Editing French horn (section)

===Double horn===
[[File:French horn detail.jpg|thumb|The [[rotary valve|valves]] of a [[Conn-Selmer|Conn]] 6D double horn. The three lever keys (above the large valves) can be depressed toward the large outer tube. The thumb key (''near the left-most valve'') moves inward toward the three finger keys.]]
[[File:French Horn back.svg|thumb|Scheme of a double horn (''view from underneath'')
{{ordered list
| [[Mouthpiece (brass)|Mouthpiece]]
| [[Leadpipe]], where the mouthpiece is placed
| Adjustable handrest
| [[Water key]] (also called a spit valve)
| Fourth valve to change between F and B{{music|flat}} pitches
| Valve levers, operated with the left hand
| [[Brass instrument valve#Rotary valve|Rotary valves]]
| [[Slide (wind instrument)|Slides]], for tuning each valve
| Long tubing for F pitch with slide
| General slide
| Short tubing for B{{music|flat}} pitch with slide
| Bellpipe
| [[Bell (wind instrument)|Bell]]; the right hand is cupped inside this
}}]]
Despite the introduction of valves, the single F horn proved difficult for use in the highest range, where the partials grew closer and closer, making accuracy a great challenge. An early solution was simply to use a horn of higher pitch—usually B{{music|flat}}. The use of the F versus the B{{music|flat}} horn was extensively debated among horn players of the late 19th century, until the German horn maker [[Ed. Kruspe|Eduard Kruspe]] (namesake of his family's brass instrument firm) produced a prototype of the "double horn" in 1897.

The double horn also combines two instruments into a single frame: the original horn in F, and a second, higher horn keyed in B{{music|flat}}. By using a fourth valve (usually operated by the thumb), the horn player can quickly switch from the deep, warm tones of the F horn to the higher, brighter tones of the B{{music|flat}} horn, or vice versa, as the horn player may choose to have the horn set into B{{music|flat}} by default by making a simple adjustment to the valves. The two sets of tones are commonly called "sides" of the horn. Using the fourth valve not only changes the basic length (and thus the harmonic series and pitch) of the instrument, it also causes the three main valves to use proportionate slide lengths.<ref>Backus, John, ''The Acoustical Foundations of Music'', 2nd ed. (New York: W. W. Norton, 1977),{{Page needed|date=June 2015}} {{ISBN|0-393-09096-5}}.</ref>