This month, writing for three instruments will be discussed. This can be for any of a combination of horns in a horn section: 2 Trumpets & Tenor Sax; Trumpet, Alto Sax, Tenor Sax; Trumpet, Alto Sax, Trombone; etc.
In writing for three horns, write the lead line first, which is usually the trumpet line. As in Part 1, observe the range requirements for this and all other instruments. Then write the next two parts just below the trumpet line. Your concert pitch work score will now look something like this:
Exp. 1, Concert pitch:
The horn section will sound more full, more powerful if the chord notes are spread out. A simple method known as "drop two" may be employed. Simply drop the middle voice of Example 1 down one octave.
Exp. 2, Concert pitch, "drop two": 
Sidebar: At this point some of you may question the fact that I have parallel fifths in these examples. So? There is nothing wrong with parallel motion. The "no parallel fifths or octaves" rule is not applicable to modern music. It is applicable to writing chorales for homework in beginning music theory classes. It has no place here. Let us forget that useless rule and move on.
Finally, the top voice is transposed for the lead trumpet, the middle voice is then transposed for the second trumpet or alto sax. The lowest voice, originally the middle part in Exp. 1, is transposed for the tenor sax.
Exp. 3, Written parts, "drop two": 
If the lowest voice is to be written for trombone, be sure to observe that instrument’s range. But if the lower two voices are to be saxophones, with trumpet lead, there will usually
be no problem. The saxophones will usually fall into their proper range
Next month, let’s add a bari sax to the horn section.
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Take Five
