-quality digital systems with multiple microphones and receivers can cost €3,000 or more. Fixed installations for larger premises can be even more expensive. For children and young people, the cost is usually covered by statutory health insurance if a medical need is demonstrated.

For adults, cost coverage is more difficult to obtain. Whilst hearing aids are typically covered by health insurance as standard, FM systems are often regarded as additional equipment. Cost coverage for adults is possible, but usually requires a detailed justification of the necessity, for example for the purposes of work or participation in educational activities. Under certain conditions, the Integration Offices or the Federal Employment Agency may also be eligible to cover the costs.

Future prospects for transmission technology

Future developments aim to further improve audio accessibility and promote inclusion. A promising new technology enables a single radio transmitter to serve multiple receivers of different types simultaneously. The advantage lies in universal compatibility: the signal can be received by suitable hearing aids and cochlear implants as well as standard Bluetooth headphones.

This would massively improve accessibility in public venues. Theatre-goers, concert-goers or conference attendees could access the broadcast using their own device as required. People with hearing loss would receive the same audio quality as everyone else, without having to rely on special hire equipment. The integration of such systems into public buildings, cultural venues and educational establishments could be an important step towards greater participation.

Integration with smart home and assistance systems

The increasing connectivity of everyday devices opens up further possibilities. In future, FM systems could be seamlessly connected to smart home systems. Doorbells, smoke alarms or telephone calls could be signalled directly via the hearing aid. Combining this with voice assistants could simplify operation and create new applications. The connection between modern televisions and hearing aids is also becoming increasingly convenient and versatile.

The miniaturisation of technology is advancing, meaning receivers are becoming ever smaller and more discreet. Future generations of hearing aids may already have FM receivers built in, without the need for additional components. This would simplify handling and increase acceptance. The move towards universal, standardised transmission protocols could also improve compatibility between different manufacturers and make it easier for users to choose.