Hoot Tube

This demonstration uses an open propane flame. Ensure adequate clearance from flammable materials, paper, clothing, and overhead obstructions. Keep a fire extinguisher nearby and know emergency shut-off procedures. Never leave the flame unattended.

The hoot tube produces a very loud, sustained tone (potentially 90+ dB) that can be startling and uncomfortable. Warn students before starting, and limit continuous operation to 10-15 seconds to avoid hearing fatigue. Consider using hearing protection for prolonged demonstrations.

Purpose

A propane flame inside a tall cardboard tube drives thermoacoustic resonance, producing a loud sustained tone. Students observe how heated convective airflow excites standing waves in the tube at a frequency determined by the tube length.

Tall cardboard carpet tube standing vertically on the floor next to a small blue propane cylinder connected by rubber hose to a Bunsen burner at the base, in front of a chalkboard

Figure 1: The hoot tube apparatus showing the tall resonance cavity (carpet tube) positioned above the propane burner. When the flame is centered within the tube, rising heated air excites acoustic standing waves at the fundamental frequency.

Bunsen Burner

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Propane Cylinder with Nozzle

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Warning: Open Flame Hazard

Warning: Loud Sound Warning

Purpose

Safety Warnings

Warning: Open Flame Hazard

Warning: Loud Sound Warning

Purpose