TOOLS for SCHOOLS
Cochlear Implants in the Classroom
Classroom Acoustics
The typical classroom presents a very difficult listening
situation for a child with hearing impairment. In a typical
classroom, the child must overcome three main problems:
Reverberation
The construction of the typical classroom (with its sharp
angles and many flat, hard surfaces) generates reflections and echoes that can mask many critical features of
the original speech signal. Refer to figure 1 for a visual
example of this concept.
Figure 1
Background noise
Classrooms tend to be very noisy places. The level of background noise in the typical classroom has been
shown to equal or sometimes even exceed the level of the teacher’s voice. Children with hearing impairment
require the teacher’s voice to be at least 20 to 30 dB louder than the competing noise, that is a +20 – +30 dB
signal to noise ratio (S/N), to achieve optimum speech understanding. Unfortunately this is almost never the
case, and control of the noise source is often outside the teacher’s hands. For example, if the classroom looks
out onto a busy street, the teacher is powerless to eliminate the traffic noise.
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Cochlear Implants in the Classroom
Distance
The size of most classrooms is quite large. The farther the child from the
teacher, the quieter the level and the poorer the sound quality of the teacher’s
voice. Teachers rarely stay rooted in one spot as they teach, so preferential
seating within three feet of the teacher is impossible on a full-time basis.
Figure 2 represents a visual illustration of the teacher’s voice in relationship
to distance. This illustration highlights the benefits of an FM System which
we will discuss towards the end of this chapter.
Figure 2
More favorable S/N ratios are achieved primarily by
•Reducing noise levels
•Boosting speech levels
Reducing noise levels in the classroom
Providing favorable listening conditions is accomplished in part by reducing noise levels in the instructional
setting. Noise-reducing measures include:
•Removing noise sources
•Increasing distance from noise sources
•Reducing areas of hard, sound-reflective surfaces
•Increasing areas of soft, sound-absorbing surfaces such as acoustic tile, carpet, bulletin boards, drapes, and
tennis balls on chair and desk feet
Boosting speech levels in the classroom
Favorable listening conditions may be further achieved by taking a number of steps to boost speech or other
primary signal input levels in the classroom setting. These steps include:
•Decreasing the physical distance of instruction
•Using FM sound systems
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Cochlear Implants in the Classroom
The energy in a teacher’s speech drops by 6 dB with each doubling in distance from a student’s microphone,
as long as there are no reflections or reverberations in the room. Thus, if the teacher’s speech is 70 dB at two
feet, it will be 64 dB at four feet, 58 dB at eight feet, and 52 dB at sixteen feet. Reducing teacher-to-student
ratios and/or seating the hearing-impaired child closer to the teacher will have a positive effect. However, these
practical measures may fall short of the S/N ratios required by some students. For this reason, FM Systems are
often used, which ensure that the signals delivered to the cochlear implant in the teaching environment are
optimized for auditory learning.
What Is an fm System?
Frequency modulated (FM) systems are composed of a teacher-worn microphone/transmitter and a frequencytuned receiver worn by or positioned close to the child. With an FM System, the teacher’s voice is captured by the
microphone and transmitted wirelessly to the receiver via radio waves. The receiver can be coupled to a student’s
cochlear implant sound processor. Therefore, an FM System brings the teachers voice directly to the student,
regardless of the distance between them. This can make listening in a noisy environment easier.
What Is the Purpose of an FM System?
Used in conjunction with physical classroom modifications, the FM System is designed to:
• Improve listening in noisy, reverberant classrooms
• Overcome the problems of listening at a distance
How Does an FM System Work?
Authorized FM transmission ranges vary from country to country. In North America, FM transmission is limited
to 72–76 MHz and 216 MHz. Within the 72–76 MHz range, FM transmission is divided into narrow bands or
operating channels. Channels are designated either by letters, colors, or numbers. Both the teacher’s transmitter
and student’s receiver must be tuned to the same channel if the system is to work properly. Receivers will
capture the signal of the closest transmitter using the matching channel, rejecting other weaker signals.
Regardless of the distance between teacher and child, the signal is delivered directly to the FM receiver at a
constant intensity level, and the proximity of the teacher’s mouth to the lapel microphone ensures that his/her
voice is delivered to the child at a level that is significantly louder than the level of any background noise.
A single transmitter can be used with multiple receivers tuned to the same transmitting frequency.
What Is the Difference Between a Personal FM
and a Sound Field FM System?
Personal FM receivers are worn on the body and attached directly to the child’s sound processor by means of
a special FM adapter cable or a wireless connection such as the iConnect. Sound field FM Systems transmit
the teacher’s voice to one or more loudspeakers positioned near the child, no direct coupling is necessary to
the sound processor. The wireless teacher-worn transmitter/microphone is identical for both personal and sound
field FMs. Boom or lapel-style microphones attached to a waist-worn transmitter are common, but some
microphones may be incorporated directly into the transmitter housing.
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Cochlear Implants in the Classroom
What Are the Advantages and Disadvantages of These FM Systems?
Personal FM Systems
Sound Field FM Systems
Advantages
Disadvantages
Advantages
Disadvantages
Optimal signal-to-noise enhancement
(+20 dB to +30 dB)
Direct connection to the FM may
cause interference
No direct connection between
CI and FM
Smaller signal-to-noise advantage
(+10 dB to +20 dB)
Portability
Sound quality and consistency
cannot be monitored by teacher
Teachers can easily monitor sound
quality and consistency
Fixed speaker classroom systems
are not easily portable
Can be worn outside during sporting
activities, field trips
Children with S-Series™ processors
cannot monitor own voice
without additional microphone
(PSP/Harmony/Auria/BTE Sound
Processors have audio-mixing option)
Desktop systems are portable
Cannot be easily used outside
Additional audio-input/output jacks
What Is the Importance of Audio Mixing?
Audio mixing allows the child’s headpiece microphone to remain active when connected directly to an FM.
This is important for the child to hear his own voice and sounds around him in addition to the teacher’s voice
transmitted through the FM. Audio mixing allows the child to continue to hear, even when the FM transmitter
is temporarily not in use.
Audio Mixing Ratios and Applications
Headpiece microphone + auxiliary input 50/50 mix
Equal gain is applied to each input. A 50/50 mix does not imply that each signal has been reduced by half.
Headpiece microphone + auxiliary input 30/70 mix
With this option, different amounts of gain are applied to the two signals. Less gain is applied to the signal
pathway from the headpiece microphone so that the input for the auxiliary device is emphasized. Remember
that sound input to the headpiece microphone will be reduced using this program, even when disconnected
from the auxiliary input.
Headpiece microphone only
With this option, no gain is applied to the input from the auxiliary audio device. Only the headpiece microphone
will be active when coupled to the auxiliary device. This programming option may be appropriate in an educational setting where the teacher does not want to uncouple the child from the FM System every time he/she turns
off the transmitter microphone. (In some FM Systems, turning off the teacher transmitter still provides an audible
hiss to the end-user from the FM receiver). The child could simply switch to a headpiece microphone-only program
when the teacher turns off her FM transmitter microphone.
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Cochlear Implants in the Classroom
Auxiliary input only
This option is appropriate when the listener wants to hear only the signal from the audio device such as a CD
player, Walkman, cell phone, or stereo. The headpiece microphone is completely deactivated. This programming option assumes that the end user has an appropriately attenuated and qualified patch cable.
Auxiliary input only attenuated
The listener wants to hear only the signal from a commercially available audiodevice and has obtained an
off-the-shelf patch cable that has not been tested with a sound processor. However, the signal level emanating
from the audioappliance is quite high and, even with the volume on that device and on the PSP turned to a
minimum setting, the signal is too loud for the user. The -17 dB attenuation applied to the audio-input signal
will allow the user to set the volume of the audio device and the PSP to a more appropriate setting.
Which Sound Processor Allows Audio-Mixing?
Sound Processor
Headpiece Microphone active with FM
receiver connected (Audio-Mixing)?
Comments
S-Series™
No
Child will not hear any other sounds in
the environment, unless the FM receiver
has an environmental microphone
PSP™/Harmony®/Auria®/BTE
Sound Processors
Yes, with variable mix ratios for different
Assistive Listening Device applications
Child will be able to hear other sounds
in the environment through their
headpiece/processor microphone
Special Considerations for Young Children
Young children typically do not have the language skills necessary to report on signal quality. As a consequence,
many clinicians are reluctant to make personal FM recommendations for young, inexperienced cochlear
implant recipients. In cases where monitoring of signal quality and consistency are an issue, sound field FM
Systems may be a practical alternative to the personal FM, since it is immediately apparent to the teacher when
the system is not operating optimally.
Are Personal FM Adapter Cables Interchangeable?
As the cochlear implant system and the FM System both use a radio signal, there is the potential for some
noise or interference between the two, which the listener may perceive as background noise. To minimize the
potential for background noise interference, custom-built FM adapter cables are used to connect the sound
processor to a personal FM. In general, these cables are not interchangeable and are specific to both the FM
and sound processor. As a reminder an adapter cable is not necessary when using the iConnect with the Auria
or Harmony Sound Processors.
The child’s cochlear implant center, FM manufacturer or Advanced Bionics can assist in obtaining the correct
FM adapter cable.
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Cochlear Implants in the Classroom
Guide to Using Same Channels in Nearby Areas
Since FM receivers will capture the strongest signal (i.e., from the closest
transmitter on the same frequency), the same channel can be used in multiple
classrooms, provided some basic guidelines are followed.
•Keep transmitters on permanently or receivers may capture and receive nearby
same-channel transmitters. Switch to Aux (if available) to mute transmitter.
•Keep two walls between nearby systems on the same channel (e.g., every
other classroom).
•Keep at least 20 meters between same-channel transmitters, especially if not
separated by walls. Keep children as close to their transmitter and as far from
any other same-channel transmitters as possible.
Tips for FM Use in the Classroom
•In group discussions, try to pass the teacher’s microphone to each child who speaks.
•If you are working individually with a child in a noisy classroom, it can be helpful to turn down the environmental microphone volume (if available) on the FM receiver or switch to the FM-only setting. Then the
teacher’s microphone can be passed back and forth between the two of you as you converse. With PSP,
Harmony, Auria® and BTE processors, contact the implant center audiologist to request an audio-mixing
program specially designed for this purpose.
•If two transmitters are being used in the same classroom (e.g., in a team-teaching situation), ensure that
the transmitting frequency channels are as distinct as possible. Remind children to change channels as they
move from group to group. Additionally, you may want to consult your FM manufacturer for other options if
you are team teaching.
•If you are using the FM transmitter with a group that does not include the child with the cochlear implant,
remind him to disconnect his FM receiver from the sound processor. Alternatively, he may turn down the
FM volume control on the FM receiver, provided a separate environmental microphone is available on
the unit.
•For children who have FM receivers with environmental microphones and PSP, Harmony, Auria® or
BTE Sound Processors, the FM transmitter may be switched off when not in use, or when conversation is not directed toward the implanted child. However, switching to the transmitter’s Aux setting
(if available) is usually preferable, to avoid the possibility of interference or reception of a signal from a
different transmitter tuned to the same channel. Please verify the audio-mixing setting on the PSP, Harmony,
Auria or BTE with the cochlear implant center.
•When working with a small subset of children and a multiple speaker sound field FM, remember to switch off
all speakers except the one closest to you so that other groups of children are not distracted.
•For multimedia lessons (e.g., on TV, tape or video), place the transmitter microphone near the sound source
or alternatively connect the TV directly to your transmitter via the auxiliary input jack (switch to AUX only or
MIC/AUX settings).
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Cochlear Implants in the Classroom
Daily Functional Equipment Checks
for FM Systems Coupled to Sound Processors
A set of simple listening checks should be done on a daily basis to ensure that all parts of the system are functional.
If troubleshooting is needed with an FM System and a Sound Processor please refer to the Sound Processor
Product Guides located on our TFS web page.
FM Check — Testing the FM System alone:
• Place the transmitter microphone approximately 6 inches from an audio source (e.g., a portable radio).
• Wear the child’s receiver with a pair of attenuated Walkman-style headphones.
• Walk several meters away from the transmitter and listen for any previously unnoticed interference or loss of
transmission.
FM and Sound Processor Check — Testing the entire system:
• Attach the microphone of the FM transmitter to teachers/speakers lapel.
• Attach the FM receive to the Child’s Sound Processor.
• Turn on the FM System and set controls appropriately.
• Turn on the processor and set controls appropriately.
• Walk a few meters away from the child and administer a simple auditory-only test (e.g., Ling Six Sound, days
of the week, numbers). Performance should not be significantly different than when the same test is administered using the implant system alone at a distance of three feet.
Ling Six (Ling, 1978) Sound Check
• Assess child’s responses to the phonemes (ah, oo, ee, sh, s, m) in the auditory-only condition. Choose a
response mode consistent with his/her level of auditory ability (Detection=have child raise hand in response
to sound, or Identification=have child point to or repeat what is heard).
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Cochlear Implants in the Classroom
JUN09_ 3-01066-C-3
©2009 Advanced Bionics, LLC.
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