© B A T O D M a g a z i n e • M a y 2 0 1 0 • 27
C o m m u n i c a t i n g c l e a r l y t o g e t h e r
T
he workshop began by going back to first principles
and the need to overcome obstacles to everyday
listening. Deaf children find it difficult to listen
in class due to background noise, distance and
reverberation. Even with the latest audiological
technology, these problems cannot be solved by a
hearing aid alone. We know that background noise
affects the understanding of speech, and we know that
the speech signal drops by 6dB with every doubling in
distance. We also know there needs to be a good
signal-to-noise ratio. For adults to make sense of a
speaker in noise they need to have the speaker’s voice
(signal) 6dB louder than the background noise (noise).
This is a signal-to-noise (S/N) ratio of +6dB. However,
a child needs +16db S/N ratio and a deaf child needs
a +20–30dB S/N ratio. An ‘uncontaminated’ speech
signal is particularly important for young children.
So how does the FM system help? It decreases the
distance between speaker and listener delivering
the sound direct to the ear. The sound is delivered
uncontaminated by noise and reverberation. There are
many different types of FM system but each consists of
a transmitter which includes a microphone and receiver
together with direct audio input (DAI) shoes for the
hearing aids. Neck loops are still available for some
systems but they are not used routinely in schools.
When to fit an FM system
In the Quality standards for the use of personal FM
systems, QS1 states that ‘every child should be
considered as a potential candidate for provision with
a personal FM system as part of their amplification
package, in line with a written policy on candidacy’.
Some services have a policy in place focusing on
audiological criteria, but a child may be considered as
suitable for other reasons such as asymmetrical hearing
loss, additional difficulties or functioning in noise, or the
school’s acoustic conditions. Flexibility must be allowed
for, and a flowchart to help the decision-making process
is detailed in the FM QS Good Practice Guide.
For children with cochlear implants there are some
important general considerations:
• The decision to trial the use of an FM system must be
one that has been agreed by all professionals and
include the support and agreement by the child/family
and local professionals.
• The child should have a stable ‘map’ and wherever
possible be able to report on sound quality.
• Any mapping changes to the child’s speech processor
need to be made before the FM fitting, by an implant
centre audiologist, for example a specific programme
may be needed with a correct mixing ratio.
• QS4 recommends that initial fitting and setting
up of an FM system must be carried out by an
appropriately trained CI professional. In this way
everyone can be assured that the FM receiver
volume is set optimally.
It is vital for both the fitting of a hearing aid and a
cochlear implant with an FM system that correct
procedures and policy are followed and that the whole
system is evaluated regularly.
Monitoring and checking considerations
The equipment must be kept in good working order to
maximise the benefits for users. There should be daily
checks of the equipment, both hearing instrument,
shoes and components of the FM system. The FM QS
Good Practice Guide gives suggestions for monitoring
and checking FM systems. For example:
• Are the batteries working in the hearing instrument?
• Has the correct shoe been used? Some slide on,
some push on, some are fixed to the battery drawer.
• Are there dirty contacts on the hearing instrument –
have the cover plates been removed?
• Have the hearing instruments been FM enabled?
Some do this automatically when the shoe is
attached; others need to be enabled through the
programming software at the hospital.
• Is the child wearing the equipment correctly?
• Is the transmitter microphone working?
• Are the transmitter and receiver on the same
frequency?
• Is the transmitter microphone muted?
Setting up an FM system with hearing aids is not
difficult and most ToDs have been trained in this
process. Some systems need verification in a test
box as they are said to give the FM advantage
automatically. Setting up an FM system with a cochlear
implant is a more technical procedure and the child’s
implant centre should be consulted as often staff there
will set up the equipment and provide troubleshooting
training. Basic fault-finding requires the process of
elimination – be methodical and start with the most
likely causes. Finally, know who to call and don’t be
afraid to ask!
Liz Reed-Beadle is an educational audiologist in
Norfolk, Liz Wood is an educational audiologist with
the UK FM Working Group and Richard Vaughan is
Customer Support Manager at Connevans.
FM – when and how!
Liz Reed-Beadle, Liz Wood and Richard Vaughan led a workshop introducing practitioners to the
rationale for using FM and the basic equipment needed to make the listening conditions easier
for a child with a hearing loss
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