Extron Classroom Sound Field User Manual

Classroom Sound Field
Amplification: An Introduction

ABSTRACT

Table of Contents

WHAT IS A CLASSROOM SOUND FIELD SYSTEM? 2

ACOUSTICAL BARRIERS TO LEARNING

Problem 1 – The Classroom Sound Environment

Problem 2 – Student Listening Difficulties

Problem 3 – Teacher Vocal Strain

COMPONENTS OF SOUND FIELD
AMPLIFICATION SYSTEMS

SOUND FIELD SYSTEMS CAN ALSO
REINFORCE PROGRAM AUDIO

BENEFITS OF CLASSROOM AMPLIFICATION

Student Achievement

Student Attentiveness

Instructor Benefits

CONCLUSION

REFERENCES

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Several factors, including lively students, noise from computers and air-handling

equipment, poor classroom acoustics, outside sounds, and minor hearing

difficulties, can have a significant impact on a student’s ability to hear the

instructor clearly.

Classroom sound field amplification systems have been successfully used to

help students with hearing impairments. Recent research has demonstrated that

even students with normal hearing ability benefit when these systems are used

in their classrooms.

This paper describes the basic components of a sound field system and

summarizes research related to the benefits that can be realized when

classroom amplification is used to support the delivery of effective classroom

instruction.

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What is a Classroom Sound Field System?

A typical classroom sound field system consists of ceiling mounted speakers, a small,

lightweight wireless microphone worn by the instructor, one or more receivers, and

an amplifier. Some systems also include a secondary wireless microphone that can

be shared by the students when giving a presentation or reading aloud. The system

amplifies the instructor's voice above ambient noise and evenly distributes the sound

throughout the room. This creates what is called a “sound field.” It enables instructors

to be clearly heard by every student, without shouting or straining their voice.

Acoustical Barriers to Learning

Instructors must overcome numerous acoustical barriers to learning in order to

effectively deliver instruction to their students. Problems include conditions in and

around the classroom, student learning disabilities, and instructor vocal strain. Schools

that have implemented classroom sound field systems have reported success in

overcoming many of these obstacles. What follows is an overview of the problems that

sound field amplification systems are designed to address.

Problem 1 – The Classroom Sound Environment

Many of the obstacles that interfere with a student’s ability to hear the instructor

stem from problems with the classroom sound environment. When noise levels in

the classroom reach an unacceptable level, it is usually due to one or more of the

following causes:

Instructors must overcome numerous acoustical barriers to
learning in order to effectively deliver instruction.

Poor Classroom Acoustics: One of the most important things to consider in

classroom design is acoustical performance. Hard flat surfaces in the classroom,

such as floors, walls, whiteboards, and ceilings promote echo, which inhibits speech

perception.

Research indicates that background noise and reverberation can adversely affect

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learning, especially for young children.

to hear individual sounds clearly, as when learning to read and spell, and their

concentration is also compromised. Poor classroom acoustics create an especially

challenging educational barrier for those children who have hearing loss, speech

impairments, or learning disabilities, and whose native language differs from the

teaching language.

A 1999 study

classrooms. The study concluded that 91 of them, or 97 percent, exceeded the

recommended acoustical standards. In 2002, the Acoustical Society of America

approved ANSI/ASA S12.60-2002, Acoustical Performance Criteria, Design

Requirements and Guidelines for Schools. The standard sets specific criteria for

maximum background noise and reverberation and is consistent with long-standing

recommendations for good practice in acoustical design.

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on classroom acoustics measured noise levels in 94 unoccupied

It is more difficult for younger students

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Word Recognition Scores

Degrade with Distance from the Instructor

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Noise Sources Within the Classroom: Classroom ambient noise can be caused by

students talking or coughing, shoes scuffing on the floor, chairs creaking and being

moved around, paper shuffling, pencil sharpeners, loud ventilation systems, and

computer and projector cooling fans. This background noise can lead to instructor

voice fatigue.

95% at 6' 60% a t 24'75% at 12'

Studies show that spoken word recognition scores decrease
systematically as the distance from the speaker to the listener
increased.

Distance From the Instructor: How far the student sits from the instructor has a

measurable impact on the student’s ability to hear and understand what the instructor

is saying. Studies show that students should be no more than six feet from the

instructor for maximum speech intelligibility.3 Unfortunately, achieving this distance for

all students given typical class sizes is not practical.

One study looked at a group of children, ages 5 to 14, in an acoustically good

classroom. Researchers found that spoken word recognition scores decreased

systematically as the distance from the speaker to the listener increased. While

students at a distance of 6 feet from the instructor achieved scores of 95 percent, the

scores dropped to 60 percent for those students seated 24 feet away.4

Noise Sources Outside of the Classroom: Sources of noise outside the classroom

can include traffic, aircraft, playgrounds, construction, lawnmowers, and noise

produced in other parts of the building, such as students in hallways, band practice,

and impact noise from the room above. Occasional isolated noise from outside the

classrom can cause a short-term disruption to communication, however, constant

noise has a greater negative impact on speech intelligibility.

Problem 2 – Student Listening Difficulties

Estimates indicate that school-age children spend up to 75% of the school day

engaged in listening activities.5 Unlike adults, whose listening abilities and skills

have fully matured, young children require optimal conditions for hearing and

comprehension. The brain’s auditory network is not fully functional until about the

age of 15.1 Children do not cognitively process what they hear the same way adults

do. For children, the instructor's voice needs to be at least 15 decibels louder than

the background noise in the classroom.6 This decibel difference is called the Signal-

to-Noise Ratio, SNR. Comparatively, adults only require an SNR of 4 to 6 decibels.

Research also shows that students learning English as a second language need a

greater SNR than those whose native language is English.

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Extron Electronics – Classroom Sound Field Amplification – Rev. A1

Unlike background noise which remains relatively constant around a room, the sound

of the instructor's voice varies greatly depending on where that instructor is located

and where the SNR is being measured.7 This is because sound decreases over

distance; specifically it drops 6 decibels for every doubling of distance. For example,

an instructor speaking at a 60 decibel level 3 feet out into the front of the classroom,

will be heard at 54 decibels 6 feet into the room; 48 decibels 12 feet into the room

and so on. Since the background noise level remains essentially the same, this decline

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For example, an instructor might say:

An insect has three body sections, three pairs of legs,
antennae and wings. Draw a picture of an insect.

in the instructor's voice means that the SNR declines the further back in the room the

student sits. At some point, that SNR will drop below +15 decibels, preventing some

students from hearing what the instructor is saying.

Creating a learning environment with a favorable SNR is especially critical for children

in the earlier grades. These students are often engaged in activities that specifically

focus on speech and sound recognition. Young, inexperienced learners have not yet

developed the ability that adults have to adjust their hearing in noisy conditions that

are unfavorable to listening, and they won’t typically have that ability until they are

13 to 15 years old (see sidebar).

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But a young learner might hear:

An --sect has --ree bo-y -ections, ---ee -airs of -egs,
ante--- and wi---, -aw a pi---- of an -sect.

A student's hearing and experience affect their ability
to understand what is said.

How Many Students Have Trouble Hearing?: The Mainstream Amplification Resource

Room Study, commonly referred to as the MARRS Project, was a study involving

repeated observations over a three-year period conducted in the Wabash and Ohio Valley

schools in southern Illinois.

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Data obtained by the MARRS Project revealed

that 20% or more of the current school population had academic difficulties coexisting

with minimal hearing loss. Approximately 43% of K-12 students suffer from temporary

hearing loss on any given day and would fail a pure-tone screening at 15 dB hearing

level and/or an immittance screening that checks for fluid buildup behind the eardrum,

a common childhood ear condition caused by ear infections.14 When placed in noisy

classrooms or seated far away from the instructor, these students are at greatest risk of

not hearing what is being said.

According to the MARRS study, the students who would benefit from classroom

amplification include those who are:

• under the age of 15

• sitting in the back of the class and may miss up to 30 percent of what
the instructor says

• struggling academically

• in a noisy classroom environment

• in a team teaching environment

• learning under a soft-spoken instructor

• learning disabled

• learning English as a second language

Problem 3 – Instructor Vocal Strain

Vocal strain is inevitable for instructors who have to teach all day in noise cluttered

classrooms, raising their voice in order to be heard and maintain order. The learning

must go on, in spite of the noise. Instructors frequently complain about hoarseness,

pain, and fatigue when speaking, as well as temporary voice loss.

Even in classrooms with relatively low noise levels, instructors must project their

voices to be heard by all students. Often, instructors are forced to project their voices

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Handheld
Microphone

Receiver

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well above a natural and healthy level. The result is higher than average throat and

voice problems.

Research indicates that students typically increase their attention-to-task and show

improved compliance when the instructor is in close physical proximity.17 Close

physical proximity is impossible to maintain for every student in the classroom, even

more so when infectious diseases are going around. When an instructor is forced to

repeatedly redirect students, often using a raised voice, it adds to instructor vocal

strain and heightens the tension and anxiety among the students in the class. It is well

known that some childrens' and young adults' response to a loud, forceful command

can be opposite to the desired behavior. A natural conversational voice level generally

results in the most favorable response.

Components of a Sound Field System

A classroom sound field system consists of a wireless microphone, receiver, amplifier,

and speakers. The instructor's voice is picked up by the microphone and transmitted

to a specialized receiver, which passes the signal on to an amplifier that sends it to

speakers strategically placed in the classroom.

The primary purpose of the system is to ensure that the instructor's voice and program

audio are clearly audible above the background sounds at all instructional locations

within the room. Research has shown that in the average classroom, the instructor's

voice usually arrives at the ears of the students at a level only 6 dB or so above the

background sounds.18 The goal of the sound field system is to amplify the instructor's

voice to approximately 15 dB above the noise level of the classroom, enabling every

student to hear as if the instructor is standing nearby.

Pendant Microphone in

Desktop Charging Station

Some of the components of a sound field system. Other components
include speakers and a mixer/amplifier.

Extron Electronics – Classroom Sound Field Amplification – Rev. A1

An overview of each of the system components:

Microphone: For best results, the instructor microphone should be lightweight to be

worn on a lanyard around the neck or clipped to the clothing. Easy to use controls for

volume, mute, and power give the instructor ultimate control and the freedom to make

adjustments while teaching. For team teaching or group discussions that include guest

speakers or students, a handheld microphone allows others in the classroom to be

heard. Wireless transmission is critical because microphone cables can get caught

on desks and other objects and restrict the instructor's range of movement within the

classroom. Additional features, such as inputs for a portable audio source and external

boom or headset microphone, are desirable.

Receiver: The wireless receiver picks up the signal from one or more microphones

in the classroom, converts the signal to analog audio, and supplies the audio to an

amplifier. Two types of wireless transmission technology are used in sound field

applications: Radio frequency (RF) and infrared (IR). See the sidebar for a comparison

of the two technologies.

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