User guide

56
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A
N EDUCATOR’S GUIDE
18. American Speech-Language-Hearing Association. (2005). Acoustics in educational settings:Technical report. Available at http://www.asha.org/members/deskref-jour-
nals/deskref/default
19. American Speech-Language-Hearing Association. (2005). Guidelines for addressing acoustics in educational settings. Available at http://www.asha.org/members/deskref-
journals/deskref/default
Introduction to FM section
All children with hearing loss require a good listening environment
and because most schools are noisy places, a child with hearing
loss should always be evaluated for an assistive listening system. A
personal FM, in which the teacher’s voice is transmitted directly to
the child’s cochlear implant processor
, will provide the highest
signal-to-noise ratio (SNR) and therefore the best sound signal.
Sound field systems—either area-wide or on the student’s desk—
will impro
ve the SNR, but not as much as a personal FM. Signal-
noise-ratio is defined as the difference, in decibels, between the
speaker’s voice and the surrounding background noise. For
example
, if the background noise in a classroom was 55 decibels
(not unusual in the typical school) and the sound source (or
teacher’s voice) at the child’s ear was 60 decibels, the SNR would
be 5. The SNR for a child with a cochlear implant should be at
least 15 decibels.
18,19
As the da
y goes on,
two things often happen:
(1) the teacher becomes fatigued and his/her voice level drops
and (2) the children become restless and classroom sounds are
amplif
ied.
Thus,
without an FM system,
the intensity lev
el of the
sound source tends to go do
wn by a few decibels in the afternoon
while the noise level in the room increases—making the situation
ev
en w
or
se! For additional inf
ormation on acoustics, please refer
to Chapter 5.
•
Introduction to
FM systems
•
Troubleshooting the
FM systems
•
FM compatibility guide
•
Other assisted listening
devices
CHAPTER 7
Accessories and assistive listening devices