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PostPosted: Wed Feb 12, 2014 3:10 pm 
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I am trying to tap tune the partially carved braces and tonebars on a soundboard mounted to a 3" thick fixture via 24 toggle clamps. I am using a good quality cardioid mike through a Behringer CS400 compressor into the Peterson Strobosoft 2.0 Deluxe software. Despite that I can "percieve" different tones when tapping the various braces, the Strobosoft display shows the same frequency for each within 20 cents. Has anyone had a similar experience and found a solution to isolating the natural frequency of the individual braces?


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PostPosted: Wed Feb 12, 2014 3:29 pm 
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Location: Hegins, Pa
Early on in my building I got into tap tuning, voicing etc. I can tell you that you are chasing a ghost. After 10 yrs I learned that brace stock is just that, that variable from a brace stock to a brace to a glued on brace is too unreliable to give you any real information. There are 2 things I look for in my brace stock aside from moisture content, that is split stock and run out, the other is stiffness.
I don't even think about this until the top is on the guitar. After all this time, for my ear, I have developed a set of patterns. This usually gets me pretty close. Then after the guitar is strung up for a few weeks I can do an initial voicing. Keep in mind that the guitar will change a good bit in the early years.
Things change so much from a free state piece of wood to a shaped piece to a piece that is on a guitar and then add to that the the stress variables with the humidity changes. Of the many books I read I would say that quite a few are full of non scientific procedures, others are pretty good and the balance are just smoke and mirrors.

Just what are you looking for? After all, so much can vary in even the same piece of wood and on different RH constants.


Some of the best guitars I hear literally broke all the rules. What this comes down to is physics and how you can control the stresses.
I am sure Alan Carruth will offer further explanation.

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PostPosted: Wed Feb 12, 2014 4:33 pm 
tippie53 wrote:
after the guitar is strung up for a few weeks I can do an initial voicing. Keep in mind that the guitar will change a good bit in the early years.


John, how do you do the 'initial voicing?'


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PostPosted: Wed Feb 12, 2014 5:38 pm 
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I reach in the sound hole and tweak the X brace if I need to.
If you keep a good log and look at how a top flexes , and where it flexes and much it takes to flex you can make some adjustments.
The more I build the more the tops are what I want when I put them on. youngs modus of elasticity will show the average of what the wood will be. I seldom have to do much anymore for the top braces. The key is you can take too much and you have to have the discipline to stop as you can go from great to crap real fast.
As you do more you will find that you will find a pattern that works for you. Off that pattern you can do a few tweaks. I don't like to overadjust . Allow a good set in time. Often about 1 yr to allow the guitar to become what it will be.

Wayne Henderson showed me that you can voice the top without the bridge plate and you can take it to the point of thuddiness and the plate brings you back so in a way it is like taking it to the edge and the plate brings you back into the zone.

It is hard to explain and I hope I may be able to do a demo at the open house at Steve Browns in June.

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PostPosted: Wed Feb 12, 2014 7:47 pm 
Maybe you can do a youtube video?
Does Glenn have a video camera that will fit inside a guitar body.....


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PostPosted: Wed Feb 12, 2014 7:50 pm 
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Location: Slidell, La
tommyboy wrote:
Maybe you can do a youtube video?
Does Glenn have a video camera that will fit inside a guitar body.....


That would be really cool!

David L


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PostPosted: Wed Feb 12, 2014 8:14 pm 
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You would be surprised at how little you can take to make a change.
that one part that is most difficult to learn isn't so much how to take off but where. I like Wayne's Method as you can take the top beyond the point you would travel and then apply the bridge plate brings you back.
The 2 things I can say is that you have to understand a dred is voice different than a 000 and a 12 fret is different from a 14. A new guitar is tight and has to open up so don't rush voicing the top until the guitar gets to become a guitar.
I will see if I can get Alan to chime in

One reason I am cautious on a new top is that without the string load applied and the top glued on the body , your top is reacting differently from a tap than a string load.

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PostPosted: Fri Feb 14, 2014 5:40 pm 
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blatz24 asked:
" Despite that I can "perceive" different tones when tapping the various braces, the Strobosoft display shows the same frequency for each within 20 cents. Has anyone had a similar experience and found a solution to isolating the natural frequency of the individual braces?"

I think there are two problems here. One is that you're trying to tune individual braces on a top. The second is the difference between software and ears.

Once the braces are glued down they lose their individuality and become part of the system of the whole top. You could tune the braces to certain pitches before gluing them down, but the stiffness and mass of the top would alter those once the thing is assembled. The top does, of course, have a number of resonant pitches, which you can hear by tapping on it. These can be visualized by the use of Chladni techniques, or in other ways that tend to need more technology.

When you tap on a top you activate all the modes that are active at the spot where you tap it. In general, you'll get more sound out of the lower order modes than the higher frequency ones, since the low modes are active over larger areas and tend to produce more sound.

Usually tuning software, or hardware tuners, for that matter, home in on the strongest signal. Your ears work differently, and can, in some circumstances, pick out higher frequencies and ignore the low stuff. In any event, a changed mix of frequencies will have a different timbre that is readily perceived, even when the fundamental is the same.

A better way to pick out pitches in a mix is to use software that can show you a spectrum, or a spectrogram. There are several packages that can do this. One free one is 'Wavesurfer', available from http://www.speech.kth.se/wavesurfer/ as a download. There's also a free book at the same source: "Acoustics for Violin and Guitar Makers" 4th edition, by Erik Jansson. It has instructions for how to use the software, which is pretty simple.

Hope this helps.

Edit: Wavesurfer Manual
http://www.speech.kth.se/wavesurfer/man.html


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PostPosted: Fri Feb 14, 2014 6:06 pm 
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Would the tap frequency of a brace of a given size be proportional to its stiffness? I just wonder for consistency sake if one could always start with equally dimensioned braces and tune the tap frequency of a brace by changing it height. The selected frequency would be based on acceptable past results. I have no plan to do this but the thought crossed my mind.

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PostPosted: Fri Feb 14, 2014 6:46 pm 
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I found that frequencies can change radically even from the same piece. I think it is possible to assume on average a certain size , shape ,length may be similar in frequency but wood is not totally homogenous.
The point one has to take is that the units make up the structure and the end result is the synergy of the sum of the parts is the end product. Glue , joint voids , all are part .

I have a question you Alan

I have found that after all the time I have been doing this I have found that my patterns get me a fairly consistent end product. Have you found a similar end result

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http://www.bluescreekguitars.com


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