Solutions: Acoustical Modifications

The speech perception and recognition difficulties experienced by ALL students and the research proving the direct relationship between poor acoustics and impaired academic performance, lead one to easily conclude the necessity to improve classroom acoustics. Because children need a signal to noise ratio (meaning the teacher’s voice to be at least 15 decibels louder than the background noise) for intelligible comprehension, one recommendation would be to modify the classroom facilities in an attempt to reduce background noise and reverberation.

In 1998, the U.S. Access Board joined with the Acoustical Society of America (ASA) to support the development of a classroom acoustics standard. These standards were adopted by the American National Standards Institute (ANSI) in 2002 and subsequently became referred to as ANSI S12.60-2002 (“the ANSI standards”), Acoustical Performance Criteria, Design Requirements and Guidelines for Schools. Some school systems have adopted these standards; however, in most cases, compliance is voluntary.

The ANSI standards specify the acoustical conditions needed to achieve acceptable speech intelligibility for teachers and students in mainstream classrooms: maximum background noise of 35 decibels and reverberation time of .6 to.7 seconds in unoccupied classrooms. These standards are most applicable in the design stage for new school construction and in consideration of major school renovation projects.
It is available for download free from ASA at http://asa.aip.org/classroom.html. ASA has also published two manuals for architects on classroom acoustical design, available at the same URL. Volume 1 is a design manual; Volume 2 outlines key acoustical issues in learning. A series 5 technical assistance documents for teachers, educator, and designers, entitled “Listening for Learning” is posted at http://www.quietclassrooms.org/ada/ada.htm.

According to the U.S. Department of Education, National Center for Education Statistics, about one-fourth (28%) of all public schools were built before 1950, and 45 percent of all public schools were built between 1950 and 1969. Seventeen percent of public schools were built between 1970 and 1984, and 10 percent were built after 1984. Therefore, the majority of schools in this country are existing older schools, and unlikely to implement the ANSI design and specification requirements; yet some may argue that acoustical retrofitting is still possible to some extent.

Before any steps can be taken to modify or improve classroom acoustics, the source of the problem must be determined. Noise needs to be controlled at the source or its path in a classroom environment. “Most remedial work will occur along the sound path, as it is likely that replacing noisy equipment (such as through-wall HVAC units) will not be feasible outside the scope of a major alterations program.” ⁱ If the source cannot be easily identified, professional help may be required.

The following are suggestions from the U.S. Access Board (taken directly from www.quietclassrooms.org/ada/adahandout5.htm) to reduce reverberation and background noise.

Steps to Reducing Reverberation

This is easier to remedy if an acoustical tile ceiling already exists. These suggestions are listed in sequence from inexpensive to costly:

• Replace existing ceiling tiles with high-NRC-rated acoustical tiles;
• Add new suspended acoustical tile ceiling if room height permits; if not, mount high-NRC-rated acoustical tiles to the ceiling with maximum possible air space;
• Add sound-absorbing panels high on walls at sides and rear of room.

If the classroom has a very high ceiling (>11feet), acoustical panels on both ceiling and walls may be needed. Carpet adds little to reverberation control, but may be useful for controlling self-noise, especially in pre-school and lower grades.

Steps to Reducing Background Noise

Windows: (often the weakest link)

• Add storm windows
• Replace existing windows with new thermal insulating units (this will improve energy performance, too)
• Install specially-fabricated sound-reducing windows.

Doors: Check doors for gaps. If they’re over 1/16” consistently, they should be treated.

• Add good quality drop seals and gaskets
• Replace doors with tight-fitting solid core doors with seals and gaskets
• Install special sound-control doors if adjacent spaces are very noisy.

Heating, Ventilating and Air Conditioning HVAC

HVAC noise is a common culprit in noisy classrooms. Teachers often turn off the HVAC during important lessons. In the past, it has been common practice to install fan-coil and similar through-the-wall heating and cooling units in classrooms. This puts the fan and compressor right in the room with the students. Children with hearing loss should not be seated near an HVAC unit (or diffuser). Noisy through-wall, through-roof, or under-window units in the classroom should first be serviced and balanced to be sure they are operating as intended. Next steps include:

• Add a custom built sound enclosure around the unit(s)
• Add sound-lined ductwork to the unit(s) to attenuate air distribution noise
• Replace the unit(s) with quieter split systems or one of the quieter European through-wall models just entering the US market.

Other “fixes” to existing noisy ducted systems may include:

• Increase open area at grilles and diffusers
• Rebalance system to reduce air volume delivered to the classroom
• Relocate ductwork and diffusers away from key teaching locations
• Add separate duct runs to eliminate noise from common use
• Add duct length to attenuate noise
• Add soundlining to ducts

Additional suggestions for reducing room noise levels are as follows:

• Position the seating arrangement so that students are distant from high noise sources (fans, A/C unit, etc.) if possible
• Use tennis balls or rubber tips on the chair legs
• Avoid open classrooms including temporary or sliding walls that separate instructional areas
• Diminish the sound from keyboards (on computers) by using rubber pads or carpets under the keyboards
• Whenever possible, locate all computer equipment in a separate “computer/technology” room in the school.
• Encourage students to wear shoes with soft-soles