Summary
A measuring-instrument maker's step-by-step method for commissioning and verifying a hearing loop against IEC 60118-4.
Key findings
- Gives the requirements, all referred to 400 mA/m: average field strength -12 dB ±3 dB (100 mA/m), maximum field strength 0 dB (400 mA/m), frequency response from 100 to 5,000 Hz within ±3 dB, and background noise of -22 dB A-weighted, all for the vertical component of the field.
- Defines the covered area as the area where all the requirements are met, measured at randomly distributed points at 1.2 m in seating areas and 1.7 m in standing areas, with exceptions where listeners' heads are not upright, as in places of worship and hospitals.
- Measures background noise with the loop off before the loop is planned: ideally at least 22 dB, and best more than 47 dB, below the reference level, repeated with floor heating and lighting on and off and with dimmers at several settings; noise with a marked tonal quality should be below -47 dB. With the loop on and no input, noise should rise by no more than 3 dB.
- Measures the maximum field strength with a 1 kHz sine at representative positions (0 dB, varying no more than ±3 dB) and the frequency response with band-limited pink noise at several positions.
- Says the standard sets no limit for crosstalk between neighbouring loops, and that -40 dB at 1 kHz has been found acceptable, or -48 dB in critical cases such as cinemas.
- Ends with a system check by a small number of hearing aid users, with talkers and other sources in their normal positions, and asks for a plan beside the loop sign marking where all requirements are met.
- Page 3 specifies an XL2 analyser, signal generator and calibrated loop receiver with flat response, such as the CMR3; its specified interface is 0 dBu RMS for 400 mA/m. Pages 4-5 require the intended listening height and vertical magnetic-field component.
Limits
A maker's note written around its own instruments, with no data on how often loops pass. Its clause numbers do not match the contents of the 2014 edition, and its -22 dB noise figure differs from the -32 dB other guides give; none of its figures has been checked here against the paywalled standard.
Read the original
www.nti-audio.com/wp-content/uploads/NTi-Audio-AppNote-AFILS-with-XL2.pdf
Cited in
- What commissioning tests and pass limits will the standards require?Open
- How is an installed hearing loop checked against IEC 60118-4, and how often does it pass?Partly answered
- What works in places of worship, and what do the rules ask of them?Partly answered
- Do neckloops give telecoil users good sound from FM, infrared, Wi-Fi and Auracast receivers?Not reliable yet
- What works in theatres and cinemas, and what do the rules ask of them?Partly answered
- Which meters and apps measure loops and Auracast, and how accurate are they?Partly answered
Cite this source
Norman DI (for NTi Audio). Application Note: Induction Loop Systems with XL2 Analyzer (AFILS). NTi Audio. 12 January 2021. https://www.nti-audio.com/wp-content/uploads/NTi-Audio-AppNote-AFILS-with-XL2.pdf (accessed 13 October 2026).
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