Hearing Loop & Assistive Listening System Monthly Performance Check

ContextMost loop amplifiers (Contacta, Ampetronic, Univox, Oval Window, and others) show a steady green power LED with no fault LED as the pass state. A flashing or solid fault LED must be investigated before proceeding — it typically signals a short circuit in the loop cable, an overtemperature shutdown, or an output-stage impedance mismatch. Never simply reset a fault without first identifying its cause. Recurring faults that are reset without investigation mask a developing hardware failure and, with some manufacturers, void the warranty if the service record shows repeated resets without a repair log.

ContextUsing the amplifier's built-in current metering or an external clamp meter on the loop cable, verify that the output current matches the specification documented at commissioning. IEC 60118-4 targets a field strength of 400 mA/m (0 dB re 400 mA/m at 1 kHz) across the designated area; your amplifier's rated current should reflect the specific loop geometry. A drop of more than 2 dB from the commissioning baseline indicates impedance drift caused by a deteriorating splice, a partial cable break, or a failing output stage. Log the value with today's date — the series of monthly readings is how you distinguish a gradual trend from a sudden fault.

ContextLoop amplifiers are designed to run warm but not hot. Ensure at least 50 mm of free airflow on all ventilated sides and dust the intake grilles with compressed air. Touch the chassis with an open palm — it should be noticeably warm but not so hot that you cannot hold your hand on it for three seconds. If the amplifier is rack-mounted, confirm the rack enclosure has active airflow; a sealed rack raises operating temperature significantly and accelerates component ageing. Thermal throttling typically begins silently, reducing output before triggering the overtemperature LED, meaning coverage degrades before you see a fault indication.

ContextIf the audio source has changed since the last calibration — a new mixing desk, a replaced PA head unit, or a different broadcast feed — the amplifier's input gain may now be mismatched with the program signal. An input set too low makes the loop inaudible to T-coil users during normal-level speech. An input set too high drives the automatic gain control into continuous clipping, turning loud speech into a series of distorted bursts. Use the amplifier's clip indicator LED (typically a red flash or solid red during clipping) and your reference signal at the typical program level to confirm the input sits in the amplifier's optimal range, usually –10 dBu to +4 dBu depending on the specific model.

ContextIEC 60118-4 specifies measurements at 1.2 metres above floor level — ear height for a seated adult — at a minimum of five points: the four quarters of the listening area and the centre. For larger spaces, extend to nine or more evenly distributed points. The pass criterion requires that at least 80% of measured positions fall within ±3 dB of 0 dBPa (equivalent to 400 mA/m at 1 kHz). Record every reading on your floor plan, not just the weakest or strongest — this creates a spatial coverage map that shows which parts of the room are degrading over time. A system where one rear quarter declines while the rest holds is a classic sign of a partial cable fault or phased-loop calibration drift.

ContextA loop can pass the 1 kHz reference measurement while rolling off sharply at high frequencies — precisely the frequencies (2–5 kHz) that carry the consonants s, f, sh, and th that are critical for speech intelligibility. IEC 60118-4 defines a passband of 100 Hz to 5 kHz with a tolerance of ±3 dB relative to the 1 kHz level, with an allowed additional roll-off of –6 dB at the band edges. A high-frequency rolloff beyond this tolerance almost always has one of two causes: excessive loop inductance in a large single-loop system (over approximately 200 m²) where inductance limits bandwidth, or a degraded amplifier output stage. Identifying which frequency is deficient at which test point guides the engineer toward the correct diagnosis.

ContextA properly designed hearing loop should attenuate by at least 20 dB within 1 metre outside the designated listening boundary. Walk the perimeter with your field strength meter. Excessive spillage into adjacent rooms creates two problems: first, a T-coil user in a neighbouring looped space (conference room, adjacent auditorium) will receive your audio as cross-talk; second, in sensitive environments such as courtrooms, interview rooms, or counselling centres, audio spillover beyond the intended zone has potential confidentiality and legal implications. If spillage exceeds –20 dB at the perimeter, the installation likely needs to be converted to a phased-array design, which uses cancelling currents to contain the field within the loop boundary.

ContextThe outer seating rows are where field strength degrades first in a single-loop installation, yet they are frequently skipped in favour of convenient centre-of-room measurements. If seats in those positions are assigned to the general public — including season ticket holders or fixed conference seating — those users must receive a compliant signal. Measure at the actual seat position at ear height. For phased-array systems, pay particular attention to the overlap zone between the two driver outputs: miscalibrated phase balance creates audible dead spots in the handover region that appear fine on a single-point measurement but are clearly perceptible to a seated listener.

ContextTechnical measurements tell you about signal levels; only a listening test tells you what the user actually experiences. Use a telecoil-equipped receiver or a behind-the-ear hearing aid set to T mode and listen to live speech — a colleague speaking normally into the primary microphone. Listen from multiple seat positions for: a persistent background drone at mains frequency, broadband hiss in quiet pauses, distortion or clipping on louder passages, and brief dropouts. A T-coil user typically notices problems within the first 30 seconds of a service or presentation that an engineer measuring at the amplifier rack never detects, because the measured signal at the amplifier output tells you nothing about interference picked up along the loop cable run through the building.

ContextIEC 60118-4 requires that the background magnetic noise floor in the listening area not exceed –32 dB(A) re 400 mA/m. Noise above this threshold begins to mask the hearing loop signal during quiet passages — exactly when intelligibility matters most. Measure background noise by powering off the loop amplifier and measuring the ambient field with your meter. Common culprits include phase-dimmer switches (which generate strong harmonic magnetic fields at multiples of 50 or 60 Hz), switch-mode power supplies inside audio equipment near the loop, fluorescent lighting ballasts, underfloor heating elements, and the electric motors in nearby HVAC equipment. Once the noise source is identified, mitigation options range from replacing offending dimmers with LED drivers to rerouting the loop cable away from high-interference zones.

ContextThe automatic gain control is designed to hold the loop output within the ±3 dB IEC tolerance window as the audio source varies from whispered conversation to amplified applause. Play a recording — or have a colleague speak at varying volumes — and watch your field strength meter. The reading should remain relatively stable rather than swinging widely. If the meter oscillates ±5 dB or more in response to normal program dynamics, the AGC's attack and release times may need adjustment through the amplifier's internal trim controls or software interface. Incorrect AGC timing is a common consequence of commissioning the amplifier with a fixed test tone and not validating it against real dynamic audio.

ContextMains hum is the most frequent reason a formally compliant hearing loop system receives complaints from actual users, and the most common cause of formal inspection failures. Set your meter to measure at the mains frequency (50 Hz in most of Europe, Asia, and Australia; 60 Hz in North America) and compare this reading to your program signal level at 1 kHz. Hum that sits only 10 dB below program level becomes perceptible to most users. The three most common entry points for mains hum are a ground loop in the audio cabling connecting the mixer to the loop amplifier (corrected by lifting the audio shield at one end), a mains transformer physically mounted near the loop cable run, and a failing bridge rectifier or smoothing capacitor in an ageing loop amplifier's power supply.

ContextCover the entire cable run, not just sections that are easy to reach. Look for: raised carpet protectors where foot traffic has flattened the cable inside, pinch points at door frames that open and close repeatedly against the cable, over-aggressive staple or tack fixings that have cut through the outer insulation, and any new furniture, fixtures, or partition walls installed over the cable since the previous check. A partially crushed cable increases resistance and can cause intermittent signal dropout that is difficult to reproduce during bench testing. Mark any suspect section on your floor plan with a measured distance from a fixed reference point so an engineer can locate it without lifting extensive areas of carpet.

ContextWith the amplifier disconnected, use a precision multimeter to measure the loop's DC resistance and compare it to the value recorded at commissioning. An increase of more than 10–15% above the baseline suggests a deteriorating solder joint, a corroded crimp connection, or the early stages of a partial conductor break. Then use an LCR meter to check inductance — a change of more than 5–10% from the commissioning baseline shifts the amplifier's frequency response and degrades high-frequency performance in ways that won't be visible on front-panel meters until the degradation is severe. These two measurements take under five minutes and detect cable ageing months before the fault becomes perceptible to users.

ContextOpen every accessible junction box and check for white crystalline deposits or terminal oxidation indicating moisture ingress, loose screw terminals (tighten with the appropriate driver — a loose terminal adds resistance and can arc at high output currents), and heat-damaged cable insulation pointing to a past overload condition. In underfloor systems, examine the points where cable enters and exits the floor through conduit — the cable sheath is under repeated abrasion stress at conduit edges, making these the statistically most likely failure points in a permanently installed system. Document each junction box location on your floor plan so future engineers do not need to search for them.

ContextFor FM assistive listening systems, examine the antenna cable along its full run for kinks, tight bends, and connector corrosion. A kinked coaxial cable can reduce effective radiated power by 50% or more while the transmitter's front panel shows normal operation. For infrared systems, visually inspect each emitter panel: check for cracked or yellowed polycarbonate covers (UV and heat degrade the plastic over time, reducing IR transmission), loose mounting brackets that allow the panel to angle away from the seating area, and contamination on the emitter face. Clean emitter surfaces with a soft, dry microfibre cloth. Solvent-based cleaners dissolve the UV-stabiliser coating on IR panels and accelerate yellowing — avoid them entirely.

ContextCreate or update an inventory list with serial numbers and test each unit against a real audio signal, not just a tone. For FM receivers: confirm clear reception on the designated frequency, check that squelch engages correctly in the absence of signal, and test reception from the seat most distant from the transmitter antenna. For IR receivers: confirm that each unit detects signal from every emitter zone in the room, as a single failed emitter creates a dead zone invisible to a bench test. For induction neckloops used in conjunction with a hearing loop system: connect to a headphone output and listen through a T-coil equipped hearing aid, specifically checking for an open-circuit winding (the most common neckloop failure mode, usually caused by a break near the strain-relief at the connector).

ContextCheck each unit for: cracked housing that exposes circuit boards to sweat or cleaning fluid, corroded battery contacts (clean with isopropyl alcohol applied on a cotton bud, allow to dry fully before reinserting batteries), missing or broken belt clips that make the device awkward to use during a performance, and worn or visibly soiled ear tip cushions. Foam eartips are the primary hygiene contact point and should be replaced whenever visibly contaminated or quarterly as a minimum — new foam eartips typically cost $0.15–$0.40 each in bulk. If your venue uses antimicrobial spray on hard components, confirm the specific product is approved by the receiver manufacturer; some disinfectants degrade the plastics and seals used around speaker grilles.

ContextFor disposable-battery receivers, replace all batteries on a fixed monthly schedule regardless of measured remaining charge — the cost per cell is negligible against the cost of a receiver failing mid-event for a user who has no fallback. For rechargeable units, run a full discharge-then-recharge cycle and measure the resulting capacity. Any unit that no longer reaches approximately 80% of its rated capacity after a full charge should be flagged for battery replacement or retirement from active service and moved to a reserve pool for short events only. Document which units were flagged and when — a pattern of units from a particular batch or purchase year often indicates a broader inventory refresh is approaching.

ContextHearing assistive devices come into contact with the external ear canal — a mucous membrane area. Beyond routine hygiene, there are genuine infection control obligations, particularly in healthcare settings, houses of worship serving vulnerable populations, and any venue where children are frequent users. The monthly check is the appropriate time for deep-cleaning: disassemble ear-worn components to the extent possible, clean all non-porous surfaces with an appropriate disinfectant wipe, and replace any component that cannot be fully sanitised (foam inserts that have absorbed moisture or wax, for example). Record the sanitisation method and date in the monthly log — this documentation demonstrates duty of care and is occasionally requested during accessibility or public health audits.

ContextWalk through each input source in sequence: lectern microphone, handheld, lavalier or lapel clip mic, and any boundary or ceiling mics used for open discussion. For each: confirm it is correctly routed to the loop amplifier or ALS transmitter input, verify that phantom power is active if required (condenser microphones need 48V phantom; omitting it causes complete silence), and perform a listening test through the ALS output specifically — not just the main PA speakers. The hearing loop path typically carries no graphic equalisation applied to the main PA, meaning a microphone that sounds acceptable through the speakers can still produce harsh sibilance or poor intelligibility through the T-coil path.

ContextThis routing check is one of the most frequently overlooked yet highest-impact verification steps. The loop amplifier input must be derived from a dedicated auxiliary send or fixed zone output from the mixing console, at a level that does not change when the main PA output fader is adjusted. If the loop is wired from the main LR output, a sound engineer turning down the room volume for a quiet speaker also mutes the loop — but T-coil users have switched off their hearing aid's directional microphone and have no alternative audio source. Confirm the routing by reducing the main output fader while monitoring the loop signal; it should hold steady.

ContextIn many venues, informal meetings, small group discussions, and one-to-one conversations happen with the main PA system powered down. If the loop amplifier is wired through the PA system's signal chain — via an insert point or speaker-level tap — it too will be silent when the PA is off. The correct installation routes the loop amplifier input from the mixing console's auxiliary send, which is active regardless of whether the main power amplifiers are running. Test this explicitly: power off the main PA amplifiers, speak into the primary microphone at normal conversational level, and confirm a measurable signal on your T-coil receiver. A failed test here represents a significant accessibility gap during meetings and smaller events.

ContextThe international symbol for hearing loop availability — an ear with a diagonal bar and the letter T — must be displayed prominently at every public entrance to the looped zone. The mere presence of a working loop is insufficient under the UK Equality Act 2010, the Americans with Disabilities Act, and equivalent legislation in Australia, Canada, and most of the EU; users must be made aware of the system in order to benefit from it. Check that signage has not been obscured by seasonal displays, new notice boards, or furniture rearrangements since last month. Signage must specify the technology available — loop (set aid to T), FM (receivers at reception), or IR — so a visitor with a hearing aid, cochlear implant, or no device knows immediately what they should do.

ContextA performance log that records only 'checked and OK' has no diagnostic or legal value. Record: the date and time of testing, the tester's full name and qualification, field strength readings at every test grid point (cross-referenced to the floor plan), background noise measurement, DC resistance and inductance values, battery replacement actions, receiver inventory count and any units removed from service, and every fault identified with its planned corrective action and target completion date. This record is the evidence of due diligence in the event of a disability discrimination complaint, the dataset that enables trending analysis, and in many UK public buildings and courtrooms, a legally required document with a defined minimum retention period.

ContextA fault that is documented but has no assigned owner and no target date is, in practice, unscheduled. For each issue from this check, write the name of the person responsible for resolving it and the date by which it must be resolved or escalated. Classify faults by urgency: a failed receiver can be retired from circulation on the day; a partial coverage failure affecting 15–20% of seating is urgent and should be resolved within seven days; a complete system outage is an emergency requiring either emergency repair or deployment of a temporary FM or IR substitute system (rental typically costs $50–$120 per day for a basic setup) while repair is arranged. In some jurisdictions, operating a public venue with a non-functional assistive listening system without providing a compliant substitute is considered an access barrier under disability legislation.

ContextThe technical performance of your system is irrelevant if the staff member at the front desk hands a T-coil hearing aid user an FM receiver without explaining that they need to switch their device to FM mode — or hands them a neckloop when no hearing loop is running. Each month, confirm that every staff member who interacts with visitors requesting hearing assistance knows: which assistive listening technologies are installed in which rooms, the physical location of all receiver storage and charging points, how to explain usage in accessible language to someone unfamiliar with their own device, and the name and contact number of the person to call if a system fault is reported during a live event. Staff knowledge gaps are consistently rated by hard-of-hearing visitors as a more significant barrier than technical system failures.