somewhere near the temporal coordinates of 10/30/01 8:00 PM, the entity
known as Michael J. Hu=DFmann transmitted the following from
michael_at_michael-hussmann.de:
> Jon Glass (jonglass_at_usa.net) wrote:
>=20
>> Each sound creates harmonics. A 20khz sound creates harmonics both upwar=
d
>> and downward into definitely audible hearing range.
>=20
> Harmonics _below_ the base frequency?
>=20
Well, picture this -- you are pushing a child on a swing. You can push
every time the kid comes back to you, or you can push every OTHER time, or
every THIRD time. With the latter two, you're forcing the system at a
harmonic frequency below the base (swing's) frequency.
For another analogy, recall the quarter-wave antenna.
(Of course, these are both analogies, but perhaps they help it seem less
nonsensical... I don't really want to turn this into a physics lecture.
We're already off-topic, no sense putting people to sleep on top of that.
:-) )
- Eric.
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