For some more reassurance I think you did no harm. The surround on the cone and the cone its self are on the thin side and will change temperature quickly. After 15 minutes I think they would be at room temperature.
The MDF and or other materials will take some time to get to room temps but they don't move (besides a little expansion and contraction due do temp.) So no harm done.
The MDF and or other materials will take some time to get to room temps but they don't move (besides a little expansion and contraction due do temp.) So no harm done.