How a transmission line tunes
A transmission-line (TL) enclosure loads the back of the driver with a long, folded duct. The line behaves like an organ pipe: it resonates when its length equals a quarter of the wavelength at the tuning frequency, reinforcing the low end at that point. Builders usually tune the line near the driver's free-air resonance Fs.
This calculator solves the quarter-wave length for your target frequency. Real lines are commonly tapered (cross-section narrowing toward the terminus) and stuffed with damping, which lowers and broadens the effective tuning — model the full response, taper and stuffing in the enclosure designer.
Results are modelled estimates — verify by measurement. Looking for another calculator? See all tools & calculators.