Valves
Valves are used to change the length of tubing of a brass instrument allowing the player to reach the notes of various harmonic series. Each valve pressed diverts the air stream through additional tubing, individually or in conjunction with other valves. This lengthens the vibrating air column thus lowering the fundamental tone and associated harmonic series produced by the instrument. Designs exist, although rare, in which this behaviour is reversed, i.e., pressing a valve removes a length of tubing rather than adding one. One modern example of such an ascending valve is the Yamaha YSL-350C trombone, in which the extra valve tubing is normally engaged to pitch the instrument in Bb, and pressing the thumb lever removes a whole step to pitch the instrument in C. Valves require regular lubrication.
A core standard valve layout based on the action of three valves had become almost universal by (at latest) 1864 as witnessed by Arban's Method published in that year. The effect of a particular combination of valves may be seen in the table below. This table is correct for the core 3-valve layout on almost any modern valved brass instrument. The most common four-valve layout is a superset of the well-established 3-valve layout and is noted in the table, despite the exposition of four-valve and also five-valve systems (the latter used on the tuba) being incomplete in this article.
| Valve combination | Effect on pitch | Interval | Tuning problems |
|---|---|---|---|
| 2 | 1/2 step | Minor second | |
| 1 | 1 step | Major second | |
| 1+2 or 3 | 1½ step | Minor third | Flat * |
| 2+3 or | 2 steps | Major third | Slightly sharp if 2+3 |
| 1+3 or 4 | 2½ steps | Perfect fourth | Sharp * |
| 1+2+3 or 2+4 | 3 steps | Tritone | Very sharp |
| 1+4 | 3 ½ steps | Perfect fifth | |
| 1+2+4 or 3+4 | 4 steps | Augmented fifth | |
| 2+3+4 | 4 ½ steps | Major sixth | |
| 1+3+4 | 5 steps | Minor seventh | |
| 1+2+3+4 | 5 ½ steps | Major seventh |
- * Note that since valves lower the pitch, a valve that makes a pitch too low (flat) creates an interval wider than desired, while a valve that plays sharp creates an interval narrower than desired. Intonation deficiencies of brass instruments that are independent of the tuning or temperament system are inherent in the physics of the most popular valve design, which uses a small number of valves in combination to avoid redundant and heavy lengths of tubing (this is entirely separate from the slight deficiencies between Western music's dominant equal (even) temperament system and the just (not equal) temperament of the harmonic series itself). Since each lengthening of the tubing has an inversely proportional effect on pitch (Pitch of brass instruments), while pitch perception is logarithmic, there is no way for a simple, uncompensated addition of length to be correct in every combination when compared with the pitches of the open tubing and the other valves.
For example, given a length of tubing equaling 100 inches when open, one may obtain the following tuning discrepancies:
| Valve(s) | Desired pitch | Necessary valve length |
Component tubing length |
Difference | Slide positions |
|---|---|---|---|---|---|
| Open tubing | A♯/B♭ | 0" | – | – | 1 |
| 2 | A | 5.9" | – | – | 2 |
| 1 | G♯/A♭ | 12.2" | – | – | 3 |
| 1+2 or 3 | G | 18.9" | 18.1" | 0.8" | 4 |
| 2+3 or | F♯/G♭ | 25.9" | 24.8" | 1.1" | 5 |
| 1+3 or 4 | E♯/F | 33.5" | 31.1" | 2.4" | 6 or T |
| 1+2+3 or 2+4 | E/F♭ | 41.4" | 37" | 4.4" | 7 or T+2 |
| 1+4 | D♯/E♭ | 45.7" | T+3 | ||
| 1+2+4 or 3+4 | D | 52.4" | T+4 | ||
| 2+3+4 | C♯/D♭ | 58.3" | T+5 | ||
| 1+3+4 | B♯/C | 64.6" | T+6 | ||
| 1+2+3+4 | B/C♭ | 70.5" | T+7 |
Playing notes using valves (notably 1st + 3rd and 1st + 2nd + 3rd) requires compensation to adjust the tuning appropriately, either by the player's lip-and-breath control, via mechanical assistance of some sort, or, in the case of horns, by the position of the stopping hand in the bell. 'T' stands for trigger on a trombone.
Read more about this topic: Brass Instrument