Hot Tips: Acoustics
Controlling Noise in Classrooms
- By Sean Browne
- May 1st, 2016
Acoustical performance is a vital ceiling selection criterion for classrooms.
The reason: students must be able to hear
and understand their instructor if they are
In the past, acoustical ceilings offered
either good sound absorption to decrease
unwanted sound levels, or good ceiling attenuation
to block unwanted sound intrusion from
adjacent classrooms or corridors, but not both
absorption and blocking in the same ceiling.
Now, the science behind the ceiling is able
to offer a new generation of acoustical ceiling
panels that provide an ideal combination of
sound absorption as denoted by their Noise
Reduction Coefficient (NRC) and sound blocking
as denoted by their Ceiling Attenuation
Class (CAC) in the same panel.
The NRC indicates the ability of a ceiling
to absorb sound. It is expressed as a number
between 0.00 and 1.00, and indicates the
percentage of sound it absorbs. An NRC of 0.60
means a ceiling absorbs 60 percent of the sound
that strikes it. A ceiling with an NRC less than
0.60 is considered low performance, one with an
NRC of 0.70 or greater, high performance.
The CAC indicates the ability of a ceiling
to block sound in one space from passing up
into the plenum and transmitting back down
into an adjacent space that shares the same
plenum. The higher the number, the better the
ceiling acts as a sound barrier. A ceiling with a
CAC less than 25 is considered low performance,
one with a CAC of 35 or greater, high
Regardless of whether it’s new construction
or renovation, the best solution for both
reducing the level of sound in a classroom and
limiting sound intrusion into it is an acoustical
ceiling panel that combines an NRC of 0.70 or
greater and a CAC of 35 or greater.
This article originally appeared in the May 2016 issue of College Planning & Management.
Sean Browne is principal scientist - Global Acoustics for Armstrong Ceilings.