Summary
A cinema-equipment engineer's notes, posted in reply to a question about neckloops, on the magnetic field that four neckloops gave when driven by a cinema infrared headset receiver, and on one hearing aid user's trial.
Key findings
- Gives the target as a field averaging 100 mA/m over 60 seconds, with peaks about 12 dB higher (400 mA/m).
- The 26 January 2019 reply at 11:32 AM describes measuring IRH-230 no-carrier noise with a FoSmeter+ standing vertically at the centre of each neckloop lying flat on a table. The unmarked loop exceeded +16 dB relative to 100 mA/m at full volume. After reducing the volume until that loop read 0 dB, the Comtek NTC-102, NoizFree and Sennheiser EZT1011 each read +3 dB relative to it. The author inferred full-volume fields greater than +19 dB for those three loops; these are lower bounds from the reduced-drive comparison, not direct numerical full-volume readings.
- In the same reply's impedance method and table, the loops were driven at 400 Hz through a 12-ohm series resistor. Voltage measurements gave approximate impedances of 34 ohms for the unmarked loop, 36 ohms for Comtek NTC-102, 27 ohms for NoizFree and 33 ohms for Sennheiser EZT1011.
- Measured 6 inches (about 15 cm) above the unmarked loop, the field was 3 dB above 100 mA/m with full-volume noise; with programme audio through the cinema system it reached 12 dB above 100 mA/m, measured 6 inches outside the loop.
- The note ending 13 August 2012 specifies that the unmarked loop lay flat on a table for the six-inches-above measurement, using IRH-230 full-volume no-carrier noise. The six-inches-outside reading used programme audio through the IRC-28C infrared panel. The centre table has no exact measurement date, and no repeated measurement count is stated.
- In a trial with one hearing aid user whose aid switched to its telecoil automatically, none of the neckloops switched it, because a neckloop produces no static magnetic field; once the telecoil was on, the user heard the audio but said it sounded better through acoustic coupling.
- Reports a local audiologist's view that most of their clients use the hearing aid microphone at the cinema, and that a magnetic induction receiver held 6 inches above a neckloop gave good audio quality at 100 to 400 mA/m.
Limits
Informal notes from tests run in 2012 and posted in 2019, by an engineer for the maker of the receiver tested. Meter positions (on a table, at the centre of the loop or 6 inches from it) do not reproduce a telecoil at the ear, no frequency response was measured, and the user trial involved one person and one hearing aid.
Read the original
www.film-tech.com/ubb/f5/t003164.html
Cited in
- 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
Cite this source
Hallikainen H. HI/VI induction neckloop recommendations? (forum reply with test notes on neckloops). Film-Tech Forum (cinema industry forum, archive). 26 January 2019. https://www.film-tech.com/ubb/f5/t003164.html (accessed 13 October 2026).
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