168 



BELL SYSTEM TECHNICAL JOURNAL 



300 400 500 600 800 1000 2000 300 



FUNDAMENTAL FREQUENCY IN CYCLES PER SECOND 



Fig. 4 — \'ariation of 2nd harmonic magnitude with frequency of fundamental. 



m -24 



eooo 10,000 

 Fig. 5 — Variation of 2nd harmonic pressure with fundamental pressure. 



2000 3000 4000 5000 6000 

 600'V PRESSURE AT SOURCE IN BARS 



Figure 6 shows the magnitude of the first order sum and difference 

 frequencies along the tube when two frequencies of equal pressure are 

 simultaneously impressed on the air in the tube. 



SUMMATION 



DIFFERENCE 



'k 



200 300 400 500 600 800 200 300 400 500 600 800 



DISTANCE FROM SOURCE IN CENTIMETERS 



Fig. 6 — Magnitude of summation and difference frequencies vs. distance from source. 



