Then and Now: Horn
The horn of the Baroque Era was a coiled length of conical brass tubing (two complete revolutions) with a metal mouthpiece inserted at its playing end and a flaring bell at its distal end. To the mouthpiece end of the tubing a combination of crooks, couplers, and spacers can be added to extend the tubing to a length that will produce a desired fundamental and the partials in its harmonic series. Three vent holes that can be stopped with corks in various combinations are present in the first turn of the main coils; these assist the performer in sounding some partials with better intonation.
The horn during the Classical Era was structurally quite similar to the Baroque natural horn. The most striking design difference between this horn and its predecessor is that it includes a tuning slide midway in the course of the instrument. Midway through the body's coil are two open and parallel lengths of tubing that accept one of two U-shaped tuning slides of different lengths, each one attuning the instrument to different pitch standards (one for A-430, the other for A-440). Crooks (four for the pictured instrument) are still added to the playing end of the tube to determine the instrument's fundamental pitch and harmonic series.
By the second quarter of the 19th century brass instrument makers in Europe were beginning to design valve mechanisms and incorporate them into their instruments, resulting in chromatic rather than natural horns. The modern 'double' horn pictured here is outfitted with three bi-level rotor valves, one level used for the 'side' of the horn tuned to F, the other for the B-flat side. An additional thumb-operated rotor valve brings into play one or the other side of the instrument. Each of the three main rotors brings into play a different length of additional tubing for each side, and seven different combinations of them, along with overblowing these lengths, are all that is needed to provide the player with the tube lengths necessary to produce a chromatic scale on each side of the horn.
Excerpts from the improvised cadenzas for the same work played on a Classic era natural horn (first clip) and the modern double horn with rotary valves (second clip) provide a comparison of the sound qualities of these two instruments.