Hey didgerimbu.
I'm afraid you've been misguided, to my knowledge, there is only one type of horn/toot/trumpet sound. Perhaps you can elaborate?
But instruments above a certain length (1m - 1m20) have more than one toot. This is because of the physics of the didgeridoo, and in order to find them, you'll have to increase the pressure of your lips/mouth/diaphragm even more than for the original toot.
For example, 2m long instruments are known to have 4 or 5 toots (or 6?).
However, in traditional playing, only the first toot is used, never the others.
I hope that answered your question!
