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Rationale and use of sound field systems: An update

Flexer, Carol

doi: 10.1097/01.HJ.0000293290.02251.08
Page Ten
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1 Remind me, what is sound field amplification?

Sound field amplification is an exciting educational tool that allows control of the acoustic environment in a classroom, thereby facilitating acoustic accessibility to teacher instruction for all children in the room.1

Figure. F

Figure. F

Sound field systems are similar to small, high-fidelity, wireless, public-address systems that are self-contained in a classroom. The teacher wears a small, wireless microphone so mobility is not restricted. The positioning of the remote microphone close to the teacher's mouth or other desired sound source creates a favorable signal-to-noise ratio and produces a nearly uniform speech level throughout the room.2 Since the purpose of the equipment is to enhance speech perception, high frequencies (consonants) are emphasized. My colleague, Cheryl Deconde Johnson, suggests that a more appropriate name for this technology is “sound field distribution system.” I agree.

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2 Why is “sound field distribution system” a better term?

Some teachers, parents, and acoustical engineers interpret the labels “sound field amplification” and “classroom amplification” to mean that all sounds in the classroom are made louder. This misunderstanding may give the impression that sound is blasted into a room, thus raising noise levels, interfering with instruction in adjacent rooms, and provoking anxiety in pupils. In actuality, when the equipment is installed and used appropriately, the reverse is true. The amplified teacher's voice can sound soothing, as it is evenly distributed throughout the room to reach every child. The room quiets as students attend to spoken instruction.

In fact, the listener is aware of the sound distribution and ease of listening only when the equipment is turned off. The overall purpose of the equipment is to have the details of spoken instruction continually reach the brains of all pupils.

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3 What do you mean by “reaching the brains” of children?

Children are rich in auditorally designated neural tissue, but this tissue needs stimulation in order to grow and develop.3 We know that all learning is really about brain access, with subsequent brain growth and development. Therefore, for spoken instruction to be worthwhile, pupils must actually hear and listen to the words. Because children's brains are in the process of developing, they listen differently from adults.

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4 In what ways do children listen differently from adults?

Children do not listen the same way as adults for two main reasons. One, the auditory neurological network in children is not fully developed until about the age of 15. Secondly, children do not bring years of listening and life experience to a learning situation.4 Hence, children cannot perform the automatic auditory-cognitive closure of missed information in the way that adults do.

What I mean is that people can fill in the blanks of missed information only if they have that information already stored in their brain's “data bank” from where they can retrieve it. Because they do not yet have those “data banks,” children need a sharper auditory signal than adults do. Thus, while a classroom might sound fine to an adult, it may be woefully inadequate for typical children who are neurologically undeveloped and have not had decades of language and life experience.

All this means that children require a quieter environment and a louder signal than adults do in order to learn.5 The quieter the room and the more distinctive the auditory signal the better acoustic access there is to a child's brain. Therefore, the real purpose of using this technology is to assist in brain development.

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5 That makes sense. Tell me, what typically happens when a child does not hear well in the classroom?

Hearing problems of any degree—whether caused by a hearing loss, a poor acoustic environment, or a combination of the two—can interfere with the child's development of spoken language, reading and writing skills, and academic performance.6 That is, hearing problems can be described as an invisible acoustic filter that distorts, smears, or eliminates incoming sounds, especially sounds from a distance—even a short distance.

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6 Are you saying that acoustic access to spoken language/instruction is directly related to literacy?


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7 Can you explain how it is related?

To answer that question, I first want to review the five levels of auditory skill development.4,7

  • Detection. The lowest, least sophisticated level, detection is the basic perception that sound is present. Obtaining pure-tone thresholds is a measurement of a person's sound-detection ability.
  • Discrimination. This involves distinguishing between two speech sounds, such as “pa” and “ba.”
  • Recognition. Recognition means selecting a target sound from a known list of alternatives, and is a closed-set task.
  • Identification. This is an open-set task that involves recognizing a target from an infinite set of alternatives.
  • Comprehension. This is the highest level of auditory skill development. Comprehension is achieved when a person can answer questions, follow directions, and hold conversations.

It is critical to note that without basic detection, none of the higher levels of auditory processing can be attained.

Therefore, comprehension, the goal of classroom instruction and the basis of literacy, is dependent on the initial detection of individual phonemes that comprise the spoken message.8 Sound field distribution systems, properly installed and used, make detection possible for every child in the class. Remember, compared with adults, children require a quieter environment and a louder signal in order to learn.

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8 How are America's children doing regarding literacy development?

In the year 2000, data showed that the percentage of fourth-grade students reading at or above Proficient, the level identified by the National Assessment Governing Board (NAGB) as the goal for all students, had increased slightly to 32% from 29% in 1992. These data mean that only about a third of fourth graders in the United States can read at their grade level. Moreover, while scores for the nation's highest performing students have improved over the years, scores of the lowest performing students have declined.9

Of critical importance is that there has been no closing of the education gap between students who are white and students who are members of minorities. Specifically, in 2000, 40% of fourth-grade students who are white and 46% of students who are Asian/Pacific Islander could read at or above the Proficient achievement level.9 However, only 12% of students who are African-American, 16% of students who are Hispanic, and 17% of students who are Native American could read at or above the Proficient level.9

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9 I knew that literacy was a national priority, but I didn't know we faced such challenges! Is there evidence that sound field distribution systems can improve literacy development?

Numerous studies have been reported.1 A recent article by Darai found that sound field systems, when appropriately used, provided significant improvement in literacy achievement of first-grade students.10

A couple of years ago, I reported a study of three first-grade classrooms in Utah where 85% of the children were Native American.11 In the 5 years prior to sound field use, only 44% to 48% of first-grade children scored at the “basic” level or above on the Utah State Core Reading Test. After only 7 months of sound field use, 74% of the 54 children in the study scored at the “basic” level or above.

In a recent study, we found that phonemic awareness skills were most effectively and efficiently taught in pre-school and kindergarten classrooms that had sound field distribution systems. In fact, the fewest at-risk readers came out of the classrooms that routinely used their sound field distribution systems.12

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10 It seems clear that sound field distribution systems can benefit all children, but don't some children require a greater enhancement of the signal-to-noise ratio (SNR)?

Several populations seem to be especially in need of SNR-enhancing technology. These include children with: fluctuating conductive hearing impairments, unilateral hearing impairments, “minimal” permanent hearing impairments, auditory processing problems, cochlear implants, cognitive disorders, learning disabilities, attention problems, articulation disorders, and behavior problems.1 In addition, children with mild-to-moderate hearing impairments who wear hearing aids might do as well with sound field distribution systems as with a personal FM system. Children for whom English is a second language also benefit from the more intelligible signal provided by an enhanced SNR.13

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11 Then, is sound field technology best used in a “treatment” paradigm?

Historically, amplification technologies such as hearing aids, personal FM systems, and now cochlear implants have been recommended as treatments for hearing loss. Because there certainly are populations for whom an enhanced SNR can mean the difference between passing and failing in school, sound field technologies came on the scene as treatments for hearing problems.

If viewed as a treatment, sound field technology is recommended for a particular child and managed through the special education system. One type of sound field technology, the small, portable desk-top unit, has special applicability as a treatment for an individual student.

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12 I'm not familiar with this device. What is it?

A relatively new type of sound field FM system is called a personal sound field unit or a desktop system.14 This is a small, lightweight, battery-powered portable loudspeaker that can be carried from class to class and delivers a clear, close-up sound right to the student's desk. Foster, Brackett, and Maxon found the personal sound field FM system to be particularly helpful for children with cochlear implants, due to the proximity of the loudspeaker to the child.15

However, with the recognition that all children benefit from an enhanced SNR comes the need to move beyond thinking of sound field technology as a treatment. Sound field distribution systems need to be integrated into the general education arena. The concept of universal design can be useful in this regard.

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13 Universal design?

The concept of universal design originated in the architectural domain, with the common examples of curb cuts, ramps, and automatic doors. After years of experience, it was found that the modifications that were originally believed to be relevant for only a few people were, in fact, useful and beneficial for the population as a whole.

In terms of learning, universal design means that the assistive technology is not specially designed for an individual child or a small group of students, but rather for a wide range of students. Universally designed approaches are implemented by general education teachers rather than by special education teachers.16

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14 Won't there be radio wave interference if we use this technology in every classroom of every building?

There certainly can be. We started out by using FM technology for sound field systems. Not surprisingly, interference has been a major problem in some locations. So, more recently, infrared technology has been adapted for the classroom. Because infrared uses light-wave rather than radio-wave transmission, interference is not a problem. Since the signal is contained in the room, every classroom in every building can have a sound distribution system without signal crossover.

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15 Can you use both sound field distribution systems and personal FM systems in the same room?

Yes. In many instances, using both at the same time creates the best listening and learning environment. In fact, I typically recommend using both because each serves a different purpose.

The sound field distribution system, when appropriately installed and used in a mainstream classroom, improves and equalizes acoustic access for all pupils and creates an atmosphere in the room that is conducive to listening.

The individually worn FM system provides the particular child wearing hearing aids with the most favorable SNR. The teacher need wear only a single microphone/transmitter if the sound field unit and the individual FM are on the same radio frequency or if the personal-worn FM transmitter can be coupled to the sound field amplifier.

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16 Aren't classroom acoustics a variable in the effective utilization of sound field distribution systems?

Very much so! The better a room's acoustics, the more effective the sound field system will be. HVAC (heating, ventilating, air conditioning systems) are the primary sources of noise.

Reverberation, the noise generated by speech that is reflected off room surfaces, is the most problematic.17 When there is reverberation, the preceding phonemes blend into the following ones, obscuring the word. Sound field systems are most effective in overcoming noise and least effective in overcoming reverberation. Therefore, reverberation should be reduced as much as possible before a sound field distribution system is installed.

A great deal of attention has been paid to classroom acoustics in the last few years. ANSI has been working on developing a national standard that should be published this year, ANSI S12.6 200_ (hopefully, 2002). This standard calls for noise levels in classrooms to be no higher than 35 dBA. The standard for reverberation of medium-size classrooms will be 0.6 sec and for large rooms 0.7 sec.18 The signal-to-noise level is not specified, but it is implied to be +15 dB because the noise level should be 35 dBA and the average speech level is 50 dBA. The goal is for the ANSI standard to be adapted into the International Building Code (ICB).

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17 How much do sound field units cost, and how can a school district find the money?

The cost of an average sound field FM or infrared system is $1000 per room. When that cost is divided by the number of people who could benefit (about 300 pupils and teachers over a 10-year span) the cost per child is only about $3. What a bargain!

Possible funding sources include community service groups such as local Quota clubs, Lions clubs, Sertoma, and Rotary; parent-teacher organizations; local businesses; state-wide technology grants; and private foundations.

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18 It seems that sound distribution systems are essential to creating a good educational environment. What could interfere with their effectiveness?

Difficulties can result from two primary sources: lack of teacher and administrator knowledge of the rationale and use of the technology, and inappropriate set-up and function of the equipment itself.

Initial in-services to teachers and administrators must emphasize the “brain development” purpose of acoustic accessibility. The relationship of hearing to literacy needs to be addressed, as does the fact that children listen differently than do adults. The concept of signal-to-noise ratio needs to be explained.

Microphone techniques need to be demonstrated to teachers so that they can learn how to use the equipment to teach “incidental listening” strategies. Teachers can speak much more softly and and with more varied vocal inflections because the sound field distribution system provides the “vocal projection.”

Problems can result when teachers place limitations on their teaching or when they teach the same way with the technology as without it. A second microphone in the classroom, a pass-around microphone for the students, can greatly enhance teacher effectiveness.

Equipment problems can result from improper placement of loudspeakers. In fact, loudspeakers are probably the weakest link in the system. If the primary problem in a classroom is noise, place loudspeakers high for coverage and to reduce feedback.17 If the primary problem in a classroom is reverberation, first treat the classroom acoustically to minimize the potential equipment problems, including improper microphone placement, lack of sound balance in the room, poor tuning (not enough high frequencies for consonant enhancement), feedback, interference (if FM transmission is used), and inadequate volume.1 Of course, teachers need on-going support. Someone needs to be designated to trouble-shoot the equipment, and replacement parts such as batteries and microphones must be readily available.

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19 Are there efficacy measures that should be used?

Certainly there is a need for a relatively easy measurement tool that teachers can use regularly to monitor the effectiveness of the sound field distribution system. The SIFTER (Screening Instrument for Targeting Educational Risk) is one such tool.19 The SIFTER relies on the teacher's observations of a child's classroom performance related to listening skills. It targets academic performance, attention, communication, class participation, and school behavior. The teacher fills out this brief checklist.

Another tool is LIFE (Listening Inventory for Education). This is a self-report inventory for school-aged children that measures a student's perceptual change.20 LIFE consists of pictures of common classroom situations that could provide a listening challenge to the pupil. The child indicates how much difficulty is experienced in each listening situation. LIFE could be administered before installation of the equipment and then after about 6 months of use.

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20 Do you have any final comments?

I certainly do! Every once in a while, a possibility arises that can transform lives. It may be so simple that it is not believable. Sound field distribution technology is just such an amazing possibility for children's classroom learning and literacy development.

Hearing is a first-order event in regular education classrooms. If a child cannot clearly hear spoken instruction, the entire premise of the educational experience is undermined. Due to poor acoustic conditions and a variety of hearing and attending problems, millions of children are being denied an appropriate education.

There has been an increasing awareness of the benefits of sound field distribution systems. For example, Oakland County, MI (Detroit area), is amplifying all 5000 of its kindergarten through fifth-grade classrooms. Momentum is building across the country.

I am so convinced about the effectiveness of the technology that my personal stand is that every classroom in this country should have a sound distribution system by the year 2005.

There are now many suppliers of sound field systems. Among the vendors that have been in the business for many years are:

Have you ever found yourself in the back of a room, struggling to hear a soft-spoken lecturer in the front? Often the room has poor acoustics, which makes your task even more difficult. You cock your head from side to side and maybe even try to peek between the people in front of you to pick up some lipreading cues. No matter how hard you try, you still have trouble picking up key words. As time goes on, frustration sets in, and gradually the distant voice of the lecturer is replaced by daydreams of more pleasant experiences.

Wouldn't it be a shame if this sort of thing happened to a child in a classroom? It does!

Sound field amplification is a readily available technology that has been proven to enhance classroom instruction. Recent data show that no more than a third of the fourth graders in the U.S. are reading at grade level. Would widespread use of sound field amplification improve this alarming statistic? Researchers say yes. Yet, after many years of documented benefit, this technology remains woefully underutilized.

If you were searching for an audiologist to devote much of his or her career to championing the cause of improving hearing and learning conditions in the classroom, qualities such as dedication, persistence, and enthusiasm would come to mind. Many of you know this month's Page Ten author, Carol Flexer, PhD, and I think we'd all agree that she personifies these qualities.

You can read about her work in this area in the second edition of her book Facilitating Hearing and Listening in Young Children. Dr. Flexer is professor of audiology at the University of Akron and a past president of both the Educational Audiology Association and the American Academy of Audiology. Recently, she received the prestigious Volta Award from the Alexander Graham Bell Association for the Deaf and Hard of Hearing for her research and contributions to children with hearing loss.

Carol tells us that when not attending to the children of the world, she also finds time to spend with her own children and grandchildren, which means frequent visits to Israel.

In this Page Ten article, Dr. Flexer clearly reviews the benefits possible from sound field amplification—or, to use her term, “sound field distribution systems.” It's hard to disagree with her conclusion that the time has come for this to become a standard feature in every classroom. In fact, Carol says she's committed to making that happen by 2005. Maybe we can help make that objective a reality!

Gus Mueller

Page Ten Editor

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