How exactly does that work? What would be the explanation for how the shield holds back the blight?
Some elements I can think of to consider:
-However it works, the effect would have to extend from the tower radially, since the blight could basically come from any direction, including underground. Since the blight travels primarily underground, you couldn't simply make a wall of these, because eventually the blight would tunnel under them and emerge on the other side. Only things within the sphere would be consistently safe.
-Because buildings would have to be inside the sphere at all times, thought would have to be given to whether this sonic field could adversely effect colonists and machinery.
-Mines would be impossible because any robo-moles that left the sphere would be instantly destroyed. MHD generators would also be impossible because their network of buckeytubes would have to extend far beyond the field.
-Magma wells and geothermal plants would be safe though, because they don't have to send out remote devices to work. As long as this sonic field can penetrate the shafts, any blight being carried by the steam/lava will be dead before it reaches the colony.
- A colony could use these structures to live in a blight infested area where they would be virtually immune to attack, but the fact that it would disable so many important structures, most notably common ore mines, would seem to make it a surprisingly balanced structure. There is no way I can see that it could be abused for too long, as any colony inside these spheres would be completely Dependant on outside support.
(consider also that a non-eden colony could be easily wiped out by using EMP missiles to disable the towers.)
