Yamaha DHR Series Owner's Manual page 12

Setup Examples
Rotatable Horn (DHR10 only)
1.
Using a No. 2 Phillips head screwdriver, remove all fixing screws on the grille, and remove the grille from the speaker.
2.
Using a No. 2 Phillips head screwdriver, remove all screws installed on the horn and pull the horn out from the speaker.
NOTE
Make sure not to push the screws too strongly with the Phillips head screwdriver. This may cause the nuts inside the cabinet to fall off.
Screws (four total)
3.
Rotate the horn 90 degrees, and re-install the horn to the speaker, reversing the steps above.
Vertical
12
Rotate 90°
Horizontal