Transcript Using Group Amplification in the Classroom

Using Group Amplification in the
Classroom
by
Pamela Schlitt
Ana Paula G. Souza
Sabrina Strudwick
I. Benefits of Using FM Systems
and Sound Field Systems in the
Classroom
To Students with Hearing Loss
To Students without Hearing Loss
To Teachers
Basic Rationale
FM systems and sound field systems
are used to improve the signal to
noise ratio by increasing the speech
input level.
A Signal to Noise Ratio
The signal to noise ratio is the difference
between the signal level and the noise level
in the classroom.
The teacher’s voice is an example of a
signal.
An example of a noise would be air
conditioners, background voices, traffic, etc.
In a typical classroom, the teacher’s voice
is 65 dB SPL, and the noise level is 60 dB
SPL.
Therefore, the signal to noise ratio is +5
dB. (65/60=5)
Many hearing impaired students need a 20+
dB signal to noise ration.
FM and sound field systems reduce the
effects of noise, making it easier for
students to understand the teacher and
improve academic performance.
Advantages of FM Systems
Individual to the child
Can be used with the child’s hearing aid
Easily transportable
Saves the teacher’s voice
Can be adjusted to maximize the signal in
different environments (lecture, group
discussion, etc.)
Enjoying our FM Systems!
Advantages of Sound Field
Systems
Cost - One system is less expensive than a
special education class for a child.
Benefits all children including normal
hearing children with ADD, learning
disabilities, and children with mild or
fluctuating hearing loss
Removes stigma of “hearing loss” from
child
Lower maintenance for children
Teacher acceptance- saves the teacher’s
voice
Teaches good communication skills during
the class (Use microphone one at a time to
speak)
Sound Field System
II. Speech Acoustics
The average conversation level is 40-80 dB
HL. To better understand that range, take a
look at loudness levels of common sounds.
Whisper
Type writer
Food Blender
30dB
70dB
90dB
Train
100dB
Chain Saw 110dB
Jet
120dB
Just as these different environmental sounds
have varying loudness levels, so do individual
sounds of our language.
Vowels, nasal consonants (consonants made
with the vocal tract-m, n, ng), and most
voiced consonants (those consonants that
require the vocal folds to vibrate- such as b,
d, g, z, v, j) are louder than voiceless
consonants (such as f, s, th, k, sh, ch, p).
However, not only do sounds of the English
language vary by loudness, they also vary
according to pitch.
Vowels, nasal consonants, and most voiced
consonants are in the low pitch range.
Voiceless consonants are in the high pitch
range.
These varying levels of loudness and pitch in
the English language affect the child with a
hearing impairment’s ability to hear and
understand all of the speech signal being
presented.
The sounds with low loudness levels and
high pitch levels may be especially difficult
for children with a hearing impairment to
hear.
Varying Degrees of Hearing Loss and the
Effects on Understanding Language and
Speech
Children with minimal or borderline
hearing losses (16-25 dB HL) can miss up
to 10% of the speech signal if the teacher is
more than 3 feet away or if the classroom is
noisy.
 These children may appear inappropriate,
awkward, or immature.
Children with mild losses (26-40dB HL)
can miss from 25-50% of the speech signal.
Without amplification, the child with a high
pitched hearing loss may miss consonant
sounds.
These children seem as if they are “day dreaming”
or “not paying attention” and cannot block out
background noise.
Children with moderate loss of 40 dB HL
may miss 50-75% of the speech signal.
Children with a 50 dB HL loss may miss
80-100% of the speech signal.
These children are likely to have limited
vocabulary, delayed or defective syntax, imperfect
speech production, and an atonal voice quality.
Children with moderate to severe losses
(65-70 dB HL), severe losses (71-90 dB
HL), or profound losses (91 dB or more)
can miss 100% of the speech signal without
amplification.
Children with unilateral hearing losses (one
normal ear and one ear with at least a
permanent mild loss) may have difficulty
hearing faint or distant speech. They will
also have difficulty hearing in noisy
environments.
These children may be accused of “selective
hearing” and may appear inattentive or frustrated
and present with behavior problems.
One can see from the previous examples, the
importance of improving the signal to noise
ratio for children with varying degrees of
hearing loss to improve their academic
performance and social functioning in the
classroom.
III. FM Auditory Training Systems
Individual FM Systems
Sound Field FM Systems
Standard Parts of FM Systems
Microphone - picks up sound in acoustic
environment and converts it to electrical signal
Transmitter - worn by teacher; uses the electrical
signal to modulate the frequency of a high
frequency carrier signal, which is then broadcast
via an antenna
Receiver - worn by child; demodulates the
frequency-modulated signal, which is then
amplified and delivered to the user
Transducer - modifies the frequency response
from the receiver
Types of Individual FM Systems
Basic
Button earphone delivers sound to child
Personal
Sound coupled to the personal hearing aid (HA) via
direct-input, silhouette, or neckloop
Ear level
FM receiver is in behind-the-ear (BTE) case which also
works as a HA
Boot
FM receiver is in boot that snaps onto BTE HA
FM Transmitter Options
Microphones
Omnidirectional - picks up sound from all
directions
Directional - distinguished by openings around
the sides, which allow for a reduction in
amplification of sounds impinging on the sides
relative to sounds impinging on the top
Boom - worn with a headband or clipped to
eyeglasses so that the microphone is
approximately two inches from the lips and
moves with the head
Pass Around
Teacher wearing an FM transmitter
with a lapel microphone clipped on
the shirt
Teacher wearing a Boom Microphone
Transmitter Frequencies
Fixed Frequency - one of 40 narrow frequency
bands between 72 and 76 mHz that are
number/letter or color-coded
Variable Frequency - dial in channels or
removable oscillator
Alternate Signal Inputs
Audio In Jack - used to hook up transmitter to
tape recorder or video player
Microphone Jack
Mic + Audio Switch - allows the teacher’s
voice to be transmitted along with the auxiliary
audio source
Transmitter Controls
No FM Light - indicates that the microphone
has not been plugged in correctly or there is a
problem with the microphone cord
Low Battery Light - only informative if the
light is on because it goes not illuminate when
the battery is completely exhausted
Automatic Gain Control Adjustment - used to
vary the loudness level of the input signal at
which the reduction in gain begins
FM Receiver Options
Microphones
Monaural Omnidirectional - one microphone port
Dual Omnidirectional - two microphone ports
Dual Directional - two ports on the front and one on
each side so that sounds impinging on the front are
amplified to a lesser degree than those impinging on the
side
Behind-the-ear - ports by the earhooks; allows for a
closer approximation of binaural hearing,
environmental microphones on the receiver case must
be deactivated
Pass Around- may be plugged into an audio-input jack
on the receiver
Receiver Frequencies
Single Channel - number/letter or color-coded
Dual Channel
Internal/External Oscillator - general frequency is
internal and class/specific frequency is removable
Input/Output Connections
Audio In Jack
Audio Out Jack - to another audio source such as a tape
recorder
Pass Around Microphone
Receiver Controls
FM signal only, FM + Environmental signal together,
or Environmental signal only
SSPL90, Tone FM Ratio, Right/Left Ratio, Gain
Environmental Microphone
Volume
No FM Light
Low Battery Light
Coupling Methods
Headphone or Stetoclip - for persons with auditory
processing problems but normal hearing
Bone Oscillator - for persons with malformed ear
canals or draining ears
Button Earphones - allow for the greatest power
Behind-the-Ear - microphone, amplifier, receiver,
battery, and oscillator contained in the BTE case
Personal Hearing Aid via:
 direct-input - electrical signal from FM receiver led directly
into HA via a boot or audio-shoe connection
silhouette - requires a HA with a T-coil and an electromagnetic
field is created in a wafer-shaped piece worn between the head
and the HA
 neckloop - electrical signal from FM receiver delivered to
neckloop that creates an electromagnetic signal which is
picked up by the T-coil of the HA and amplified
Button receiver
Direct input receivers
Behind-the-Ear FM Receiver
Direct Input- FM Receiver coupled with the hearing aid
FM Receiver completely located in the “shoe”
which would be attached to the hearing aid
Student wearing a neckloop arrangement
FM Battery Options
Batteries
Removable Nicad Battery Pack - packs may
stay on the transmitter or receiver during
charging or can be removed and charged
separately; charge lasts 18-25 hours
Removable Nicad Battery (9 or 3-volt) batteries remain in the units during charging;
charge lasts 7-14 hours
Removable Alkaline (9-volt or two 1.5-volt) charge last 15-20 hours
Charging Units
Case charger - spaces for 12 units, charging
time is 8-12 hours
Modular charger - two-pocket charger used for
a transmitter and receiver pair; can be expanded
by adding on sections to charge up to 12 units
Wall charger - charges a transmitter/receiver
pair; plugs are connected to the units and the
charging unit is plugged into a standard wall
socket
Ideal Transmitter
Variable transmitting channels for
maximum flexibility in case other signals
interfere
Audio input with talkover option so the
teacher can provide input during a video,
etc.
Boom directional microphone for a
consistent signal as the head turns
Low Battery Lights
No FM Lights
Ideal Receiver
Dual Channel Oscillator for flexibility in
case other signals interfere
Input/Out jacks
Options for FM, FM + ENV, ENV so that
the student may receive the best possible
S/N ratio relative to the instructional task
such as class discussion or lecture
Direct-input coupling because internal
noise is lowest, the signal is most
consistent, and the child may wear his or
her hearing aid all day
Low Battery Lights
Ideal Battery
Operate on Nicad or Alkaline so that the
user is not dependent on electrical sources
for chargers
Modular charger with auto off
Sound Field FM Systems
Components
Microphone - worn by the teacher
Transmitter - worn by the teacher
Base Receiver
Amplifier
Speakers - send the signal throughout the room
 Sound field systems vary by how many speakers
are in the room, where they are placed, whether a
pass around microphone is used for class
discussion
Once again, sound field systems are important
because they can benefit all children in the
classroom
Sound Field System
IV. Room Acoustics
Things that affect room acoustics
Room Noise
Reverberation
Distance
Room Noise
 is considered any undesirable noise in the
classroom that may affect listening.
Even in an unoccupied classroom, there is
background noise.
When occupied, background noise in the
classroom increases.
Factors that cause room noise
Inside the classroom:
projectors
computers
fluorescent lights
fans, air conditioner
fish tanks, animals
chairs sliding on floor
clocks
Outside the classroom:
noisy streets
hallways
music rooms
gymnasiums
auditoriums
lawn services
Measuring Noise
Noise can be measured using a sound level
meter. This meter has a scale that relates to
the same sensitivity curve as the human ear.
Studies have been done to measure noise in
decibels for activities occurring in
representative classrooms in Dallas and
Chicago areas.
Noise in a carpeted class for hearing
impaired children in a mainstream
environment with 15 students and 2
teachers is about 59dB HL.
A normal teacher speaks at about 65 dB
HL.
This gives us a signal to noise ratio of +6dB
which is not adequate for hearing impaired
students.
Ways to Reduce Classroom Noise
Cover bottom of chairs, desks, and tables
with tennis balls to keep them from sliding
on floors.
Choose a classroom away from external
noises.
Keep windows and doors closed.
Place rubber strip around door to keep out
hallway noise.
Have noise rules in the classroom
use “inside voices”
only sharpen pencils at certain times
don’t slam books down
take “marshmallow” steps
No fans
Avoid fish tanks and animal cages
Turn off computers when not in use
Seat hearing impaired students in front of
classroom near the teacher and away from
internal and external noises.
Reverberation
When sound leaves a source it travels in
sound waves.
Sound waves may deliver direct sound
before they come into contact with a
boundary.
Once sound waves collide with a boundary,
they are reflected.
Reverberation is sound reflected in the
room after the source has stopped producing
sound waves.
Both direct sound and reverberated sound
reach the listener.
The reverberated sound interferes with
listening to the direct sound.
Reverberation can be measured by how
long it takes a sound to stop reflecting.
Reverberation time can be measured using a
reverberation meter or calculated manually by
using measurements of the classroom and
absorption coefficients from a table.
Important Things to Think About When
Choosing a Classroom for Hearing Impaired
Children
Ideal reverberation time is 0 seconds.
Recommended reverberation time for a
classroom with hearing impaired children is
0.3 seconds.
Recommended reverberation time for a
classroom with normal hearing children is
0.5 seconds.
Rooms with high absorption time have low
reverberation time.
Rooms with high volume have high
reverberation time.
Auditoriums typically have reverberation
time of 1.5 seconds.
Classrooms have typical reverberation time
that varies between 0.5 and 1.5 seconds.
A Finitzo-Heiber study was done to
.
measure average speech understanding of
normal hearing and hearing impaired
students in classrooms of different
reverberation times and signal to noise
ratios.
Overall, classrooms with lower
reverberation times and higher signal to
noise ratios provided better listening
conditions for both groups of children.
Effects of Reverberation on Understanding
Speech
Decrease overall understanding of speech
Vowels interrupt the understanding of lower
loudness consonants. Vowels tend to be 1015dB louder than consonants.
Silent intervals between syllables, sounds,
and words are filled with reflected energy
resulting in a smearing effect of the sound.
Ways to Reduce Reverberation Time
In order to reduce reverberation time, you
need to increase absorption.
Absorption can be increased by replacing of
covering hard surfaces with softer ones to
minimize the amount of reflection
In a classroom with no absorption or attempt
to reduce reverberation, the reverberation time
is about 1.65 seconds.
Draperies added
RT= .95 sec
Carpet added
RT=.52 sec
Foam padding under carpet
RT = .36 sec
Acoustic Tile on Ceiling
RT = .22 sec
Padding can also be added to walls:
bulletin boards
tapestries
felt boards
carpet squares on walls
Distance
The greater the distance between the
teacher and the child, the more difficult it is
for the child to receive the speech signal
due to decreased loudness.
V. Daily Inspections of FM
Systems in the Classrooms
Daily visual inspections of the FM
equipment is important to ensure that the
students are getting a clear signal and that
the equipment is functioning properly.
Once a FM is chosen and fit for a child, the
teacher should have information about the
FM system handy on file.
The file should include items such as: correct
settings for FM, troubleshooting equipment,
who to contact in case of problems, and how to
charge the system.
Each morning, the teacher should inspect
each child’s FM system following an
auditory trainer check guide:
Physical inspections- check for wax and debris in
ear molds, feedback in the ear, visible cracks/cuts in
external cords, and movement of on/off switch.
Check receiver in hearing aid only mode- check for
no FM light on, low battery light on, static in
right/left output jacks, and movement of volume
control.
Teacher transmitter- make sure unit is on mic/audio
and that the microphone has no static when wiggled.
Check receiver in FM only mode- make sure
frequency same as teacher transmitter, check for no
Fm light, check for clear and static free signal.
An audiology notebook should remain
close-by containing equipment information
and a troubleshooting guide.
If a problem is encountered, the teacher can
reference the audiology notebook, the
child’s individual file, and/or an audiologist.
VI. Motivating Students
Establish a program where older students
help the younger ones with their daily
inspections
Develop a Daily Inspection Log where the
children get stickers to “check off” the steps
taken to reinforce the procedures that must
be taken to receive optimal benefit from the
FM system and to promote future
independence from the teacher
Give other rewards such as certificates or
monthly report cards describing the
student’s success with using the FM system
to encourage the students to consistently
wear their aids/FM systems at home and
school, to perform daily inspections on their
own and inform the teacher of any
malfunctions
VII. Resources for Teachers
Web Sites:
www.utdallas.edu/~thib
www.audioenhancement.com
www.members.tripod.com/listenup/assist.htm#13
www.members.tripod.com/listenup/assist.htm#14
www.agbell.org/programs/programs.html#information
Books:
Acoustics and Sound Systems in Schools,
Frederick S. Berg
Facilitating Classroom Listening: A Handbook
for Teachers of Normal & Hard of Hearing
Students, Frederick S. Berg
FM Auditory Training Systems:
Characteristics, Selection, & Use, Mark Ross