The passage of an ANSI standard for classroom acoustics makes setting school acoustic standards easier, but who is listening? If the intention is to modify classrooms, what factors should be considered?
"Attention to appearance instead of functionality lies somewhere near the root of the persistence of poor acoustical design of classrooms."1 The passage of an ANSI standard for classroom acoustics makes setting school acoustic standards easier, but who is listening? If the intention is to modify classrooms, what factors should be considered? David Lubman (D. Lubman and Associates) and Louis Sutherland report on how the standard is being received, while Murray Hodgson provides acoustic lessons and pitfalls learned from studying fourteen classroom acoustical renovations at the University of British Columbia.
The Extent of the Problem
The ANSI standard limits classroom background noise and reverberation time. A long reverberation, which allows sound to reach the hearer over time, generally decreases speech understanding. The standard limits noise for unoccupied classrooms to 35 dB(A) for small classrooms, or core learning spaces, with a 0.6 second reverberation limit. Other sizes and types of spaces have slightly different standards. Lubman and Sutherland “estimate from very limited data that about two-thirds of American classrooms fail to meet the 35 dB(A) standard.” Hodgson, using different criteria when surveying 279 classrooms at the University of British Columbia, found that 19% of the classrooms had less than good acoustical quality when assuming a typical-volume male instructor, but the majority of the classrooms studied fell short for a soft-spoken female instructor.
Design Changes Required
Lubman and Sutherland report that open-plan classrooms and rooms with partial-height partitions will not meet the ANSI standard, nor will classrooms without acoustical enhancement, such as acoustical ceilings. They, along with Hodgson, note that the most significant change toward improving acoustics will most often be reducing background noise through ventilation system renovation. Hodgson’s research on university classrooms uses a set of calculations based on acoustical measurements to calculate a numeric value for speech intelligibility. His article provides acoustic snapshots before and after renovation of six university classrooms, and a comprehensive discussion of factors that influence classroom acoustics. To be effective, classrooms must be designed to project sound energy to the back of the room. In the unsuccessful renovations, he found that a major factor was adding too much sound-absorbing material, thus decreasing an instructor’s perceived volume, lowering the sound-to-noise ratio, and making it harder to hear, rather than easier. Hodgson believes that this particular situation occurs because sound-absorbing materials make amplified sound systems perform better. However, he found through questionnaires that “student reaction to the classroom listening environment decreases if the instructor uses an amplification system.” Because occupants absorb and create noise, acoustics can be significantly different depending on classroom occupancy, Hodgson finds—a factor the ANSI standard does not address.
Lubman and Sutherland report that even with the ANSI standard, convincing school planners to invest in acoustics is not easy, due in part to competing priorities and lack of studies on the impact of acoustics on learning outcomes. They advocate increased awareness, including the online resource - http://www.access-board.gov/publications/acoustic-factsheet.htm. Hodgson, Murray. 2004. Case-study evaluations of the acoustical designs of renovated university classrooms. Applied Acoustics, vol. 65 no. 1, pp. 69–89.
1. Lubman, David, and Louis C. Sutherland. 2004. Education stakeholders and the ANSI standard for school acoustics. Sound and Vibration, vol. 38 no. 6, pp. 12–14.