All the crooks, a list of the principal of which is appended, therefore necessarily give real sounds lower than the above series according to their individual length.
Table of Principal Crooks now in Use.[17]
| Key of Crook. | Actual Sounds of Range of Useful Harmonics. | Length of Crook in Inches. | Transposes to | |
| B♭ alto | 2nd to 10th | 16 | major 2nd lower | |
| A♮ | 2nd to 10th | 22½ | minor 3rd lower | |
| A♭ | 2nd to 10th | 29½ | major 3rd lower | |
| G | 2nd to 12th | 36¾ | perfect 4th lower | |
| F | 2nd to 16th | 52½ | perfect 5th lower | |
| E | 2nd to 16th | 61 | minor 6th lower | |
| E♭ | 2nd to 16th | 70¼ | major 6th lower | |
| D | 2nd to 16th | 80 | minor 7th lower | |
| C basso | 3rd to 16th | 101 | 8ve lower | |
| B♭ basso | 3rd to 16th | 125 | major 9th lower |
The practical aggregate compass of the natural horns from B♭ basso at the service of composers therefore ranges (actual sounds) from
or with 3 valves from
By means of hand-stopping, i.e. the practice of thrusting the hand into the bell in order to lower the sound by a tone or a semitone, or by the adaptation of valves to the horn, this compass may be rendered chromatic almost throughout the range.
The principle of the valve as applied to wind instruments differs entirely from that of keys. The latter necessitate lateral holes bored through the tube, and when the keys are raised the vibrating column of air within the tube and the ambient air without are set in communication, with the result that the vibrating column is shortened and the pitch of the note raised. The valve system consists of valves or pistons attached to additional lengths of tubing, the effect of which is invariably to lower the pitch, except in the case of valve systems specified as “ascending” tried by John Shaw and Adolphe Sax. Insuperable practical difficulties led to the abandonment of these systems, which in any case were the exception and not the rule. The valves, placed upon the U-shaped slides in the centre of the horn, are worked by means of pistons or levers, opening or closing the wind-ways at will, so that when they are in operation the vibrating column of air no longer takes its normal course along the main tube and directly through the slides, but makes a détour through the extra length of tubing before completing its course. Thus the valves, unlike the keys, do not open any communication with the ambient air. Even authoritative writers[18] have confused the two principles, believing them to be one and the same.