Transcript Optimizing Classroom Acoustics and Classroom Amplification

Optimizing
Classroom
Acoustics and
Classroom
Amplification
Systems
Jeffery B. Larsen, PhD, CCC-A
Utah State University
How Important is Classroom
Listening?
 Two-thirds of a student’s day consists of
listening to and participating in spoken
communication
 Listening environments need to be free of
acoustic and non-acoustic barriers
The Problem – Classroom
Communication
 Classrooms can be difficult places for good
communication to take place
 TEACHER TO STUDENT COMMUNICATION
 STUDENT TO TEACHER COMMUNICATION
 STUDENT TO STUDENT COMMUNICATION
 Communication in the classroom can be
difficult because of NOISE, REVERBERATION,
AND DISTANCE
Results of poor acoustics on kids
in school
 Poor performance on cognitive tasks
 Cohen, Evans, Krantz, Sokols, & Kelly, 1981
 Poor reading skills
 Bonzaft & McCarthy, 1975; Green,
Pasternack, & Shore, 1982; Gertel, McCarty,
& Schoff, 2004
 Poor math skills
 Zentall & Shaw, 1980
 Poor attention and on-task behavior
 Palmer, 1998; Ryan, 2009
One problem is reverberation
 Reverberation occurs when sound
encounters a hard wall
 Sound bounces around a room
 The effect of reverberation is slurring of
speech as you move away from the talker
 Normal listeners do best when
reverberation times are below .6 seconds
Other Problems
 As talker moves away from the listener the signal
decreases 6dB every time the distance is doubled
(distance is the least thought about problem)
 Start at 65dB HL, 6” from mouth, at 1 foot the
intensity is 59dB, at 2 feet the intensity is 53dB, at 4
feet 47dB, at 8 feet 42 dB, and at 16 feet it is 36dB
 Noise is usually the biggest problem
 At the back of a typical classroom with no children
present, the signal-to-noise ratio (SNR) would be
+1 dB
 With children present, the background noise is
going to be at least 45dB, resulting in a SNR of
about -3dB
The Overall Problem
 When noise, distance, and reverberation are
combined the result is speech is difficult to
understand
 For normal listeners a +6dB signal-to-noise ratio
leads to a 9% decrement in speech recognition
 When a reverberation time of .7seconds is combined
with a signal-to-noise ratio of +6dB word recognition
scores decrease by as much as 20%
 A student at the back of the room has a huge
disadvantage
A study to demonstrate the
overall effect
 Young adult listeners (18-30 years old) were
asked to write down words while seated at
desks in a quiet elementary school classroom.
 Acoustic measurements showed that the
classroom had about 45 dB SPL of noise when
empty and the reverberation time was 0.7
seconds.
 Results showed that those students seated in
the back row got scores between 65% and 75%
So Why Don’t We Complain
 It’s always been this way
 We figure out strategies
 We get notes from the teacher/presenter
 We read the text or the references
 We talk to our friends about what was discussed
 We sit close to the front of the room
 We would never allow children to be taught in
a dark room, but we will allow them to be
taught in a room in which they can not hear
well
WHAT SHOULD WE DO?
 Change the acoustics or amplify the teacher?
 I am not an audiologist who believes that
amplification is always the solution
 Dispensing hearing aids can sometimes lead us to
think this way
 Apparently the Acoustical Society of America is
also not thrilled about the amplification option as
they released a position statement in 2006
claiming that classroom amplification, as a
general policy, was a bad idea.
Concerns of the Acoustical
Society
 Classroom amplification…
 will amplify bad acoustics
 equipment can break down
 will add more sound to an already loud room
 does not address student to student
communication and student to teacher
communication
 Improving the acoustic properties of the room
is a permanent fix that does not need repairs
and will help everyone in the room
Acoustic Modifications VS
Classroom Amplification
 As with everything else, there are no silver
bullets
 The truth about what is best probably lies
somewhere between the Acoustical Society
and supporters of Classroom Amplification
 Or maybe what is best is to do what both
suggest…
Tips for Improving SNR without
classroom amplification
 Place rubber tips on chair and desk legs
 Move kids away from high noise source
 Use acoustically treated furniture
 Use doors with solid cores
 Install double paned windows
 Keep doors and windows shut
 Improve classroom discipline
Study – Larsen & Blair 2008
 Five different classrooms used in the study
 All were similar in size – all 4th grade
 30 to 35 feet deep
 32 to 40 feet wide
 All met ANSI standard for noise and reverberation
 RT 60 .32
 Noise Criteria 32 dB
 Four teachers used classroom amplification, one did not
 A pass-around microphone was used in one classroom
regularly, but either sporadically or not at all in the other
three classrooms
Procedures
 A measuring microphone was placed on a tripod,
positioned at the level of the child’s ear (placed
near a child’s ear)
 Measurements were made at 9 different locations
in each room (back center, left back, right back,
left center, middle center, right center, front
right, front left, front center)
 Measurements were made in 10 minute
increments
 The Time, Energy, Frequency (TEF) system was
used to obtain measurements
SNRs with infrared classroom
amplification
 Obtained signal-to-noise ratios were on
average between +13 to +20 dBA at every
position measured in the rooms
 One classroom was not fit with a classroom
system and all other teachers were asked to
turn off their systems for 5 minutes during
the data collection
 The average signal-to-noise ratios were
between +2 and +6 dBA without amplification
Actual Conditions (unamplified)
 Teacher asked children to read in a random
order around the classroom.
 Average sound level at the microphone based
on distance away from the microphone.
 2 feet - 59dB
 3 feet - 56 dB
 6 feet - 55 dB
 12 feet - 46 dB
 There are times when the sound level is 13
dB less intense than at other times.
Results: Unamplified Classroom
 Teacher’s measured vocal intensity;
 Front of the room at nearest student’s desk was
58 dBA, with a range of 50 to 65 dB
 Middle of the room at child’s desk, the level was
52 dB, again with a range of 40 to 60 dB
 At the most distant point, this is measured as
being 18 feet from the most common place
from which the teacher presents information,
was 48 dB with a range of 40 to 52 dB
Implications
 The results indicate that, without amplification,
at the front of the room the average signal-tonoise ratio was +15 with a range between +8 and
+20
 In the middle of the room the S/N ratio was 8 dB
with a range between +1 and +10
 At the back of the room the S/N ratio was 0 dB
with a range of -15 to +6 dB
Implications (continued)
 Depending on where the child is seated at any
given time changes the amount and quality of
input available
 There are times when everything is audible and other
times when information is not audible at all
 The child who has any kind of hearing problem is
getting at best variable auditory input (about
10% of the students)
 Remember this room meets ANSI standards
Amplified Classrooms
 In these classrooms all speakers were in the
ceiling, providing direct sound to the children.
 No matter where the child was seated in the
room they were getting no less than a +10 signalto-noise advantage.
 When the hand-held microphone was used the
same advantage was present for the children as
for the teacher, when not used it was like the
results in an unamplified room.
Observations without
amplification
 Many students did not listen well when the
teacher was talking
 After the teacher explained an assignment on a
poem and the children started to work, the
teacher noticed one child looking around as if
trying to discover what to do. When the teacher
asked if she had started to look at the poem, the
student said, “Oh, I thought you were talking
about some kind of foam and I didn’t know what
you wanted us to do.”
 Little differences can make for a great deal of
confusion
Logan City School District
 Few classrooms have used systems for many years
 Middle School was convinced that a system for their
school was important
 Opted not to repave a parking lot and used the money
to purchase audio enhancement for all instructional
classrooms
 Legislature provided money for technology
 Superintendent and Board decided to use the bulk
of the money to put audio enhancement in every
classroom in the district
Current Findings in Logan City
Schools
 Three-hundred five teachers (K-12) were surveyed
 One-hundred sixty-five responded (54%)
 Questions and answers:
 Do you have classroom amplification in your room?
 93.9% yes; 6.1% no
 Do you personally use the equipment?
 89.6% yes; 10.4% no
 How often do you use the equipment?
 All day, every day: 48.2%
 When presenting information: 28.4%
 Occasionally, for special presentations: 10.6%
 When I think about it: 5.7%
 Other: 7.1% (don’t use it when there are groups in the class)
Findings (continued)
 Do students use the microphone?
 Yes, 59.1%
 No, 40.9%
 How often and under what conditions?
 Pass the microphone around during class discussions: 3.3%
 Use the microphone when presenting in front of the class: 68.5%
 They use the microphone whenever they are talking to the whole class: 17.4%
 Do guests in the classroom use the system?
 Yes: 62.3%; No: 37.7%
 How often and under what conditions?
 When reading a story to the children: 29.5%
 When presenting information to children formally: 61.1%
 Whenever a guest talks they use the system: 61.1%
Findings (continued)
 What is your impression of the system?





I believe students are more attentive: 80.1%
I can control classroom behavior more effectively: 65.2%
It helps children in my class perform better: 53.9%
The children like it when I use the system: 65.2%
Because I don’t need to talk loud, or yell, I am less tired at the end of the day:
66.0%
 I don’t think that the system helps at all: 5.7%
 How important do you think an amplification system is in a
classroom?






Detrimental: 0%
Not too useful: 8.6%
Useful: 13.2%
Quite useful: 11.8%
Very useful: 35.5%
Essential: 30.9%
How to make it better
 Put it in the gym: 2
 Need hand-held mic:
 Too soft: 2
 Dead places in the
19
 Cuts out all the time:
2
 Mic too heavy: 18
 Need smaller mic: 15
 Needs to connect to
all systems: 13
 Mic
Reverberates/Feedba
ck: 6
room: 1
 Too loud: 1
 I have a loud voice,
don’t need it: 2
 I wear it for hard of
hearing child: 2
 We need complete
technology
classrooms: 2
How can we make it better?
(continued)
 We need someone to maintain it and teach
about it: 3
 I love it: 6
 It is wonderful: 3
 Amazing: 1
 Nothing: 2
Some Considerations
 Installation of classroom amplification follows no
systematic procedure
 In most states they are installed by the
companies
 They are fit subjectively
 We are finding considerable variability across
classrooms and we have had to retrofit a
number
Some Considerations (cont.)
 Many teachers will not wear the systems
 Too loud
 I speak loudly already
 Does not work well
 Unwieldy
 I rarely teach the whole class at one time
 What to do when it does not work well
 I forget to put it on
 Microphone is too heavy and gives me a
headache
Unresolved issues for classroom
amplification
 We know that anything is better than nothing
(unless it is not loud enough to make a
difference)
 We don’t know what is truly feasible in a
classroom (research says +15)
 Comfort
 Feedback
 Overflow
 We are not sure what is usual (study in process
says we are at about +8)
Student’s Opinions (N=258)
 It is easier to hear the teacher
 It is easier to listen when the teacher is talking
 “I like it when the teacher uses the system”
 “I feel that what I have to say is important”
 “I feel listened to when I can use the microphone.”
 Where it is used, all student respondents had only
positive comments to make about the use of sound
enhancement
Teachers’ Opinions (4 large school
districts)
 Students are more attentive
 Teachers can project their voices more easily
 Teachers feel less fatigued at the end of the day (no need to talk
loud or yell)
 Teachers experience less vocal strain
 Teachers report that students like it when they use the system
 Teachers believe that students achieve at a higher level
 Of all the equipment in the schools audio enhancement is ranked
as first or second as ”the piece of equipment that has the greatest
direct influence on learning”
Does it matter where the
speakers are located?
 Choices:
 Speaker in the front of the room
 Speakers on the walls
 Speakers in a cluster
 Speakers in the ceiling
 Any speaker is better than none
 Provided they are turned up loud enough to improve the
signal-to-noise ratio
 The best placement is in the ceiling so as to be over the
head of the children.
 This arrangement provides the most consistent sound to
every child in the room.
 Other arrangements provide variable intensity as the child is
moved away from the speaker
Loudspeaker characteristics
 Two-way loudspeakers
 Woofers and tweeters
 Results in an increasingly directive beam of sound
with increasing frequency
 Flat panel loudspeaker
 Multiple excitation points
 Spreads high frequencies well
 Not as great for amplifying low frequencies
Two-way loudspeakers – 1000 Hz
Two-way loudspeakers – 2000 Hz
Two-way loudspeakers – 3150 Hz
Two-way loudspeakers – 4000 Hz
Academic Findings
 Ray, Sarff, and Glassford, 1984
 Higher scores on academic achievement tests
 Gertel, McCarthy, and Schoff, 2004
 District improved academic achievement test scores
by as much as one grade in one year
 Especially helped Title I students and ESL students
 More and better research is needed to establish this link
between academics and classroom amplification
conclusively
Other Findings
 Teacher absences due to loss of voice or fatigue is
reduced
 Student’s interest in and attention to teacher
improved
 Behavior problems are reduced
 Fewer questions asked that are for clarification
purposes
 Increased student participation in class when a pass-
around microphone is used
SUMMARY
 We need to do better in helping kids have an
acoustic environment where they can have the best
chance for success
 The current debate between whether its better to
modify classrooms to improve classroom acoustics
or put a classroom amplification system is a
distraction – we need both
 We need more and better research to optimize all
options to help remove the classroom as a barrier to
learning