Albino guinea pigs were stimulated simultaneously with two tones (F
1, F
2) of different frequency (
f1=2000Hz,
f2=2500Hz), and the phase of evoked DPOAEs (θ
DP) were 2θ
1-2θ
2+
c, while θ
1 and θ
2 were the phase of F
1 and F
2 respectively (
c: constant).
When the wave F
1 and F
2 are expressed as
a1cos(2π
f1t-θ
1) and
a2cos(2π
f2t-θ
2) (
a1,
a2: amplitude of F
1, F
2), the third distorted wave at the frequency of 2
f1-
f2 is mathematically calculated as
ka12a2cos{2π(2
f1-
f2)
t-(2θ
1-2θ
2)} (
k: constant, the rate of its distortion). Since this formula indicates that θ
DP is 2θ
1-θ
2, the results obtained suggested that the generation mechanism of DPOAE is not the simple vibration of the outer hair cells but the limited vibration related to the distorted wave of F
1 and F
2.
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