SmartSMS User Manual
Soft dB inc.
User Manual
p. 94
10.6 Openings in the Ceiling
Openings in the suspended ceiling can create sound level irregularities in the rooms. Many
ventilation systems have their air return through the plenum space. These systems have many air
return grills located on the suspended ceiling. These openings do not provide much transmission
loss and, therefore, the sound is louder below the opening, resulting in uneven sound masking in
the building. This effect is increased if the loudspeaker is near the opening and it is reduced if the
loudspeaker is more than 5 feet away, but still, irregularities are detectable.
Figure 88: Illustration of the problematic openings
In typical closed offices, it is strongly recommended to add acoustic treatment on the air return grills
to obtain better sound masking results in the room. The easiest solution is to install acoustic
deflectors on the air return grills. These deflectors are treated with acoustic liner material and are
simply placed on the air return grills to reduce the noise that comes out.
Figure 89: Acoustic deflector
In open areas, these openings are generally less problematic, probably because of the larger size
of the room. Thus, the installation of acoustic deflectors is not often required. However, in some
cases, when air return grills are large (2 feet by 4 feet for example), or when the ceilings are low,
acoustic deflectors may be required.
