Glossary
End correction
Definition
The end correction describes the additional air that moves along at the ends of a tube. As a result, the tube is acoustically longer than it is built.
Values
Link to section “Values”Common factors, relative to the inside diameter D:
- both ends free: 0.614 · D
- one end flush with the baffle: 0.732 · D
- both ends flush: 0.850 · D
An end that terminates flush in a large surface lengthens the tube acoustically more than an end that terminates freely inside the enclosure.
Example: A tube with a diameter of 100 mm, one end flush, is acoustically approx. 7.3 cm longer than built. The port tube calculator subtracts this correction.
Further reading
Link to section “Further reading”- Knowledge Bass Reflex: How the Enclosure with a Port Works
- Calculator Calculate a bass reflex port – length from volume and tuning Calculates the length of round bass reflex ports from net volume, tuning frequency, diameter and number – with end correction depending on mounting.
- Glossary Port The port is the opening of a bass reflex enclosure in which a mass of air oscillates. Whether a tube, slot or shaped channel, together with the volume it determines the tuning frequency.
- Glossary Tuning frequency (Fb) The tuning frequency Fb is the resonant frequency formed by the enclosure volume and the port. Around this frequency it is mainly the port that radiates; the cone barely moves.
Sources
Link to section “Sources”-
Tier C · community
Subwoofer Port Length Calculator – Vent Size & Tuning
AJ Design Software · accessed on 14 September 2026
Port length formula Lv = 23562.5·Dv²·Np/(Vb·fb²) − k·Dv with k = 0.614 (both ends free), 0.732 (one end flush), 0.850 (both flush); reference according to the page: Lindeburg, Engineer In Training Reference Manual, 8th ed. 1992.
-
Tier B · secondary source
Wikipedia · accessed on 14 September 2026
Resonance frequency f = c/(2π)·√(A/(V·L_eq)) with end correction of the neck length.
Updated: 14 September 2026