I've been considering doing a DIY sub for a few weeks now. First I was thinking of just getting a kit, now I'm thinking of doing everything myself. Now I'm considering DIY loudspeakers too, but I have a few questions regarding both.

1. If a sub or speaker calls for 1ft^3 (for ease of understanding) do the dimensions matter? Could it be 12x12x12, 18x16x6, or 24x12x6? Or should these dimensions be as close as possible to a cube?

2. If builing an MTM speaker and let's say each driver calls for .25ft^3 if used separatley does this mean the enclosure should be .75ft^3? Or is there a formula of some sort for this?

3. Let's say the speaker from #2 above has all 3 drivers at 50w RMS/ 75w max, what would the speaker be rated at in terms of watts? 150? Or, again, is there some sort of formula for this?

I appreciate any input you might have for me.

Mike