Naked Science Forum
General Science => General Science => Topic started by: neilep on 23/10/2007 15:17:21
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Dearest Tunas,
See this Tuning fork ?
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Nice isn't it ?..notice has tranquil it is but ready to emanate a C sharp at a moments notice!!
What are tuning forks made from ?...can other materials be used ?...does not holding the stem have an effect on the performance ?...and how do they calibrate them ?
Ewe see....I just want to know !
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Tuning forks are, almost certainly, made of steel. It is a nice, resilient, metal and tough.
One from lead would vibrate, but not for as long - the metal 'flows' too easily and would absorb the energy.
The Q or quality factor of a tuning form in air is over 3000. That means that it will oscillate 3000 times before the vibrations have died to half their energy. In a vacuum, it can be as high as 50,000. The accuracy of the frequency of oscillation can be as good as 1/Q. (1 in 3000!)
You tune it by filing bits off (symmetrically). Filing the ends, to raise the pitch or making the middle thinner, to lower the pitch. The steel is bent into a fork shape to make the oscillations balanced and to remove the effect, as much as possible, of holding the stem. The energy loss (Due to the sound coming from it) tends to slow the vibrations down a bit (damps them) so the design reduces this to a minimum.
The earliest (?) electronic wrist watch (Bulova Acutron, I think) used a tiny metal tuning fork with its vibrations sustained by a small coil, driven by an amplifier. Modern quartz crystals oscillate in much the same way in watches but their Q factor is better (10,000 to 100,000). This makes them accurate to seconds per month. And they are incredibly cheap.
Quartz crystals are bar shaped and vibrate like a xylophone . they are mounted by being held loosely a little way from each end and, of course, in a vacuum.
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THANK YOU VERY MUCH sophiecentaur,
So , from what I understand, the stem, which is held has an indiscernible effect...if any.......
...so, do they have some kind of tone generating thing that displays a waveform that the tuning fork is then matched up against via a microphone ? (i'm guessing here)
Fascinating about the early electronic wrist watches !!
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The way to tune it best is to use an oscilloscope and a callibrated electronic tone source. The tuning fork vibrations (via a microphone) are displayed on the Y axis and the standard tone is displayed on the X axis. The up/down - backwards / forwards motion of the spot will be a steady circle / ellipse / diagonal line when the tuning form is in tune. When its frequency is a bit out, you get a wiggly set of closed curves. You keep filing until you get your steady pattern.
http://www.youtube.com/watch?v=OBmhoGRDuOE (http://www.youtube.com/watch?v=OBmhoGRDuOE)
http://www.youtube.com/watch?v=DXpntnHxNZQ (http://www.youtube.com/watch?v=DXpntnHxNZQ)
http://www.youtube.com/watch?v=sYYyJvVFj4Q (http://www.youtube.com/watch?v=sYYyJvVFj4Q)
pretty pictures / sounds
Alternatively, you can do what a piano tuner does; he listens to the 'beat' between the fork and the standard as he adjusts the tension in the string. When it disappears, the fork is forking well in tune.
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The way to tune it best is to use an oscilloscope and a callibrated electronic tone source. The tuning fork vibrations (via a microphone) are displayed on the Y axis and the standard tone is displayed on the X axis. The up/down - backwards / forwards motion of the spot will be a steady circle / ellipse / diagonal line when the tuning form is in tune. When its frequency is a bit out, you get a wiggly set of closed curves. You keep filing until you get your steady pattern.
http://www.youtube.com/watch?v=OBmhoGRDuOE (http://www.youtube.com/watch?v=OBmhoGRDuOE)
http://www.youtube.com/watch?v=DXpntnHxNZQ (http://www.youtube.com/watch?v=DXpntnHxNZQ)
http://www.youtube.com/watch?v=sYYyJvVFj4Q (http://www.youtube.com/watch?v=sYYyJvVFj4Q)
pretty pictures / sounds
Alternatively, you can do what a piano tuner does; he listens to the 'beat' between the fork and the standard as he adjusts the tension in the string. When it disappears, the fork is forking well in tune.
THANK EWE sophiecentaur...FANTASTIC INFORMATION !!!...and great youtube links too ....thank you very much.
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You can use a frequency counter program on a computer to measure frequency too. For example, on one of my web pages http://www.techmind.org/audio/ you can download the Tuner12.exe program which will then tell you the frequency of a tone on the "audio mix" input (use the Windows "Recording Mixer" to select the microphone input).
Of course my program effectively measures the frequency relative to the 44.1kHz crystal-derived clock in the soundcard. Good enough for most purposes!
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WONDERFUL TECHMID..THANK YOU ALSO VERY MUCH !!
Love your site too !!
thank you.
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Everything I've *ever* wanted to know about tuning forks [;D]
but you know, they still freak me out a bit
when you strike the fork and a clear A rings out
and the guitar in the corner answers back.....
eerie, yes, cool - but also eerie .....
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That has resonances with me too.