Acoustics & Sound For Musicians - Online Book

The Theory Of Sound Which Constitutes The Physical Basis Of The Art Of Music.

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Bl                                RESONA TORS.                     [HI. § 42.
simultaneously sustained it is generally difficult, and often impossible, for the unaided ear to decide whether an individual note is, or is not, present in the mass of sound heard. If, however, we had an instrument which intensified the note of which we were in search, without similarly reinforcing others which there was any risk of our mistaking for it, our power of recognising the note in question would be propor­tionately increased. Such an instrument has been invented by Helmholtz. It consists of a hollow ball of brass with two apertures at opposite ends of a diameter, as shown in Fig. 25.
Fin. 25.
The larger aperture allows the vibrations of the external air to be communicated to that within the ball; the smaller aperture terminates in a nipple of convenient form for insertion in the ear of the observer. The air contained in the ball resounds very powerfully to one single note of definite pitch, whence the instrument has been named by its in-
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