Bandpass Enclosure
This page is the fast math bridge for a 4th-order bandpass box: one sealed chamber, one ported chamber, and one tuning target that punishes sloppy guessing.
Tiny Version
Bandpass boxes trade bandwidth for efficiency around a target range. The sealed chamber and ported chamber have to agree, or the whole box becomes a complicated mistake.
Core Relationships
- Sealed chamber - usually starts around 0.6 to 0.8 times Vas.
- Ported chamber - often starts around 1.5 to 2.5 times Vas.
- Port tuning - treat the vented chamber like a real ported enclosure, not a decoration.
Useful Approximations
Peak frequency:
f_peak ~ sqrt(f_upper x f_lower)
Simple chamber start:
Vs ~ 0.7 x Vas
Vp ~ 1.5 to 2.5 x Vas
What The Math Is Telling You
- Smaller bandwidth usually means a stronger peak.
- Higher efficiency around the target band usually means worse behavior outside it.
- The ported chamber still needs the same honest port-area and port-length work as any vented box.
Common Mistake
Do not treat bandpass as a shortcut to "louder." It is a more constrained design than sealed or ordinary ported, and it gets ugly fast if the chamber ratio or port math is guessed instead of calculated.