It is important

It is important to note that there are two (2) different types of piping and ductwork
noise that are typically encountered. Breakout noise is noise that radiates radially out
away from the pipe or duct. Breakout noise is caused by the wall of the pipe or duct
vibrating due to the fluid passage within. Stream noise is noise carried along with the
fluid as it flows down the pipe or duct. This noise is most apparent at outlet grills or
registers in ducting systems. Stream noise must be controlled via the introduction of
silencers, attenuators, turning vanes and similar into the air path within the ductwork
which serve to minimize air turbulence. This paper will not discuss the control of
stream noise.