Page 126 - The Master Handbook Of Acoustics

101
SPEECH, MUSIC, AND NOISE

Wind Instruments
Resonances in the three-dimensional room are discussed in detail in
Chap. 15. In many musical instruments, resonance in pipes or tubes
must be considered primarily one dimensional. Standing-wave effects
are dominant in pipes. If air is enclosed in a narrow pipe closed at both
ends, the fundamental (twice the length of the pipe) and all its har-
monics will be formed. Resonances are formed in a pipe open at only
one end at the frequency at which the pipe length is four times the
wavelength, and results in odd harmonics. Wind instruments form
their sounds this way; the length of the column of air is continuously
varied, as in the slide trombone, or in jumps as in the trumpet or
French horn, or by opening or closing holes along its length as in the
saxophone, flute, clarinet, and oboe.
The harmonic content of several wind instruments is compared to
that of the violin in the spectrograms of Fig. 5-10. Each instrument has
its characteristic timbre as determined by the number and strength of
its harmonics and by the formant shaping of the train of harmonics by
the structural resonances of the instrument.

Nonharmonic Overtones
4
Harvey Fletcher tried to synthesize piano sounds. It was emphasized
that piano strings are stiff strings and vibrate like a combination of solid
rods and stretched strings. This means that the piano overtones are not
strictly harmonic. Bells produce a wild mixture of overtones, and the
fundamental is not even graced with that name among specialists in the
field. The overtones of drums are not harmonically related, although
they give a richness to the drum sound. Triangles and cymbals give
such a mixture of overtones that they blend reasonably well with other
instruments. Nonharmonic overtones produce the difference between
organ and piano sounds and give variety to musical sounds in general.

Dynamic Range of Speech and Music

In the concert hall, a full symphony orchestra is capable of producing
some very loud sounds when the score says so, but also soft, delicate
passages. Seated in the audience, one can fully appreciate this grand
sweep of sound due to the great dynamic range of the human ear. The
dynamic range between the loudest and the softest passage will be on
the order of 60 to 70 dB. To be effective, the soft passages must still be