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Old 03-09-2018, 09:21 AM
Picker2 Picker2 is offline
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Quote:
Originally Posted by KevWind View Post
I understand the scientific use of a tests of one thing to predict results of something else , in very specific instances , But there is no reason to do so in this particular case.

Of course there is a point recording the string pluck to test and verify the body resonance produced by plucking the E string at the 12 fret (the statement you claim is not true) and there is no logical reason not to , in order to prove or disprove AP's specific statement. It does not matter how many body resonant frequencies the string pluck will produce, because those frequencies are the only salient frequencies involved in AP' statement.

I may not have a degree in physics, but I have a Masters Certificate in Advanced Audio Production in Pro Tools and 15 years experience recording digital audio. So I am knowledgeable enough to know there is no logical reason not to use the same recording chain you used to record the bridge thump to record the string pluck . And your assertion that in this instance recording the tap will yield applicable results is flawed reasoning because it introduces unnecessary variables. Like the for example the bridge will not vibrate the same nor as long, as the string. The reality is that if you record the string pluck just like you recorded the tap, the resulting graph will show if there is any increased signal peaks below the E5 note . And might even prove you right .
OK, I see your point. Your proposed experiment will not provide additional information, but it probably gives better insights in this matter. And it's fun! So, especially for you , I went through the trouble to spend another three seconds, TWICE, to produce the measurements below.

This is the spectrum of the open E string of my Taylor GC BTO, plucked with my fingernail:



As you see, there is the narrow peak at 329 Hz (the fundamental), the first harmonic at 659, and many more higher harmonics. And... WAIT, there are 'subharmonics' too! One at 190 Hz and even one at 108 Hz!

Wrong.

These are not subharmonics. This is the fundamental resonant frequency of the guitar's top (108 Hz) and another resonant frequency of the top at 190 Hz. I can verify this by tapping on the bridge, this time with my fingernail:



See? There they are again, at exactly the same positions. As I explained earlier in this thread, plucking the string generates a shock wave in the string, which propagates through the string to the bridge. The effect of this is essentially the same as tapping the bridge. This causes the 'subharmonics' in the upper graph, except these are not caused by the string, but by the body. So they are not subharmonics, they are body resonances.

If you perform a real-time measurement of the plucked string, you will see that the body resonance peaks only last a short time. They appear, and are gone within half a second. The peaks caused by the string last as long as the string rings out - much, much longer.

This is the reason I conclude that body resonances don't 'fight' or interfere with the vibrations of the string. Because, and I repeat:

1. They last very short
2. They don't produce a distinct tone, but a 'thud' sound.

Stating that body resonances interfere with the 'in-tune-ness' of a guitar is like stating that the bass drum in a band interferes with the notes produced by the piano.
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Last edited by Picker2; 03-11-2018 at 12:34 AM.
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