HANDBOOK OF ACOUSTICS - online book

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

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110
HAND-BOOK OF ACOUSTICS.
opening apertures in the side, and thus practically altering the length of the pipe; and secondly, by so increasing the wind pressure, as to bring out the first harmonic to the exclusion of the funda­mental, all the tones thus springing up an octave. The quality of its tone is sweet but dull, owing to the want of upper partials. When very softly blown, it gives tones that are all but simple.
Reed Instruments. Two kinds of reed are used in musical instruments, the free reed and the beating reed. Fig. 58 shows the construction of the former.
Fig. 58. It consists of a thin narrow strip of metal called a "tongue" fastened by one end to a brass plate, the rest of the tongue being free. Immediately below the tongue, there is an aperture in the brass plate, of the same shape, and very slightly larger than the tongue itself. Thus the tongue forms the door of the aperture, capable of swinging backwards and forwards in it. If a current of air be driven upon the free end of the tongue, the latter is set vibrating to and fro in the aperture between its limiting positions A and B, fig-. 59. When in the position A, the current of wind
passes through, but when the tongue reaches the position B, the current is suddenly shut off; only when the tongue resumes the position A, can the air again pass. As the vibrations of the tongue are periodic, a regular succession of air pulses are thus produced, giving rise to a musical sound, precisely as in the case of the Syren.
The action of the beating reed is similar to that of the free reed; in fact, the beating reed only differs from the free reed, in having its tongue slightly larger than the aperture, so that it beats against the plate, in closing the aperture, instead of passing into it.
The reed is used in its simplest form in the harmonium, American organ, and concertina. In the harmonium and concertina, the