The Subwoofer DIY Page
6th Order Bandpass Systems: Design Notes
last updated: 06 June 2018

The Subwoofer DIY Page

Choosing an alignment
Be careful when choosing a 6th order bandpass alignment for your driver. An ultra-large box with an ultra-low cutoff frequency may not produce the best results, because of the reduced power handling and lower efficiency. Examine carefully the cutoff frequency and box size and tradeoff in efficiency to determine whether or not this alignment lives up to your expectations.

Where should I put the ports?
Ports should be placed at least one diameter away from any adjacent walls. If this is not possible to do this, the tuning frequency for a given port length will be lower than that predicted by the equations, and this may adversely affect the results.

Lining the box
One layer of lining on every wall for each section will generally give better results, as the lining will help to reduce the out of band noise. Ensure that no lining obstructs the ports. Fiberglass will work here, but make sure that none's located near the port entrance, as air turbulence can rip chunks of it off the walls and eject it through the port. Any change in the tuning frequency introduced by lining the enclosure can be adjusting by shortening the port(s) slightly.

Port size
Use the largest ports possible for your design. This will reduce power compression effects and port noise caused by turbulence. Flaring the ends of the port will also produce better results.