Tuning transforms a hollow tube into a resonant chamber. You must seal every joint with silicone caulk.
Leaky joints kill bass efficiency. They cause annoying rattles that ruin your mix.
Stuff foam inside the enclosure. It eats standing waves and tames unwanted resonance.
Blow into the pipe to test your work. Any hiss means you missed a spot.
Re-seal until it is airtight.
Proper sealing forces all energy through the drivers.
This makes the sound tighter. It feels more controlled.
Skip this step and your audio will sound muddy.