Baffle and bullet-type silencers block a portion of the air stream and will cause additional pressure drop (PD). Since the silencer itself can generate noise (because it disturbs the airflow), its self-generated noise has to be added to the attenuated sound level.

The baffles/bullets are usually filled with sound absorbing material.Īcoustic performance of duct silencers is generally described in terms of “insertion loss”-the measure of noise level reduction determined by comparing the noise level without a silencer to the noise levels with silencer. The silencer is basically a series of perforated sheet metal baffles (rectangular silencers) or bullets (circular silencers) placed inside a silencer single or double wall outer solid shell. The most common acoustic attenuation method for HVAC duct systems is to install a silencer (i.e., sound attenuator or sound trap).Ī silencer attenuates sound when it is directly inserted in the ducted air stream (path). Acoustic remedies are required if the sound pressure levels within the critical space exceed the sound pressure levels per frequency of the corresponding NC or RC curve.

Sound trap sound control systems