Poor acoustical design in classrooms can result in excessive noise that is disruptive to the learning process and affects speech perception, student behavior, and educational outcomes. Good acoustical design enhances speech clarity and limits background noise to protect speech quality for both students and teachers. Speech clarity is dependent on the architectural design of a classroom, including size, shape, and surface treatments. Poor acoustics can impact all students, not just those with hearing loss. And teachers, who use their voices most of the time in learning environments, are at risk for vocal injury if they need to talk over the classroom noise to be heard by students.
Although the importance of improving acoustics in classrooms used by children with hearing problems is often recognized, there is often less understanding of the benefits for individuals with typical hearing, including
- students under the age of 15 who are still developing mature language and are less effective listeners for speech in noise (Nelson, Sacks, & Hinckely, 2009);
- students with learning disabilities, delayed development, central auditory processing difficulty, and other speech and language disorders; emotional and behavior disorders; periodic otitis media; chronic illness; and those whose native language is not English;
- teachers who should be able to use a natural teaching voice free from vocal strain.
Classroom noise includes any auditory disturbance that interferes with what a listener wants and/or needs to hear, including
- noise from outside of the building (i.e., exterior noise intrusions, such as highway traffic, playground noise, jets) heard through the building structure;
- noise from within the building (e.g., children walking and talking in the halls, class bells, noise heard from room to room);
- noise from within the classroom (e.g., mechanical noise from the HVAC, clanking water pipes, technology used in the classroom).
Excessive reverberation in a classroom causes additional disturbance due to acoustic reflections. The desired signal is temporally smeared due to reflections, which can also cause an increase in background noise levels.
Typically, if an acoustic environment allows for a +15dB SNR (signal-to-noise ratio) throughout the entire classroom, individuals with normal hearing can hear well enough to receive the spoken message fully. In many U.S. classrooms, however, the speech intelligibility rating is 75% or less, meaning that listeners with normal hearing can understand only 75% of the words read from a list (Acoustical Society of America [ASA], 2000). Students with hearing disabilities, however, will have additional limitations that will not allow them to reach levels for normal-hearing students, irrespective of the SNR (Iglehart, 2009).