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Hi folks,

I’m in the process of building two more 00 instruments. The one I just finished is sounding good to me and opening up. I was talking to Don this past weekend and mentioned that it sounds really full in G2 and up, good mid and clear trebles. Where it’s lacking is below G2 and I wonder what I can do with these next two to try to move the needle?

The box is 4.25” at the tail, 3.375” at the neck. The bracing is as below.



What would you consider to try to make it more responsive in the low end? Understood that the box and shape are what they are and that will dictate a lot of it.

Maybe scallop the bass side leg of the X?

Brad


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I should add that all the braces in the pic taper to 0 so the value indicated is the highest point and then expect them to taper to 0.


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Scale length / body / frets to body joint all come into it too, but I'd maybe think about some scalloping or maybe 1/2 tone bars instead of 2.
Or, maybe open up the X brace angle, looks a bit too tight.
This would encourage T1, first top response frequency.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Good call, the plan I used was #55 from the GAL for a 37 L-00. https://luth.org/instrument-plans/guita ... tar-plans/

The scale length is 24.75, 14 fret to the body. This pushes the bridge very close to the sound hole, which looked odd to me when I was first laying it out, but it is same as the plan.


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X looks tight to me too. Almost like the E and e bridge pins would hit the X. Lower face braces could possibly be separated a little more and splayed a bit.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

I can confirm that the guitar sounds great. It has a rich midrange and treble. Brad and I listened to someone else (also a builder) play it in a large room, and I thought there was nothing missing. Sweet smaller body guitar.

If I were tempted to try to get more bass out of a smaller body guitar like that, I think the levers to pull are ones Robbie O’Brien talks about. Here, I would consider decoupling the X from the tone bars and the finger braces a bit more (by cutting down the butted ends of those braces) and gradually taking more bulk off the tone bars and the lower arms of the X.

But again, this one came out great!

That room was quite big, and nothing much to bounce off of. Mine sounds loud when I play it, but it didn't sound loud when I heard it played. Brad's sounded brighter than mine. I should have played it some to compare with mine. I have really never played any other guitars.

How about moving the sound hole up and the X brace with it? I've never made a steel string so I have no clue; but it seems like it would make a bigger soundboard. Braces always look big to me, but maybe that's why mine are more mellow.

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Why be normal?

widen the angle of your x brace

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I agree with most of the others, move the X up a bit and widen the angle. Is the soundboard equal thickness all over? If so, you could try some perimeter thinning.

An active back might help you.

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Brad, this is a 00 size that I made for myself—it has a wide fingerboard (1 13/16”) nut and is built for extra light or silk and steel strings only. The guitar sounds and feels wonderful to me when I play it. For me, the bass is very satisfying. All braces are 1/4’ wide (other than the lower two on the back) to provide sufficient gluing surface) Rather than going by dimension on the braces, I carve them by feel and sound. I set the X-brace angle such that the braces pass 1/2” from the edge of the soundhole and they just cross the corner of the bridge. That usually works out to a 97 or 98 degree spread for me. Given that this is for extra light strings, I started the X at 1/2” high and worked down from there (for light gauge, I would start 1/16th to 1/8th taller). My bridgeplate is Osage Orange and around .110” thick. I want it to feel stiff when I try to flex it. I sand it to the same 25’ radius as the top so that there is not any ambiguity on the fitting of the bridge to the top.

I want the whole center area of the top to be stiff so that no energy is lost to local vibrations. So, I do tuck the fingers and tone bars into the X. I peak the upper tone bar at the center of the top. I want it stiff across there to minimize bellying and energy loss.

I usually carve a bit aggressively from the cross of the X to the center of the bridgeplate and then taper from there to the rim. When I tap on each side of the bridge, I like to hear tones a fifth apart with a satisfying bong on the lower note. With each end of one of the x arms supported, I like to feel just a bit of flex when I push it in the middle.

On the back, the two braces closest to the head block are tall and stiff to promote body structure and delay a reset. The lower braces are low and wide (for strength, not stiffness). I lower them until I can feel flex along their length.

When I thicknessed the top (way before the bracing description above), I sanded until it started to flex under pressure from the heel of my hand. For Sitka, this usually ends up around .100 to .105” thick. When I rest it on supports 300 mm apart and put a 1 kg weight in the middle, it usually deflects between .025” and .043”. That’s not as wide a spread as it looks given that the gauge is the heel of my hand.

This process works pretty well for me. I realize that much of the measuring is subjective feel. When that’s gone, I’ll either have to measure for real or retire.

What Pat Foster said; an active back is often the best way to improve the bass. Without going into it too much, most back resonances steal energy from the strings that can be better used to drive the top. However, the 'main back' resonance can work with the 'main top' mode to pump air through the hole in the low range. Getting the back resonance closer in pitch to the top can actually enhance the output in the low range, and drop the 'main air' pitch.

You could check this out non-destructively on your present build. First, find the 'top' and 'back resonances. The easiest way to do this is to hold the guitar up by pinching the UTB and fingerboard with your fingers through the sound hole. The idea is to block as much of the hole as possible with your hand (which keeps the 'air' resonance from masking the higher pitched top ad back modes), without touching the top if you can help it. Tap in the center of the back to find the 'back' mode, trying different spots to get the lowest pitch and clearest tone. Tapping on the bridge should get you the 'top' resonance. In some cases these can be clear enough for a tuner to pick up, but usually you have to hum along. The 'top' resonance is often around the pitch of the open G string, but can be higher or lower. The 'main air' pitch is often around an octave below that, G on the low E, although on 00s and smaller bodies it's often around A.

It's usual to see the 'back' resonant mode a third or more higher in pitch than the 'top', and not uncommon for it to be a fifth higher: so somewhere between B and D (if the 'top' is at 196 Hz, the back will often be between260 and 293 Hz). The top can't drive the back very effectively when they're that far apart. When they're working together the top and back act like a bellows, and the closer they are in pitch the stronger that 'couple' is. Getting them to be less than a third apart strengthens it. A exact match give the strongest couple, but can cause problems too. Many of the 'best' guitars a friend tested had the back about a semitone (~6%) higher in pitch than the top.

An easy way to test this is to load the back of an existing guitar by sticking a wad of poster adhesive on the outside just over a brace, on the center line of the back, in the most active area of the mode, where you get a strong tap tone. This drops the pitch of the mode. You can play the guitar to get an idea of the effect of the change, and it's easy to undo it if you don't like the result. If you want to make the change permanent, just shave down the brace in the area where you had the added mass. Note that reducing the stiffness in the center has more of an effect than shaving down the ends. Doing this camn, in some cases, drop the 'air' pitch by a semitone or even two, and make it much stronger.

Of course, a 00 doesn't have the internal air volume of a Dread or Jumbo, so even if you get the 'air' pitch down to G or even F# to match that of a larger box it won't have the power in the bass the Dread does. OTOH, in many ways it's easier to make a powerful small guitar than a powerful big one, and the 00 is likely to 'carry' or 'project' well, and with more clarity.

The last two posts are about the most interesting I've seen about guitar plate tuning. Thanks guys.
Notice how Bob's bracing can create a situation where the treble side could actually be a fifth higher.

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Why be normal?

Didn't read any of the other responses so pardon me please if my suggestions are redundant.

Two things from me:

1). With every guitar I built I was sure to limit the number of things I changed, variables if you will to 2 - 3. Reason being I'm trying to isolate my variables so any changes are not skewed by other variables. Worked for me. I was into 12 or more guitars before I started to be pleased with the frequency response.

2). Time. I know this is not what any of us want to hear but time makes a difference and can make a big difference on the bottom end. I'm sure use loosens things up too but time is amazing in and of itself.

There is mention on this forum of a BRW/Adi OM that I built, took to Uncle Bob's place for a gathering and then brought home and stuck in a case for five years untouched that entire time. Previously it had OK bass but after five years the bass was more...... profound . It's one of my favorite guitars these days. There is a lot to be said for the wood seasoning and we do not fully understand the impact(s) on tone of seasoning.

And I know that I said only two things but Brad I wanted to suggest something to you that was once suggested to me here by Mario P. that brought it all enough together for me that some of this finally made sense. By making sense I mean changes I would make started being productive in the directions I had hoped.

Mario suggested that a guitar was really very much like a fireplace bellows and it is or has to be engineered to pump. Of course extrapolating from this that looser tops and even more movable backs will move more air in pumping may be an over simplification but it also worked for me, worked very well. With this said top plate, back plate thickness, stiffness of back braces as well as the top bracing all play into a guitar being able to move air.

And all of a sudden our braces may be viewed differently as no longer immovable objects but calculated stiffeners strategically positioned to let the top and back move (if into active backs...) but still prevent cracks and splits. It's all a balance and then there is tone....

PS: Your bracing looks nice and light to me from here, good going that's half the battle.

Another thing you might try is using a long scale (25.4) rather than the short scale and build the guitar to use light gauge strings. The longer thinner string with less tension may give better base response. When I am perimeter sanding I will stop periodically and while playing a musical recording use my finger tips to feel how and where the top is vibrating depending on the frequencies being heard. Further sanding those places will usually increase the strength of those vibrations - but don't get carried away or you might weaken the top too much and lose "headroom" (the ability to drive the top forcefully).
Changing from the 14 fret body to the 12 fret body (longer soundboard) I think improves the bass response.
Every piece of wood is a little different, and although we can dial in our own recipe to some degree, at some point we are still "in the hands of the gods". Like our children, they may share the same DNA, but they will all be a little different.

Note that on the assembled guitar there is no 'bass side' or 'treble side' to the top. The whole lower bout moves like a loudspeaker cone at low frequencies, and as you go up in pitch it starts to break up into a number of smaller areas that move out of phase with each other. In most steel stings the next top resonant mode up from the loudspeaker-like 'main top' (at ~200 Hz)is the 'cross dipole', usually at around 300 Hz, and then there's a 'long dipole' (bridge rocking fore and aft) at around 375. The strings, of course, put in energy at a lot of different pitches at once, so the actual top motion gets pretty complex, but what you hear is a sort of sum of everything that's going on.

I used to make tops with asymmetric bracing, on the assumption that it would increase the output of those 'multipole modes' because there would be larger and smaller areas involved, but it didn't work out that way. Now I try to make things as symmetric as I can.

Standard Martin-style bracing is, of course, asymmetric, with the two tone bars running the same way. You can easily feel this asymmetry if you try flexing the top along the two diagonals: it's easier to bend the treble side of the X brace than the bass side because you don't have to bend the tone bars along with the treble side of the X. In the sense it automatically makes the treble side looser than the bass. Dana Bourgeois scallops the bass side of the X along with the tone bars on some of his tops, leaving the treble side of the X tall, which evens out the stiffness along the two diagonals. This shows up in Chladni patterns of the 'free' top, and produces better treble response. I get the same result by using a symmetric top brace pattern and scalloping both legs of the X. It's not so much that the 'treble side' of the top has been made stiffer, as that the whole top has been made more symmetric.

I'll note something that my voice teacher said once: "The way to get good sounding bass notes is to work on your trebles". It's not just about power; clarity goes a long way toward making the low notes sound good.

IMO…

The three easiest ways to increase bass response are…

1) Increase your top monopole mobility. IE make it so that your top moves in and out more, driving more air. Generally, increasing the tops mobility will also lower the monopole frequency.

2) Dial in your back to couple with your top in a productive way. The G/G books suggest 4 semitones above the top, but I’ve found with 00 sized guitars, 3 semitones works too.

3) Change the freq of the air chamber by either making the sound hole smaller, or the box deeper. There’s some risk in that however, as it increases the chances of having the air chamber and the top monopole couple, which is something you very much don’t want. As has been mentioned much by many, the standard design parameters have been shaken out a long time ago. It may not be wise to stray from that until you know exactly why you’re doing so.

In general, my advice would be to get the Gore/Gilet books and take a week or two out of the shop to do some heavy reading.

Then build the very most basic guitar you can build with no froo fra. Get yourself an FFT setup, which is a very powerful diagnostic tool to actually measure what is happening to your guitar, and start measuring. As you build more guitars and collect more data, the info in the books will make more and more sense. There’s no need for any of this to be a mystery anymore…

Lot of good info in here, thanks to all for the feedback.

Regarding the X splay, when I was bringing the plan into CAD I took a birdseye picture of the plan and marked out the layout. The plan is ~95 deg for the X. It’s hard to get a very perfect very flat pic from the plan. I rounded up to 95 in my top bracing template. What should I consider opening it up to?



Brad


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Thanks, Ed. I’ve read the build book and as much as I could understand of the design book. I use the process for determining the starting point for the top, that’s about as far as I take it. I haven’t yet started taking samples of the closed box, making adjustments, etc… I’ll get there.


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It’ll be the most important step you take. Unless you’ve sold or passed on the last 00 you’ve made, you’ve got an on hand example that you can measure and make design decisions accordingly…:)

Probably around 100. I never measure the angle, just do it graphically. The upper ends of the X look good, so keep those where they are, and move the lower ends until the legs cross under the corners of the bridge.

At least that's what I'd do. Whoever drew that plan clearly has a different opinion. I was thinking the plan would have the X legs closer to the bridge corners whereas the bridge on yours was moved up for the shorter scale, but it looks like that was an intended aspect of the design.

maddlingfool wrote:
"Change the freq of the air chamber by either making the sound hole smaller, or the box deeper. "

Fred Dickens showed that making the box deeper did not change the pitch of the 'main air' resonance much. He did it by simply making a guitar that was 6" deep (out of BRW!), and progressively cutting the ribs down and re-gluing the back on until he could go no further. The 'main air' pitch rose by (drum roll) 7% going from 6" ribs to ~2". I've pretty well confirmed that for lesser changes in depth.

Making the box deeper would, of course, drop the pitch of the 'real' Helmholtz resonance, assuming the walls of the box were rigid, but they're not. The guitar is a bass reflex enclosure in the low range, with the 'main top' resonance changing the air pressure in the box and the 'main air' resonance pushing on the top. Rossing's experiments of burying guitars in sand while leaving the hole open showed that the isolated 'top' resonance would often be in the range of 160 Hz, and the Helmholtz air resonance at about 125 Hz. When the two work together the coupling pushes the 'top' pitch up and the 'air' pitch down, so that they often end up somewhere near 100 and 200 Hz.

Making the box shallower would raise the isolated ('in sand') Helmholtz pitch. However, since a given amount of top motion would produce a larger pressure change in the box it also increases the coupling strength between the 'top' and 'air' resonances, which increses the pitch displacement. The rise in the 'real' Helmholtz pitch is prettyy much cancelled out by the increased downward displacment. My experience is mor limited than Fred's but it does suggest that the 'top' pitch could rise in an experiment like his. I didn't get to see his data when he decsribed the experiment to me, and he didn't say what happened to the top pitch.

It was Fred who first mentioned to me that dropping the back pitch could also drop the 'main air' pitch. The back can be seen in this range as a sort of adjunct to the top; making it more mobile in effect adds to the vibrating area (mobility) of the top. In theory the effect would be maximized if the isolated pitches of the top and back could be made the same. In practice getting them closer than a semitone or so is risky. They can couple so strongly that you end up with a nasty wolf note. It is, of course, difficult to really isolate the 'top' and 'air' pitches on actual guitars, which is one reason for the uncertainty about the 'best' pitches to go for.

Making the hole smaller drops the 'air' pitch, and also reduces it's power. You can get the same effect by putting in a sleeve ('tornavoz').

I’m not sure how 7% in that frequency range would translate to Hz, which is the important number I feel, or at least one that has more relevance to me.

Dropping the back frequency absolutely drops the top frequency as well as the air chamber freq, but not equally. So 10hz off the back does not take 10hz off the top as well.

In theory, it wouldn’t be too difficult to make the top and back pitch the same and place them between scale tones so as not to be triggered (or at least have the wolf note spread out over two notes and halved). I’m not sure what that would do to the tone of the guitar. The only guitars I’ve taken data on that were somewhat near that approach are Lowdens, but Lowdens tend to have heavy stiff tops in general, with top freqs considerably higher than more conventional guitars of the same size. I like the sound of Lowdens, so it could be a good approach, circumstances depending.

With FFT software, it is quite simple to isolate the coupled frequencies, which I think are more important than the isolated freqs, as the guitar is working as a system when it’s being used.

That’s correct, the plan was drawn from two sample instruments that Kerry Char had in his shop. I agree that the bridge is way up on the X, I actually asked that question in a previous thread because it looked so odd.

viewtopic.php?t=55354

All in all I’m happy with the instruments sound. I wanted to make sure I built this first one as true to the plan as possible and go from there. Then, ala Hesh, could tweak one thing at a time. Appreciate all the input!

Brad


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A semitone is a change in pitch of almost 6%, so seven percent is just a bit more than a semitone. I've gotten a drop in the 'air' pitch of more than a semitone by dropping the back pitch.

I wish I had known more when Fred told me about that experiment. I didn't have enough of a background to ask useful questions, and now it's too late. Somebody will just have to repeat it.

meddlingfool wrote:
"In theory, it wouldn’t be too difficult to make the top and back pitch the same and place them between scale tones so as not to be triggered "

The worst wolf I ever ran into was from a guitar where the coupled top pitch was 7 Hz below the coupled back pitch, around, iirc, G#~208 Hz (so, about 1/2 semitone). It came across as a strong fret buzz when there was no string buzzing anyplace. Adding a small amount of mass to the top at the bridge (a gram or a bit more) dropped the top to 11 Hz below the back, enough to move it out of the half band width of the resonance, and reduce the coupling usefully. I'm not sure I'd want to go any closer than that, even right in between played pitches. The pitches and relationships of the top and back resonances can change with changes in humidity, and maybe even with time and playing: a have a guitar that has a 'wolf' at G=196 when the humidity is 'normal', that goes away when it gets dry.

"With FFT software, it is quite simple to isolate the coupled frequencies, which I think are more important than the isolated freqs, as the guitar is working as a system when it’s being used."

Indeed. Again, though, things can change with altered conditions; even holding the guitar differently can change things. This is another whole discussion: what's the 'right' way to test stuff?