If the problem is for low C, then it is almost certainly to do with the pad seating (or a linkage problem causing bad seating). This is the most common adjustment to become `out` on a flute.

If it is only low B, then it is more likely to be the configuration of those rollers, which cannot be avoided no matter what flute.

To check low C, get somebody else to hold those two key cups firmly closed, and see if low C is easier to play. If so, you have a seating (or linkage) problem.

I own a Gemeinhardt 3SB and I can project the lowest C through a 50 piece orchestra at most mp sections. It really must be supported well.

A great deal of flutists that I`ve played with in community orchestras cannot play a low C when it is called for and when it is played it is quite often weak without the airflow to support it and that is on Pearls, Yamahas, Gemeinhardts, Bundys, Armstrongs etc.

A great deal of flute music doesn`t give you the chance to practice low Cs. A nice simple book such a Melodious and Progressive Studies for Saxophone is a wonderful collection of melodies ranging from low B to high E/F. A nice lower tone workout.