Assistive listening: what the law asks and what the room needs

By Joey Calkins · Section House

Assistive listening is usually treated as a compliance item, which is why so many installations satisfy an inspector and fail an audience. The mechanism is worth understanding first, because it explains why the common failures are failures.

It is a ratio problem before it is a volume problem

Hearing loss is not simply reduced sensitivity. A listener with hearing loss typically needs a substantially better ratio of wanted signal to unwanted noise than someone without it, in order to achieve the same understanding.

That is why turning up a hearing aid does not solve the problem in a theatre: the aid amplifies the room along with the performance, and the ratio is unchanged. An assistive listening system works by delivering a feed that never went through the room at all.

Which is why the source of the feed decides whether the system works. A programme feed carries the words. A microphone hung in the auditorium carries the words plus the room, reproducing the exact problem the system exists to remove, and it is a surprisingly common installation.

The four ways of getting it to the listener

An induction loop drives a wire around the seating area and is picked up directly by the telecoil in a hearing aid. Nothing is collected, worn or returned, which removes the practical and social barriers that keep receivers in a drawer. Performance is defined by an international standard, and a loop that has not been commissioned against it is an assumption rather than a system.

Radio systems broadcast to receivers handed out at the door, which work with or without hearing aids and require staff, batteries and hygiene procedures. Infrared systems do the same using light, so the signal does not pass through walls, which suits adjacent auditoria and demands line of sight to the listener.

Newer broadcast audio over short range radio, received directly by compatible hearing devices and phones, promises the loop's convenience without the wire. It depends on what the audience already owns, which changes slowly.

What the law asks, and where

In the United States, assembly areas are required to provide assistive listening systems, with the number of receivers scaled to seating capacity and a proportion of them compatible with hearing aids, under the accessibility standards issued for the Americans with Disabilities Act. In the United Kingdom the duty arises differently, as a requirement to make reasonable adjustments under equality legislation, and other countries differ again.

The requirement is a floor and not a specification of adequacy. It is possible to meet it exactly and still have a system nobody can use.

Where compliant installations fail

Receivers exist and their batteries are flat. Front of house staff do not know where they are, or have never been shown how to pair one. There is no sign at the box office, so nobody knows to ask. The loop covers only part of the seating, so a patron who needs it has no choice of where to sit or who to sit with. The loop was installed and never verified, and a decade of building work has since put metal through the field.

Every one of these is an operational failure rather than a technical one, and every one of them is cheap to fix compared with the installation. Checking that a system works, from the seats, with the show running, is the single measure that catches all of them.

Latency matters here in a way it does not elsewhere

Systems that carry audio over a general purpose network or through a phone application accumulate the delays described in the article on latency, and in this application the delay is not a matter of convenience. A listener who can see the stage receives the words after the lips have moved, which is the one direction of error people find hardest to tolerate.

Loop and infrared systems are effectively immediate. Any system built on packet delivery and a consumer device needs its delay measured rather than assumed, and measured on the devices the audience will actually be holding.

Choice of seat is part of the requirement

The point of accessible provision is equivalence, and a listener confined to the back three rows because that is where the coverage reaches has not been given the same evening as everyone else. Coverage that spans the range of price bands and locations, and the ability to sit with the person you arrived with, are part of what the provision is for.

What we cannot verify

Legal requirements vary by country and are summarised here in general terms; the applicable rule is the one for the building, and this is not legal advice. Coverage, field strength and battery figures published for particular products come from their manufacturers and describe laboratory or ideal installations. Estimates of how many hearing aids include a telecoil vary by country, by market and by year, and we do not reproduce one. The reliable test is a measurement in the room against the published standard, repeated after building work, plus somebody actually sitting in the seats and listening.