Ok, back online again. As mentioned I've done quite a lot of measurements, and posts some here. First of all I wanted to determine the difference in port tuning with 45 cm vs. 55 cm vents.
First I measured the port resonance frequency with one port stuffed and both open and 45 cm vent tubes. One port stuffed gives about 17 Hz, both open it's about 22 Hz. I'm a bit confused over this because theese are the figures I got when simulating 55 cm vents.
Measuring the driver gives this picture. Blue curve: both open, red: one stuffed and grey: both stuffed.
This is the driver and port measurements in one picture, 45 cm vents, one port stuffed. I have not adjusted the magnitude of the two signals.
So, what about the 55 cm vents? Well, I expect something is wrong, there's a leakage or something disturbing the resonance of the tube, because I did not expect anything like this. Here we compare 55 vs 45 cm vents, both open. Black is 45 cm, purple 55 cm. As we see, when both are open, the resonance of 55 cm is lower than 45 cm vents.
This is one port stuffed. Green line is 55 cm, blue 45.
I'm not sure what causes the difference in magnitude in these measurement, but I might have posisioned the mike differently or something. They are taken som time apart because I had to disassemble the side panel. I did have some trouble attaching the bends, because they don't actually fit the vent tubes outer diameter. Event though the tuning is not lower with 55 cm vents, they give more output at the lower frequencies At 12 Hz the 45 cm vents is down by 5,5 dB from it's peak at 17 Hz, but the 55 cm vents is down only 3 dB at 12 Hz from it's peak at 17,5 Hz.