Young minds (ears) hear only what they know, if
the acoustics interfere.
with inferior acoustics is a long-standing
American tradition. I can remember re-learning
the Pledge of Allegiance when “under God” was
added, having not yet understood who Richard
Stans was, or why the republic was for him.
Later, it became clear that the phrase was “for
which it stands,” not an unknown person.
While small class size may be ideal for
individual attention to the student, the size,
shape, and structure of the classroom is equally
important. College lectures are often in large
auditoria, but the professor can still be heard
The recent trend to larger church sanctuaries
does not prevent the message from reaching an
expanded congregation attending the service, if
acoustics have been addressed and the sound
system is adequate. The same principles hold
true for any classroom, if the students are
well-behaved and attentive.
Classrooms often have a speech
intelligibility rating of 75 or less. This is
the equivalent of missing every fourth word.
This impossible and stressful situation faces
many young students everyday. Acoustics have
most often been improved for the hearing
However, bad acoustics deprive those with
normal hearing but who may have learning
disabilities or problems in processing sound. It
is an increasing problem for those where English
is a second language. Young children are less
able to “fill in the blanks” due to their
limited vocabulary. How many have sung “Bringing
in the Sheep” not knowing what “sheaves” were?
Acoustical requirements vary with room size,
shape and purpose. Where a traditional musical
performance can sound much better with extra
reverb (everyone sounds good singing in the
shower), speech intelligibility generally
requires that reverberation be significantly
less than one second.
The good news, and the bad news, is that
correcting acoustics is a relatively low cost
even before taking into account the toll taken
by poor acoustics on learning. The bad news is
how few know this.
Sound radiates in waves from a point source
until it encounters obstacles. Walls and
ceilings reflect sound back into the room and
block sound from passing through.
Attention to wall detail during construction
will prevent the distraction of outside noise
(analogous to watching outside activity through
a window) and is inexpensive compared to fixing
after the fact. Materials that are heavy, dense,
block sound, but require that air be
trapped to prevent them from acting like a drum,
thereby defeating their purpose.
The material to avoid the “drum effect” is
the same as that needed to reduce reflections,
echo, and reverberation within the room:
Absorption traps sound and is
typically a porous material with many internal
pathways. Sound must travel through the
labyrinth and loses energy in the process,
literally wearing itself out.
A common material for
acoustical wall covering. Although
it has a lower sound absorption coefficient than
the common acoustical wall panel, effectiveness
is made up by having more surfaces covered.
Acoustical wall coverings are often called “wall
carpet,” but floor carpet, although having
acoustical properties, will not always meet fire
codes for vertical installations.
Completing the acoustical picture, there are
two other common components to sound control:
sound diffusion reduces
the intensity of sound by redirecting,
spreading, and scattering it throughout the
Diffusion devices have limited
application to typical classrooms and might only
find use in school band and choral rooms where
ambiance is an enhancement.
vibration isolation for HVAC and
other equipment will prevent machinery vibration
from traveling through the building structure
and using the classroom as a “speaker” to put
noise in the air.
As mentioned earlier, good student behavior
and attention in class are necessary to
learning. Bad acoustics make both harder. When
the brain must sort the important information
from background noise, and try to guess missing
words, it creates stress.
Stress can be manifested as bad behavior.
When someone gives up trying to understand, it
may be seen as lack of attention. Removing the
barriers to learning will clarify cause and
effect in the classroom experience.
Installing an acoustical ceiling and adding
carpet can greatly improve room acoustics. Care
should be taken to ensure that ceiling tiles
have a high rating. Price usually follows
acoustic effectiveness, with cosmetics having
some influence, also.
Acoustical wall covering wears well, is easy
to install, and provides a uniform reduction in
sound throughout the classroom.
panels require less wall surface to achieve the
same acoustical effect and can be made tackable
to double as bulletin boards. However, covering
the panel with excessive amounts of art can
defeat its acoustical purpose.
In summary, the classroom is most effective
as a teaching environment when it is free of
interfering sound reflections (echo and
reverberation), outside noise, and internal
vibration. When speech is clearly heard and
understood, learning can begin.
Nick Colleran is past-president of SPARS
(Society of Professional Audio Recording
Services), past president of the VPSA (Virginia
Productions Services Association), a former
recording artist and recording engineer. He is a
principal of Acoustics First Corporation, which
designs, manufactures, and distributes products
to control sound and eliminate noise for
commercial, residential, and industrial uses, www.acousticsfirst.com.