I generally size the holes to the size of the box, especially if I am putting them on the "face". I used 1" on the last build I did. I have used 3/4" on others. I have a pic of a build using a Black Pearl box with 3/4" holes. You can see the pics on my profile page.
It kinda matters, and yet kinda doesn't. Assuming you have a soundboard that is less than 1/4" thick, say, 3/16" or 2mm, then the larger the hole / holes, the brighter / emphasis on higher frequencies the box will be. The smaller the hole / holes, the bassier / lower frequencies will be emphasized. String selection also plays an important part, as do the dimensions of the box. I'm working on an Excel spreadsheet that allows box volume to sound hole size to string gauge calculations, using the Helmholtz resonator equation, to let builders such as yourself have the tools to calculate a jumping off point for further experimentation in your builds. It is based on the reference pages that Mark Werner is alluding to. I hope to have it finished for attest run in a few days. I'm doing this to see if we can take at least a little bit of the variability out of our builds; it may not work, but that's OK. At least it makes the ideas testable.
Realize that guitar design and construction is about the subtle interplay of lots of factors, in addition the the ones I mentioned above. Following Chip's advice is perfectly valid, too. No Rules!
the only thing the soundholes are for is to let air pass from the inside of the box to the outside so the soundboard can resonate, size doesn't seem to matter. Go for the look you want!
Someone had a reference page up indicating a rather small soundhole was quite efficient on these small boxes.
I've done several different sizes and all seem to work well. 2 1/2" on my mandola, 1 1/2" on a couple of my guitars and my uke, a pair of 1/2" holes on a couple of others...
Feel free to experiment!
Comments
It kinda matters, and yet kinda doesn't. Assuming you have a soundboard that is less than 1/4" thick, say, 3/16" or 2mm, then the larger the hole / holes, the brighter / emphasis on higher frequencies the box will be. The smaller the hole / holes, the bassier / lower frequencies will be emphasized. String selection also plays an important part, as do the dimensions of the box. I'm working on an Excel spreadsheet that allows box volume to sound hole size to string gauge calculations, using the Helmholtz resonator equation, to let builders such as yourself have the tools to calculate a jumping off point for further experimentation in your builds. It is based on the reference pages that Mark Werner is alluding to. I hope to have it finished for attest run in a few days. I'm doing this to see if we can take at least a little bit of the variability out of our builds; it may not work, but that's OK. At least it makes the ideas testable.
Realize that guitar design and construction is about the subtle interplay of lots of factors, in addition the the ones I mentioned above. Following Chip's advice is perfectly valid, too. No Rules!
I've done several different sizes and all seem to work well. 2 1/2" on my mandola, 1 1/2" on a couple of my guitars and my uke, a pair of 1/2" holes on a couple of others...
Feel free to experiment!