Large spiral duct acts like a drum and carries fan rumble

Large thin-wall round duct can resonate. Check vibration source first, then add approved acoustic isolation, wrap, or stiffening.

Airflow, Noise, Vibration & TAB 1st Year GREEN

Watch out

Do not assume more sealant will fix low-frequency duct rumble.

Check

Confirm the noise source: fan, vibration, air velocity, or loose support.
Check flex connector and equipment isolation.
Look for loose hangers or duct skin vibration.
Verify approved acoustic treatment before wrapping.
Retest after each correction to avoid chasing noise blindly.

Steps

Confirm the noise source: fan, vibration, air velocity, or loose support.
Check flex connector and equipment isolation.
Look for loose hangers or duct skin vibration.
Verify approved acoustic treatment before wrapping.
Retest after each correction to avoid chasing noise blindly.

Say this to your foreman

The spiral main at [location] is amplifying fan rumble like a drum. I checked supports and isolation. Do you want acoustic wrap/stiffening or equipment isolation reviewed first?