Audio Visual Design Guidelines

Hearing augmentation

91 views November 19, 2019 aetm 0

A significant proportion of the population is affected by some form of hearing impairment, and hearing augmentation systems are deployed to provide equitable access. Whilst the term itself is broad and includes closed captioning and signing, in this context we consider the provision of assistive listening systems only.

As the basic requirement is always to provide equitable access, the goal must be to provide clear, measurable amenity to the affected group. Legislation and the relevant National building codes define a minimum provision and institutions may choose to offer a higher level of coverage. Building code requirements differ between Australia and New Zealand.

Three types of systems generally satisfy the Code requirement in most countries:

  • Audio Frequency Induction Loop Systems (AFILS)
    • Current is passed through a metal loop in the floor (typical) or ceiling and generates a magnetic field. This is converted back into electrical energy via a telecoil in the hearing aid.
    • Great majority of adult hearing aids in Australia and New Zealand include a telecoil.
      • Hearing aids for children and youth must be replaced more frequently and telecoils are often omitted
      • Hearing aids in other countries may not be telecoil-equipped in the same proportion as Australia and New Zealand
    • AFILS-equipped rooms cannot be considered secure/private as the magnetic field can propagate far outside their boundaries. 
    • Systems in adjacent rooms may interfere with each other.
  • Infra-Red (IR) systems
    • Audio is modulated onto an infra-red (light) carrier and demodulated by a personal receiver. Headphones or a neck loop (to drive a telecoil-equipped hearing aid) are used.
    • IR systems are easier to maintain and can provide confidentiality as the light is blocked by solid walls and heavy curtains. Conversely, IR systems may be adversely affected by sunlight. 
    • Room surfaces may reflect some IR energy and provide a small coverage improvement which assists in meeting code.
    • IR systems require near line-of-sight to operate, meaning the receiver is typically visible on or near the listener..
  • Radio Frequency (RF) Systems
    • Audio is modulated onto an RF carrier in the ‘low interference potential’ spectrum and received by a personal receiver. Headphones or a neck loop (interface to a telecoil-equipped hearing aid) are used.
      • Digital RF modulation techniques are now common and may allow higher density of systems in learning environments
      • WiFi streaming systems may satisfy code where performance is demonstrated to comply and will increasingly allow users to use an app on their personal device
        Australia: AS1428.5 clause 4.5.1: Specialised systems using advanced or other communication technologies such as digital communication systems…
        New Zealand: There is no clear ‘deemed to satisfy’ provision for a WiFi-based RF system. Technical Manager should pursue this with the project Access Consultant and Building Surveyor for consideration as an alternative solution. 

Sound Field Amplification Systems (Soundfield) are encountered in some environments, and AS1428.5 acknowledges they may provide some benefit for mildly impaired listeners. The standard does not, however allow Soundfield systems to be used as compliant Assistive Listening Systems..

Signage, generally using the International Symbol for Deafness, must be installed as part of any hearing augmentation system, and must be designed and installed according to local building codes.


Institution-specific standards

Many institutions have developed internal operational policies which govern the deployment and maintenance of hearing augmentation systems to best address the requirements of their own populations and facilities. They are intended to be applied uniformly throughout the institution, so students are well supported, and are often developed by – or in close cooperation with – the institution’s Accessibility or Disability Support teams. 

The implementation and performance of any such system must always meet or exceed Australian or New Zealand code requirements, so technical managers should coordinate closely with these teams to ensure these requirements are met.

Technical Managers must take care with any new building or substantial refurbishment which will require certification against the prevailing Building Code or standards by an independent building surveyor. The operational policy must be reviewed for suitability by the project’s Access Consultant and approved by the Building Certifier/Surveyor before a Certificate of Occupancy will be issued. Where an institution’s operational policy differs from the code it must be assessed as an ‘alternative solution’.


Country-specific requirements: Australia

The requirement for assistive listening systems is defined in National Construction Code (NCC) clause D3.7:

Minimum compliant coverage requirement is 80% floor area (AFILS) or 95% (IR, RF).

Whilst the NCC is silent as to the underlying standard, AS1428.5 is the only Australian standard dealing specifically with the design, commissioning and certification of hearing augmentation systems. This standard expands on the minimum performance requirements for AFILS described in AS60118-4 and adds performance criteria for IR and RF systems. Prescriptive testing and certification requirements are also defined for each system.

Signage is mandated in the NCC at D3.6 and defined in AS1428.1. Designers should exercise caution as international signage and that provided by manufacturers often does not satisfy Australian standards:

  • Only a single colour blue is compliant
  • The International Symbol for Deafness is trademarked locally, and must be used as drawn
  • The location of signs and form of words must be compliant
  • Braille may be required on some signs

The Deafness Forum (trademark owner) publishes a signage guide which may aid designers to develop compliant signage. 

Note: The NCC defines different criteria (clause H2.13) for Class 9b and 10 public transport buildings only. Designers should be careful if designing systems for public transport interchanges on campus.


Country-specific requirements: New Zealand

The New Zealand Building Code is less prescriptive than Australia’s, however several provisions apply to communal non-residential and commercial buildings:

The underlying standard (NZS4121) provides guidance to those responsible for design to enable people with disabilities to use the building with the same convenience as those who do not have disabilities.  Appendix H provides the framework for ‘listening systems’; including:

  • Usable by people with and without hearing aids (such aids with or without telecoils)
  • Suitable for the intended use
  • Not to cause or be subject to interference 
  • Should be infra-red where privacy is required

Recognised types:

  • AFILS (H3.1)
    • Field strength to AS1088.4 (now AS60118.4)
    • No defined minimum coverage requirement
    • Noted as inappropriate where crosstalk/spill will occur between adjacent spaces
  • Infra-Red (H3.2)
    • No additional performance/coverage criteria are defined
  • Radio Frequency (H3.3) 
    • Permitted on ITU-allocated VHF frequencies 
    • Permitted, but no performance/coverage criteria are defined
  • Induction field radio system (H3.4) 
    • Permitted on 3175kHz allocated by ITU
    • No additional performance/coverage criteria are defined
    • Appears intended primarily for ‘tour guide’ systems

The signage requirement is defined in E3 and provides only broad guidance:

  • The International Symbol for Deafness must be used and rendered proportionally as shown in the standard.
  • The symbol shall be white over a “safety blue” (BS5252 colour 18E53) – though other colours may be used to fit the décor sufficient to adequate contrast.

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