Acoustic Guitar Construction

First, some terms. Stiffness is a property of the material and doesn't depend on the dimensions. Also called the Young's modulus , the elastic modulus, or the flexural modulus, and usually denoted the the symbol 'E'. It is measured in Pascals. You can look up averages for each species on the wood da...

Using your numbers, I calculated a density of 553 kg/m³ for the DF and 483 for the Sitka. So the DF is about 15% heavier.

Averages for the species are 510 and 425. These are based on wood dried to 12% moisture content. In equilibrium with air at 60% relative humidity.

Greg

Sized to produce the same stiffness as Sitka, it will be smaller but still heavier. For example, if your Sitka braces were 6.0×14.3 mm triangular, then your DF braces would be 5.8×14.0 mm triangular, but still weigh 14% more. Keep in mind that stiffness increases linearly with width but by the cube ...

Greg - thank you for the reply and info. Its a tad over my head but I think I understand the reasoning, just not sure how much I’d need to reduce the sound hole diameter by - would 1/8” make a difference or are talking more? Well, I'll take a crack at it. You said the depth was supposed to be 4.125...

What I'm about to say is based on equations, not experience, so take it with a grain of salt. But... A smaller volume of the body cavity will raise the lowest natural resonance of the guitar, which is the vibration of a plug of air in the sound hole (the Helmholtz frequency--like blowing on a glass ...

I've never tried it, but I've read that ammonia is good for bending wood. A bit dangerous though. I think you need an air-tight container and only do it outdoors.

Greg

John-- I followed your build log on your website. When you thicknessed the top, you showed the density ρ and Young's modulus E for the Sitka panel. From that I calculated a sound radiation coefficient R = SQRT(E/ρ³) = 13.9 So that's an exceptional piece of Sitka, considering the average for the spec...