Vertikale Feldausbreitung von induktiven Höranlagen (Vertical field spread of hearing loops)

Summary

A German acoustician's analysis of how far a hearing loop's field reaches into rooms above and below, how much different floor constructions block it, and how to size loop segments for stacked lecture halls.

Key findings

• Shows that a perimeter loop's field falls to the level of magnetic background noise (about -47 dB re 0.4 A/m) only at about three loop widths away, horizontally and vertically alike; an 8 x 5 m seminar room loop would be receivable up to 15 m away, and with 3 m storeys the next looped room above could only be five floors up.
• Finds that phased arrays narrow the spread but often not enough vertically: because the listening height is large compared with the narrow segments and so needs a higher loop current, spill can reach up to five segment widths; with 2 m segments, the next loop could be three floors up.
• Says passive magnetic shielding cannot be complete; conductive aluminium sheet or mesh reduces the field more than iron reinforcement, and the simulation programs of the three loop makers it names (Ampetronic, Bo Edin, Humantechnik) do not model shielding by floors.
• From first measurements in real buildings, which it says vary widely, gives provisional extra attenuation through the floor of 0 dB for timber joist floors, 6 dB for reinforced clay-block floors and 12 dB for reinforced concrete floors.
• Works an example of three stacked lecture halls with metal seat frames and concrete floors: allowing 12 dB through the floor, array segments could be 1.4 m wide (one or two seat rows), instead of 0.8 m without it; for two stacked rooms, laying the lower loop on the floor and the upper one in the ceiling increases separation.

Limits

A three-page conference paper: the floor attenuation figures are described as provisional, from first measurements in an unstated number of buildings, and the field plots come partly from a maker's software (credited to Ampetronic). It addresses spill between rooms, not coverage within them. The conference ran on 16-19 March 2015.

Read the original

pub.dega-akustik.de/DAGA_2015/data/articles/000428.pdf

Link checked 9 October 2026. We link to the original and do not host copies.

Cited in

• Where do hearing loops fall short: metal, spill, noise and upkeep?Partly answered

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