Roaring

Effect: A roaring weapon causes target to become shaken and, on a critical hit does 2d6 sonic damage to the target.

Found on: (8) Roaring items:

Improved Roaring

Effect: A roaring weapon causes target to become shaken and, on a critical hit does 2 to 12 sonic damage to the target.

Found on: (6) Improved Roaring items:

Notes: (MrCow's information)

Improved Roaring causes shaken, a -2 morale penalty to-hit, saves, and skills (the description was a poor copy and paste, it is a -2 penalty, not -4 penalty, although they may have put the improper number for the actual penalty amount as well).
Shaken should not stack with shaken. Regardless, Improved Roaring's Shaken stacks with standard Roaring's Shaken.
Shaken is not a curse, thus it stacks with Cursespewing.
Improved Roaring's shaken effect allows a reoccurring save to shrug off due to its duration (as it lasts longer than the standard 6–12 seconds for shaken, it has a maximum duration of 1 minute).
The Improved Roaring effect neglects to mention that it requires a DC will save (DC 28 if I remember, but I'm not certain).
This is also a fear effect so it falters heavily in places like Shavarath where critters get a large bonus vs. fear and mind afflictions.