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Reprinted From the Minnesota Association of School Maintenance Supervisors Newsletter, April 2005

Submitted by IEA

Many classrooms are too noisy for effective learning. According to the Acoustical Society of America (ASA), only 75% percent of speech is intelligible in many U.S. classrooms due to background noise. Recent studies have shown that children, with less developed listening and language skills, are less proficient than adults at understanding speech in noisy environments. Background noise levels need to be at least 15 decibels (dBA2) below the target signal (e.g. the teacher’s voice) for children to understand what is being said.

Background noise levels vary widely. A survey of 32 unoccupied classrooms in eight Ohio schools found background noise levels from 32 dBA to 67 dBA. Classrooms were 14 to 15 dBA louder with the HVAC system operating. A typical teacher’s speaking voice is about 65 dBA. In order to be heard, teachers may raise their voices (to about 78 dBA) which can result in vocal strain, stress and fatigue. Alternatively, some teachers will turn off the HVAC system, resulting in reduced comfort and compromised air quality in the classroom.

Sources of Noise

Background noise may originate from outdoors, adjacent areas, or inside the classroom. The most significant noise source contributing to background noise levels is often the HVAC system. To address this, the Minnesota Department of Education (MDE) requires that mechanical ventilation projects funded under ‘Health and Safety’ meet NC3 (Noise Criteria) 35 at any location where students are seated in the classroom. This requirement must be inserted as performance criteria in the relevant contract language. A third party entity must verify that approved HVAC upgrade/replacement work meets NC-35. Resources for School Districts

The American National Standards Institute (ANSI)/ASA Standard S12.60-2002 addresses acoustical issues impacting speech intelligibility in the classroom. This standard provides limits on noise levels and reverberation 4 times in classrooms and specifies minimum values for sound insulation. It also provides design considerations including selection of construction materials and HVAC systems and arrangement of classroom and non-classroom spaces.

Compliance with the ANSI/ASA standard is voluntary unless it is adopted into code or regulation. However, it provides a “best practices” which can be specified in construction documents for new facilities. School systems in the City of Minneapolis, New Jersey, New Hampshire, Washington DC, and New York City have already adopted acoustical design standards which are comparable to ANSI S12.60-2002.