The B1-3D S5 is a deeper version of our B1-3 S5, and it’s a great orchestral mouthpiece with a very deep cup and huge sound.  The inside rim contour is rounded, but the outside edge has a medium contour.  It is comfortable on the chops without too much “bite,” but the rim feels a little wider and less rounded than the B1-1 series.  The cup depth is slightly deeper than the conventional 1B, and it’s popular with player who like that size and depth, but want better intonation, an easier upper register and more consistent feel in all registers.