Great site and lots of great info. I finished my first CBG build last night. It is a fretless 3 string. I learned a lot and am looking forward to my next build. I was wondering what makes the guitar sound louder or softer? Do bigger sound holes make the guitar sound louder? Does sound hole placement make a difference? Does the type of wood or size/material/placement of the bridge make a difference (I understand that it does as far as scale) for sound?
Thanks for the help. Happy building.
Welcome aboard Josh! All sorts of interesting brains to pick for good ideas. The hole placement thing has had me thinking too. Sorry I have no solid info for you except that when I build a standard type CBG, 2 holes about 40-something mm seems to work pretty good. As for neck material, I use a lot of English Oak or Mahogany, occasionally other stuff. Yes there is a tonal difference, as much as I've sussed the neck wood wants to be stiff but with a certain amount of spring that gives the instument....for want of a better term....life. I guess this is why mahogany gets used so much.
One thing I AM sure about is placing the bridge well inside the box lid, that is at least a 50mm gap between the bridge and tail. I've made CBG's that had the bridge hard on the back edge of the box and generally speaking, they are not the best players. The amount of sound a small box can produce is limited, none of mine ever won a shouting match with a regular git. Make your bridges and nuts from something hard. I use well dried Rosemary wood a fair bit, hard, seems to work well and not difficult to get. Alumin(i)um angle stock is good stuff too, easily worked and a nice hard twangy sound. Pics, man pics!
In order (in my opinion) the factors affecting (or limiting) the volume of an acoustic CBG are:
size (area) of the soundboard (larger area = louder)
tension of the strings on bridge (higher tension/heavier strings = louder)
thickness of soundboard (thinner = louder)
placement of bridge (louder as you get closer to center of soundboard)
presence of sound hole (placement and size realtively unimportant)
Every factor can be pushed to extreme, so that you will get little additional return or will compromise other design factors.
The single reason why CBGs will never be as loud as a conventional acoustic is the size (area) of the top. The amount of vibrating surface is the largest contributor to volume.