MIMF

Two topics in one day from the same MIT article! It discusses how the evolution of the violin F-hole, probably less through intent than craftsman error, got to a point where the master makers found that they had hit a sweet spot and varying the size, location, length, width, etc, of the F-holes resulted in lesser power in the instrument. So everyone has done it pretty much the same since the 17th century.

Archtop guitars have not had the same evolution. People put all sorts of F-holes, and other holes, somewhat randomly on the top and it doesn't seem to make a whole lot of difference. It's kind of like "got a hole, the Helmholtz God is satisfied, let's make it really pretty". I was brought to consider this over the past two days as I started the design process for my next project and saw the Guild Acousti-lectric model from another thread. What a cool idea, sez I. What an odd thing to do to the top of an acoustic guitar, was my next thought. Followed by "maybe all the stuff you think you know about archtop tops, bracing, sound field vibration, is totally imagined and doesn't matter..." Maybe it's OK to put big holes right in the middle of the part of the top that I always thought produced most of the sound?

My last guitar had sound holes roughly equal to the area of traditional F-holes in the two upper bouts, beside the neck. My next project was going to take the same body and have two somewhat traditional F-holes in the normal location. My goal is to explore the idea of what F-holes do to the sound. My theory is that the F-holes free up the vibration of the top quite radically compared to a recurve around the perimiter of a top with no F-holes, such freeing allowing the longitudinal center of the guitar to vibrate more at the expense of the sides of the lower bout top. If that makes any sense. My further experiment will hopefully include cutting the F-holes into the top of the fully closed and finished-in-white box with a cunningly designed series of router templates, so that I can string up and play the instrument with a succession of no holes at all (really wonder about that one), and successively longer and wider F-holes. I figure if I go too wide I can then bind them to make them smaller again. Has anyone ever done this, I wonder, hopefully?

Again, and as always, thank you for your support on this 20th anniversary of MIMF.

Brian

So, in reading more on this it seems clear that the area of the sound hole(s) is not very important but the length of the periphery of the hole is. I've just done very rough measurements of three instruments I happen to have handy. A jumbo flat-top with a 3.75" diameter round sound hole has a periphery of 11.8". Rough measurement of the F-holes on a traditional archtop has the periphery of each side of each F-hole at around 8", for a total periphery of 32". Rough measurements of the periphery of the "flame" holes on my red archtop project show a total periphery of 44". In other words the length of the periphery of the holes is close to 300% of the flat-tops "quasi-standard 3.75" round hole" for the traditional archtop and close to 400% for my experimental guitar.

Area is another story entirely. the area of the round hole is 11.2 square inches, the area of the F holes will be around 10.25 square inches and the total area of the flames will be around 11 square inches. Oddly all within 10% variance. Since the Berklee, MIT and The Royal Society studies I've read today all conclude that the critical evolution to the violin we know from the 17th century to now was the increase in periphery of the sound holes as they approached the shape and size of the F-holes we see today, it seems that focusing on area is probably not the way forward. What is the way forward is the question that I want to find the answer to. I remember Alan Carruth writing on this subject in some posts.

As an aside, one study said that the reason those complicated rosette sound-holes you find on lutes work is that the area of the hole (which obviously is pretty small with all the carved wood piercings covering up the hole) isn't nearly as important as the dimension of the periphery of the hole itself, and possible of the sum of the peripheries of all the tiny holes in the rosette. Which might be immense.

If I had a clue what any of this meant, I'd be happier now than I am, but this was kind of fun to read and compare instruments.

As another aside, it means that the periphery of those square holes with the pickups installed inside them on the Guild George Barnes Acousti-Lectric is what matters, and the fact that the middle of each hole has a pickup in it doesn't matter much at all. The periphery of each of those holes is going to be around 11 inches, for a total of 22 inches for two pickup holes.

As a final aside, it turns out that I knew all about the air flow in the periphery thing all along, I learned about it decades ago when I was building race engines and flowing cylinder heads. We talked a lot about where the air actually flowed in the port and around the valve head.

Brian