Agent27 said:When doing a subtone, you dampen the vibrations of the reed. This is often accomplished by putting more lip on the reed. The more surface area of lip on the reed, the more the sound is dampened. I do this moving my lower jaw back and rolling out my lip (pouting) so that more of the inner part of my lip in on the reed. You have to blow a little harder to get a solid sound when you do this.
There's also a technique called sub-tonging. That's where, with a normal embouchure, you lightly touch your tongue to the reed. Again, it dampens the vibrations of the reed. You have to do it light enough so that a sound is still produced. Think of pronouncing the letter "n". Say "dud-nnn".