Ductulator

More complex systems with direction changes
(elbows/offsets) within 3x diameter upstream or downstream of the fabric
inlet
need lower velocities to prevent duct movement from turbulent airflow.

Sound sensitive applications such as recording
studios,
libraries, classrooms, etc. need even lower velocities to reduce air
movement
noise. Sound attenuation prior to fabric should be considered (fabric or
metal
silencers, duct lining).