Enhance the bass of 000 size?

[Henning]

Thank you so much for your engagement and concern. A particular big thank to Alan C. for your post that l will consider and "think through".
Of course, a better, more expensive and finer instrument will always be exactly that.

What i do find, the sound of the low tones of the A string is satisfying. But the sound of the low E string is not quite so.

[John Arnold]

Stiff bracing on a 000 size guitar will shift the top resonance closer to an A instead of a G. That would explain your weak 6th string.

Rounding the edges of the bracing isn´t worth the trouble?

Not in my experience. You get more result from reducing the height of the bracing. Stiffness is proportional the the cube of the height, so it doesn't take much trimming to have a big effect. Example: Cutting the height in half results in a brace that is only 1/8 as stiff. As a result, the most common mistake when scalloping braces is to go too far.
As Alan indicated, you would best be served by learning how to obtain the top and back resonances. The fundamental resonance is determined by stiffness and mass. Increasing mass or reducing stiffness will lower the resonant frequency, which will increase the bass. Cutting the height of the braces lowers the stiffness more than it reduces mass. That is why it lowers the resonant frequency.
Adding poster putty (mass) has a similar tonal effect as scalloping, but the added mass will tend to increase sustain and reduce volume. Since is it reversible, the poster putty is a good way to simulate the effect of scalloping, with the stated caveat.
When doing aftermarket scalloping, I have target frequencies for the top and back. On a scalloped dreadought, the target is F to F sharp for the top, and G to G sharp for the back. 000's will tend to be a bit higher.

[Brucebubs]

Originally Posted by phavriluk

I can't turn a Volvo into a SAAB. Same applies to guitars. Please don't make irreversible, and potentially damaging, changes to your guitar in pursuit of goals that can't be predicted.

Someone tried that and the end result was the Trabant

[Henning]

Originally Posted by John Arnold

Stiff bracing on a 000 size guitar will shift the top resonance closer to an A instead of a G. That would explain your weak 6th string.



Not in my experience. You get more result from reducing the height of the bracing. Stiffness is proportional the the cube of the height, so it doesn't take much trimming to have a big effect. Example: Cutting the height in half results in a brace that is only 1/8 as stiff. As a result, the most common mistake when scalloping braces is to go too far.
As Alan indicated, you would best be served by learning how to obtain the top and back resonances. The fundamental resonance is determined by stiffness and mass. Increasing mass or reducing stiffness will lower the resonant frequency, which will increase the bass. Cutting the height of the braces lowers the stiffness more than it reduces mass. That is why it lowers the resonant frequency.
Adding poster putty (mass) has a similar tonal effect as scalloping, but the added mass will tend to increase sustain and reduce volume. Since is it reversible, the poster putty is a good way to simulate the effect of scalloping, with the stated caveat.
When doing aftermarket scalloping, I have target frequencies for the top and back. On a scalloped dreadought, the target is F to F sharp for the top, and G to G sharp for the back. 000's will tend to be a bit higher.

Thanks John, great information!

[Henning]

Hello, I measured the thickness of the top and found it to be 3,50 mm which would be 0.138" and is a rather thick top from the way I understand it.

I tried to do some tap tuning leaving the strings on and damping them with my hand. Is that an acceptable way to do it, or do I need to loose the strings completely, to obtain a true value please?

Stopping the sound hole; this gave the tap tone of the top to ~A3 or the A at 220 Hz.
The tap tone of the back was slightly harder to record as it has a noticeably shorter sustain. I do estimate it to be ~293 Hz or close to D4.

I am wishing a way to find out where to rework the back and/or top to obtain the desired result. Any advice in the direction of how to find that is truly appreciated. The braces seem to be rather wide, perhaps 8 - 10 mm.
Where to start?

Kind regards

[Fathand]

3.5mm top would be on the thick side. X Braces on a 000 would normally be 1/4" or 5/16" wide (6.35 or 8mm). Should be able to measure with a micrometer or even a cheap plastic Vernier.

[koolimy]

Originally Posted by Henning

Hello, I measured the thickness of the top and found it to be 3,50 mm which would be 0.138" and is a rather thick top from the way I understand it.

I tried to do some tap tuning leaving the strings on and damping them with my hand. Is that an acceptable way to do it, or do I need to loose the strings completely, to obtain a true value please?

Stopping the sound hole; this gave the tap tone of the top to ~A3 or the A at 220 Hz.
The tap tone of the back was slightly harder to record as it has a noticeably shorter sustain. I do estimate it to be ~293 Hz or close to D4.

I am wishing a way to find out where to rework the back and/or top to obtain the desired result. Any advice in the direction of how to find that is truly appreciated. The braces seem to be rather wide, perhaps 8 - 10 mm.
Where to start?

Kind regards

Did you get the putty as recommended by Mr. Carruth? I would start by putting the putty on the back braces (or if you can't reach them, just put them on the back of the guitar close to the braces) and measure how the tap tone drops. You of course should also play and listen to the guitar while doing this. You should find a semitone calculator online and find what is the frequency that is 4 semitones away from 220hz, and try to get your back to hit that frequency.

[Henning]

Hello, I´ve tried the tap tuning again finding slightly different "values":

Top: G3 +40%

Back: C#4 -10% to +20% (meter fluctutates)

What would be a suitable difference between the top and back ground tone frequency in your opinion please?

The width of the braces in the X-bracing is about 7,5 mm or 0,30"

I find by adding an amount of ~21 g of putty to the outside of the lower bout brace, the tap tone of the back turns to be G3 +35& to +45%.

What now please?
Kind regards

[koolimy]

Originally Posted by Henning

Hello, I´ve tried the tap tuning again finding slightly different "values":

Top: G3 +40%

Back: C#4 -10% to +20% (meter fluctutates)

What would be a suitable difference between the top and back ground tone frequency in your opinion please?

The width of the braces in the X-bracing is about 7,5 mm or 0,30"

I find by adding an amount of ~21 g of putty to the outside of the lower bout brace, the tap tone of the back turns to be G3 +35& to +45%.

What now please?
Kind regards

I heard that you want to be in between 1 and 4 semitones apart. If the frequencies are closer than 1 semitone, you risk getting wolf notes. 4 semitones seem to be the threshold for getting an active back. I could be very wrong, but using this semitone calculator it seems like your back and top are around 4.8 semitones apart. You probably want to drop your back frequency just a bit, maybe around B3, to get into the 4 semitone range.

Did you play the guitar with the putty on? What was your impression? It will sound quieter but you should be able to hear the changes that are not related to volume, such as increased overtones and bass.

Also, when you start actually attacking the braces, you'll see the most dramatic changes by lowering the height of the braces and by lowering the middle part of the braces. But be careful, as you are weakening the braces! It is best to go slow and measure as you go along.

P.S. It might be good to find a way that consistently measures your tap tones. G3 and A3 seem pretty far apart, so you want to make sure that whatever method you use gives consistent tap tones before proceeding with the surgery. I used a mic and recorded the thumps on audacity and used the spectrum analyzer function in Audacity. I found it gave consistent results for me.

[Alan Carruth]

A friend of mine has written an Android app called 'Luthier Lab' that has a spectrum analysis module. It's free, and works well, even on my cheap tablet. It makes it fairly easy to find the pitches of the main top and back resonances with a bit of care.

If you want to geek out a bit more, it also has a signal generator. You can use the output from that to drive a speaker through a power amp (at least 12W) to excite the top and back at whatever frequency you want. This is used to generate 'Chladni patterns'. You lay the guitar flat on the bench and sprinkle some sawdust or glitter on the top or back. Then you sweep slowly up through the frequency band of interest, using a pure 'sine' wave signal. When you hit a resonance the dust will jump off the moving 'antinodes' and gather along the non-moving 'node' lines, forming a pattern. The 'main' top and back modes move like a loudspeaker, so the central area of the plate will be clear, with the dust gathered up near the edges. You can also use the speaker to drive the 'air' mode at the sound hole; it gets a lot louder when you hit the right pitch.

[Henning]

This Sigma 000 has four back braces. The two in the lower bout are very sturdy. Yesterday I worked the upper sturdy brace to around 1/4" in the centre of the back. The edges are somewhat thicker. This was hard work, even though I had a new small planer. Scratching my lower arms against the sound hole edges, so now the skin is red and irritaded there.

Yes, I tried the putty on! It did what you could expect except that adding the putty made the tap tone frequency drop(!).
I tried the putty both on the top and the back too, putting it on the outside of the guitar back all along the upper, more sturdy, mid waist lower bout brace.
(That should be a node, if you put the mass on the mid point of an anti node instead?)

I will try to rework the inner sturdy lower bout brace and work it down too. Don´t expect very much to happen. Don´t expect very much to happen of the whole of this operation either.

I´ve managed to lower the back tap tone to about A3 +40%. Along with this the top tap tone has lowered somewhat too and is now maybe around G3, though I´ve so far havn´t really done anything to it.

[craigj]

I would try a «Norman Blake» string set. From Premier Guitar: “Though his choice of gauges can vary, he favors .012, .015, .024, .032, .042, and .054 or .056 for strings 1-6.”

[koolimy]

Originally Posted by Henning

This Sigma 000 has four back braces. The two in the lower bout are very sturdy. Yesterday I worked the upper sturdy brace to around 1/4" in the centre of the back. The edges are somewhat thicker. This was hard work, even though I had a new small planer. Scratching my lower arms against the sound hole edges, so now the skin is red and irritaded there.

Yes, I tried the putty on! It did what you could expect except that adding the putty made the tap tone frequency drop(!).
I tried the putty both on the top and the back too, putting it on the outside of the guitar back all along the upper, more sturdy, mid waist lower bout brace.
(That should be a node, if you put the mass on the mid point of an anti node instead?)

I will try to rework the inner sturdy lower bout brace and work it down too. Don´t expect very much to happen. Don´t expect very much to happen of the whole of this operation either.

I´ve managed to lower the back tap tone to about A3 +40%. Along with this the top tap tone has lowered somewhat too and is now maybe around G3, though I´ve so far havn´t really done anything to it.

It is not an easy job! I did a similar operation to you and it was a lot of sweat and tears (thankfully no blood, LOL). The top tone dropping is a phenomenon I encountered also. It is strange how the back influences the top tap tone, but it does. The air mode should also drop, increasing the bass of the guitar.

As I said before, go slowly and be careful with the operation. It is very much possible to cut the braces too much. If you have the strings somewhere I would test the guitar from time to time, to see how the sound has changed during this operation. Constantly measure the back and top tap tones and use the calculator to see if they are inside 4 semitones apart, while more than 1 semitone apart.

[John Arnold]

As difficult as it can be, you need to trim the ends of those back braces. The idea is to reduce stiffness, particularly on the edges of the plates.
I may be reading your post wrong, but did you say you placed the putty near the edges of the guitar, where the nodes are? That should have little effect. To lower the frequency, you need to add weight in the antinode areas. For the fundamental mode, that would be near the center of the lower bout.

[Alan Carruth]

"Yes, I tried the putty on! It did what you could expect except that adding the putty made the tap tone frequency drop(!)."

Adding mass to an active area does drop the pitch of a mode. Braces do tend to be nodes because of their stiffness, but not in all modes. The 'main back' resonance, where the lower bout moves like a loudspeaker, shows a lot of motion at one or more brace locations, and reducing the stiffness of those braces will drop the pitch.

Several years ago Evan Davis ran a computer model to look at the effects of removing wood from various parts of the bracing. Generally speaking, taking wood off in the center had more effect, both in dropping the mode pitches and in enhancing the amount of air that was pumped by the plate. We often think of the plates as if they were 'long throw' speakers with soft edges, but that's not really how they work; there's a lot of stiffness there just from the way the plates are glued at the edge. This, is, of course, what's done with 'scalloped' braces, and we know how effective that is.

It's hardly surprising that the top pitch drops when you shave back braces. As the back moves more it has to get the energy from the top. In effect, the top can 'bounce off' a very rigid back on the air 'spring' and not lose much energy, but once the back starts to move it's adding mass that the top has to drive. An active back, in effect, adds some area to the top, so you're moving up a half-size without having to reach around a bigger guitar.