Extraneous Frequencies Generated in Air Carrying Intense Sound Waves

In high quality reproduction of sound the trend toward large power output necessitates a consideration of the more exact equations of wave propagation in air. If the displacement amplitude of a plane sound wave is not small the equation representing the propagation is not linear, and consequently harmonics and combination tones are generated. The pressure of these extraneous frequencies in terms of the fundamental pressure, frequency, and distance from the source has been mathematically determined by Earnshaw, Rayleigh and others. Rocard has recently applied the equation to exponential horns.Measurements of the second harmonic and combination tones have been made at various points within a long tube, and in front of an exponential horn. Measurements, in general, agree with theory, but the absolute values are 3 to 4 db lower than the calculated values. An experimental demonstration will be given.