Hearing Assistive Technologies — Loops, FM, IR, and ADA Compliance

Hearing assistive listening systems (ALS) allow individuals with hearing loss to receive audio from a public address or presentation system directly in their hearing aids, cochlear implants, or dedicated receivers — without ambient room noise, reverberation, or distance degradation. The ADA Standards for Accessible Design (2010) and IEC 60118-4 establish legal requirements and technical performance standards. For AV integrators, ALS is increasingly a standard specification item in any venue with a PA system.

Why Hearing Assistive Systems Matter

Hearing aids amplify all sound, including background noise and reverberation. In a large auditorium, a hearing aid user 30 feet from the speaker array receives the same reverberant, noise-contaminated signal as everyone else — amplified. An ALS delivers the clean, processed audio signal directly to the hearing aid or receiver, bypassing room acoustics entirely.

Populations served: Approximately 15% of US adults have some degree of hearing loss (NIDCD). In venues over 50 seats, a significant percentage of attendees may benefit from ALS. In senior-oriented venues (worship, community centers, healthcare), that percentage is higher.

System Types

1. Induction (Audio Frequency Induction Loop — AFILS)

An induction loop is a wire installed in or around a listening area that carries audio current, creating a fluctuating magnetic field. Hearing aids with a telecoil (T-coil) pick up this magnetic field directly, converting it back to audio inside the hearing aid.

How it works:

• The audio signal (from a mixer or DSP output) is fed to a loop driver amplifier
• The driver amplifier outputs current into the loop wire
• The loop wire is installed around the perimeter of the listening area (perimeter loop) or in a grid (tile/phased array configuration)
• Any T-coil-equipped hearing aid or cochlear implant processor within the field receives the audio

Advantages:

• No receiver hardware required — works directly with existing hearing aids (70%+ of hearing aids sold in the US include T-coils)
• Completely private — no visible equipment for the user to carry
• Works with cochlear implants
• No battery management, no receiver checkout desk

Disadvantages:

• Magnetic field leaks outside the loop boundary (spillover into adjacent rooms)
• Metal structures (steel decking, rebar) absorb and distort the magnetic field
• Requires professional installation and measurement to meet IEC 60118-4 field strength standards
• Higher installation cost than FM or IR

IEC 60118-4 performance standard: The loop must deliver a magnetic field strength of −22 dBV/m ±3 dB measured at 1 kHz across 80% of the listening area, with a frequency response of 100 Hz–5 kHz (±3 dB from the 1 kHz reference). Field uniformity and overshoot outside the coverage area are also specified.

Loop driver amplifiers: Ampetronic (ILD series, C series), Univox (ProLoop), Contacta (IL-300+), Williams Sound (PPA T27). Proper amplifier sizing is critical: underpowered drivers fail to achieve required field strength; overpowered drivers cause spillover.

Loop configurations:

• Perimeter loop — Single wire around the room perimeter. Simple; works well in rooms under ~6 m wide. Metal structures in the floor degrade performance.
• Figure-8 (phased array) — Two overlapping loops driven 180° out of phase. Cancels the magnetic field outside the room, reducing spillover to adjacent spaces. Required in multi-room facilities (adjacent conference rooms, classrooms).
• Low-loss tile array — Multiple small loops covering the floor area in a grid. Used in large spaces (airports, railway stations) where a single perimeter loop cannot achieve uniform coverage.

2. FM Assistive Listening Systems

FM systems broadcast audio over a dedicated FM frequency (72–76 MHz in the US, per FCC Part 74) using a low-power transmitter. Users carry a pocket FM receiver and use neckloop, headphones, or earbuds.

Advantages:

• Wide coverage area; no installation of wire in the room
• Works for users without T-coil hearing aids (uses headphones or earbuds)
• Portable transmitter units can be used in any room

Disadvantages:

• Requires receiver hardware (users must check out and return receivers)
• Receivers need battery management and cleaning
• RF interference possible from other FM sources
• Coverage limited to line-of-sight and room boundaries (FM bleeds through walls)
• Less private than loop (signal is transmitted beyond the room)

Common FM platforms: Williams Sound (WIR TX9N transmitter, WIR RX22 receivers), Phonak Roger (education-focused), Telex (FMR-900 series).

Design guidance: One transmitter per room. ADA requires a minimum number of receivers based on seating capacity (see ADA requirements section). Provide charging/storage cabinet for receivers. Transmitter input connects to the same audio output as the hearing loop driver — typically a balanced line-level output from the DSP or mixer.

3. Infrared (IR) Assistive Listening Systems

IR systems transmit audio using infrared light (95 kHz or 250 kHz carrier). IR receivers are worn by users (neck loop, headphone, or behind-the-ear style).

Advantages:

• Fully contained within the room (IR does not pass through walls) — important for confidential proceedings (courtrooms, boardrooms, medical facilities)
• High audio quality (typically better than FM)
• No RF interference

Disadvantages:

• Requires line-of-sight to IR radiator panels; obstructions cause dropouts
• Sunlight can interfere with IR systems (avoid direct sunlight on radiators or seating areas)
• Requires receiver checkout; battery management

IR radiator placement: Mount panels on side or rear walls, aimed at the listening area. Avoid mounting behind the audience (shadows). Multiple panels overlap coverage for large rooms. Panel count and placement are calculated based on room geometry.

Common IR platforms: Williams Sound (IRT D2 transmitter, IRS U8 receivers), Sennheiser (SZI1015 radiator, SET840-S receivers), Bosch Integrus (high-capacity for large venues).

4. Bluetooth and RF Neckloop Systems

Emerging Bluetooth-based ALS platforms (Contacta BT2, Otojoy ClearCast) allow direct Bluetooth audio streaming to modern hearing aids with Bluetooth LE Audio (Auracast). This standard, released in 2022, is designed specifically for broadcast audio scenarios.

Auracast (Bluetooth LE Audio): A one-to-many broadcast mode where a single transmitter streams to unlimited Bluetooth LE Audio-capable devices. Hearing aid manufacturers are beginning to implement Auracast receivers in their products. Not yet widely deployed but will become the dominant wireless ALS technology as hearing aid adoption of LE Audio grows.

Current limitation: Most installed hearing aids (2023 and earlier) do not support Auracast. FM and loop systems remain the primary ADA-compliant ALS technologies for the near term.

ADA Requirements for Assistive Listening Systems

The 2010 ADA Standards for Accessible Design (Section 219) require assistive listening systems in assembly areas that have audio amplification systems and have fixed seating.

Coverage Requirements

Hearing aid compatible means the receiver has a neckloop output (or is a neckloop itself) that inductively couples to T-coil hearing aids — receivers with only headphone outputs do not count toward this requirement.

Signage: ADA requires the International Symbol of Access for Hearing Loss (ear with diagonal slash) posted at venues with ALS. Post at entrance and at the ALS receiver checkout location.

Which System is ADA Compliant?

All three primary types (loop, FM, IR) are ADA-compliant when installed to applicable performance standards. Hearing loops satisfy the "hearing aid compatible" requirement inherently (T-coil users need no receiver). FM and IR systems satisfy the requirement by providing neckloop receivers.

Signal Sourcing for ALS

The ALS input signal should be a clean, processed version of the PA signal — not a tap off the raw microphone. Best practice:

• Source from a post-EQ, post-compressor, pre-reverb auxiliary send on the mixing console or DSP
• Apply a presence boost (+2–4 dB, 1.5–4 kHz) to improve speech intelligibility for hearing-impaired users — reverb and room reflections are not present in the ALS feed, so presence boost compensates without sounding harsh
• Apply a gentle limiter to prevent clipping in the loop driver or transmitter on loud transients
• Do not include reverb or room effects in the ALS feed — hearing-impaired listeners benefit from the driest possible signal

In a QSC Q-SYS or Biamp Tesira design, the ALS output is typically a dedicated output on the DSP with its own processing block, fed in parallel with the main PA output.

Design and Installation Checklist

Hearing loop:

• Conduct metal survey before installation (rebar, steel decking affect field uniformity)
• Size loop driver to room dimensions and target IEC 60118-4 field strength
• Select perimeter vs. phased array based on adjacent room spillover sensitivity
• Commission with a calibrated field strength meter (Ampetronic FSM or equivalent)
• Measure field strength at multiple points across the listening area
• Test with an actual hearing aid in T-coil mode

FM/IR:

• Calculate receiver quantity per ADA seating chart
• Provide 25% neckloop-compatible receivers minimum
• Install charging cabinet near entrance or reception
• Label transmitter input and post signage
• Test receiver range at farthest seating position

Common Pitfalls

• Loop wire in the wrong plane — The magnetic field from a floor loop is strongest when the telecoil is held vertically. If loop wire is installed in the ceiling rather than floor or wall perimeter, field orientation may not couple efficiently with hearing aids. Install loop wire in the floor or at baseboard level wherever possible; ceiling-mounted loops require phased array design to compensate.
• Insufficient loop driver power for room size — A loop driver rated for 50 m² installed in a 200 m² room will not achieve the −22 dBV/m field strength across the coverage area. Always size the driver to the room geometry, not just the wire length. Use manufacturer sizing software (Ampetronic Designer, Univox LoopCalc).
• ALS fed from post-reverb signal — Sending the wet PA mix (including room reverb and echo effects) to the ALS system delivers a reverberant, difficult-to-understand signal to hearing-impaired users. Always source ALS from a dry, pre-effects signal path.
• Forgetting receiver checkout logistics — A technically perfect FM system becomes useless if there is no staffed checkout location, no signage directing users to receivers, and no charging station. Address receiver management in the project handoff; train building staff.
• No T-coil neckloops provided with FM/IR receivers — ADA requires 25% of FM/IR receivers to be hearing-aid compatible via neckloop. Simply ordering headphone-only receivers and assuming compliance is a common oversight that creates ADA liability for the building owner.