Sometimes the satire doesn't transmit.Trevor Gore wrote: ↑Thu Jul 05, 2018 10:28 pmInevitably to E#.Costantino Proietti wrote: ↑Thu Jul 05, 2018 1:54 pmHello,
for myself first guitar I'm using cedar for the soundboard and madagascar rw for back and sides. The bracing is Torres a bit creative, 7 fans with open harmonic bar. All the struts and fans are cedar except for hole patch that is laminated mahogany. The finished sb weighs 157 grams. Before bracing the tone was D and after braced and scalloped it raised to E. As an apprentice I'm very intrigued by the debates about voicing, but just as insecure where changes on structure could bring. My first thought is that lightening up again the struts, scalloping the harmonic bars , the pitch could move back to an intermediate note. Or could it move to E# o F?
Most of the sound that you hear that comes from a guitar is radiated by the low order resonant modes (about 85% according to research published in the 1980's (iirc)). Up to about 4kHz, it is only the resonant modes that radiate sound. The resonant modes are the ones you see with Chladni patterns on a completed guitar, the low order ones being quite efficient radiators quite a way from their centre resonant frequencies. If you want to alter the sound of a guitar, you therefore need to alter the amplitude, bandwidth and centre frequencies of the resonant modes, because very little else produces sound.John higgon wrote: ↑Thu Jul 12, 2018 7:30 amIt seems to me that there are at least three ways of voicing a soundboard - tap tones, Chaldni patterns, and measurements of the board's flexibility. Do people use a combination of these methods, or do they gravitate to one favourite method? And if so, which one!?
However, the free top mode resonant frequencies tell you very little about the resonant frequencies of the finished guitar, because so much changes between the free plate and the closed box. In theory, they should be relateable, but in practice, two chassis are never identical enough to produce identical results even if you were able to make identical tops. The nature of the linings, their glue area, their stiffness, the side stiffness and mass, the air volume, the back, the bridge, the finish etc.etc. etc. and how they all couple together all interact to alter the performance of the top in a way that is impossible to predict with sufficient accuracy to be useful. Which is pretty much what Alan sees, too:
...which makes all this tapping and tuning of free plate resonances of doubtful benefit. Indeed, if you watch the video, more emphasis is actually placed on working to dimensions rather than tap pitches.
So what to do?
Alan gets benefit from closing the ring and a half free plate mode. I'm agnostic on this, as the bracing patterns I use mostly seem to produce closed ring and a half modes naturally (which happens much more easily with symmetrical bracing) on the odd occasions I've tested plates just before gluing down. But I also thickness the panels and size the bracing according to the material properties (the elastic moduli and the density) of the wood, which pitches them on the closed box close enough to my preferred mode frequencies that I can trim them to where I want them. Which means you mostly hear the sounds that I designed it to produce. This is a similar sort of technique to that which Martin Schleske uses to make tonal copies of violins using modal analysis, but the violin makers maybe have it easier, as the free plate modes do relate more readily to finished instrument modes, apparently. All the details, analysis, modeling and testing can be found in the usual place.