Split Peaks

[luke_lee]

Hi all,
I have been working on a S-String, the shape is similar to a Taylor grand concert with X bracing like the J-45 detailed in the book. Sound hole diameter of 95mm, a live back detailed the same as the book.
I am aiming for T(1,1)1 - 90Hz T(1,1)2 - 169Hz T(1,1)3 - 215

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Here are the numbers for the peaks in the graph.
91.5Hz 191.3Hz 224.8Hz 293.8Hz 319.6Hz 477Hz 572Hz 610Hz

The body is boxed up, today I thinned the edges and checked the frequency response. I was expecting to see a spike near the 330Hz but I have a split peak 293.8Hz / 319.6Hz. Any ideas what may be causing this and will it be a issue when the instrument is finished?
I was also wondering if my target frequencies are reachable from this point without adding more than 200grams of side mass?

Any thoughts would be appreciated.

Thanks Luke

[jeffhigh]

Presuming you don't have a bridge on it yet I reckon you are on target.
On an x braced guitar the bridge mass will drop the main top substantially and when you trim the back resonance it will also drop the air and the top

[Trevor Gore]

Hi Luke,

A 20Hz drop for adding the bridge might be a bit too much to expect unless you have quite a heavy bridge. However, a bridge and some side mass should get you there. If you find that you only drop a few Hz when you add the bridge, you could always re-direct to 95, 180, 226 (224 should be good enough). Enlarge the sound hole a little to get the air up to 95Hz. If you get it finished and get the bridge on (plus saddle and bridge pins) then check it again, you should have a few options available to aim for.

The peaks at 293 and 319 are likely long and cross dipoles and could be either way round. You can check the Chladnis to be sure. I don't think they'll cause you any problems.