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I have closed the box and now waiting for the bindings glue to dry.

I managed to bring the plate to a desired target both before and after bracing.

The problem is that the rims stiffened it too much.   The thickness is about 2.1 in the center, slight taper to 2.0/1.9 at edges.  The central 3 fan braces are a bit stronger than the rest, as usual.

Question is, what would you do to loosen it up a little.  Increase the taper at the edges and leave the center alone, or sand all over. 

I think it got too tight because i have used linings a little too wide, about 8-9mm. They vary a little because i was cutting them by hand from a billet and in a hurry to glue to the top asap - humidity was right at that moment.

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Just for the sake of the ignorant providing advice, I sure wouldn't thin any in the center.  Most approach 2.5 in the center and 1.8 - 2.0 on the edges, from what I have read, and been told.  8 - 9mm does not sound too wide for dentillones.  I think Romanillos recommends 8mm width at the top and alternates between 10mm and 6 mm high. 

What are your fan bracing sizes - height and thickness, and how did you taper?  How wide is the area where the top is in the 1.9-2.0?  Shawn told me that Romanillos uses an area about 35mm wide to thin to 1.9 - 2.0 or so, depending on stiffness, and then tapers to the bridge area which is maintained at about 2.5.  The 35mm thinned area extends from just on the upper bout side of the waist all the way around the lower bout to the other side at the same point.  I'm sure all of this is dependent on the piece of wood, of course.

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Waddy

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String her up before you decide to do anything.

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This is built in Greg Byers' style. Byers was a student of Romanillos, and the way he is bracing is very similar. David Russell recorded and played live with one of his guitars and that is a good endorsement for me :)
Byers changed things a bit, he uses a larger plantilla, and an angled Rodriguez-type treble bar. He is also taking tops very thin, often under 2 mm with spruce, and puts a pad.   My Italian top fit well in the parameters and i should have taken it very thin but I chickned out and braced it. That made it sound extremely tight, and from there I shaved both the braces and outer face to get the desired result.  In the end I got a top which was slightly thicker, the braces thiner and not so tall, and no pad.

My linings are wider than Byers', he is using i suppose 5mm wide solid linings.  In his view the solid stiff linings should help with the volume and sustain, but that was too complicated to me and i was in a hurry to glue things up while humidity was ok.  

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Btw, right now the top's main resonance is 2 notes higher than the target.

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Alex - what are you trying to achieve? What is too stiff and how are you judging that?

If you're judging the soundboard as being too stiff based on its main resonance your overthinking things - too much theory to little practice.

I go by feel. On occasion I'll make adjustments after the guitar has been strung but before I french polish her. This way you are getting a very direct result that you can understand and you're working toward trying to achieve something specific (like better responsiveness for example). I'm not sure what you're trying to achieve here?

Also, fan brace dimensions are helpful.

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I am being helped by a student of Byers. They both record the main resonances at every stage:  bare plate, braced, attached, after bridge is attached.

Statically there seems to be a direct relationship between stiffness and the main mode.  The crossgrain is very important too, the floppier it is, the lower the point.

Byers tries to stay within certain points of resonance at every stage, just as other people record and judge by deflection testing. It's just another method.


Anyway, Byers' bracing is very very similar to Romanillos', traiangular shaped tapered braces, just that he makes them a tad thiner.  I ended up making mines a little smaller.  The central brace is 5.5mm wide, 5 tall, the others are app. 5 wide and the outer bass ended up being 4mm tall.

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edit, i guess the central is still more like 6mm tall.   The top was very stiff across the grain. As i said it now ranges from 2.1 to 2-1.9mm.  

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If the top was very stiff across the grain I'd have gone lighter on the bracing, at least in terms of the strut coming out of the lower harmonic bar and the cutoff bars.

This is a very different design then I'm used to. I am using the basic Torres usually but sometimes opt for the Romanillos bracing if a top is very stiff across the grain. The way a Romanillos is, the fans don't cross as many grain lines, the harmonic bars are opened and scalloped in the center, the cutoff bars are much smaller, etc.

Have you asked the person you're working with about the current prediciment? I'd be careful thinning that top too much and I'd be most likely to still do it once strung up. Try using a very light bridge and see if that helps you get back to whatever resonance you want in the end product.

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He is being away for a few days, and I want to glue the bridge today :)

Regarding the fans not crossing many lines, this is much the same.  It has a focal at the 8th fret, while a Torres is at the 15th.

Regarding the open transverse.  What happens above the transverse has a big impact on the resonance of the bridge area. For example I was stuck at a certain note, and thining the lower bout and the braces was not helping. It turned out I had to shave half of the thicknes of the soundhole donut to kill the stubborn peak.  The difference between a light and a heavy transverse is as much as a half tone which is significant.   And so on... 

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Joshua, first, many thanks for spending your time with the top dilemma.

In the mean while I need to finish the bridge, which still weights a ton and is very bulky.

The lenght i think is fine, 185mm.

wings -  6mm thick, should be 4.5 - 5 ?
central block, 12mm thick. 
tieblock lenght, 82mm, I need to shave 1mm off both ends and make it 80.
tie block width 12.5-13mm I guess I need to thin it to 10 since the access to the hole is difficult right now.

I plan to shave 1mm off the bottom, that will make the wings 5mm and the center 11.   After sanding to allow the doming, the wings will be the same or towards 4.5, while the center 10mm.

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edit...

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Alex - if you're intent on building in this manner, mostly paying attention to the resonance, you're best to wait for your friend to return and ask his advice. Especially if he's been helping you along the way.

The thing for me is that the resonance is just one piece of the puzzle. If the resonance is too high it may not be that your soundboard is too stiff, it could be anything.

The resonance is likely a great guideline to build consistent guitars. If Greg Byers (I really love his work) says it should be at whatever note it would change significantly if you are not using the same shape as he, the same size soundhole, the same species of wood, attaching it to the body in the same way, with the samd sized blocks etc.

I'm not sure if you're keeping this all the same or not.

My question is this: what is the "right" resonance and what exactly are you trying to achieve?

It can be helpful, but if you have a certain resonance that does not in the end take into account how you got there or what the effect will be. Getting there different ways is likely to have different effects, because the resonant note does not really determine how a guitar functions.

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What jfrench said.

Why not string it up in the white, and hear what it sounds like? The actual resonant frequency is only one part of the equation, and maybe not the most important one at that. Do you know what the deflection under load is? What about the 'free' plate mode shapes? These are not the system you've been following, but others use those parameters with some success, and it's quite likely that your guitar could be 'perfect', or, for that matter, 'terrible' if those other measurements were used.

If you insist on removing some wood from the top, I'd say you could most safely thin the top out toward the tailblock. This will tend to drop the 'main top' tap tone pitch a bit, and bring up more bass on the completed guitar.

What's the back doing? You might find you could drop the top pitch by shaving back braces. Or maybe not.

;o)

[QUOTE=AlexM] Joshua, first, many thanks for spending your time with the top dilemma. In the mean while I need to finish the bridge, which still weights a ton and is very bulky. The lenght i think is fine, 185mm. wings -  6mm thick, should be 4.5 - 5 ?central block, 12mm thick.  tieblock lenght, 82mm, I need to shave 1mm off both ends and make it 80. tie block width 12.5-13mm I guess I need to thin it to 10 since the access to the hole is difficult right now. I plan to shave 1mm off the bottom, that will make the wings 5mm and the center 11.   After sanding to allow the doming, the wings will be the same or towards 4.5, while the center 10mm.
[/QUOTE]

Alex, no problem!

In general I am using 4 to 4.5mm for the wings. Your dimensions sound fine. you may be able to fine tune the bridge some as well once its one to get where you're wanting to be.

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Dear Alan,
The back is lightly braced, with feathered ends.  Its main mode right now is a full tone lower than the top. 

The top right now, 2 tones higher than it should be, and app. 3 tones higher than it should be with the bridge on.

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dang bridge is driving me nuts :)  I am close to the final dimensions and it is still some 38 grams !  

I've calculated the density of the other 2 blanks I have and it came at a whopping 960 Kg/cubic meter. 

These 3 blanks were all similar, a very nice purple color, not the plainer brown, and with very tight grain. I've picked the darkest of them. 

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What did you make it out of? Mine come in around 21 grams and they're 190mm long. Thats for BRW and Mad RW.

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 Indian RW ... 

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You also might think about reworking your harmonic bars a bit if you have strung the guitar and feel that it is too stiff.

The one in the pic looks pretty stout. I like to taper the profile of these toward the free edge (keeping them parrallel of course in the Torres style). This reduces the mass and makes them a bit flexible...........just how flexible you make them of course depends on the rest of your design........ 

Alex:
Taking height off in the center of a brace usually drops the mode pitches more than feathering the ends. The braces bend more in the middle. If you can get the back down to the same pitch as the top before you glue on the bridge that should work.

Oh it is actually lower ! while feathering the ends I got carried away and "feathered" the middle too.  I guess what i had in mind was the ideea of "responsive back".

The cavity resonance seems to be quite low as well, about 86 Hz, and I would imagine that might be related to the weak back ?

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Update:

I had to sand the top anyway, because well, it was dirty and had some small dents and scartches made during binding and all...

That light clean up pushed the main mode maybe a full tone lower.  That is very interesting because while the plate was free, unattached to the box, it really needed a lot more sanding or brace tuning to go down in pitch.   It seems that the whole assembly is considerably more sensitive.

The bridge ended up at app. 30 grams.  185x28, 9mm tall center, 4.5-4.8 wings.  I guess I'll shave a couple grams more while doing the final polishing.  I might also want to make the saddle slot deeper.

So, will see how she sounds in about 6-7 h :)

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Alrighty, the bridge glued up nicely it seems, and it didnt pop in my face once I tuned to pitch.

I love the sound.  This is really better than my first :)

What i don't like is that strings are a bit hard to push in vibrato (they are hard tension, but don't feel stiff on it)

I would also like a bit more treble power.

The main top resonance went straight were i wanted it to go, but, I think it didn't do that the proper way. the proper way is a balance between the weight and stiffness of the plate and those of the bridge, which i needed to be between 20 and 27grams.   I think the plate is still too stiff, while the very heavy bridge (i guess it is about 32 grams)  drove the resonance down with it's weight.  As a result, it is probably too heavy in all respects and hard to move. 

Here are a couple sound samples.  Just a non-sense ramble, I really don't claim to have much skill.  Theres a ton of buzz because I really didnt have the patience to properly set it up yet.  The string to plate distance is 11mm, I need to add more tapering to the neck and reduce the saddle height.  Also the saddle doesn't stay too well in the slot, which is rough still. Needs refining with a quality saw, once I'll buy one.

First sample is recorded in the shop, which is very crowded with stuff and dead acoustically.  The mic is close to the hole:

sample one.

The second is in the hallway, where I have good resonance.  The mic sits at a longer distance.

sample 2.

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Alex, it sounds pretty good to me.  The dead acoustics is a better representation of the guitar.  In the hallway, you hear too much reflected sound to get the true sound of the guitar.  Maybe the mic was too far away.  I would try (don't try this at home, because I know not what I am saying) getting the saddle with a good tight fit before I did anything else.  That will probably give you better response across the strings, and boost the treble side a bit.  Then you can decide what the next step would be.  Also, I would try medium strings, unless you think your top is so tight it takes high tension to excite it.  You will get nicer nuances from mediums.  This advice is only the opinion of the writer, and does not represent the opinion of any OLF Official or any other members thereof.

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Waddy

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Sound Clips of most of my guitars