ABC box for XXX

[jmanpc 5,000+ posts]

So yeah, I want to try something new for the XXX I just got... and I thought... I've never made an ABC box before... sounds like fun...

Does anyone know how to make them around here? I know you're supposed to have 2 chambers, one which is 2/3 of the sub's optimal volume, and a second chamber which has 1/3 of the volume. I also know that there are supposed to be three ports of equal length.... one for each chamber, and one separating the two.

But what I'm confused about is which chamber do you use to determine the tuning of the port? While figuring port area, do you figure in both external ports, or just one? What SQ benefits does it have? I've heard it has a better low end.... but does it do well in upper frequencies?

Fill me in, yo. Help a brotha out.

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[Rawr-DQ 10+ year member]

A bandpass box?

 

[pwnt by pat 10+ year member]

1) model an enclosure for the response you want for a single chamber ported enclosure with two ports of the same diameter (round ports are slightly easier to work with).

2) come up with the design. use net internal volume, plus sub displacement and displacement for three ports

3) divide the box into exactly 2/3 and 1/3 sections.

4) put a third port of the same length as the first two between the two separate chambers.

Tuning will be initial tuning + 1 octave higher. So tune for 30hz and you'll have effective tuning of 30hz AND 60hz. Determining port length comes from using a unified chamber to start with.

I remember hearing of ABC boxes winning a lot of SQ championships years ago. Most of the time you won't notice any real difference in sound as the second resonance doesn't have near the impact of the first. Mostly think of it as a point of extra impedance rise = more cone control.

Here are pics from my build:

 

[Immacomputer 10+ year member]

In my experience, the ABC/DCTV enclosure is a waste of time, space, effort, and supplies. I would only use it in a case of putting large amounts of power into a low excursion driver while tuning in the low 20s. This would give you more cone control over the frequencies that need it. Cone control is the main key in these enclosures.

I noticed no gain in output compared to a ported enclosure tuned to the same fundamental frequency with the same size. It was a little smoother sounding and not as peaky around tuning. The transient response was also a little worse with the ABC. Both enclosures also had the same amount of port area.

Like said before though, you calculate the tuning based on the net volume of both sections and with two of the ports. At lower frequencies, the port between each chamber just acts like a pass through and it pressurizes the other section so the two exterior ports are then loaded.