Gateway Engineering Coalition Home Page   Frequency, Wavelength, and Propagation Speed


The purest acoustic signal is that of a sine wave of frequency f . This corresponds to air density and pressure at a single point increasing and decreasing at regular intervals. When the pressure is above the ambient (or quiescent) value, the density also increases, as a result of the air molecules being compressed together. The pressure then falls to a value below the quiescent pressure, with a corresponding decrease in the density as the result of the air molecules moving away from each other (show image of molecules undergoing alternating compressions and rarefactions).

where g is the ratio of specific heats, which is equal to 1.4 for air, p the absolute pressure, r the mass density, R the thermodynamic gas constant, and T the absolute temperature of the gas.



where E is the elastic constant for the solid and r the mass density of the solid.



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Sources of Acoustic Signals 

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Support for the development of this module was provided by the National Science Foundation and The Cooper Union for the Advancement of Science and Art.

Please send questions or comments to Professor Ron Adrezin or Professor Daniel Raichel.