The science of sound, or acoustics,

The science of sound, or acoustics, as it is often called, has been made over radically
within a comparatively short space of time. Not so long ago the lectures on sound in
colleges and high schools dealt chiefly with the vibrations of such things as the air
columns in organ pipes. Nowadays, however, thanks chiefly to a number of electronic
instruments engineers can study sounds as effectively 1) ________ . The result has been a
new approach to research in sound. Scientists have been able to make far-reaching
discoveries in many fields of acoustics 2) _______ .
Foremost among the instruments that have revolutionized the study of acoustics are
electronic sound-level meters. These are effective devices that first convert sound waves
into weak electric signals, then amplify the signals through electronic means 3) _________
. The intensity of a sound is measured in units called decibels. “Zero” sound is the faintest
sound 4) ___________ . The decibel measures the radio of the intensity of a given sound
to the standard “zero” sound. The decibel scale ranges from 0 to 130. An intensity of 130
decibels is perceived not only as a sound, but also 5) __________. The normal range of
painlessly audible sounds for the average human ear is about 120 decibels. For forms of
life other than ourselves, the range can be quite different.
The ordinary sound meter measures the intensity of a given sound, rather than its
actual loudness. Under most conditions, however, it is a quite good indicator of loudness.
Probably the loudest known noise ever heard by human ears was that of the explosive
eruption in August, 1883, of the volcano of Krakatau in the East Indies. No electronic
sound meters, of course, were in existence then, but physicists estimate that the sound at
its source must have had an intensity of 190 decibels, 6) __________ .