Physics

Sound energy

Energy (signal processing)

Optics

Sound (geography)

Acoustics

Amplitude

Quantum mechanics

Sound wave

Sound intensity

Proceedings of the Royal Society of London

Scarcely any attempts have been made, so far as I am aware, to measure the actual amplitude of sound-bearing waves, and, indeed, the problem is one of considerable difficulty. Even if the measurement could be effected, the result would have reference only to the waves actual experimented upon, and would be of no great value in the absence a some means of defining the intensity of the corresponding sound. It bad policy, however, to despise quantitative estimates because they are rough; and in the present case it is for many reasons desirable to have general idea of the magnitudes of the quantities with which we have deal. Now it is evident that a superior limit to the amplitude of wave giving an audible sound may be arrived at from a knowledge of the energy which must be expended in a given time in order to generate them, am of the extent of surface over which the waves so generated are spread a the time of hearing. An estimate founded on these data will necessarily be too high, both because sound-waves must suffer some dissipation their progress, and also because a part, and in some cases a large part of the energy expended never takes the form of sound-waves at all. The source of sound in my experiment was a whistle, mounted on a "Wolf’s bottle, in connexion with which was a siphon manometer for the purpose of measuring the pressure of wind. This apparatus was inflated from the lungs through an india-rubber tube, and with a little practice there was no difficulty in maintaining a sufficiently constant blast of the requisite duration. The most suitable pressure was determined by preliminary trials, and was measured by a column of water 9½ centimetres high.

II. On the amplitude of sound-waves