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Curious on how you guys make your classical bridge patches.

What thickness ? Wider than the bridge or the same ?

What thickness for the wings ?  Do you bring them to that figure after creating the radiused bottom? Otherwise, they become a little thinner and weaker next to the tieblock.

What is your tieblock lenght ?

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Build log

Classical bridge plate? I don't need no classical bridge plate!! Seriously I know many luthiers that don't. The string tension is so low it is not really much of a structural issue Those that don't use a bridge plate tend to leave a little more thickness to the to in the area of the bridge.

Well I don't think I need it on the top i work on now either because it feels stiff enough across the grain.

But I'd still need to know a thing or two about these things. I have another top which is floppy across the grain and I'd want to put a patch on it.

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Build log

Torres never used a bridge patch, and if it worked for him.... :)

I generally control crossswise stiffness by varying the fan angle. On a recent classical with cedar top that had very high cross grain stiffness I used a convergence point that was 10cm above the body edge, rather than at the edge as is usually done. It worked fine.

I have seen 'bridge patches' that were in fact simply pieces set in between the fans. They seem to work well.

There are a couple of ways to think about the bridge patch on a classical. One is, from a woodworking sense, that it's a 'backing veneer'; a piece on the inside of the top with the grain running the same direction as that of the bridge on the outside. When used in veneer panel construction, the backer helps keep the piece from warping due to unequal expansion with changes in humidity. This sort of bridge patch would be low, and not much wider or longer than the footprint of the bridge.

The other way to think of it is as a brace, adding mass and stiffness across the top. One example of this is the so-called 'Bouchet brace'. I've used this a couple of times, and one of my students put one on a 'practice' top last fall, just to see what would happen.

What it seems to do is to add both stiffness and mass about in proportion. That is, when I have shaved such a brace entirely away, the resonant pitches of the top don't seem to change much, but it is less stiff. In acoustic terms, what you end up with is a top with higher 'impedance': that is, it's harder to push it.

Guitars with higher impedance tops tend to require a bit more force to speak clearly, but, on the other hand, you can push them harder before the tone breaks up. They tend to be good instruments for players who spend time on the stage, or have a strong technique.

Of course, a low, wide bridge patch is still a 'brace' of sorts, and a tall narrow one should help back up the bridge and keep the top from distorting with humidity changes. It's a continuum, in other words, and where you plop yourself down along the line will depend on what you're trying to do.       

Drat the lack of an Edit button!

I should have mentioned that a bridge patch/brace will also tend to nail down the location of resonant mode node lines. In particular, the line of the 'long dipole' mode across the top will tend to run along that brace if it is stiff or heavy. To the extent that the rocking motion of the bridge that is caused by the twice-per-cycle tension change of the strings wil be effected by that node line, the brace can change the tone in that range. The jury is out on how important that might be, and I suspect it won't be back in any time soon.

I use them and theyre usually about 2-3mm thick.

Tie block length on my classicals is in the region of 83mm but actual length depends on string spacing and asthetics (eg width of bridge).

Might as well give you all the dimensions on my current bridge:

width: 29mm
height: 9.5mm at saddle slot, 6mm at tie block (allow 2mm for ivory cap on same).
width: 182mm wing to wing, saddle and tie block width are 83mm
Thickness of wings: 4 - 5mm.
string hole spacings: 11-12mm between strings with balance halved to give distance from outer strings to end of tieblock.
Front of tieblock and saddle are flush with front of bridge.