[pianotech] Tuning fork puzzle

[Ron Nossaman]

John Delacour wrote:
> 
> This afternoon I was planning an experiment today and messing about with 
> a tuning fork, a board and various things in between.  Listening for all 
> sorts of things I realised that I was hearing the octave of the 
> fundamental very strongly.  In several situations the octave sounded 
> almost as strongly as the fundamental, sometimes equally strongly, and 
> in some cases, for example when holding the fork near the top of the 
> long bridge, the octave prevailed significantly over the fundamental.
> 
> Now I am told that the first overtone of a tuning fork has about 6 1/4 
> times the frequency of the fundamental, so where is this octave coming 
> from?

It's coming from the handle. You get pulses at the bottom of 
the handle because the fork changes length slightly as the 
tines vibrate. It's longest when the tines are straight, and 
shortest when the tines are at *both* the inner or outer limit 
of their excursion. This happens twice with each full 
excursion of the tines, so the contact pulse at the handle 
bottom is twice the frequency of the fundamental.
Ron N