This is a subject on which players can never seem to get enough information. Some are unsure where the main tuning slide is located; others think there should be a Bb tuning slide located someplace on the instrument. There are even experienced players who pull the wrong slides when trying to tune one or the other of the horns. Still, one of the greatest problems players face is learning the correct procedure to get the Bb and F horns in tune with each other.How to tune a double French horn
Step 1. Push the tuning slides all the way in. Then throw the horn into Bb and tune the open tones of the Bb horn, using the main tuning slide. It's usually necessary to pull the main tuning slide from 1/4 inch to 1/2 inch to bring the Bb horn down to pitch. The whole horn is purposely built sharp when the main tuning slide is pushed all the way in. When the main tuning slide is pulled and the Bb horn is brought down to pitch, the F horn will still be sharp. From this point on, do not touch the main tuning slide.
Step 2. Release the change valve; the horn will go back to F. Tune the open tones of the F horn by pulling the F tuning slide. At this point, both the Bb horn and the F horn open tones are in tune.
Step 3. When the open tones on both the Bb and F horns are in tune, first draw the valve slide on the Bb horn, then the valve slide on the F horn to bring all valve-tones into perfect tune.
Be sure never to tune the F horn first. That's because it will be thrown out of pitch when the main tuning slide is moved to tune the Bb side of the horn. The main tuning slide affects both horns simultaneously.
DOUBLE FRENCH HORN
A. WATER SLIDE
Not used for tuning. (See below)
B. MAIN TUNING SLIDE
Tunes both Bb and F horn open tones.
C. F HORN TUNING SLIDE
Tunes F horn open tones.
ABOUT THE WATER SLIDE
This slide is used as a water slide and as a convenience when cleaning the instrument. However, it is a part of the F horn circuit and will affect the tuning of the F horn only, and the slide should always be pushed all the way in.