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  #16  
Old 01-28-2013, 07:18 PM
gitnoob gitnoob is offline
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I probably skipped over that part. Seems to me a very odd way to go about tempering cross- and long-dipole modes.

Here's a scalloped Martin:



If Martin wanted to attenuate cross- or long-dipole modes, the peaks would have lined up in those directions. They're at odd angles, and simple adding bracing for stiffness in those directions would have been much more straight-forward.

It's possible that somebody at Martin thought that those peaks represented the best stiffness and mass distribution to get the tone they wanted, but I think it was probably more a function of the tools they used.
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Last edited by gitnoob; 01-28-2013 at 07:23 PM.
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  #17  
Old 01-29-2013, 07:34 AM
redir redir is offline
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Quote:
Originally Posted by Pat Foster View Post

P. S. On some guitars, it would take a while, like weeks or months for the changes in sound from brace shaving to fully develop.
Most people it seems tend to go too far when getting crazy shaving braces. I think this is very good advice. Make small changes and then wait it out. Also if you are stringing and restringing with the same set of strings over and over again they may tend to not sound so good either. Or at least, they may sound different and distort your judgment of tone as related to shaving the braces.
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  #18  
Old 01-30-2013, 03:33 AM
Sam VanLaningham Sam VanLaningham is offline
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Hi all - I have no idea if you want to waste some time (10 minutes - I usually dont listen to audio posts myself) but I decided to do a quick audio comparison of the Guild (Maple b/s) with my Santa Cruz D12 (mahogany b/s). I dont expect them to sound similar but I wanted to give an idea of the volume, sustain, notes up the fretboard vs low etc. I also threw in one comparative riff on the GS Mini (mahogany top) because most people know what those sound like.

http://soundcloud.com/sam-vanlaningh...gcd12-vsgsmini

The moral of the story:
1) wish I had recorded it before brace shaving because it sounds way louder, much better bass (although some muddiness is there too), sustain is much better. Note to note, string to string clarity even seems better but Im not sure. I did add a bone saddle and bridge pins near the end of the shaving, which also added a lot to both tonal richness, sustain and ability to transmit low end.

2) The guild sounds very nice strummed hard - better than the cruz, though its hard to tell on recording.

3) Santa cruz balance is way better. Sustain is better. High note presence is worlds better. Bass is more focused, refined, etc.

4) Im really glad I did this (though I still kind of think it might have sounded best when just a bit of wood was removed).

OK, I'm would love to hear any thoughts, regardless of type. Id really love it if someone said "wow sounds like this and that is a bit scooped and this and that are missing. Maybe if you shave a bit on the some-part-of-brace it might bring this and that back in". Whateva!
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  #19  
Old 01-30-2013, 05:41 PM
Pat Foster Pat Foster is offline
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Quote:
Originally Posted by Left of Sam View Post
. . . . So you just chopped the handles off of a spokeshave? . . . .
Yup! There are some brass body spokeshaves around that would probably work OK too. Problem with these is trying to get a grip on the iron while honing a decent edge on them. The steel is generally of pretty poor quality so they don't take a great edge, but at least the edge they do take seems to hold up pretty well, being used mostly on spruce.

Pat
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  #20  
Old 01-31-2013, 08:29 PM
Jackknifegypsy Jackknifegypsy is offline
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...And for sure they are going to break if they are lite gauge.

I've already gone thru 5 high E's, 3 B's and at least two of each of the others from stringing, unwinding, and stringing again.
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  #21  
Old 01-31-2013, 10:05 PM
Sam VanLaningham Sam VanLaningham is offline
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Originally Posted by Jackknifegypsy View Post
...And for sure they are going to break if they are lite gauge.

I've already gone thru 5 high E's, 3 B's and at least two of each of the others from stringing, unwinding, and stringing again.
Yes. I did go through 1 E and 1 G.

I'm going to search now but is there a good reference on bracing? I'm wondering how I can determine some ballpark braces heights. Thicknesses etc for a particular top.

Cool. Sam
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  #22  
Old 01-31-2013, 10:14 PM
gitnoob gitnoob is offline
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Originally Posted by Left of Sam View Post
I'm going to search now but is there a good reference on bracing? I'm wondering how I can determine some ballpark braces heights. Thicknesses etc for a particular top.
There's no real formula -- depends on top thickness, wood species, and what voice you're after. But Martin set the standards for X-bracing, and the Martin guys are fanatical about such details:

http://theunofficialmartinguitarforu...Y#.UQtAr788B8E
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  #23  
Old 02-01-2013, 01:59 AM
Sam VanLaningham Sam VanLaningham is offline
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Quote:
Originally Posted by gitnoob View Post
There's no real formula -- depends on top thickness, wood species, and what voice you're after. But Martin set the standards for X-bracing, and the Martin guys are fanatical about such details:

http://theunofficialmartinguitarforu...Y#.UQtAr788B8E
Excellent! No kidding about fanatical. More than 25 pages of Martin braces! I looked through about 10 pgs.

The gibson brace library was more helpful for my guild, I think.

And wow! Did you see the larrivee bracing? Huge! I've always thought they sounded a bit "compressed" but I'm no expert with them either.

My main questions were related to:
- how tall should braces be near X for a jumbo?
- is there tonal reasons for the placement of the peaks in a scallop?
- what are some realistic ranges of brace width for a jumbo?
- how important is a particular brace layout to tone and what happens tonally when they are layed out differently?
- what would happen if I essentially removed one of the three tone bars (maybe the middle one)? There almost no 6 stringers with that many, right?
- if one "goes too far" shaving, what can be done to overcome that? Shave the top?
- is top bracing dependent on back bracing for strength? My guild has laminated maple back with no bracing. I started to wonder if that was why the top braces were so huge?

Also, is there any literature about tap tuning and what common tap frequencies are? I've seen a lot of people tuning to middle C. I'm super low right now, somewhere around an E or F? I was wondering if its a no no to have it tuned to any of the big string open notes because the thing might resonate right out of my hands....or more likely rattle tuning pegs etc?

Ok, way too many questions for one post.

Last edited by Sam VanLaningham; 02-01-2013 at 02:09 AM. Reason: Additional question added-sorry!
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  #24  
Old 02-01-2013, 02:30 AM
gitnoob gitnoob is offline
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Quote:
Originally Posted by Left of Sam View Post
- how tall should braces be near X for a jumbo?
Typically a little more than 1/2". Perhaps 9/16".

The Martin thread should have some measurements in there somewhere.

Quote:
is there tonal reasons for the placement of the peaks in a scallop?
They should affect tone somewhat, but Alan Carruth's answer is about as good as you're going to get. Stiffness increases with the cube of the height, so those peaks add a significant stiffness to a fairly small area.

Quote:
what are some realistic ranges of brace width for a jumbo?
Stiffness varies linearly with width. 5/16" is pretty typical for the X. Sometimes 1/4" for the tone bars.

Quote:
how important is a particular brace layout to tone and what happens tonally when they are layed out differently?
It's a major factor. I'd probably rank it 3rd behind size and plate thickness.

The bass is pretty easy to adjust with just brace height. The placement and tone bars are more about higher-frequency response.

Quote:
what would happen if I essentially removed one of the three tone bars (maybe the middle one)? There almost no 6 stringers with that many, right?
Two effects: resonance frequency drops and damping drops. From computer models, I believe the damping effect is larger than the resonance frequency effect, but both are significant.

Those lower bars also offer some structural support, but the one closest to the bridge is more important in that regard.

Quote:
if one "goes too far" shaving, what can be done to overcome that? Shave the top?
No, thinning the top has essentially the same effect as shaving a brace. You'd need to add stiffness and/or mass back to the top where you went too far.

Quote:
is top bracing dependent on back bracing for strength? My guild has laminated maple back with no bracing. I started to wonder if that was why the top braces were so huge?
They should be independent structurally, but you can try for a certain relationship between top and back resonance frequencies that way. Typically an unbraced back would have a lower resonance frequency than a braced back, so that would suggest lighter top bracing to me.

Quote:
Also, is there any literature about tap tuning and what common tap frequencies are? I've seen a lot of people tuning to middle C. I'm super low right now, somewhere around an E or F? I was wondering if its a no no to have it tuned to any of the big string open notes because the thing might resonate right out of my hands....or more likely rattle tuning pegs etc?
I think Simonoff has a book out and he targets specific frequencies. Most builders just target "sounds good to me." Some people think wolf tones can be a problem, but note durations are short on a guitar, and it produces lots of resonances, so I personally don't think it's a big deal.
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  #25  
Old 02-01-2013, 02:45 AM
Sam VanLaningham Sam VanLaningham is offline
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Man, you are fast! To bust out such solid answers in about 5 minutes is amazing! We are lucky to have gitnoob around!

Ok, while I was awaiting your reply, hehe, I read this thread about ideal resonances for the top.

http://www.acousticguitarforum.com/f...d.php?t=236047

Excellent stuff from Alan Carruth. No wonder you are a fan.

Your point about an unbraced back having a lower tap frequency is so helpful/insightful for his particular guitar. I think originally the tops main air was 220-240 hz - really high, right? Now it's 160 ish (at least I assume this is the main air?). So, yes, it probably really needed some shaving to open it up to the world.

I LOVE shaving the braces. It's actually a problem because I'm pretty sure I need to stop. I thinned them all today and I do believe I improved its sustain and higher frequency characteristics.....but it's hard to tell and I'm being really lazy not recording into audacity and getting more quantitative.

But now I want to set a target for tuning if that's realistic? Anyways, your help is beyond great. Thanks. Sam
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  #26  
Old 02-02-2013, 01:36 AM
Sam VanLaningham Sam VanLaningham is offline
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OK, I got un-lazy in this pursuit of tone! Here is a comparison of the Guild JF30 both a couple days ago and then from today after I thinned but did not remove height from the braces. I also compare the Guild with the Santa cruz D12.

These are tap tones using my index finger on the top just behind the bridge. The soundhole is not covered.

I had audacity calculate averages of 10 taps per plot.

What I see is that the mid- to higher frequencies were reduced after thinning (if these plots are that accurate???). But generally there isnt much difference, although it seems like the main peak did drop at least 2 hz and would probably be statistically meaningful.

Comparing the Guild to the Santa Cruz it appears that the mid to high frequencies are louder, leading to a "fuller" spectrum. Also, a 10 hz difference in the main peak seems to distinguish the two.

I'll do backs tomorrow but I'd also like to know other places to hit and whether any of these plots are useful without the sound hole covered?

Thanks everyone. Sam

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  #27  
Old 02-02-2013, 02:10 AM
gitnoob gitnoob is offline
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Originally Posted by Left of Sam View Post
I'll do backs tomorrow but I'd also like to know other places to hit and whether any of these plots are useful without the sound hole covered?
If you like the way it sounds now, I'd leave the back alone. In my experience, the back's tone contribution isn't huge (and most players mute the back with their belly anyway), and thinning the back braces may reduce projection.

Personally, I think the plot you're getting is useful. Alan Carruth did say that he thinks you mostly hear the "main air" when you thump the top, but I disagree.

I think you're getting an "impulse response." You're essentially setting the entire guitar in motion. The strongest peak you see is the "main top." To the left of that is the "main air." Looks like you've gotten pretty close to the Santa Cruz's signature.

If you want to isolate certain parts of the guitar, then it makes sense to do things like cover the sound hole. For example, when I try to get the back's tap tone in isolation, it sometime helps to mute the top since the top is so much more active than the back.
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  #28  
Old 02-02-2013, 02:42 AM
Sam VanLaningham Sam VanLaningham is offline
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Originally Posted by gitnoob View Post
If you like the way it sounds now, I'd leave the back alone. In my experience, the back's tone contribution isn't huge (and most players mute the back with their belly anyway), and thinning the back braces may reduce projection.
Sorry! I meant that I was going to do tap tones on the back. I don't blame you for thinking I was going to get in there hacking away.....I mean I did actually admit to using a dremel inside, which has apparently driven away the other luthiers on this site from my thread!!!! Hehe.

Thanks for the thoughts on the spectrograms. I agree they do look pretty similar. And I don't want it as balanced as the sc or else it won't sound like a guild. It still very much sounds like a guild (I think?).

So, if I isolate parts and tap them, if I don't think the tap tone is right in that area, would I shave braces in that same area? EG, if I tapped along the cross dipole and thought it was too high freq, would I shave right beneath where I tapped? Thanks a zillion. Sam
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  #29  
Old 02-02-2013, 03:05 AM
gitnoob gitnoob is offline
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Quote:
Originally Posted by Left of Sam View Post
EG, if I tapped along the cross dipole and thought it was too high freq, would I shave right beneath where I tapped?
That is an interesting question to me because I can say with absolute certainty: "I don't know."

The cross-dipole is a higher-frequency mode. It describes a motion of the top from side-to-side at some resonance frequency that is higher than the "main top."

How do you excite that mode? Probably not so well by tapping, but I haven't really explored that.

How do you shape that mode? My understanding is that it's pretty brute force: you can add bracing to deemphasize that mode or you can "free" that mode to do its thing. Not sure how you shift the frequency per se.

To get a sense of what parts of the guitar are responsible for which resonance frequencies, I do a pretty simple test:

1) play a note
2) mute parts of the guitar to see which area has the largest effect

For example, you'll see that the lower bout has the largest effect on bass by muting that area with your hand when you play a bass note.

Try the same when you play a treble note, and there's not a big effect. But mute the area on either side of the sound hole or perhaps even the upper bout above the sound hole, and you may experience a fairly large high-frequency effect.

I haven't really experimented with shaping that higher-frequency response. If you do, let us know what happens.
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  #30  
Old 02-06-2013, 03:28 PM
Sam VanLaningham Sam VanLaningham is offline
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OK, couldnt help myself......I had to shave braces until I really thought I shouldnt go anymore (with my criteria being a look that is similar to classic scalloped X-bracing).

I noticed that the treble vs bass upper bouts had different tap tones. So, yeah, I didnt listen to anybody and shaved the front structural brace on one side. I did get the tap tones more similar. But then I thought it sounded wierd so I re-shaved it relatively evenly (and I didnt take that much off, probably a 1/16th).

Here's the final product:






And here is the spectrogram compared with the previous ones:




It sounds pretty good. Its got really big low end but seems a bit better balanced than before. I think the ability to drive the top with hard strumming is reduced with all the movement on the top. Makes sense right? I kind of dont like that. So Im thinking this might be the trade off of a light build. That being said I can drive the Santa cruz pretty hard and it sounds great at any volume. But I still think the Santa Cruz might perform better with hard strumming with an adi top.

I like that I am getting down to 94 hz on that low peak because I read a report that showed a jumbo Gibson was 90hz, 180hz for the two main low peaks.

Aside: How do you get a main air lower and and not bring down the main top as well?

OK, cool. Sam
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