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Hearing Accessibility: FM, IR and IL

Assistive listening devices are designed to help those individuals whose main method of communication is oral. These devices are designed to amplify sound/speech up to a level that is comfortable for the individual with a hearing loss. These devices do not work as well for individuals who have diminished speech recognition abilities. Mainly assistive listening devices (ALD’s) are designed to capture the sound a hard of hearing individual wants to hear as close to the source as possible before any background noise can blend into the signal. This signal is then delivered into the person’s ear. If a cleaner signal with less blended noise can be presented to the individual, then the individual can be provided a greater chance of gaining more intelligibility from what they are listening to. This idea of providing a better speech to noise ratio is the primary premise behind this category of technologies.

ALD’s are composed of a group of technologies designed to assist or help a person with a hearing loss to gain more speech clues in difficult listening situations. Many people ask what the difference is between an ALD and a hearing aid since they are both designed to help amplify acoustical information to improve clarity to speech. The main difference between the two devices is the ALD device is designed to work very well in a particular listening environment or situation by collecting the sound information close to the source and overcoming the listening environments acoustical clarity problems by delivering the acoustical information the person wants to hear directly into the person’s ear or hearing instrument before much background noise can blend in with the primary acoustical information and thus degrading the information. With the hearing instruments the acoustical information must travel from the source to the individual’s physical location and during this transit the background sounds can blend with the acoustical information and when the blended sound reaches the microphone on the hearing aid the important speech information has been degraded to such an extent the clarity to what is being said or heard is no longer there. The reason there are so many different ALD’s is each ALD is designed to overcome the listening obstacles in a particular listening environment. The ideal situation is to couple an ALD with a person’s personal hearing instrument. This gives the hard of hearing person the best of both technologies, the ALD designed for the best clarity in the listening. We attempt to cover the three major types of Wide-Area ALDs in the sections below with each section covering one of the three types of ALDs; FM using radio frequency transmission, IR using infrared light beams, and IL using a loop of wire (called an “induction loop”) to generate an electro-magnetic field (EMF) that can be picked up through a telecoil or induction loop placed within the EM field.

FM Radio Frequency ALDs

Wireless FM radio technology ensures that listeners receive direct, clear communication of your message. Each system provides peace of mind — simple, turn-key solutions that have stood the test of time.  These systems are composed of a FM transmitter and one or more small FM receivers.  These systems are connected to an individual's ears through earbuds, headphones or coupled to the person's hearing aids equipped with a telecoil via a neckloop or direct coupled to a hearing aid streamer.

FM System

 Commercial FM listening systems (using the 72-76 MHz band) are designed to comply with 2010 ADA guidelines

IR Infrared ALDs

Wireless IR technology using an invisible light beam provides clean and clear communication and is ideal for  theater complexes that have side by side venues and need to contain the sound within one room from interfering with the sound in another room without worrying about channel management.  These systems generally use multiple emitter arrays design to spread the light source across the venue so everyone can receive the signal without it being blocked by structure or people.   Individuals use small IR receivers, either under the chin or small box receivers.  The under-the-chin receiver hangs in the ear using small domes that fit into the ear canal while people using the box receivers can use either earbuds, headphones or a neckloop.  IR systems can be setup to provide true stereo reception and is the only one of the three wide-area systems, FM, IR or IL, that can provide this. 

Infrared listening system
IL Induction Loop ALDs

Wireless IL technology is the oldest of the three main technologies used for Wide-Area ALDs. Developed in the 1950’s for use in schools for the deaf and carried over into the public schools in the late 60’s and 70’s. IL technology involves generating an electro-magnetic field (EMF) from a loop of wire laid around the area to be used by the hard of hearing individual. When the hard of hearing individual enters the EMF zone they simply turn on a telecoil in their hearing aids or CI processor and can pick up what is being sent over the induction loop directly into the hearing device. Since the hearing device is designed to provide them with the best clarity they are getting the best of both worlds.

Induction Loop System

Wide-Area FM Systems: A Primer

FM assistive listening devices (FM ALDs) are one of the three main line of products designed to provide hearing accessibility in public venues like; auditoriums, public meetings, classrooms, sporting events, arenas, places of worship and theaters. With this type of system an FM transmitter is connected to the audio source and transmits the source program out to small FM radio receivers used by the person wanting to understand what is being said at an event, program or meeting. The receiver is coupled to an individual’s ear(s) through the use of an earbud, headphones, and neckloop (used to couple the sound to a telecoil in hearing aids or cochlear implant processors equipped with telecoils) or through a hearing aid audio streamer connected directly by a patch cord.
FM systems are wireless, radio-wave systems designed to help individuals needing auditory assistance or language interpretation to overcome background noise, reverberation and distance from the sound source. Ideal for large-group listening scenarios. Individuals use personal FM receivers anywhere within the coverage area to hear crystal clear sound directly from the sound source.
The FM transmitter is relatively easy to install and can cover a fairly large area, like a football stadium or ballpark. Portable FM transmitters are available making the system extremely portable for use with tours, small meetings, classroom settings, locations where the speaker is mobile, or when a combination of installed and mobility is required as by simply adding the portable transmitter and using the existing receivers the use of the system for the cost involved is more than doubled making this a very good investment. Generally an FM system is the very cost effective and easiest system to install which reduces install costs greatly.
Receiver management is the biggest disadvantage to an FM system. The second disadvantage is frequency interference. While the 72-76 MHz band is set aside for Assistive Listening Devices it is also a shared band for some other devices that may cause problems in some areas. A site-evaluation can generally determine if there will be a problem with interference issues. The third disadvantage, when many FM transmitters are located close together (like in an educational system or multi-venues like a conference center or theater complex within the same general area) would be channel management. FM also does not provide privacy within, or outside a venue.
In Closing
FM systems are the workhorse of the wide-area ALD lineup. They are cost effective, easy to install (can generally be installed by a maintenance worker or sound technician), can provide mobility easily, is extremely scalability and last a long time. This technology has the go to line of products for the last 35-years.

Wide-Area IR Systems: A Primer

IR assistive listening devices (IR ALDs) are the second of the three main line of products designed to provide hearing accessibility at public venues just like we stated for FM, the only real difference is the method used to accomplish this task. While with FM we used radio frequencies, with IR technology we are using modulated light waves to transmit the sound from the source, generally a speaker system or public address system, to the individual taking advantage of the improved clarity of the ALD system.
The IR system is composed of a modulator unit, sometimes built into the emitter panel, a single or group of emitter modules and some form of infrared receiver worn or carried by the individual using the system along with some type of personal coupling method of getting the sound from the receiver to the ear, hearing aid or CI processor.
The biggest advantage to IR technology is twofold, one is channel management (any receiver can work with any emitter) and the second is security as the light wave is kept within the confines of the walls of the room being used. People outside the room the IR system is being used in cannot tap into the sound source. In addition the wide-area infrared system provides the greatest bandwidth and can be used, in a two-channel mode, to provide true stereo sound to the system users. Infrared also, because of the wide bandwidth, the best clarity, especially for music, of any of the three systems.
Infrared hardware costs more than FM systems and require a greater degree of design work to insure good coverage of the venue seating area. Installation costs are higher and require professional installation generally. Not only must power be run to each emitter being installed but also the audio source from the modulators to the emitters be figured in the costs involved. The transmission can be blocked by a number of things including people moving in front of the receiver, the emitter throw is off and the light beam is going over or not reaching the person’s receiver. This is generally do to design errors.
In Closing
Infrared systems are great for venues having multiple offerings within one location as any receiver will work in any of the offers without having to worry if channels match. This is the only choice when the program offering is in stereo which must be transmitted. When venues offer a wide variety of performances ranging from single speakers to Broadway productions and musical performances where a broad bandwidth Is needed for better fidelity.
Wide-Area IL Systems: A Primer

IL assistive listening devices (IL ALDs) are the third class of devices with the main line of products designed to provide hearing accessibility at public venues. Like the first two classes, FM and IR, the IL classes provides hearing accessibility in public venues but uses an electro-magnetic field, called EMF, to convey the sound from its source to the individual needing assistance to hear clearer.  

The IL system is composed of an amplifier and either a multi-strand round or flat wire plus a lead-wire to connect between the amplifier and the field wire.   The system must be designed so the EMF generated will reach everyone within the venue's seating area at shoulder level without causing a spillover effect into adjoining areas.  When designing an induction system some of the parameters that must be taken into consideration are age of the building, type of construction, amount of steel or iron used, electrical conduit placements, and location and type  of performance venues, i.e. stage for musical performances, what facilities or shops are close to the seating area.  These are some of the many questions that must be addressed for a good design. 


The biggest advantage is many people have a telecoil, magnetic induction coil, built directly into their hearing aids and all they need to do when entering a room or venue that uses an induction loop is switch their personal hearing aids into  the telecoil mode and they are connected to the system, no special equipment needs to be checked out.   People don't have to worry about who used the equipment last and was it cleaned properly.


Almost half the people wearing hearing aids don't have telecoils on their hearing aids or have never had the telecoil turned on in the fitting software.   In addition a well installed induction loop system is the most expensive of the three classes once design and installation costs are figured in to the bottom line.   Also class of ALD is more subseptiable

Prepackaged Systems can be found in our Catalog.  Please call if you need help  on choosing a system.

Call for information on Custom Designed Systems. Custom systems generally requires an on site survey