Dyads on the contraforte are possible but only have a dynamic range between pianissimo and piano. I use a very tight embouchure with equal lip pressure at the back of the reed to execute them. Below is an example of a mezzo-piano dyad progression with the fingerings: Dyads #1

Examples of Isolated Dyads:
Dyad #2

Dyad #3

Dyad #4

Dyad #5

Dyad #6

Dyad #7

Dyad #8

Dyad #9

Dyad #10

