Fourth-order bandpass

One side of the driver fires into a sealed chamber and the other into a vented chamber. The sealed side creates the low-frequency high-pass behavior; the vented side creates the upper low-pass behavior. Output exits through the vent. Chamber ratio and tuning control bandwidth, efficiency and ripple. A narrow, high-efficiency alignment can be loud but intolerant of music outside its intended band.

Sixth-order parallel tuned

Both sides of the driver load separate vented chambers and both chamber outputs radiate to the outside. Each chamber has its own volume and tuning. Called “parallel” because the acoustic outputs reach the listener through parallel external paths, it can provide broader bandwidth or two strong operating regions. Interaction is complex; simply picking a low number and a high number does not guarantee a smooth bridge.

Sixth-order series tuned

In a series-tuned arrangement, one chamber vents into another chamber, which then vents outside. Energy passes through coupled resonators in sequence. Terminology and drawings vary across modeling programs and shops, so specify the physical layout instead of relying on the label. The intermediate opening and outside port do different jobs and must not be swapped casually.

Eighth-order systems

An eighth-order bandpass generally uses three reactive chamber/vent stages, but several physical layouts can earn the name. More order can create steeper acoustic boundaries and more control points; it also creates more stored energy, more delay variation and more opportunities for misalignment. A diagram showing every chamber, driver face and vent destination is mandatory before construction.

Bandwidth, ripple and group delay

Efficiency is purchased over a selected band. Narrow alignments can build a pronounced peak; broader alignments surrender some maximum gain. Multiple resonances create rapidly changing phase and group delay. Group delay is not automatically audible or evil, but a highly resonant box can sound detached when its decay and passband do not suit the system.

The cone is hidden

Because the driver is internal, you may not hear mechanical warning sounds clearly. Model excursion on both sides of every tuning and use high-pass and low-pass protection. Provide inspection access, strong cooling paths where appropriate and a grille or screen that does not choke the vent. Never treat a bandpass port as a convenient handhold.

Design and build sequence

Start with verified driver parameters and a defined bandwidth/output goal. Model chamber volumes, tunings, vent velocity, excursion, power and losses. Add all displacements. Build access panels with airtight gaskets, brace each chamber and measure the completed resonances before applying serious power. One wrong chamber volume can move multiple features.

Naming without confusion

Online arguments often arise because two people use “series sixth” for different ducts. The only safe language is literal: front chamber volume and its destination, rear chamber volume and its destination, and every port’s area, centerline length and termination. Physics follows connections, not nicknames.

Frequently Asked Questions

Final Word

Enclosure design is controlled energy management. Choose a topology because its size, passband, efficiency, excursion and construction demands fit the vehicle and listener—not because a nickname wins an internet argument. When the drawing, math, build and measurement agree, the “sorcery” becomes repeatable engineering.