Port Length Calculator

Your details

Inside diameter of one round port tube.
in
How many identical port tubes you are using. Two ports each half the area of one large port give the same tuning.
Internal airspace after subtracting woofer displacement, bracing, and port tube volume. Start with gross volume and subtract those items.
ft³
The Helmholtz resonance frequency you want the box to hit. Lower values give deeper extension; higher values give more output at mid-bass.
Hz
A flanged end (flush-mounted or T-nut) adds a small effective length. Most car-audio ports are one flanged (inside) and one free (outside), so 0.732 is the correct default.
Port length
8.05

Physical length of each port tube needed to hit the target tuning frequency

Port length unitin
Port area (each)12.57
Port area unitin²
Total port area12.57
Area-to-volume ratio5.03
Estimated port velocity5.4m/s
5.4 m/s
Quiet<17Moderate noise17-30Chuffing30+

Port length: 8.05 in at 35 Hz

  • Each port tube needs to be 8.1 in long to tune the box to 35 Hz.
  • Estimated port velocity is 5.4 m/s, well below the 17 m/s quiet threshold. Port noise should not be an issue.
  • Area-to-volume ratio is 5.0 in²/ft³, below the 12 in²/ft³ minimum. Port noise at high excursion is likely.

Next stepA tuning of 35 Hz targets musical deep bass, well-suited for daily listening. Subtract the port tube volume from your gross enclosure volume to confirm the net volume used here is accurate.

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