Sound waves(a neat experiment)

Richard Brekne Richard.Brekne@grieg.uib.no
Sat, 19 Jan 2002 14:13:24 +0100


Ron Nossaman wrote:

> Richard, and anyone else still reading these,
>
> I forgot to mention. Looking at my description of how the fork oscillates
> along it's length, it might strike you that for each tine excursion cycle
> from all the way out to all the way in, to all the way out again, the
> handle would move up and down twice.

The vertical and horizontal reactions in the handle, grin.. what ever they are,
follow this relationship yes. At least thats my reading.  But tell me Ron. How
can you except the out and in excursion (expansion / contraction) and not be
able to accept the same type of action lenghtwise, insisting on actual up and
down motion instead ?

> The handle contact produced frequency should be twice that of the tines.
> Listening to the pitch of the two tones,
> they sound the same. One of the downloadable shareware FFT spectrum
> analyzers, or Tunelab, shows the peak at the fundamental tone of the fork
> in air, and the same fundamental peak with a similar-to-stronger peak at
> double the fork frequency from tabletop contact with the handle. Actually,
> you'll get more partials than that, but the second partial in the table
> contact test is disproportionately strong.
>
> Note also that a ringing fork, twirled slowly next to your ear, gets quiet
> at 45° off plane.

The 45 degree off plane is because of compression waves (this time in the air
so we can not dispute them ..grin) interfereing with each other. I would
suspect that if you put the butt end by your ear and rotated it you would not
hear any difference in amplitude, I will do this myself a bit later on.

> Interesting stuff about the forks we thought we knew.
>
> Ron N

Yes. I agree 100 %



--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html




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