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I’ve feel these numbers are more of a way to understand and make decisions regarding your own idiosyncratic praxis as a builder, rather than a way to understand how guitars work in general - there are too many variables at play in how the testing is carried out. My first exposure to testing of this sort used sawdust, a speaker and a frequency generator to test things. When I later adopted the practice of FFT software and tapping with a rubber mallet I retested instruments and realised I was now getting different results. Further changing the software and the microphone and the mallet all altered the result. So as a tool it is primarily useful within the confines of a single workshop and builder in order to understand how the current instrument differs to those previous which were tested with a (hopefully) close to identical methodology. I don’t feel it is that useful for diagnosing someone else’s guitar remotely.

I'd have to believe what Josh says here. You do need some sort of guideline to go for. Sometimes you can't get there, and you see what happens. I had a flame birch violin back that was very low from the beginning. I paired it with a very light curly spruce top, and it is extremely easy to play. The tap tones were very different, but the main modes, when tested with some of my other violins a while back were very similar. All different models, Birch, Sycamore, Maple; all basically the same main modes.

I tested my 2 guitars and the Less Paul body yesterday with audacity.
Stauffer:
tonehole C#3
top mode C4
back mode C#4
notes with no peaks: E F F# G G# A Half the instrument. Play from Bb to Eb and you are good?

Archtop:
Tonehole G3/G#4
top mode A#3
back mode C#4
notes with no peaks: C D E G A only single notes, no spans. But look at the notes. Tonehole helps G A?

Less Paul (body only)
Toneholes B2 B3 D4?
top mode C#4
back mode D4
Notes with no peaks: G G# A# B C. Toneholes help A# B C?

In reality;
the Stauffer rings on the top string on E F F# G G# A. It doesn't sound like a loudspeaker on C/C#
the archtop has a mellow sound (low pitch of belly? curly redwood) but the C may be not as powerful (I have noticed that)
On both, the low E is not really there, it is the B
low A is still not prominent.
The D string is louder than the G (on the FFT)
The B is higher than the high E (on the FFT)
All the plates have peaks between A#2/C#3 and A4/B4

So they are interesting. Obviously they are very different instruments. Not violins to violins; or 00 guitar to 00 guitars. But they still are very similar.

I still think that getting as many tap tones as you can out of a plate is a good thing. Testing and tuning on ribs or a fixture would probably be a good thing. On a guitar you don't have to have a sound post in for that.

It is still a mystery to me.

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Why be normal?

Here is where I’m landing. Any suggestions please share them. The X splay is opened up ~3 degrees and shifted forward.

Everything else is the same.




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You could change it up completely (rather than shifting the deckchairs) by using falcate bracing. This guitar is 00 sized.

Attachment:

snapshot.jpg

It's a high res. vid so needs a decent connection for best viewing and listening.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Hmm, I think something's gone wrong. I tried overlaying it with the original, and it looks like the soundhole and upper X ends have moved quite a lot.

If I move everything except the bridge down until the soundhole matches the original location then it looks good, except that the new outline is way out of place.

The bridge location, and the soundhole to some extent, are fixed relative to the upper edge, assuming you're placing a fret (12 or 14) at the body junction. The bridge measures from that, and the hole has to be far enough down to allow for at least a partial 19th fret. THEN you draw in the bracing. The lower legs of the X need to go under the bridge at some point; outside of the pin holes, and no further out than the ends of the bridge (which length can be adjusted to suit). The upper ends of the X have to go below the UTB ends, and that, with the bridge location, more or less constrains the X angle.

Mark Blanchard, who's smarter then I am, and keeps better records, did a long research project on the relative effects of the top and bracing on sound, and decided that the sound is in the top. Bracing, at best, fine tunes it. In theory it would be almost possible to dispense with top bracing altogether, IMO, the exception being the UTB, which is needed to keep the neck from folding in. The problem is that you'd need to leave the top quite thick, which would add a lot of weight, and cut down on power. We use bracing to keep the weight down. You can't really make a very bad top much better no matter how you treat the bracing, but it's pretty easy to ruin a good top by messing the bracing up. From what I've seen, just about any reasonable brace pattern can be made to work well if you can adapt it to the particular top it's on, and the top is the right thickness. It's best to choose the top to suit the shape: wide shapes, like the Dread or Jumbo, need to have a top with relatively high cross stiffness, while something that's narrower, like your 00, doesn't need that so much. Mark worked out a way to allocate his tops to the proper shapes by the simple expedient of looking at the way they vibrate, and cutting them down progressively to find the shape that works. You can also meaasure the long- and cross-grain Young's moduli and sort them out that way.

Martin, of course, worked all of this out via 'cut and try' methods, to produce satisfactory instruments in their setting. Things like the brace angles are all compromises, but over the years they've become religious icons that are the subjects of heated discussions on lists like this. We're not in a production setting, and can alter things to get the 'best' results from each top, however you want to define 'best'.

That’s a lovely guitar, Trevor. I do want to experiment with falcate bracing. It’s in the queue, which is ever growing .


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Thank you for checking my work, Dennis! Regarding the shape, I did change the profile. It’s now one I drew up for another builder and was given permission to use it myself. It’s a more clean flowing shape. I forgot to mention I was moving to that shape here as well. That was my plan all along before I started down the tinkering with the braces path.

Regarding the sound hole location, this has to be moved up to accommodate the shifted X. If I were to leave the X where it was originally and just widen the splay until the tips of the bridge were on the X, it would be very, very wide.

To take a step back, my goal was to make an adjustment to allow for more low end. I built V1 based on the plan from Kerry Char of a 30’s L00 and I think what I ended up with is representative of that. However, my goal is not really to build 30’s L00 replicas specifically, but to use that as a starting point. Widening the X to get the wings of the bridge over the X in a more typical pattern like we see a lot today made sense to open up the lower bout. Am I correct to assume this will introduce more low end by freeing up the top?

Appreciate your help!
Brad


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In that case you may not want to widen the X at all, since it looks like the distance between UTB and bridge is longer on this design.

To be clear, when I said "move the lower ends until the legs cross under the corners of the bridge" I should have said "lower corners of the bridge", meaning something like this. Although your placement should be structurally fine too, so you could stick with it and see how it sounds as a more extreme difference from the previous guitar.



Also some kind of bracing around the soundhole to restore the lost stiffness there, unless you put the soundhole(s) somewhere else like in the corners above the UTB and/or the side of the guitar.

Two of my best guitars so far have minimal bracing. A nylon string based on an old Torres (which has a thin strip of wood glued across the lower bout to prevent the spread of cracks if they ever happen, but adds basically no stiffness)


And a 12 fret 00-ish steel string (14" wide). It ended up getting a larger bridge plate due to my miscalculating the position the first time (better to reduce peeling stress at the back edge of the bridge anyway, since redwood peels easily).


And my work in progress for the past several years, a very small fan fret steel string (less than 13" wide, and soundboard even smaller due to armrest bevel) with bracing similar to the nylon string. Cross brace below the soundhole defining the active area, with the bridge itself being the only brace below that. And like the nylon string, the bridge width is equal to the waist width. Quite curious to see how it will sound


Use of cedar or low density redwood certainly helps to keep the weight down for this style. But the last one is so small that the weight is basically irrelevant, so spruce is fine.

Hi Brad,
I like the proposed design as drawn. The soundhole shifted up may help the bass some, even if you lose a fret or two. Some of the old guitars had 18 fret boards and some only 17 frets total. You could add a small "tongue" over the sound hole if you really wanted to have that highest possible note, but most never use it.
I like to make the braces around the soundhole relatively stout because that is where I have seen old guitars improperly strung with steel strings fold up, and I don't think you want a whole lot of "soundhole flutter" anyway.
If I were to change anything on your drawing I might move lower tone bar a little bit further down, closer to the tail block, but it is probably fine where it is.

Here is where we landed with the new brace layout. I’m about to close the box on this one.







Will know the outcome in about two months. I work so slowly.


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Looks good Brad,
I would use taller braces around the soundhole, but most do not - it interferes with some pickup installations.

Great thread my friends, love this subject.

I'm a beginner but trying to model my top's resonance characteristics using the GUITAR ANALYSIS and TESTING with TREVOR GORE course method from Robbie's site. Just ordered a new Audio-Technica ATR2100x-USB Cardioid Dynamic Microphone to use with VA visual analyzer spectrum capture software- my cheapie sub-$20 USB microphone isn't directional enough, sensitive enough or repeatable enough to capture anything useful from the frequency spectrum captures. After reading and re-reading this thread, I'm really eager to give it another go with a better microphone.

My 1st and 2nd guitars were Rosewood/ torrefied spruce dreadnaught kits from StewMac. Both builds exceeded my wildest expectations for both appearance and tone. I voiced both from information in books I've accumulated into a guitar building library. The 3rd guitar fell off a table onto hard concrete, cracked the top and the binding and is in re-hab. I'm eager to hear #3 to see (no pun intended) if my skills are improving. I still need to read the book on secrets to survive a 3 foot drop onto hard concrete floor.

These 2 dreads. to my ear, are big on bass and mid-range, but lack on the treble end. Treble is not crystal clear and not as "present" or loud as the bass. Can't wait to hear this #3 as I had a slightly better idea of what I was doing, overall. Or even better, #4 which I've started while #3 is getting repaired. I will get to brace, build and evaluate #4 with even more voicing experience (and incredibly useful information from the good people contributing on this thread). The OP was interested in improving the low end of an OO so sorry for the digression....

p.s.:
For low end response, on #1 and #2, I thinned the outer most 1 1/2 inches of the top, with a block plane, on the bottom side, from ~.110 to 0.090", south of about the bottom of the sound hole, before bracing, based on a chapter in Cumpiano's book. I was not disappointed. Didn't do that on #3......

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Measure Twice,

Karl Borum

use a hard maple plate. Not a fan of rosewood
I do like osage orange , Brazilian Rosewood is ok but east indian in my opinion is too soft and won't wear well.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

when you tune your tops what are you tuning them too and are you making the backs a semi tone different to avoid wolf notes?

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it