Audio Frequency Induction Loop Systems (AFILS)

AFILS Code of Practice
The AFILS Survey
Appointment of Responsible Person
System Manual, Training and Technical Support
Trails
Limitations of Hearing Loop Systems
General Notes

AFILS CODE OF PRACTICE: BS 7594 (1993)

The AFILS Code of Practice is an extensive technical document (over 80 pages) covering all aspects of the design, operation and customer service, relating to AFILS in public places. The Code of Practice is also followed in so far as it may be applied to our range of portable loop systems.

Ferrosound do not accept commissions that require us to depart from the AFILS Code of Practice, or to install inferior quality equipment, or to lower our engineering standards in any way, in order to cut costs. However, we will use selected low cost equipment of proven reliability and quality, where customers are on a limited budget.

Departures from the Code of Practice may sometimes be necessary for good reasons anticipated within the Code, which we will discuss and agree with our Clients.


THE AFILS SURVEY

Where a hearing loop system is to be used, it is important to make a thorough survey.The purpose of the survey is twofold. Our engineer will consult with the customer, to gain a full picture of how the loop will be used, and then assess the suitability of the venue for the operation of an AFILS. As such, it is an essential prerequisite for good design, especially for a first-time loop installation in any venue.

To this end, the survey includes the following essential elements:

  1. Measure loop area dimensions in order to calculate theoretical loop current.

  2. Measure electromagnetic interference (EMI) within loop area from all possible sources, especially lighting circuits, to assess viability of AFILS.

    It is not uncommon for EMI to be so bad, often due to mains lighting loops, that a loop system simply cannot be used. Sometimes it may be possible to re-route electrical wiring to remove the mains cable loop. Failing this, we can supply wireless infrared or radio systems, for which each user will require a receiver unit and phones. This is far from ideal for someone who needs to use a hearing aid.

  3. Assess metal loss effects: install test loop, and complete basic loss and frequency response tests. Determine metal loss correction. It is often necessary to specify a loop amplifier with a higher current rating than the theoretical design requires. This will compensate for loses due to the metal content of the building, such as steel frames, suspended ceiling grids and steel reinforced concrete floors.

  4. Evaluate other factors that may have a bearing on the design of an AFILS or, in the worst case, preclude its use altogether. Such factors include: unusual loop shape, ambient noise from traffic or air conditioning, a requirement to loop more than one room, and the close proximity of loop systems in neighbouring venues. Please see general note 7 below.

 

APPOINTMENT OF RESPONSIBLE PERSON

The Code of Practice requires an organisation to appoint someone to be responsible for the care and correct operation of their audio frequency induction loop systems (AFILS). This person need not be technical but should have a good working knowledge of how to operate (where applicable) and monitor the system for correct operation.


SYSTEM MANUAL, TRAINING AND TECHNICAL SUPPORT

The Code of Practice also requires that the AFILS supplier provides a service schedule, operating instructions and full training for the responsible person and any other people who may be involved with the use of the system. Ferrosound provide this training and long-term technical support as part of their service to all their AFILS customers.


TRIALS

On completion of installation, all Ferrosound systems are subject to proving trials, usually for a period of 30 days. During this period our engineer will provide the training session, and attend two meetings for the purpose of evaluating the system. The first is informal, when we hope that at least four people with hearing aids can be present, as required by the AFILS Code of Practice. The second may be either informal or a formal 'public' meeting, attended by as many people as possible.



LIMITATIONS OF HEARING LOOP SYSTEMS

It is important to note that most but not all hearing aid users will benefit from the hearing loop. Please note the following limitations:

  • People who cannot hear clearly, even with a hearing aid, may not benefit from the use of the AFILS.

  • Profoundly deaf people may derive only limited benefit from a hearing loop, though this will depend on the nature of their hearing loss and the extent to which their hearing aid effectively corrects this loss.

  • Not all hearing aids are fitted with the "T" (telecoil) option. This applies mainly to canal and other in-the-ear aids. Although most NHS hearing aids are fitted with the "T" option, many commercial aids are not.

  • Some smaller hearing aids have very poor "T" sensitivity. It is not good practice to increase the loop level of an AFILS in a public place, to meet a particular person's need, since this is set to the level specified by the BS EN 60118-4.

  • AFILS in close proximity may not be used simultaneously. Please see general note 7 below.

 

GENERAL NOTES

  1. Loop Area. In accordance with the AFILS Code of Practice, we recommend that the full seating area of your church, hall, conference room or other venue, be covered by the hearing loop system. This ensures that all people with hearing aids have full and normal access.

  2. T-Logo. It is also good practice to display the T-Logo to let people know that a hearing loop system is in operation. This is required to show the name and contact number of your supplier and the person responsible for your loop system.

  3. Microphones. Ferrosound use condenser microphones, where possible, especially when they will be used within the loop area. This type of microphone is more sensitive and will not interact with the loop. (Please see note 4 below).

  4. Electromagnetic feedback. Dynamic microphones and some other equipment, including tape recorders and electric guitars, are prone to interference from the loop signal, which may give rise to electromagnetic feedback - a high pitched whistle. For this reason care must be taken to correctly connect and test any external audio equipment to be used with the System. Ferrosound will be pleased to advise on this matter, during the design consultation & trials period.

  5. Monitoring. Full performance monitoring is required by the AFILS Code of Practice, including headphone monitoring of actual loop signal. Full details will be supplied with the System Handbook.

  6. Induction receivers may also be used for monitoring. They may also be used with headphones by hard of hearing people who do not use a hearing aid.

  7. Multiple loops. Conventional, perimeter loop systems transmit well beyond the area of the loop albeit at a lower level. Therefore, multiple systems loops in close proximity may not be used simultaneously. This limitation may be overcome by special "low-spill" system designs for which full and detailed drawings will be required showing full dimensions of the building and details of the metal content.

  8. Confidentiallity. Low-spill systems may also be used where confidentiality is required. Although over spill can be limited to a very low level, if possible, 40 dBs below the normal signal level, more complex designs are required for secure systems where absolute secrecy is vital.

  9. Electromagnetic interference (EMI). This may be a problem for people using hearing aids. EMI may be heard as a loud buzz in the hearing aid switched to "T", even when the loop system is switched off.


    EMI may take many forms, most commonly a hum from installed mains cables. This is often due to mains loops created by switched lighting circuits. It is therefore most important for electricians to avoid creating mains loops, since in the worst case, the radiated interference will make it impossible to use a loop system. PC monitors (except TFT flat screen type) and other electrical apparatus may also seriously interfere with the hearing aid on 'T'.
    Ferrosound test and record the levels of EMI in all loop locations, as part of the essential Survey and prior to installation.

 

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