Balancing FM Systems.
BATOD March 2013
Colin Peake
Educational Audiologist
South of England Cochlear Implant Centre
Two Questions ……
• Why Use Personal FM Systems?
• What is the purpose of balancing FM Systems?
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Why Use Personal FM Systems
FM AUDITORY TRAINING
SYSTEMS. Characteristics,
Selection, and Use.
Ross, 1991
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Why Use Personal FM Systems?
The ability to discriminate individual phonemes, to hear
words/sound differences, is defined as intelligibility, as
distinguished from audibility, which is the ability to detect the
presence of speech. If because of hearing loss, poor classroom
acoustics, and/or poor attending skills, a child cannot
discriminate wave from raise, for example, he or she will not
learn appropriate semantic distinctions unless deliberate
intervention occurs.
•
Carol Flexer in, FM AUDITORY TRAINING SYSTEMS. Characteristics, Selection, and
Use. Ross, 1991,
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Why Use Personal FM Systems?
“The purpose of using technology is to promote the
child’s right to hear and to benefit from
educational instruction.”
Carol Flexer in, FM AUDITORY TRAINING SYSTEMS. Characteristics, Selection, and Use. Ross, 1991,
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Kimberly
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What is the purpose of balancing FM
Systems?
• To ensure that the level and quality of sound a child
hears through the FM Systems microphone matches what
he hears through the hearing instrument’s microphone.
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Importance of Level
• Too High
– Serious risk of distortion
– Danger of Compression
• Too Low
– Makes little difference to the child
– Denied the right to access and benefit from instruction
– Waste of resource
– Disenchantment
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Importance of Quality
• Frequency response curves
Frequency response curves for
Medel Opus 2 (curve #1 @ 60 dB
and with CA Digisystem (curve#2
@ 65 dB
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When Should Balancing be Done
• At initial fitting
• Change of hearing instrument
• Change of FM system
• Disturbance of controls
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Good Practice Fitting Procedure
 Listening check of speech processor and FM system where
possible, adjust settings.
 An objective test-box method for setting up levels (see
Quality Standards and Good Practice Guidelines)
 Validate the settings with a speech test (eg McCormick)
or
 Validate the settings with a speech in noise test
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But, what if a child can’t do a speech test?
• May have poor discrimination years after implantation
• May not co-operate due to
– tiredness
– immaturity
– language difficulties
– behavioural difficulties
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• Callum
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Other Inputs Applied to FM Transmitters
Output from
– Television.
– CD player, other audio devices
– Computer/Whiteboard
– Soundfield device.
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Other Inputs Applied to FM Transmitters
Television, CD player, other audio devices, computer/
whiteboard.
All should be used with caution – only on children who
can report accurately.
Soundfield systems .
Used in the context of learning so must be balanced.
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Balancing Soundfield Systems
• Obtain FR curve for hearing instrument
• Obtain FR curve for FM system and adjust volume so
curves match
• Set FM transmitter to re-broadcast, place soundfield
emitter in the test box – lid open.
• Obtain frequency response curve and adjust output of
soundfield system so curves match.
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Demonstration
• Re-broadcasting.avi
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Any further enquiries to:
c.peake@soton.ac.uk
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