Hollow Frequencies

A sharp metallic ping caught my attention as I stepped out from beneath the canopy. Ahead stood an empty, tall galvanized steel marker pipe fixed firmly into the earth. I approached with slow, measured strides until I stood parallel to its height. Extending one long hand, I lightly struck the hollow rim with the tip of my knuckle. A rich, ringing resonance vibrated up the steel tube. Tilting my top speaker downward toward the open rim, I emitted a synchronized low-frequency hum, listening intently as the cylinder doubled the pitch and sent a warm acoustic vibration pulsing back into the quiet morning air.