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Here are the last two post from my YouTube brace question which leads me to this new topic for discussion.

Chris Paulick wrote:
I used 5/16" braces as that's what is in my gibson j 45 and I'm building a j 45. How far from the edge should the peak of the scoop be and what is the min. heigth of the scallop for tone bars? On my J 45 plans the scoop on the X braces are 1"- 1 1/8" and that's what mine are. What are you guys shooting for? And thanks for your comments.
The tap tone to me has a pretty good ring so it might be the computer speakers.

Robbie O'Brien wrote:

My next Luthier Tips du Jour video addresses top bracing. I just need to find the time to finish it. Anyway, this topic is like religion, politics and Brazilian football clubs...Don't mention them unless you want opinions from everyone and be ready for a bunch of different opinions.
So, to answer you question, the peak of the X brace scallop should be 3 inches in from the outer perimeter. The height of the X brace at the lap joint should be about 5/8ths. For a dred, never go lower than 3/16ths or even 1/4 at the lowest part of the tone bars. A lot of guys use 1/4 inch wide braces and a lot of guys use 5/16th wide braces. Find one that works for you. I can't really comment on the tap tone unless I have the top in hand.

I replied:

I'll be waiting to see the brace video and I hope you would explain why you choose to use those measurements. For someone to just say a measurement in this case with out an explaination doesn't give me any understanding of what is happening. It's like saying the sine of 90 degrees is 1. That does't help me understand if I know nothing about the unit circle. And I think it would be great to get a good discussion going here on bracing and all the opinions of what and the why. That's exactly what I want to hear actually. A good explaination of your, meaning all the forums members thoughts on this so I can choose from the wealth of your knowledge. I think there's alot to be said on this subject and alot to be learned from a healthly discussion on it. What Say You All? I Thirst, Will You Not Give Me Drink?

i'd like to hear opinions on this too, but how do you think this thread will ever be found in the archives?

I'm not just looking around for things to complain about, but proper thread titling is crucial to having an archive worth searching.

Frank

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Frank

As a newbie can't really comment but I like to hear a good sustain, then worry about the tone all the while feeling the stiffness of the top final tweaks can be done by sanding the perimeter of the lower bout if once the box is closed you think you want to increase the bass responce a little. All I know I thank Hesh, and Joel Thompson for plus some great vids from John Mayes The advanced tap tone one is a must in my view

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Formerly JJH

I learn more from my mistakes than my successes

A search for top bracing? Good point though. I wonder if there is a way to add /Bracing to the title?

I have those videos but there isn't any explanation as to why he designs his braces as he does. Just blanket statements as here is how I ruff out my braces. I want to know why that way. And what is the purpose of the tone bars and how the interact with the rest of the braces and why the brace pattern is what it is. What structural purpose are the different type of braces to preform and etc. What are the forces on the top we are trying to balance out with getting a good voicing. I don't expect this to be a short discussion as like I said I think there is a lot to be learned here. But I don't know? Maybe that is a well kept secret that no one wants to give away. I 'm hoping not.

William Shakespear !
How are thou !

Mike

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Mike Collins

Will thou not give me drink Mike, for that I buildest my J-45 from thouest plans?

"I Thirst, Will You Not Give Me Drink?"
Very interesting quote.... I wish the answer was more like "drink from this water and you won't thirst again..."

Well, the truth of the matter is that a majority of builders take on tried and tested plans and work from there. Sure there is a reason. The reason is to reinforce the soundboard in certain areas and restraint or strengthen others. There is no exact science as every soundboard is different along with scale lengths, domed tops and size of box. One thing is certain, if you want to increase stiffness on your braces you need to increase height rather than width. Don't scallop too deep or you'll create a weak spot where it will concentrate tension and may lead to a break. Also, you want to generate a center of reinforcement starting at the bridge weakning its stiffeness towards the edges and letting the soundboard move more freely towards the kerfing(kinda like a speaker cone). The closer to the edge the peaks are, the more the soundboard will resist movement at the edges and the floppier it will be in the center..... you don't want that.

Best of luck,

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Peter M.
Cornerstone Guitars
http://www.cornerstoneukes.com

Thanks Peter, that's very helpful. Are there any ruff ratios along the brace to start at.? And are the braces also used to transmit some of the strings energy from the bridge plate through the top? And what is going on with those tone arms?
That's one good sip.

Chris, I have John's [i]Advanced Voicing[i], but not the first of the series. Does he not discuss nodal points in Voicing 1?

It would be easier to work with your question by focusing it more. The top is a system, but I'm not sure which part of that system would be a good starting point to discuss. I could learn from a topic like this, too. I always enjoy it when it comes up.

I wish Ervin Somogyi's videos were still available for download. I think they would help you focus your questions.

He touches on a couple of nodal points. But I think that understanding braces and there design and purpose and how it all relates to one and another is next in step from understanding about brace wood and runout and the such. Shaving the braces and voicing the top is the final step I think. Thickness the top probably is before the braces which I missed as I just was told thickness it to this. I think this stuff is like math in that if you don't understand the first step then it's pretty hard to get the next step or at least understand it fully as you can. Without the understanding as to what's going on how can I correct the problem or at least attack it or trouble shoot it. I'm an electrician by day and if I don't know circuitry then how can I figure out why a light doesn't turn on? Change the lamp? Change the switch? change the breaker? It might sound like I'm not focused but with one answered question comes another question until there's an understanding is there not? Or is that just with me? Maybe I'm just a liberal thinker???
Yes, I agree with you that's it's a system and I'm hoping those who teach and know this stuff know where to start. When people ask me where I learned to build guitars I tell them from the internet and forums.

Chris,
Your tap tone on your youtube video tells you that your top resonance is A flat below middle C or 210 Hz.
Your back resonance is A# or 230 Hz . This resonance is what some call the ring mode. But the important thing is how it defines the stiffness of your plate. It is the longitudinal stiffness of your plate.

Since wood materials can vary in stiffness and weight, if you follow the plan to the mm there might be some variability between yours and the original instrument. If you don't know the tap tone (stiffness) and weight of the original, the best you can do is keep records and decide which way to go on the next one you make.

Stiffness can be defined by the mathematical formula Stiffness = Weight X mode frequency squared/100000. If you want to know how stiff the plate is across the plate you will have to tap it in a different place. The long grain stiffness is probably the most important.

Tap tones from individual braces and end to end are more of a refinement in the timbre of the instrument unless they effect the major stiffness tones.

I hope this helps.

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Ken

Thanks Ken, one more piece to the puzzle.

You are welcome, but it is more like the "big picture".

What is the plates weight?

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Ken

Top-240g, Back 305g
Thats if you believe my little food scale.

I also noticed the difference between the notes of the top and back. Hadnt actually gone as far as identifying them as A sharp and A flat
I am intersted to know if anyone actually tries to tune the tap tone. Wouldnt a top resonating on a true A or even B be more resonant given the way a guitar is tuned. Wouldnt a semitone difference between top and back be a bit "wolfy" ?

I thnk we are jumping ahead here. I want answers to bracing and not voicing at this stage. I would kindly ask that another discussion be started on Voicing and tap tuning tops and backs. There is plenty to be discussed on that issue too.

Chris, I think your questions are great; it's just hard to know where to start because for there to be any clarity there needs to be some organization.

Tell us this---what do you believe a guitar top physically doing when it makes sound?

I think the strings vibrate and and drive the top mainly. The braces support the top mainly from the forces and stresses caused by the string pull which include the neck pull on the neck block etc. OK. that being said let's get back to the string being plucked. The string energy goes through the saddle and bridge to vibrate the top at that center point. Now you take it from there. What part does the bridge plate play as to moving the energy and tell me about the mass issue. Do the braces also serve as to move the energy and help drive the top. Are we trying to get the bridge centered more near the center of the lower bout? Discuss opening up the X braces or closing them and the effect and why. What are the tone bars fuction. how are we trying to get the top to move and how the brace placement effect that. Do long braces vibrate at a different frequency then short ones and does that come into play with the top being tuned and if so then how. How's that for a start?

Chris,

Slow down there buckaroo.
You are asking a lot of questions. Some of them are structural questions and the others are tonal questions and some are both.
For a classical guitar think of the braces as tone distributors. For a steel string guitar think of the braces as tone distributors with a structural purpose as well. I just finished the youtube top bracing clip and will have it on youtube shortly. Some of your questions will be addressed in it. However, most if not all of your questions will be answered in Kent Everett's upcoming acoustic guitar voicing DVD. Be patient. We are going through another review process this coming weekend.

Well James asked . And man I got a million of them!

The top IS a system: you can't talk about 'the braces' and 'the top' seperately, or even about 'the tone bars' and 'the finger braces' as having very different functions. Everything effects everything else.

It's interesting that you can find many of the same key resonant mode shapes on an unbraced top that you see on a braced one that's set up properly. This suggests that the function of bracing, both on classical and steel string guitars, is to add to the stiffness without increasing the weight much, but NOT to alter the way the stiffness and mass are spread around too much. Mark Blanchard has pointed out that it's hard to use the bracing to get a top to do something that it doesn't 'want' to do: to have key mode shapes that are very different from those of the un-braced top. The top is the sound, and the bracing is, at best, a fine-tuning mechanism. Noty that that's trivial: the differences between 'good' and 'great' sound are often minute.

Overall tone seems to depend more on the relationships between the resonant modes of the assembled top than it does on their exact frequencies. If, for example, the 'cross dipole' mode is low in pitch relative to the 'main top' frequency, then the guitar often has a 'sharp' or forward' sort of tone, rather than a 'full' one. 'Tapered' bracing tends to raise the pitch of the 'main top' resonant mode, which bends a lot in the center, and lower the pitch of the 'cross dipole', which bends more in the wings, thus yeilding a 'sharper' and maybe 'clearer' sound than 'scalloped' bracing, which has the opposite effect.

Sustain has a lot to do with the 'impedance' of the bridge area of the top, which depends on the mass and stiffness of the bracing there, as well as that of the bridge and bridge plate. More mass and/or higher stiffness will raise the impedance, keeping the energy in the string rather than allowing it to 'leak' out into the top. Obviously, the tone will vary depending on which way you go about this.

I've always felt that the structurally critical area of the top is between the bridge and the soundhole. In general, it seems to me that as long as that area is not too dished in, the guitar will work well, but once that collapses, it's gone. It's no accident, IMO, that the most succesful brace patterns, the X and fan, concentrate bracing in that area.

A rule of thumb that I tell my students is that the area of the top at the neck is all about strength, and has nothing to do with tone, while the area near the tail block is all about tone, and very little about strength. Obviously this is not _strictly_ true, but helps. Shaving braces near the lower edge tends to have more of an effect on sound, and less on strength, that shaving them further up. Once you get up above the bridge (assuming things aren't 'way out of whack) shaving braces doesn't effect the tone nearly as much, and can be detrimental to strength. Thus I don't get too worked up about finger braces, for example: their function does seem to be mostly strength, although, of course, you don't want to make them as heavy as, say, the upper cross bar.

I could probably go on all night if I had the energy. As you learn more, you'll understand that some of the questions you've asked are 'way too broad, some are so specific as to be almost trivial, and some are simply not very meaningful. You're making a guitar, not an assemblage of parts, and you can't really 'mix and match' them at random and expect good results. The sort of tone bar shape that will work with tapered bracing won't work with scalloped, and you can't divorce 'brace shaping', 'voicing', 'tuning', and 'tone'; they're aspects of the same process.

Before I ever built a guitar, I would ask similar questions and try to seek answers that would lead to measurable components fitting into some clever formula that would help to solve for that unknown final tone. All of my career, measurable facts were the answers to most issues and problems that were worth solving. It rook me a while to think about guitar building a bit differently.

The frustrating answer that I got from the builder masters then was always, "It depends". And after 5 years and almost 10 acoustic guitars the answer is no longer frustrating, but it still continues to elude a formulaic approach for me. So after a short time I gave up asking and began the quest to develop an instinct about stiffness, tone and the changes that I could hear when I made purposeful changes to a soundboard's thickness, its bracing as well as string type, action, neck wood, ad infinitum! It resulted in more than one occasion where I went too far, lost the tone and had to remove braces and start again. Another epiphany occurred when I had the opportunity to tap and flex hundreds of spruce tops of various species and learn about stiffness, density, mass and how each affected how the wood sounded when tapped. The more I handle wood and observe its character the more I learn.

So for me, I still don't know the answer...I just feel as though I have found a direction that is working. And I'll bet that 5 years from now I'll be taking a still different approach but only slightly.

Chris...Good luck on your quest for the answers but don't forget to just build, observe and try new approaches that result in differences that you can perceive. It's really hard to screw up the sound of a guitar if you follow some tried and true plans first...then make changes from there.

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JJ
Napa, CA
http://www.DonohueGuitars.com

You bring up a rather interesting question for me when you describe your bracing technique. I was hoping to build using rather old plans. circa 1810 for a guitar. Is it your opinion to use newer bracing paterns as opposed to those laid out by the original designer? My only concern is in losing the sound the instrument would produce when built to original specs. My reading on this subject has been conflicting. I understand the speaker analogy well enough. The height is the concern for me. Many of the older instrument plans, and museum photos show low bracing that barely rises 1/4 inch above the soundboard. I'll attach a picture to show what I'm talking about. Was this phased out for a reason, or is it merely an issue of esthetics, and the fashion of the day. My goal is not really to reach maximum volume, but clarity of tone. I'm not going to be building guitars for guys like clapton any time soon, or likely ever. I just want to build a decent sounding classical instrument that replicates period music as best as possible.