Busy printing.

The centre line of the transmission line is about 0.8 m long.  If undamped, this would have a 1/4 wave resonance at 106 Hz, this is quite a bit lower than the 175 Hz resonance of the driver in free air.  However, the plan is to heavily dampen it to avoid issue with resonances.  There may be a small amount of reinforcement around 106 ish Hz which would be helpful too.  The little driver should see a perfectly absorbent transmission-line and give a clean and clear response with a pleasant and gradual bass roll off.

Going for too long a line was purposful, deeper clean bass, even if attenuated is quite nice.  A roll off at the resonance would be perhaps a bit too high.  Considering that they will generally be playing music from a PC that's running Equaliser APO, with a profile tailored to flatten their response and extend the bass a bit, longer seemed better than shorter.  Also it looks cool.