Induction Loop Calculator

This calculator will help system designers and installers determine which induction loop amplifier and cable they should use to create a BS7594 (2011) compliant AFILS installation.

It is fully compatible with any Mac or PC computer running Microsoft Excel and is designed to work in five easy steps:

  • Enter the room length and width on the spreadsheet
  • Select/alter the number of turns in your loop (extra turns can provide increased field strength in smaller rooms and rooms with excessive ferrous metal content)
  • Select the reference level (normally -3dB but this can be reduced to -6dB — see BS7594:2011 Section 3, Table 1 Field variation in the useful magnetic field volume)
  • Set the height of measurement in metres from the plane of loop. This would be 0 if the listener is directly in line with the loop cable, approx. 1.8 for loops laid on the floor or 1.5 for ceiling mounted loops (adjust these measurements based on the actual ceiling height and typical listening height of the user)
  • Consult the wire dependent loop choice box on the spreadsheet to see exactly which amplifier and loop cable best suits your application

Important Notes

  • The calculator assumes a perimeter loop is being installed in a room with very little metal content (i.e. a square or rectangular loop that is being run around the edge of the covered area).
  • Although the amplifier recommended by the calculator WILL generate the required magnetic field it is the responsibility of the designer/installer to ensure the amplifier has the required inputs and features pertinent to the job in hand.
  • It should be noted that steel reinforced flooring and/or roofing can considerably attenuate the field strength of the completed system — if in doubt, refer to our Induction Loop section on the website.
  • Prior to installation we always recommend a trial loop is run around the covered area and that the system is tested to ensure correct operation using an FPROK1 test kit which includes a handheld magnetic field strength meter and a handheld signal generator (complete with test tones and headphones).

Further Information

For further information on the full range of Induction Loop Equipment, please contact our Technical Service Team on 0845 884 7000.