Wayne Parham Messages: 18791 Registered: January 2001
Illuminati (33rd Degree)
15" x 15" x 15" would be a nice box size for that woofer.
But PiAlign won't calculate a port for that box. It was designed to recommend a cabinet size, used mostly for mains cabinets really. It's literally a 1970s program. Not that electro-mechanical alignment software is or even needs to be more modern than that, but still, my point is that is a single-purpose design tool.
You could calculate the port using standard Helmholtz formula. That will be plenty for a sub, no need to do any more analysis.
Subtract the volume displaced by the driver and wood thickness. Without offset, a 15" x 15" a 15" box is 3375in3. If you use 3/4" wood, that will reduce it by about 9003 to ~2450in3. Estimate the volume offset by the woofer at 250in3. That leaves volume at ~2200in3. So calculate Helmholtz frequency using that volume, using the formula below:
Here's a little BASIC program that will calculate the formulas for you:
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