How important are dimensions?

[Lewis Moon]

If I get the volume correct on a sub, how important is it to get the actual dimensions in the right ratio? I have heard it is not as important on a sub....but this design is actually more of a "supplemental woofer" to go with my monitors (weak-ish bottom end). It will be tuned well into the directional range (probably ~ 140 hz). I'm looking more at a tall square box rather than 1-2-3 ratio. The front baffle will be a bit wider than I would like because of shape constraints imposed by a small living room.

[GM]

Until one dimension reaches 1/4 WL long in the speaker's BW to affect vent tuning, not much beyond the fact that as you move away from a golden or acoustic ratio in a large cab it typically requires more damping material to quell any eigenmodes (standing waves) that might reflect back through the driver. For sealed it's just a matter of damping to 'taste', i.e. removing any 'hollow' sound.

Of far more importance is placing the sub ideally within a 1/4 WL of the XO's -12 dB point to each main, but unless multiple subs are used it severely limits the mains' spread and room location to between them, so up to ~1 WL is often used, though with a 140 XO point it may sound a bit disconnected on some music if this far away.

GM