The sound level allowed in a space is defined by its function. In a residential apartment, for example, the highest allowed sound level from ventilation units is 28 dB. On the other hand, in concert halls only 25 dB is allowed.

The sound level produced by ventilation and air conditioning units depends on the sound pressure level of the appliances, the air ducts and all the adjustment and terminal parts. To control the sound level in a space a proper sound damping has to be designed in the ducts.