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Hello gents, I´ve built a few classical guitars and this is my first attempt at SS. Its an OM with Euro spruce and Pau Ferro and have tested the 2 free plates with chladni before assembly.
Since I don´t have much prior reference and I´m not very familiar with this new to me instrument, would you guys tell me what you see on the samples?
Te spruce top is thinned to a 2,7 and 2,6mm, and weighthed about 170 grams before bracing, it was pretty stiff for euro. The back is around 2,5mm braced with spanish cedar, no a great taptone in this case and because I have small speakers to run the tone generator I really coudn´t "move" the back very much so the figures are not very good...
I´d apreciatte any input, thanks!
Bruno

Those two top modes look good for a scallop braced top. I'm having trouble reading the little frequency labels, so it's hard to say much about that aspect. The mode I usually look most closely at is the 'ring+'; it's the on on the right, with another node line across the upper bout. If that tag reads '327' it's high, while '227' is a bit low, but acceptable. I usually try to get that mode to come in at around 250-280. OTOH, I don't build scallop braced guitars usually, so maybe those are good frequencies.

Thanks for the reply Alan! Its 227 indeed, I was digging some info on the forum these days and found some threads with similar results on the ring mode, but wasn´t 100% sure it was the right mode on my samples.
Knowing im on the low side, I will try to keep the bridge weight low also to compesate a bit.
Thank you!

The frequency of the mode is a rough indicator of the ratio of stiffness to mass. This one is a bit low, but not bad. It could be that the top itself is heavy but with low stiffness, but it's more likely that the braces are a tad on the low side. Again, I've made steel strings with the ring+ mode as low as 215, and they worked OK. If the stiffness does seem low to you there are several ways you can compensate.

The scalloped braces have low stiffness at the bridge. This is what gives that profile the 'attack' and bass. The low stiffness in the middle drops the 'main top' resonant pitch which enhances the bass. It also helps the plate displace a lot of air as it moves, actually being better than way than thinning around the edge, according to Evan Davis' mathematical model. So that's good.

The problem associated with this is that the large excursion of the bridge can cause a 'wolf' note at the main air or main top pitch. Strings need to 'see' a stationary termination (or, technically, a large impedance mismatch) at the end in order to work well. Low stiffness at the bridge can cause the energy to 'leak' out of the string too fast, giving a note that's twice as loud for half as long; the good (?) old 'thuddy G'. Since impedance is a product of both stiffness and mass one way to control that is to use a heavy bridge. On my guitars, with 'tapered' bracing that's tall at the bridge, I use one in the 20-25 gram range, usually of rosewood or Morado. Martin uses a 30-35 gram ebony bridge on their scalloped braced tops for a reason. Yes, it drops the top resonant pitch, and may limit the treble response some, but it helps control that wolf.

The other main issue with scalloped bracing is low static stiffness. Over time the top can belly up under the load of the strings. What counts here is the torque of the bridge, and that's a product of the string tension and the height of the strings off the top. Setting the neck such that you get the action you want with the strings 10-11 mm off the top instead of 12-14 mm reduces the torque load proportionally. The top itself is strong enough to take the tension load, if the strings were pulling in the plane of the top; the only structural reason you need bracing at all is that the strings are up above the top.

That´s some very useful information Alan, So a better move here is to make a heavier bridge, or I can even chisel off the X braces, start over and leave them a little taller. I made it scalloped because I prefer a deeper sound with some punch. But of course I wound`t want a wolf note.
Thanks again Alan, you are very generous!