References (download and view these PDFs):
of Classroom Design
Precursor to ANSI
New Zealand Experience
Many aspects of our busy modern times have deteriorated the public schools
classroom acoustical environment, such that teaching in them is more challenging
than ever (ask any public school teacher). In past times one could create
a quiet and pleasant classroom with natural ventilation to a quiet outdoors,
or convection heating. Absorbent ceilings (often of asbestos) were installed in the early to
mid 20th century. But changes occured. Mechanically driven air conditioning
became the norm. Asbestos has had to be removed, and that was not always
replaced by an equivalent sound absorber, thus introducing more reverberation.
Noise in the classroom became the norm.
Around 1995, the acoustical attributes of classrooms became a serious matter
of attention to members of the Acoustical Society of America, including Mike
Nixon, Dave Lubman, Lou Sutherland, and later myself. It was clear by then
through studies by John Bradley of NRC Canada that speech intelligibility
in rooms suffered when any amount of noise was introduced. More than a decade
previous, in 1983 and 1987, I had participated in a study on the acoustical
design of building interiors, bringing to my attention the results of John
Bradley of NRC Canada. He had concluded that only a reverberation time of
1/2 second or less and a noise level as low as NC-25 provided optimimum speech
intelligibility in a room, especially for young listeners and in the United
Sates and Canada for listeners for whom English was a second language (ESL)
. A decade later, it was evident that these conclusions should become the
goal for good classroom acoustical design.
These members of the Acoustical
Society then formed a Working Group under the American National Standards
Institute. We first produced a 'white paper' on classroom acoustics;
Download and view:
White Paper Precursor to ANSI
Then we produced ANSI 12.60, a standard that contains the recommended classroom
acoustical design methods and objectives. It is largely a compendium of facts,
data and architectural design recommendations that are adopted in whole or
in part by municipalities and school administrations to ensure that their
renovated and new schools will be optimum places of learning. Others had been thinking about this as well. Download
In a nutshell, classrooms should be designed to have
a background ambient (HVAC and net external noise) level of less than 35
dBA (less than NC-30) and a reverberation time of less than 1/2 second. In
detail, they considered the following factors:
- HVAC has advanced to the point where air
conditioning has been designed into and retrofitted to many old classrooms.
It is now clear that that the ideal background noise level for the
teaching environment is a maximum RC/NC/NCB-25. Both address the problem
of speech intelligibility across a room.
- Reverberation time (RT) must be reduced
to 1/2 second by installing sound absorption materiel on the walls and ceiling.
In previous years, sound absorption material often contained asbestos. That
has all been removed or passivated. Carpet has a lesser effect on reverberation
time. Its main function is to minimize surface generated noise (foot
and chair scuffing). Carpeting may be targeted for removal, due to its propensity
to harbor molds, .
- Urban noise has increased due to transportation
evolutionary developments. The noise isolation of windows and doors to the
exterior may not have been proportionately upgraded.
- Student behavior is perturbed by social
and family changes.
Recent research by several
acoustical interests clearly shows that excesses beyond RT=1/2 and NC-25
will result in proportionately poorer teaching environments. ANSI
S12 W/G 42 has profduced the ANSI 12.60 standard that recites these problems
and presents clear guidelines for good engineering and architectural design
practices for classroom noise control, reverberation reduction and sound
What to do? Where
Steps that noise control consultants,
architects, administrators and parent teacher associations in your district can now take are as follows:
Survey classrooms and teachers to identify noisy environments. Inspect these
rooms for the presence of sound absorbers. An acoustical tile ceiling, or
walls covered with loose fabrics or bookshelves will suffice. Determine the
reverberation time if possible. If you have access to a sound level meter,
determine whether the ambient noise (vacant room, normal air conditioning
fan on) is not more than 30dBA.
With a companion, evaluate the room-to-room sound isolation.
You should not be able to carry on a conversation between rooms using your
raised voices. "Open-Plan" spaces might
have been inadvertently designed according to 'open-office' parameters that
are NOT recommended for classroom learning spaces.
Clearly, demising walls
that do not extend to the ceiling or roof above will leak distracting sound
from one classroom to another. When acoustical tile is lightweight (e.g.
fiberglass), sound will purvey through them to the adjacent room despite
that wall. It is preferred that the wall partition be extended to the underside
of the floor or roof above. If good room-to-room sound isolation is not found,
make a careful record of these facts (notebook entries). Then bring this
matter up at the next PTO, PTA or School Board meeting.
The HVAC and background noise limit of any room is determined by the intended
use of that room, e.g. a private residence, bedroom, classroom, auditorium,
etc. In the case of classrooms of any size, reduction down to and including
RC/NC/NCB-25 is productive. The offending noise source is most commonly a
ventilation fan associated with air conditioning or room air recirculation.
Sound attenuation devices for built-in fans, and alternative air fans need
to be required. The addition of acoustical tile and/or sound absorber panels
for reverberation control - to achieve the 1/2 second reverberation time
- will reduce background noise in any room. Construction suppliers
or manufacturers can be surveyed for these practical noise control materials.
To reduce reverberation, sound absorber panels and acoustical
tile are appled to the classroom surfaces.
To reduce the transmission of sound from outside sources
(traffic, adjacent rooms) wall and window materials are chosen that have
higher sound transmission loss (TL and STC) vales. Transmission loss (TL,
STC) data are often available from manufacturers on a frequency band basis.
(TL applies to windows and walls, usually of concern only for noisy outdoor
environments such as near freeways and airports.
Design and test for quiet HVAC and reverberation control often requires the
services of an experienced acoustical consultant. Our successful projects
include numerous school and higher education projects in Ohio, for instance,
download and view this PDF:
If you have acoustical or noise control design problems you would like to
discuss, feel free to call, FAX or E-mail us any time.
3201 Ridgewood Drive
Hilliard, Ohio 43026
PHONE 6 1 4 - 8 7 6 - 5 1 0 8 & FAX
// Cell 6 1 4 - 5 6 0 - 0 5 1 9
For more information on this topic...
Angelo J. Campanella,
P.E., Ph.D., FASA, (Principal)
Last updated 26-December-2014
Site by Point & Click Software,