Re: Odd acoustic effect

["Eric Benjamin" ericbenjamin2]

Or perhaps it was comb-filtering from the ground bounce.=C2=A0 As the plane=
 nears,
the difference in path lengths between the direct arrival from the plane an=
d the
bounce becomes progressively shorter.=C2=A0 The ground bounce acts to eithe=
r
reinforce or to attenuate the sound depending on the path length and the
frequency.=C2=A0 So if your microphones happen to be about 1.6 meters above=
 the
ground, then the path length for the sound going down to the ground and bou=
ncing
up will be about 9.3 msec longer, which will attenuate sound at 55 Hz,
accentuate sound at 110 Hz, attenuate again at 165 Hz, and so on.