4th-Order Bandpass Estimator

This is a STARTING POINT, not a validated design. It does not model the true coupled bandpass frequency response — that requires simulation software (WinISD, BassBox Pro). Run whatever this produces through real simulation before cutting any wood. See data/bandpass-enclosure-design.md for the full sourced reasoning on why bandpass can't be hand-calculated the way sealed/ported boxes can.

Only 4th-order (sealed rear chamber + ported front chamber) is covered here. 6th-order (parallel or series dual-ported) and 8th-order are deliberately out of scope — 8th-order is genuinely SPL-competition-only territory, and 6th-order (especially series-tuned, with 7 interacting variables) is complex enough that a hand-calculated starting point wouldn't be defensible. Both need real simulation software, not a general calculator like this one.

Driver & rear (sealed) chamber

Pick a driver from the database (optional) Vas (driver's rated equivalent volume, ft³) Qts Target Qtc for the rear chamber

0.707 is a flat, daily-driver tune — same default as the sealed-box formula elsewhere in this app. Higher = boomier, lower = tighter/more damped.

Front (ported) : rear (sealed) volume ratio

Sourced guidance disagrees between roughly 1.2:1 and 3:1 — this is a real, documented disagreement, not a single right answer. Try a few values in this range; only real simulation will tell you which one actually lands on your target frequency for your specific driver.

Front (ported) chamber tuning

Target port tuning frequency (Hz)

Guidance found: tuning near 0.9x driver Fs narrows the passband (tighter bass); near 1.1x widens it; up toward 1.6x raises peak output at the cost of looseness/accuracy. This is a real tradeoff, not a default to blindly copy.

Port diameter (in) Number of ports

Port end condition

One flanged, one free (typical) Both ends flanged Both ends free (rare)

Result (starting point only)

Fill in the driver parameters and tuning target, then hit Estimate.