Solutions: Acoustical Modifications
ECH’s Position on Acoustical Modifications and the ANSI Standards
ECH fully supports any attempt to reduce
reverberation and background noise both in existing classrooms
and in new construction. Particularly in new school construction,
it makes sense to design and select building materials, aware
of acoustical implications. Ideally, ECH would like steps
taken to ensure the optimal acoustic environment AND integration
of sound enhancement technology. The sound enhancement system
will itself be more effective under better acoustic conditions.
However, school districts are constantly
forced to make decisions under the constraints of limited
finances and human resources, reducing the number of options
available. ECH is concerned with the economic feasibility
and the realistic attainment of the ANSI specified standards.
We believe that use of sound enhancement equipment is the
most COST-EFFECTIVE method to ensuring that ALL students regardless
of seating proximity can hear their teacher and peers.
Use of these systems and the positive impact on student academic
performance has been validated in over 50 research studies,
including those funded by the U.S. Department of Education.
To better understand why we recommend sound enhancement over
acoustic modifications (when schools only have one option),
please refer to “Problems:
Enhancement Systems: Description and Rationale”
and “Sound Enhancement
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
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
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:
- 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