Tuning forks/Vibrators

[David & Mary Kelly]

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I hope I don't get banned from the list for the subject of vibrators!

A number of years ago when I tried different techniques for analysing the s=
ound of a bell at St Michael with St Paul, Bath. As I didn't (and still do =
not) have a set of tuning forks I used a high power output oscillator conne=
cted to a solonoid to elecit the harmonic tones from a bell. The technique =
was as I understood to be similar to using a tuning fork except the solonoi=
d acted as a variable frequency tuning fork tp produce sympathetic vibratio=
ns. I swept the frequency range, or if truth were to be admitted the "expec=
ted" frequency range for the partials. Sure enough I managed to get resonan=
ce and duly noted the figures.

Some years later we had the bells re-tuned. Nigel Taylor's figures for the =
bells were generally similar to mine apart from one bell, the Warner 7th wh=
ere my figures for some of the partials were totally incorrect. What was wr=
ong? the answer was simply that I was expecting a frequency in a particular=
range and what I heard was resonance of a another partial being excited by=
half the frequency! The actual frequency was no-where near the band I had =
swept! The moral of this story is that unless you really know what you are =
doing you can get incorrect results unless you use techniques that examine =
the SOUND of the bell. Bill Hibbert's Waveanal program does this superbly; =
I beta tested his program against my own version using similar fourier anal=
ysis techniqes and found Waveanal to be accurate and very easy to use. So f=
ar I have found sound analysis programs to produce accurate and consistant =
results - something I couldn't achieve using other means.

Dave


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