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I want to make a ukulele, and I'm just wondering about little blocks of wood that are inside them. Are they for structural support, or does it help the sound somehow?
I'll be making it via unconventional methods (a tough paper mache for the walls, ply for front and back), and I don't know if I'll need those blocks structurally. Should I put them in for acoustics?
You can see what I mean in the picture below—the ribbing around the edges and the little planks across the body.
The answer is actually "for both reasons". The bars are necessary to resist the downward pressure of the strings on the bridge, otherwise the flat surfaces of the instrument would bend inwards or even collapse.
They also change the way the wood vibrates, by converting a single large panel (which would have a relatively low vibration frequency) into several smaller panels which vibrate at higher frequencies.
The small blocks round the edge of the panel are necessary to make a strong joint between the bent sides of the instrument and the top and bottom.
Note that the bent wood sides also create tension across the top and bottom of the instrument, because of the "locked-in" stresses when the complete body of the instrument was clamped together and glued. If you make the case out of moulded papier-mâché and they don't have that pre-stress, the instrument may sound quite different.
