Assistive Listening Knowledge Base
  • Conference paper (consultant's case study)

Electromagnetic Interference in Hearing Aid T-Coil Applications

From https://assistivelisteningknowledgebase.org/evidence/mckinnon-1994/ · record checked 9 October 2026

  • McKinnon B (Mc² Systems Design Group)
  • Mc² Systems Design Group (paper first presented at the 1994 CAA Conference, Ottawa)

Independent (Mc² Systems Design Group, an acoustics and sound-system design consultancy that specifies assistive listening systems, retained by the building's architect to investigate complaints)

Summary

A consultant's investigation of the magnetic interference that made telecoil listening difficult in a new university building, with field readings, the sources traced and the limited remedies available.

Key findings

  • Investigated complaints from staff using telecoils in a newly built University of British Columbia building, using a telephone-type magnetic field meter (300 Hz to 3.3 kHz) carried at ear level.
  • Fluorescent ballasts were ruled out (one meter bar, about -31 dB re 1 A/m, only within 300 mm of a fitting); a television monitor and computer gave broadband noise up to the meter's pass level within 1.5 m, and listeners could reduce it by finding a head orientation that picked up less.
  • The worst hum came from ground currents of about 1 A, from other buildings, flowing on steam and water pipes under the floor; the author puts the signal-to-noise ratio for telephone listening at about 0 dB in most cases.
  • Grounding the pipes at the service entry cut the field along them by about 4 dB but raised it near the worst-affected office; the ideal fix, insulating breaks in the pipes, was no longer possible. Interference across a basement seminar room from the building's 600 A three-phase service was dealt with by using an FM listening system, as shielding the room was impractical.
  • Reports that a follow-up found interference in some locations in most buildings on the campus, and recommends keeping electrical service entries, major electrical rooms and transformers away from rooms where people use telecoils.

Limits

One building investigated in the early 1990s, with a meter designed for telephone handsets, so levels are not on the IEC 60118-4 scale; the signal-to-noise figure refers to telephone use rather than a loop, and the noise sources include CRT monitors of the period. The campus-wide finding is reported without data. Presented at a 1994 conference and republished on the consultancy's own site; its security certificate could not be verified when read.

Read the original

www.mcsquared.com/classic/caa94.htm

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Cited in

Cite this source

McKinnon B (Mc² Systems Design Group). Electromagnetic Interference in Hearing Aid T-Coil Applications. Mc² Systems Design Group (paper first presented at the 1994 CAA Conference, Ottawa). 1994. https://www.mcsquared.com/classic/caa94.htm (accessed 9 October 2026).

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