Since the top is on the guitar, you're not going to get any real modal data besides pitches it reacts at; the glitter patterns won't be super varied and useful like they are on a free plate. By being glued to the rims, the top is forced to work in a certain mode whether it wants to or not. The deal with 'free plate' tuning is that it allows you to make sure the top wants to vibrate in the mode it will be forced to when it's on the rims (ie: you're making sure it's good at the job it'll be forced to do).

You might/should be able to tweak the frequency of the main mode to where you want it; the more material you remove, the lower it gets. But you can't get much data on where to best remove the material from a glued-down top using glitter patterns. The two goals are to get the modes at the pitches you want, and the shapes you want, and you can't get much good feedback on their shapes unless the plate can move at its edges.

Since the top is on the guitar, you're not going to get any real modal data besides pitches it reacts at; the glitter patterns won't be super varied and useful like they are on a free plate. By being glued to the rims, the top is forced to work in a certain mode whether it wants to or not. The deal with 'free plate' tuning is that it allows you to make sure the top wants to vibrate in the mode it will be forced to when it's on the rims (ie: you're making sure it's good at the job it'll be forced to do).

You might/should be able to tweak the frequency of the main mode to where you want it; the more material you remove, the lower it gets. But you can't get much data on where to best remove the material from a glued-down top using glitter patterns. The two goals are to get the modes at the pitches you want, and the shapes you want, and you can't get much good feedback on their shapes unless the plate can move at its edges.

I agree that the soundboard has a different response before it is glued to the sides...but it is ONLY the response after being glued that matters. I would be perfectly happy if they all sounded like crap before being glued up, but once assembled they sang like crazy...

Modal testing isn't about how the plate 'sounds' before it's glued to the rims, a deaf person could do it. It's measuring stiffness distribution, an engineering property, and one that is rather important given the top's future role. I take it from the content of your message and desire to post it that you believe that we have no ability to change the probable response of a top before it's on the rims?

I didn't read Parser's response as disagreeing about the ability to change the top's response before the top is glued to the rims, but only that the final response is the critical issue. But I agree with Parser that the final result cannot be absolutely established after the top is on the guitar...

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I didn't read Parser's response as disagreeing about the ability to change the top's response before the top is glued to the rims, but only that the final response is the critical issue. I don't have a lot of experience with guitar tops, but did a lot of vibrational analysis on industrial products. Without the final boundary conditions established (ie, the glue joint between the top and B/S's- including the bindings), I believe it is difficult to predict the final vibration modes. If the luthier is very consistent in how he/she glues on the top and binds the guitar, results will be more predictable. But since each piece of wood is different, the final vibration patterns are only going to be visible after the guitar is finished. Don't mis-understand, I believe in tap testing and Chladni pattern testing. But I agree with Parser that the final result cannot be absolutely established after the top is on the guitar...

I'm not sure of your set-up, but here are some suggestions.
1. Use poppy seeds instead of salt.
2. Make sure the back is not dampened when testing the top and visa versa. I usually do this before the neck is on and suspend the body on two strands of monofilament. You can just clamp the guitar by the neck and suspend it.
3. Don't try to get the top mode by blasting it with the speaker below the bottom of the guitar and visa versa. You need to hold the speaker in your hand and move in around very close to the plate you are testing. You may be doing this already.
4. Test with the soundhole open.

Is anyone familiar with Roger Siminoff's tuning method using strobe tuners and tuning the tap tone exactly to a particular note? I'm trying to learn and understand this method, but I think when you get the plates where you want them, everything will change once you glue them to the rim, add the binding, and finish the guitar.

Chuck

Why do I get double posts sometimes?