Key Takeaways:
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- FM assistive listening systems use radio waves to deliver sound to listeners. This transmission method helps reduce the effects of distance, background noise and room reverberation, making speech easier to understand.
- FM technology has been used for decades in schools, theaters, places of worship and other public settings. Its long history makes it one of the most established assistive listening technologies available today.
- FM systems transmit radio waves and do not require a direct line of sight between the transmitter and receiver. Since the signal is not typically affected by the furniture, people or architectural features of a venue, listeners and speakers can move around without risking steady access to the transmission.
- Listeners typically use an FM receiver to access the audio signal. Depending on their preferences or circumstances, users may listen through headphones, earbuds, neckloops or other compatible accessories.
- FM remains particularly valuable in situations where portability and reliable wireless coverage are important.
What is an FM Assistive Listening System (ALS)?
FM assistive listening systems (ALS) use radio waves to transmit sound from a microphone or other audio source to a receiver used by the listener. FM stands for frequency modulation, the method used to encode the audio signal onto a radio-frequency carrier. FM systems have been used for decades in classrooms, lecture halls, theaters, places of worship and other settings where people need to hear a speaker more clearly.
FM systems can be designed for a single listener, a classroom or a large public venue. They are particularly useful when the listener needs to move around or when the transmission area is not completely enclosed.
How do FM systems work?
An FM assistive listening system typically has three basic components: a microphone, a transmitter and a receiver. The microphone picks up the speaker’s voice or another desired audio signal. The transmitter converts that signal into a radio-frequency transmission. A receiver worn by the listener receives the radio signal and converts it back into audio.
Because the sound is transmitted by radio rather than traveling acoustically across the room, the listener receives a signal that has not been weakened by distance or substantially affected by the room’s reverberation and noise away from the source microphone. This can improve speech understanding, particularly when a speaker is several feet away or when there is significant background noise.
FM systems use low-power radio transmission for assistive listening. The radio signal can travel around obstacles and does not require the listener to have a direct line of sight to the transmitter. This is one of the principal differences between FM and infrared systems.
Where are FM systems used?
FM technology has been widely used in education. A teacher can wear a small microphone and FM transmitter while a student uses a receiver. The student can hear the teacher’s voice directly, without depending on the sound reaching the student’s hearing device across a classroom.
FM systems can also be used in lecture rooms, theaters, places of worship, guided tours, meetings and other public settings. Portable FM transmitters can be used when a speaker moves around a room or when the listener needs to move between locations.
FM can also be useful outdoors. Unlike infrared, FM transmission is not dependent on light and therefore is not disrupted by direct sunlight. This makes radio-frequency transmission an option for some outdoor or partially enclosed events where infrared would be impractical.
FM technology can be used for applications ranging from a microphone worn by one speaker to a larger system connected to a public address system. In a theater, for example, the FM transmitter can receive the same audio feed that goes to the theater’s loudspeakers and transmit it to receivers distributed to patrons.
How FM differs from other ALS
FM is a radio-frequency transmission technology. This distinguishes it from infrared systems, which use light, and hearing loops, which use a magnetic field. Wi-Fi systems use a computer network to transport audio, while newer Auracast™ systems use Bluetooth Low Energy broadcast audio.
Because FM does not require line of sight, the signal can spread. Therefore, in a school where multiple classrooms have FM receivers, for instance, care is needed to ensure each FM system is using its own radio “station” to avoid interference. Care is also needed to ensure that the speaker (often a teacher) turns the microphone off before leaving the classroom.
The characteristics of a particular FM system depend on its transmitter, frequency, antenna, receiver and installation. As with any ALS, good system design and appropriate signal levels are important for effective communication access.
What equipment does a listener need?
A listener using a conventional FM assistive listening system generally needs an FM receiver. The receiver may be a small body-worn device or, in some systems, an integrated component designed to work with a particular hearing device. Rarely, the receiver is incorporated Ito the hearing device itself. This is, in part, because an FM system is often an educational expense, while the hearing device is a medical expense. Schools may purchase an FM system capable of being used by multiple students.
The receiver can provide sound through headphones or earbuds. A person who uses hearing aids or a cochlear implant with a telecoil may instead use a neckloop connected to the FM receiver. The neckloop converts the received audio into a magnetic signal that can be picked up by the hearing device’s telecoil.
Other coupling options may be available depending on the hearing device and FM system. For example, some systems can connect to hearing devices through manufacturer-specific accessories or direct audio connections.
Because FM systems use different frequencies and equipment, a receiver supplied by one venue will not necessarily work with another venue’s FM system. When attending an event, it is useful to ask what type of FM system is being used and what receiver or coupling accessories are available.
FM remains an established ALS technology, particularly in education and other situations where mobility, portability and freedom from line-of-sight restrictions are important.
FAQs
An FM assistive listening system uses radio waves to transmit sound from a microphone or other audio source directly to a listener. By sending the sound directly to a receiver, FM systems can help people hear more clearly when distance, background noise or poor room acoustics would otherwise make listening difficult.
An FM system is typically composed of a microphone, transmitter and receiver. The microphone captures the desired sound, then transmitter converts it into a radio signal and broadcasts the radio waves. Finally, the receiver captures the transmission and delivers the audio to the listener.
FM systems are commonly used in classrooms, lecture halls, theaters, places of worship, meeting rooms, guided tours and other indoor or outdoor environments where clear communication is important. They can be used for a single listener, a small group or larger audiences.
The primary difference is that FM systems use radio waves as the method of transmission. This can make FM technology useful in situations where people need to move around freely, possibly at a distance greater than what other systems might be able to cover without losing signal strength—including outdoors.
Most FM systems require a compatible FM receiver. The receiver is connected to headphones, earbuds, a neckloop or other accessories that work with hearing aids or cochlear implants. Available connection options vary based on the specific FM system, as well as the assistive device(s) used by the listener.