HANDBOOK OF ACOUSTICS - online book

A complete view of Acoustical Science & its bearings on music, for musicians & music students.

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114
HAND-BOOK OF ACOUSTICS.
All instruments with cupped mouth-pieces are constructed on the same principle as this primitive instrument; that is, they are tubes without lateral apertures, the notes producible upon them being the harmonics of the tube. Now, as will be seen from the table on page 72, there are various gaps in this harmonic scale, as compared with the diatonic and chromatic scale, and accordingly it will be found that the most important departures of brass instruments from the rude type selected above, have been made for the purpose of supplying these missing notes.
The chief instruments of this class are the French Horn, Trum­pet, and Trombone. The French Horn consists of a conical twisted tube of great length, expanding at the larger end into a bell. The fundamental, which is a very deep tone, is not used. As will be seen on reference to the table on page 72, the higher harmonics (for example, those from the seventh upwards) form an almost un­broken scale. To supply the missing notes, the hand is thrust into the bell to a greater or less extent, thus lowering the pitch of the note which is being produced at the time. These instruments are also frequently supplied with keys, which vary the effective length of the tube, and thus produce the missing tones, but at some expense of the quality of tone.
The Trumpet supplies the notes which are wanting to complete its scale in a much more effective manner. An U shaped portion of the tube is made to slide with gentle friction, upon the body of the instrument, so that the tube can thus be lengthened or shortened, within certain limits by the player.
The Trombone is simply a bass trumpet, and in principle is the same as the above. In these brass instruments, the tension, &c., of the lips only determines which of the proper tones shall speak, the actual pitch of the tone being almost entirely independent of the tension itself
The vocal organ, or larynx, is essentially a reed instrument. The reed itself is a double one, and consists of two elastic bands, called the Vocal Chords, or Ligaments, which stretch from front to back across the larynx. When they are not in action, these ligaments are separated by a considerable aperture. By means of muscles inserted in the cartilages to which the vocal ligaments are attached, these latter can be brought close together with their edges parallel. The air from the lungs acting upon them, while in this position, sets them in vibration, in the same way as the air from a bellows operates upon a reed. Variations in pitch are effected by