I know I shouldn't worry about it too much but here's the thing... to go from a 14.5 Hz tune with the same port to a 13.0 Hz tune would require around 23% increase in net cabinet volume, or a 28% increase in the length of the port (all other things staying the same). A 5% discrepency I wouldn't worry about. Even 10% I could understand, but over 20% seems like something must be wrong, so I just want to try to understand what is going on.
The cabinet fill definitely was/is playing a role, and I did not properly account for it in my design plans. So last night I yanked a bunch of the polyfil out and tested it again. The Fb came up to around 13.5 Hz. However, my crusty old piece-of-**** signal generator is producing something that looks halfway between a sine wave and a triangle wave, so that is probably skewing the results. I need to get a real signal generator or maybe use the soundcard in my PC as a signal source and try the test again.
Another reason I'm concerned about the tune: 13 Hz wouldn't be a bad tune for a larger box but at 17 cubic feet, it's far from ideal. Even my target of 14.5 Hz could be considered a little low relative to the size of the box.
It's not the end of the world or a crisis or anything. Just trying to understand what's going on and learn from it. With the second sub in place and a little EQ, I'm sure I won't be wanting for output and low end extension.
