The classroom is an auditory verbal environment in which accurate transmission and reception of speech between the teachers and students is essential for effective listening and learning to occur. Undesirable room acoustics can degrade the quality of the speech signal and make education more difficult for many children. If the premise of our educational system is to provide learners with the best opportunity to learn, undesirable classroom acoustics undermine the premise and are cause for great concern.
Several key acoustic characteristics of classrooms determine the adequacy of the speech signal received by the student. The two of greatest importance are the signal-to-noise ratio (SNR) of the teacher's signal received by the student and the long-duration reverberation time (RT) of the room.
The SNR refers to the relative intensity of the teacher's speech compared with the level of any background noise in the classroom as measured at the student's location. RT refers to the length of time a signal persists in a room after the original signal has ended. Sometimes this persistence of sound is referred to as sound reflection or echoes in the classroom. Research has demonstrated that inappropriate levels of classroom noise and/or reverberation can compromise not only speech perception but also reading scores, spelling ability, behavior, attention, and concentration in children with normal hearing. Inappropriate SNR and RT are even more deleterious to children with hearing loss or children who are at risk for listening and learning (see Crandell, Smaldino, & Flexer, 2005, for a review of these studies).
Background noise and reverberation occur simultaneously in the classroom, and it is important to understand their combined effect on speech. A dramatic example of the interplay between classroom acoustics and speech was reported by Leavitt and Flexer in 1991 using the Rapid Speech Transmission Index (RASTI)—a measure of speech energy as it traverses a room and an index of the amount of energy available to be perceived when influenced by SNR and RT. The researchers showed that 84% of the speech energy delivered in the front of the classroom was available to a listener sitting in the front row of a typical classroom-sized environment. In the back row of a classroom, however, only approximately 50% of speech energy was available. Even less of the signal would be available to the listener with hearing loss and/or reduced auditory/language processing, further decreasing the student's actual perception of available speech energy. When the impact of the classroom acoustical environment is added to the signal distortion imposed by a damaged or incomplete auditory or linguistic system, it is readily apparent why simply using a hearing aid is unlikely to result in a satisfactory communication environment in the classroom.
Classroom Acoustics Standards
Professionals have been aware of the impact of acoustics on speech perception for some time, but it was not until 1995 that ASHA published a position statement and guidelines for acoustics in educational settings. These documents focused on the adequacy of classroom environments for children with hearing loss and made recommendations for SNR and RT in classrooms. In 2002 the American National Standards Institute (ANSI) published the ANSI S12.60 standard, Acoustical Performance Criteria, Design Requirements and Guidelines for Schools (ANSI, 2002), which for the first time designated a standard
methodology and targets for achieving adequate acoustic environments in schools. The targets include a background noise level not to exceed 35 dBA and long reverberation not to exceed 0.6 seconds in a typical classroom. The acoustic recommendations are similar to those in the earlier ASHA document and, also like the ASHA document, make compliance with the standard entirely voluntary.
These standards can be adopted when designing classrooms. Building codes also can be modified to include good acoustics, making the classroom listening environment no less important than items already in most building codes, such as adequate lighting and ventilation. Every effort should be made to meet the background noise and reverberation standards as a first step in improving listening and learning environments for all children.
Five Steps to Better Acoustics
In 2005 ASHA updated the 1995 document and published Guidelines for Addressing Acoustics in Educational Settings. The revised document essentially affirms the SNR and RT recommendations in the 2002 ANSI standard. The ASHA document also describes the important professional roles of audiologists and speech-language pathologists in raising awareness of classroom acoustics issues and improving classroom acoustics environments, including five action steps listed below.
1. Advocate and Educate
Audiologists, SLPs, and veteran teachers are aware of the impact of undesirable acoustics on classroom listening and learning. Generally, however, acoustics are not taken seriously by administrators during classroom construction and/or renovation. Anderson (2004) gives four reasons for this situation: as adults with mature auditory-linguistic systems, they do not experience the difficulties experienced by children when listening in a degraded environment; they are not familiar with the database of information regarding the impact of acoustics on learning; they believe that only children with hearing loss require good acoustic environments; and they are unaware of health consequences to teachers and costs to the school.
Audiologists and SLPs, especially those who work in the schools, have a responsibility to take an active role in educating administrators and advocating for classroom environments in which students can learn. Audiologists and SLPs can be proactive by:
- Developing primers on classroom acoustics and/or the effects of poor acoustics on listening and learning
- Identifying themselves as resource people on classroom acoustics for teachers, parents, principals, and other administrators
- Playing an active role in disseminating information about classroom acoustics to the public and to policymakers
2. Take a Survey
Audiologists and SLPs typically are the first professionals to identify at-risk populations or situations. Educational audiologists have long assessed classroom acoustics and student performance within their learning environments. The ANSI standard specifies acoustic measurement procedures that should be used to determine background noise and reverberation, and audiologists are uniquely positioned to take these acoustical measurements in the classroom and compare them to the standard.
The ANSI performance criteria require that the background noise level not exceed 35 dBA (the "A" weighting is used in environmental acoustics because it approximates how the human hears), and that the RT60 (the amount of time it takes an average sound pressure level in a room to decrease 60 decibels after a source stops generating a sound) not exceed 0.6 seconds for an average classroom.
Audiologists can choose from a variety of behavioral inventories, such as the SIFTER (Anderson, 1989), the LIFE (Anderson & Smaldino, 1998), or the CHILD (Anderson & Smaldino); speech recognition inventories (spondaic words and sentences); and classroom performance measures (on-task behavior measures, achievement test scores) to demonstrate the link between acoustic conditions and actual behavioral performance of students in the classroom.
3. Modify Conditions
A clear and complete speech signal greatly facilitates the development of oral expressive language and reading skills, so improvement in the speech-to-noise ratio and reverberation must be made across all of a child's learning environments that do not comply with the ANSI criteria (Anderson, 2004). Audiologists and SLPs can identify undesirable acoustical conditions and recommend improvements. Consultations with an expert in room acoustics can provide recommendations for physical modification of the classroom environment; these acoustic improvements can maximize the advantages of other technologies audiologists frequently recommended.
Proper hearing aid fitting is often a first step for children with hearing loss, but hearing aids are not designed to deal with all listening needs. The biggest limitation of hearing aids is their inability to make the details of spoken communication audible when there is competing noise and/or when the listener cannot be close to the speaker. Assistive listening devices include a range of products designed to solve the problems of noise, distance from the speaker, and room reverberation or echo that cannot be solved with a hearing aid alone (Boothroyd, 2004). These products include a personal FM unit or installation of SNR-enhancing technology such as sound-field systems.
Sound-field technology is an exciting educational tool that allows control of the acoustic environment in a classroom and facilitates acoustic accessibilty of teacher instruction for all children in the room (Crandell, Smaldino, & Flexer, 2005). A sound-field system looks like a wireless public address system but is designed specifically to ensure that the entire speech signal—including the weak, high-frequency consonants—reaches every child in the room. By using this technology, an entire classroom can be amplified through the use of up to four wall- or ceiling-mounted loudspeakers.
The teacher wears a wireless microphone transmitter, and his or her voice travels on radio waves (FM) or infrared light waves to an amplifier that is connected to the loudspeakers. There are no wires connecting the teacher with the equipment; the radio or light wave link allows the teacher to move about freely, unrestricted by wires. The loudspeakers are designed and positioned to improve the SNR uniformly throughout the room in the areas in which instruction occurs.
It could be argued that virtually all children benefit from sound-field amplification systems because the improved SNR creates a more favorable learning environment. Studies continue to show that sound-field amplification systems facilitate opportunities for improved academic performance (Crandell, Smaldino, & Flexer, 2005; Mendel et al., 2003). Recognizing the positive impact of better SNR in classrooms, some school systems have the goal of amplifying every classroom in their districts (Knittel, Myott, & McClain, 2002). The populations that seem to be especially in need of SNR-enhancing technology include children with fluctuating conductive hearing losses (ear infections); unilateral hearing losses; "minimal" permanent hearing losses; auditory processing problems; cochlear implants; cognitive disorders; learning disabilities; attention problems; articulation (speech) disorders; and behavior problems.
Teachers report that they also benefit from using sound-field technology. Many report that less energy is needed for voice projection; they have less vocal abuse and are less tired at the end of the school day (Blair, 2006).
Sound-field amplification systems enhance the classroom learning environment to facilitate inclusion and response-to-intervention (RTI). Inclusion refers to the practice of placing children who previously would have been educated in self-contained classrooms into mainstream classrooms, where they require a good acoustical environment. RTI modifies instruction for struggling students to help them improve performance and achieve academic progress. To meet the needs of all students, the educational system must use its collective resources to intervene early and provide appropriate interventions and supports to prevent learning and behavioral problems from becoming larger issues (Butler & Nelson, 2005).
4. Establish Efficacy of Improvements
Classroom modifications to improve listening and learning must be validated. Validation can be accomplished with pre- and post-modification physical acoustic measurements, behavioral report inventories, speech recognition tests, or other classroom performance measures. Any acoustical improvement must be documented to demonstrate that improvements persist over time.
5. Provide Interventions
The behavioral and psychological effects of trying to listen and learn in a poor acoustic environment may linger after the physical acoustic inadequacies have been addressed. Additional intervention may be necessary to implement a comprehensive approach to removing all of the listening and learning barriers produced by poor room acoustics. Some (re)habilitation interventions include listening training in the classroom and/or home, use of clear speech, phonological awareness training, visual communication training, communication repair strategy training, or auditory training.
The importance of providing a high-quality speech signal for classroom listening and learning for all children is well-documented. Recent standards and guidelines have provided acoustic criteria and offer suggestions for how audiologists and SLPs can promote implementation of the standards. We must all work to make good classroom acoustics a norm in our schools—not a luxury.