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Thanks so much for the tips, Trevor! I do enjoy using my knife but I think I'll use a sanding drum here.

Once again, I nearly wrote a caveat regarding the .85hz/mm; I'll do my best to measure what change is made on this one and report my findings. Someone must've made a camera shutter soundhole!

I hope to achieve decent monopole mobility but I'm only really guessing (and being advised on the OLF). I'm aiming for a 2mm top [not very scientific, I know] and the bracing is light. I'll have to hide my disappointment from this guitar's young owner if I didn't guess well!

All the very best!

There is an iris type camera shutter soundhole out there but I don't remember who did it. Someone else may remember who it was; I do remember the builder saying it was an awful lot of work.

_________________
Steve Smith
"Music is what feelings sound like"

I'm sure. Not something I'm planning on! Maybe for a test guitar... Iris soundhole, removable lower bout for bracing changes, soundports with corks.... Just so I could experience these variables first hand.

To be honest, I'm trying to focus on improving my wood working skills at the moment. As I become a more competent guitar builder, I'll try to become a more competent guitar ..erm... scientist [?]. I'm having a hard enough time processing everything I do know about guitars let alone all that I could know! Hence my endless questions on here! (Not to say that I don't want to read and learn, I can't wait to, I'm just really grateful to have a community like this to make a difficult project that much more manageable, and hopefully make the final product slightly more predictable!)

A lot of people seem to enter guitar building from another woodworking field. Me? First thing I ever really made was a guitar [building #3 now]. Apart from a bird feeder I suppose!

FWIW, The Physics of Musical Instruments, by Fletcher and Rossing, gives this formula:


fo = (c/2π) * sqrt(1.85a/V)

where c is the speed of sound, a is the port area, and V is the volume. My ASCII math skills aren't great, hopefully I got that right.


It seems to me that there are two main things going on when you change the soundhole size. Firstly, the main air resonance shifts. Secondly, as it gets bigger, more high frequencies can escape through the soundhole.

Changing the size doesn't really shift the main resonance a whole lot, though it's something that can be tweaked to get you off a scale note. The second effect - HF leaking through the soundhole - might be more important overall.

Thanks for the info Greg, very intriguing formula.


To me, that makes a smaller soundhole sound like a good thing for such a tiny guitar... Unless my assumption that decent trebles won't be much of a problem is wrong!

Actually... How does one get a good estimate of the volume of a guitar body? I've been kinda eyeballing it and comparing.

Depending on what the back stiffness is to begin with, sometimes shaving back braces can drop the 'main air' pitch a fair amount. Who'd a thunk?

Drop it? Interesting. Won't be able to get my hand far into this soundhole though, gonna be fiddly enough fitting the bolts!

Should be bracing next week so got some decisions to make there!