Decades of research on the topic of room acoustics and the effect of poor acoustics on listening and learning in the classroom have led to certain tenets concerning classroom acoustics (Crandell & Smaldino, 1999; Nelson, 2000).
These tenets are so important, that they have formed the basis for guidelines and standards designed to ensure adequate acoustics for listening and learning. In 1995 the American Speech-Language-Hearing Association (ASHA) published “Position Statement and Guidelines for Acoustics in Educational Settings,” that called for background noise levels not to exceed 30 dBA, reverberation times not to exceed 0.4 seconds or less, and an overall teacher signal-to-noise ratio (SNR) of +15 dB. Generally, these specifications were confirmed in 2002 when the American National Standards Institute (ANSI) published “ANSI S12.60-2002 Acoustical Performance Criteria, Design Requirements and Guidelines for Schools” (ANSI, 2002), that, based on room size, recommends that background noise level not to exceed 35 dBA, reverberation time (RT) not to exceed 0.6–0.7 seconds, and a SNR of +15 dB.
It is clear that audiologists and acoustical consultants can and should work closely together in order to accomplish improvements to acoustic conditions in schools. Since guidelines for this collaboration do not exist, it is appropriate to first consider the complementary roles of audiologists and acoustic consultants by examining a tailored description of each profession:
As can be seen, both professions are concerned with maximizing the desirable perception of wanted acoustic signals in rooms and minimizing undesirable noise and reverberation. This common ground forms the basis for the complementary roles undertaken by each profession in improving classroom acoustics. Table 1 shows the typical professional roles of audiologists and acoustic consultants.
It is evident that children with hearing loss require special consideration of their listening needs in a classroom setting if they are to access verbal instruction as fully as possible within the limitations of their hearing loss. Careful monitoring of the use of teacher and supplementary FM microphones is necessary to ensure that the full spoken message is conveyed to the child using the FM system. The use of an FM system alone will not adequately address these listening needs when a classroom is noisy or reverberant. For the young listener with hearing loss, the combination of adequate classroom acoustics and FM technology is necessary to assure that noise will not be a barrier to learning within a classroom. The use of a sound field classroom amplification system in a classroom that meets the ANSI acoustics standards may benefit children with normal hearing and the teacher. However, the use of this technology alone cannot be considered appropriate to meet the needs of students with hearing loss, whether they are hearing aid or cochlear implant users.
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Sound field amplification improves the signal-to-noise ratio (SNR) in a classroom by using a microphone transmitter to amplify the teacher's voice over low levels of background noise and deliver this signal to one or more speakers in the ceiling or along the walls of a classroom. Sound field amplification technology has been used in classrooms since the inception of the Mainstream Amplification Resource Room (MARRS) Project in 1978. A National Distribution Network project for 15 years, MARRS actively distributed information throughout the 1980s and early 1990s to educators describing the benefits of sound field amplification use for children with normal hearing and mild hearing loss. The MARRS Project research indicated that amplification of the teacher's voice in the classroom resulted in greater academic achievement at a faster rate for all learners, at 1/10th the cost of instruction in unamplified resource rooms for identified children with hearing loss (Sarff, 1981; Ray, 1987, 1989, 1992; Ray, Sarff, & Glassford, 1984).
Subsequent researchers found that the use of sound field amplification in the classroom provides significant improvement in word and sentence recognition for typical students with normal hearing (Crandell & Bess, 1986, Jones, Berg, & Viehweg, 1989; Crandell, 1993), students with developmental disabilities (Flexer, Millin, & Brown, 1990), non-native English learners (Crandell, 1996; Hodgson & Montgomery, 1994; Crandell & Smaldino, 1996b; Mayo, Florentine, & Buus, 1997; Eriks-Brophy & Ayukawa, 2000; Nelson & Soli, 2000), and for students with minimal degrees of hearing loss (Jones, Berg, & Viehweg, 1989; Neuss, Blair, & Viehweg, 1991). In addition to improvements in speech perception, consistent use of amplification of the teacher's voice has been found to improve the academic performance of typical learners (Sarff, 1981; Flexer, 1989; Osbourn, VonderEmbse, & Graves, 1989; Ray, Sarff, & Glassford, 1984; Flexer, 1992; Ray, 1992; Zabel & Tabor, 1993; Flexer, Richards, & Buie, 1993; Rosenberg, Blake-Rahter, Allen, & Redmond, 1994) and learners with minimal hearing loss or histories of fluctuating middle ear effusion (Schermer, 1991; Flexer, Richards, & Buie, 1993). Improved on-task or listening behaviors have been indicated as a benefit of sound field amplification use for preschool, primary, and secondary school students (Benafield, 1990; Gilman & Danzer, 1989; Allen & Patton, 1990).
The use of sound field amplification can improve the SNR of listeners in a typical classroom setting, thereby improving speech perception and learning. Sound field amplification can overcome the effects of low level background noise and speech degradation due to student-teacher distance; however, this technology cannot overcome the smearing effects of inappropriate levels of reverberation. Therefore, sound field infrared or FM technology can be one tool that may help to improve the SNR to the desired +15 level in classrooms with reverberation times of 0.6 seconds or lower. When appropriate levels of reverberation and low background noise are present in a classroom, this technology may be beneficial in addressing the listening needs of children with normal hearing, those with minimal or fluctuating degrees of hearing loss, those with developmental learning problems, or students who are non-native English speakers.
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As has been discussed, classrooms are recognized as reverberant and noisy learning environments with typical levels of noise ranging from 53–74 dB (Finitzo-Hieber, 1988). Hearing instruments have been found to be ineffective in providing benefit to speech perception in environments with noise in excess of 60 dBA (Duquesnoy & Plomp, 1983). Every single dB gain in SNR results in an increase in the intelligibility of speech by listeners with hearing loss (Duquesnoy & Plomp, 1983). A SNR of +15 or better is recognized as being necessary to assure that noise will not be a barrier to learning within a classroom (ANSI Standard, 2002).
Although it is possible to achieve a +15 SNR in a classroom through use of adequate acoustic treatment and noise control, it cannot be assumed that adequate acoustics will overcome the effects of degradation of speech across distance and interference of minimal or fluctuating noise for children with hearing loss. In addition to a highly favorable SNR, studies have indicated that the child with hearing loss also requires the primary signal to be present within the critical listening distance (Picard & Lefrancois, 1986, Crandell, Holmes, Flexer, & Payne, 1998; American Speech-Language-Hearing Association, 2002; Anderson & Goldstein, 2003; Anderson, Colodzin, Iglehart, Goldstein, 2003) or in an environment that has a reverberation time of less than 0.4 seconds (Blair, Myrup, & Viehweg, 1989; Noe, Davidson, & Mishler, 1997; Iglehart, 2003) if true access to verbal instruction is to be achieved.
Listeners consistently have a higher level of speech perception performance when ear-level or desktop FM devices are used, whether they have hearing that is normal (Nabelek & Donahue, 1986; Nabelek, Donahue, & Letowski, 1986; Smith, McConnel, Walter, & Miller, 1985; Blake, Field, Foster, Platt, & Wertz, 1991), whether they are hearing aid users (Picard & Lefrancois, 1986; Blair, et al., 1989; Benoit, 1989; Moeller, Donaghy, Beuchaine, Lewis, & Stelmachowicz, 1996; Noe, et al., 1997; Boothroyd & Iglehart, 1998; Toe, 1999; Anderson & Goldstein, 2003; Anderson, et al., 2003) or whether they are cochlear implant users (Foster, Brackett, & Maxon, 1997; Crandell, et al., 1998; Anderson, et al., 2003). Under classroom acoustic conditions that meet the ANSI standards, the use of an ear level FM system can result in an improvement in word discrimination up to approximately 20% (Picard & Lefrancois, 1986) as long as the individual with hearing loss has a word discrimination ability in quiet of at least 40%–60% (Boothroyd & Iglehart, 1998). An increase of up to 25% improvement in word discrimination can occur under ideal reverberation conditions (i.e., 0.3 RT) (Boothroyd & Iglehart, 1998). Listeners with severe to profound hearing loss that have word discrimination scores in quiet above 20% can benefit from the use of personal FM by an increased attention to verbal instruction and a decrease in dependency on note taking or cued/signed supplemental information (Toe, 1999). The use of desktop FM can provide equal benefit to speech perception of listeners with mild to moderate-severe hearing loss that have word discrimination scores in quiet above 75% (Anderson, et al., 2003).
Listeners who are cochlear implant users need a minimum of +10 SNR to function communicatively (Fetterman & Domico, 2002) but require at least a +15 SNR if they are to be expected to access verbal instruction (Hamzavi, Franz, Baumgartner, & Gstoettner, 2001), even in a classroom that meets the ANSI acoustic standards. An improvement of approximately 15–20% in word discrimination scores may be achieved by children using implants in +15 SNR conditions as compared to +10 SNR (Hamzavi, et al., 2001). Enhancement of SNR provided by a desktop FM device can improve word discrimination scores by approximately 20% (Foster, Brackett, & Maxon, 1997). Cochlear implant listeners with word discrimination scores of 60% or less may perform better with the FM signal input into their speech processor directly rather than via a desktop FM device (Anderson, et al., 2003).
Research investigations have determined that the use of classroom sound field amplification provides no significant benefit over hearing aids alone (Anderson & Goldstein, 2003; Anderson et al., 2003) or cochlear implants alone (Crandell, et al, 1998; Anderson, et al., 2003) unless the reverberation time is very low (Blair, et al., 1989; Noe, et al. 1997; Iglehart, 2003). Even in a low reverberation environment, performance is better with devices presenting the improved SNR signal within the critical listening distance than presentation by soundfield FM or infrared devices presenting the teacher's voice throughout the classroom (Nabelek & Donahue, 1986; Nabelek, et al., 1986; Noe, et al., 1997).
Research indicates that the use of hearing assistive technology (e.g., FM systems, sound field amplification) for children with normal hearing, children with hearing loss or listening problems, as well as nonnative English learners is often beneficial. This is true in classrooms with appropriate acoustics as well as those that do not meet the ANSI acoustical criteria. The use of hearing assistive technology must be considered on and individual and classroom-by-classroom basis. Audiologists are uniquely qualified to evaluate the need for and provide expertise in recommending, selecting, and fitting hearing assistive technologies and should be consulted prior to the application of these devices and systems.
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