It has been shown by Thuras, Jenkins, and O'Neil that the theoretical magnitude of the extraneous frequencies, generated in air by very intense sounds, are obtained from an approximate solution of the exact differential equation of wave propagation in air. The solution shows that the pressure of the extraneous harmonic frequencies generated in air increases with (1) the frequency of the fundamental, (2) the magnitude of the fundamental pressure, and (3) the distance from the source. Taking into consideration the loss at the side walls of the tube in which the plane wave is propagated, we may write the ratio of the pressure of the generated second harmonic to that of the fundamental pressure asP2/P1 = KP0XR, whereK = (√/4) (γ+1/γP0) (ω/c),P0is the rms pressure of the fundamental atX= 0,Xis the distance from the source,Ris the loss factor1 minus; (α2X/2), α2is the loss per unit distance in the second harmonic pressure. It was found that the loss along the tube was essentially that at the side walls of the tube. This was expressed by Beranek asα equals; 3.18 × 10−5 (f12/r) nepers/cm, wherefis the frequency andris the radius of the tube. Thuras, Jenkins, and O'Neil found the absolute magnitude of the generated tones in the tube, of all measured values, to be about 3 db lower than the theoretical values. In this restudy of the problem, done under a Naval Research contract at U.C.L.A., it was found that the measured values of the generated second harmonic pressure were in good agreement with the theoretical values.