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 classrooms acknowledges that younger students require more favorable listening conditions because they are still developing their language skills.
Considering Conditions in
Occupied Active Classrooms
A great deal of work has gone into the development of ANSI/ASA S12.60, LEED certification requirements, BB93, and other classroom acoustics standards around the globe. They have filled an important void and provided a much needed basis of acoustic design, but their recommendations do not tell the whole story; they do not encompass the entire range of acoustic experiences found within occupied active classrooms.
Many studies evaluating the effects of background noise on speech levels refer to the Lombard effect. The Lombard effect is the involuntary increase in vocal level to compensate for higher background noise levels, originally observed by French otolaryngologist Etienne Lombard (1911; Brumm and Zollinger, 2011). The Lombard effect is often cited as the reason occupied noise levels in classrooms should be strongly correlated to the unoccupied noise levels. An assumption is made that the background noise level in a classroom is consistent, regardless of occupancy and primarily the result of HVAC systems. Therefore, unoccupied background noise levels should significantly relate to the signal-to-noise ratios experienced by students in occupied conditions due to the Lombard effect. That is, higher unoccupied background noise conditions should result in proportionally higher talker levels in the occupied classroom. However, students in modern K-12 occupied active classrooms experience background noises that stem from more than the HVAC systems.
Our observations from visiting classrooms for our study confirm that assorted instructional equipment is in common, though not constant, use. Such equipment should not be discounted in guidelines recommended in standards. Video projectors are still staples in most classrooms in the United States. Some classrooms use interactive whiteboards, like SMART Boards, but many of these interactive whiteboards still use projector technology (Figure 4). These projectors have fanstodissipateheat,butthefansradiatenoisethatcontributes to the background noise level in the classroom. We have also observednumerouslaptop/tabletchargingcartsinclassrooms with whirring fans that ultimately interfere with speech levels in the room (Figure 5). Instructional equipment can and does contribute to the background noise levels teachers must compete with to communicate with their students.
Figure 4. Many classrooms still use video projector technologies. This is an example of a typical interactive whiteboard that uses a video projector. Video projectors can contribute to the BNLs that teachers must compete against.
Figure 5. The integration of computers into the curriculum necessi- tates charging stations for laptops and tablets provided by the school. These charging stations, like the one shown here, have fans that dis- sipate heat through vents. This is a source of operational noise that can interfere with a teacher’s speech levels.
The sound levels created by the occupants themselves should also not be disregarded. Picard and Bradley (2001) summarized levels of noise in occupied classrooms for students in assorted grades and found the highest levels in the classrooms of the youngest children. K-12 classrooms are complex learning environments in which a number of teaching modalities are used, ranging from single instructor
Fall 2018 | Acoustics Today | 19 Spring 2020, Special Issue | Acoustics Today | 11
   Reprinted from volume 14, issue 3

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