Can't figure out how to see my posts on the resonator box group, so I'm reposting here.


I've been testing my hand built box with a tuning fork, looking for bridge placement sites.  I have found a few areas that vibrate very well with nice tone.  Next question would be, where to place the sound holes, since some of these placement sites are mirrored on the opposite end of the box.


One spot is 1.5" away from the longitudinal edge.  The surprising part is that there are two bands that vibrate well, both at almost exactly 1/3 of the box length, so, one at 1/3, and one at 2/3, with sound production better towards the ends than at the center.


When I place the tuning fork at any of these positions, the other points vibrate well.  At the center of the box is sort of dead.
Question is, would these vibrating bands also be a good place for a sound hole, or, should I let them resonate and add to the sound, and place the sound hole offset from there.


Box is 8x12x3, so, bands are at 4" and 8" of length.
Must be a standing wave going on.  I used an A turning fork.  Hope other note values don't shift the optimal points.
Please see attached photo.

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David,

There is a long-standing discussion on a related topic, using tuning fork methodology, on the Super Advanced Cigar Box Building group, called " testing a box for bridge placement," started by Roadkill aka John Maw. Soundhole shape and placement have also been touched on in the same thread. There you will find numerous offsite links to guitars, soundboards, Helmholtz resonance, Chladni patterns, bracing, etc. There is a similar discussion on Rand Moore's Group, Homemade Resonator Boxes 101 v2.

Just for grins, my homemade boxes test out very similarly with an A tuning fork. Other values will indeed resonate differently. Doesn't matter, because, as it turns out, even commercially produced acoustic guitars are designed to resonate most strongly at either A or G frequencies. Why, you ask? Read the discussion on Rand's group. Realize too that if you add bracing to a CBG top, it can seriously enhance the sustain and resonance. This, too, is in the "bridge placement" thread.

Welcome to the Addiction!

Suffice to say, lots of us ( myself, Mark Bliss, John Maw, Rand, etc.) are interested in these mysteries. Oh, also do a Search under Rand Moore's group for Antonio Torres and papier mache'. Fascinating stuff.
I did start reading that thread, then my brain shut down.  I'll revisit I guess.  What wood is used for bracing?
Again, my brain spazzed out trying to read through that.  At this point, I'm looking for info on sound hole placement, and that thread is primarily about bridge placement.

I have quite a few thoughts on this subject (having read a lot of the scientific literature on the subject and done some research of my own). However I know I tend to get carried away and my posts get long and rambling so I'll confine myself to one observation for now.

When you make a hole in a soundboard or add bracing to it you alter the way in which it will vibrate - more specifically you are likely to change the positions of the nodes and anti-nodes of its natural modes. In other words, there are potential pitfalls if you base your design on testing the box before you do anything to it. If you place the bridge at a point which seems good on the basis of testing the plain box you might later find that it isn't such a great position once you've made some soundholes and added some bracing (and maybe made a hole for a pickup). Now it's possible the changes won't be huge and things will still be reasonably OK - but there's no guarantee.

 

This subject has a tendency to get more complex the more you look into it. People will quote you lots of rules or principles or seeming snippets of traditional wisdom - some from renowned professionals - but a lot of it turns out to be dubious at best when subjected to rigorous scientific scrutiny. Certainly there are few if any simple answers...other than "build a guitar, see how it sounds, and if it sounds good then you got it right".

OOOOHHHH NOOOO!

Ok, so if I put two sound holes in it they might cancel each other out and I will have a silent guitar!

 

Mark makes a valid point. Test away then drill a sound hole and you have altered the basis for all your testing. Attach a bridge and everything changes. And given the limitations of size and materials, it may not make that much difference anyway. So all that said, I'd say put the bridge at 1.5" and put a modest/small soundhole at about 1/3 from the other end and it will be perfect! Well it will be good anyway.

For the record I warned David NOT to read that thread, as I believe it leads to brain rot! At least it did for me. I blame it all on John Maw and I think he did it on purpose to distract us as with some shiny object.

And also for the record, my brain was "shut down" when I wrote there, so dont hold me to any of that stuff. (Now wheres that moveable bridge idea photo I was saving at.........)

You're right.

David should have NEVER asked his question. Now his brain is beginning to deliquesce.

Soon, he will have another sound hole...in his head. This will affect the way he thinks.

His family will notice the difference. They will recommend counseling.

It will not work. Not long after, court-appointed attorneys will recommend psychiatric evaluation and hospitalization.

Some months after David goes to live full time at Shady Acres, a man will come to visit. It will be Friday.

Craft Day.

This mysterious stranger, dressed in a sharp black pin stripe suit, wearing a snap brim fedora, and sporting an eerie, gold-toothed smile, will say in a sweetly encouraging voice, "Now, who wants to learn how to build a CBG?"

David's hand will shakily rise in the air. He will be unable to control it.

Actually there's no good reason why this stuff should fry your brain. It kind of pisses me off a little when these sorts of discussions drift off into implying people fall into two stereotypes - the brainy but tedious geek or the plain Joe Everyman who shouldn't go fuddling his mind with complicated stuff. Science is no more than repeated application of simple methods for separating fact from fiction - all it requires is a bit of dedication and not giving up. (But maybe I'm just a tedious geek?)

If you really have no enthusiasm for reading up on the science and you just want to get on with building a guitar then there are some simple logical things that might help improve your chances of success.

First is the idea that good functional design often kind of 'looks right' as well. I don't have a hard scientific proof for this but I do have some experience - from studying for an engineering degree many years ago and continuing through building all kinds of stuff. As an engineering student I was taught that the mathematics of structural design often throws up results which contain proportions favoured by ancient civilisations whose design methods relied more on aesthetics (eg. the so called "golden ratio"). 

Second, it's worth learning from traditional designs. Conventional guitars (and other stringed instruments) look the way they do because lots and lots of builders have done a vast amount of trial-and-error work over many decades. The result of that evolutionary process is acoustic guitars that are remarkably consistent in form. What I mean is that although there are various types of guitars (different sizes, round or f-shape soundholes, etc.) there are also quite a few features that are similar in some ways across many different guitars. For example, the bridge of an acoustic guitar is never placed very near the edge of the soundboard nor right in the middle. There might be various schools of thought about exactly where it should go in between those two extremes but that might not matter as much as you think. The important lesson is that when you stand back a bit and look at the general picture then you see there's a range of things between certain limits that seem likely to at least work to some extent.

So my principles for quick simple CBG design go like this:

(1) Look at lots and lots of guitars so that basic forms and proportions seep into your subconscious.

[and I guess point (1a) is do a similar sort of thing with materials - learn which types of shape or which types of join are strong and which are weak]

(2) Work with what you've got in terms of boxes and other components - learn to accept there will be limitations and learn to appreciate quirks that produce surprisingly good results.

(3) Begin work by laying stuff out in an approximate way. Do plenty of sketches. Let your subconscious tell you when it looks like you've got things well proportioned.

(4) Refine your design from stage (3) by checking basic practical stuff - eg. Will things fit where you've put them? Have you avoided needing to cut the box or neck in such a way that there will be narrow or weak points? Will the action be about right? Will the strings pass over bridge and nut at sensible angles?

(5) Try to design in such a way that you can make critical bits first and then adjust the proportions of subsequent sections once you've seen how the first bits work out. eg. Ideally I'd like to be able to do all the cutting work on the box and install as much of the hardware as possible then try a little tap testing. The tap testing might suggest the bridge should be in a slightly different position. If so then I can alter the measurements for the neck to accommodate the necessary change to the bridge.

(6) Small soundholes can be made bigger but it's not easy to do the reverse.

(7) Once you've built a guitar there will always be a period of "settling in" during which you might fix minor problems and make small improvements. Andinstruments often seem to just "play in".

 

Finally, something more specific about soundholes. They AREN'T the part of the guitar from which most sound is emitted. Good scientific research has shown most of the sound radiated towards the audience comes from the soundboard. Soundholes obviously do affect the sound of a guitar, but seemingly in more subtle ways than most people think. One important thing they do (as I mentioned before) is alter the way the soundboard flexes as it vibrates in response to the strings. The size of the hole also affects the Helmoltz resonance (the resonance of the air inside the guitar body), but the significance of this is more subtle and complicated than people often think - it ain't a simple matter of adjusting the resonance to a particular note. There's a theory that the most important thing about the air inside the guitar is how it couples the soundboard to other parts of the instrument. My feeling is don't worry about it too much.

So...choose from some classic examples - a simple round soundhole, a pair of f-holes or a small cluster of small holes (as per Ovation acoustics).  DON'T MAKE THE HOLES TOO BIG (hole area detracts from soundboard area). Put the holes where they look right to your eye.

If it works then you've got a good design you can use again.

If it doesn't sound great at first then don't give up. It might improve with time. Try different strings and tunings because one of the secrets of CBGs is finding the best tonal range for a given box.

Keep going and try different designs - that's the only real way to learn. If you don't mind risking a box and some wasted time then throw all these principles out the window and build something totally different - you never know, you might just chance upon something that sounds fantastic.

 

 

"Craft Day"!!!!  Love it.



Oily "Strat-O'-Nine-Tales" Fool said:

You're right.

David should have NEVER asked his question. Now his brain is beginning to deliquesce.

Soon, he will have another sound hole...in his head. This will affect the way he thinks.

His family will notice the difference. They will recommend counseling.

It will not work. Not long after, court-appointed attorneys will recommend psychiatric evaluation and hospitalization.

Some months after David goes to live full time at Shady Acres, a man will come to visit. It will be Friday.

Craft Day.

This mysterious stranger, dressed in a sharp black pin stripe suit, wearing a snap brim fedora, and sporting an eerie, gold-toothed smile, will say in a sweetly encouraging voice, "Now, who wants to learn how to build a CBG?"

David's hand will shakily rise in the air. He will be unable to control it.

Mark, thanks for your thoughtful response.

 

I guess I was writing in shorthand about my brain frying.  What I meant was, I was looking for one specific bit of info, and trying to wade through the multitude of posts, without a search function specific to that thread, was wearing my mind down.

 

I am absorbing info, particularly about sound hole size, etc, but trying to absorb a lot of detail, before my mind has formed the specific question regarding some of those details (I know, I did ask a question about the general topic, but not some of the various details) can wear my mind down.

 

What I am coming away with, though, is, it's not an exact science, given the number of variables, and experience counts.

 

It was fun modeling the Helmholtz equation in a spreadsheet, and reading up on that stuff.  That's not the part that fries my brain.  It's wading through a lot of discussion that goes in different directions, and trying into retain the various threads in my head in a useful fashion.

 

Various people have developed their own rules of thumb along the way, and they can conflict, and it's trying to glean the consistent info from the rest.

 

And, I must add, I felt a little like a blue collar scientist with my tuning fork, poking around on my box top.


Mark said:

Actually there's no good reason why this stuff should fry your brain. It kind of pisses me off a little when these sorts of discussions drift off into implying people fall into two stereotypes - the brainy but tedious geek or the plain Joe Everyman who shouldn't go fuddling his mind with complicated stuff. Science is no more than repeated application of simple methods for separating fact from fiction - all it requires is a bit of dedication and not giving up. (But maybe I'm just a tedious geek?)

If you really have no enthusiasm for reading up on the science and you just want to get on with building a guitar then there are some simple logical things that might help improve your chances of success.

First is the idea that good functional design often kind of 'looks right' as well. I don't have a hard scientific proof for this but I do have some experience - from studying for an engineering degree many years ago and continuing through building all kinds of stuff. As an engineering student I was taught that the mathematics of structural design often throws up results which contain proportions favoured by ancient civilisations whose design methods relied more on aesthetics (eg. the so called "golden ratio"). 

Second, it's worth learning from traditional designs. Conventional guitars (and other stringed instruments) look the way they do because lots and lots of builders have done a vast amount of trial-and-error work over many decades. The result of that evolutionary process is acoustic guitars that are remarkably consistent in form. What I mean is that although there are various types of guitars (different sizes, round or f-shape soundholes, etc.) there are also quite a few features that are similar in some ways across many different guitars. For example, the bridge of an acoustic guitar is never placed very near the edge of the soundboard nor right in the middle. There might be various schools of thought about exactly where it should go in between those two extremes but that might not matter as much as you think. The important lesson is that when you stand back a bit and look at the general picture then you see there's a range of things between certain limits that seem likely to at least work to some extent.

So my principles for quick simple CBG design go like this:

(1) Look at lots and lots of guitars so that basic forms and proportions seep into your subconscious.

[and I guess point (1a) is do a similar sort of thing with materials - learn which types of shape or which types of join are strong and which are weak]

(2) Work with what you've got in terms of boxes and other components - learn to accept there will be limitations and learn to appreciate quirks that produce surprisingly good results.

(3) Begin work by laying stuff out in an approximate way. Do plenty of sketches. Let your subconscious tell you when it looks like you've got things well proportioned.

(4) Refine your design from stage (3) by checking basic practical stuff - eg. Will things fit where you've put them? Have you avoided needing to cut the box or neck in such a way that there will be narrow or weak points? Will the action be about right? Will the strings pass over bridge and nut at sensible angles?

(5) Try to design in such a way that you can make critical bits first and then adjust the proportions of subsequent sections once you've seen how the first bits work out. eg. Ideally I'd like to be able to do all the cutting work on the box and install as much of the hardware as possible then try a little tap testing. The tap testing might suggest the bridge should be in a slightly different position. If so then I can alter the measurements for the neck to accommodate the necessary change to the bridge.

(6) Small soundholes can be made bigger but it's not easy to do the reverse.

(7) Once you've built a guitar there will always be a period of "settling in" during which you might fix minor problems and make small improvements. Andinstruments often seem to just "play in".

 

Finally, something more specific about soundholes. They AREN'T the part of the guitar from which most sound is emitted. Good scientific research has shown most of the sound radiated towards the audience comes from the soundboard. Soundholes obviously do affect the sound of a guitar, but seemingly in more subtle ways than most people think. One important thing they do (as I mentioned before) is alter the way the soundboard flexes as it vibrates in response to the strings. The size of the hole also affects the Helmoltz resonance (the resonance of the air inside the guitar body), but the significance of this is more subtle and complicated than people often think - it ain't a simple matter of adjusting the resonance to a particular note. There's a theory that the most important thing about the air inside the guitar is how it couples the soundboard to other parts of the instrument. My feeling is don't worry about it too much.

So...choose from some classic examples - a simple round soundhole, a pair of f-holes or a small cluster of small holes (as per Ovation acoustics).  DON'T MAKE THE HOLES TOO BIG (hole area detracts from soundboard area). Put the holes where they look right to your eye.

If it works then you've got a good design you can use again.

If it doesn't sound great at first then don't give up. It might improve with time. Try different strings and tunings because one of the secrets of CBGs is finding the best tonal range for a given box.

Keep going and try different designs - that's the only real way to learn. If you don't mind risking a box and some wasted time then throw all these principles out the window and build something totally different - you never know, you might just chance upon something that sounds fantastic.

 

 

And a quick reply to your original question. My feeling is that you want to avoid having soundholes at points that would otherwise be vibrating strongly. However - for reasons previously mentioned - it is tricky to determine before you make a hole how the box will behave after the hole has been made.

Different tuning fork notes shouldn't significantly change the points where you find strong response from the surface of the box. What you're locating are anti-nodes of the various modes of vibration (conversely nodes are characterised by little or no reponse). These modes are a characteristic of the geometry, structure and material of the box. Modes can be driven at different frequencies, although each mode will have its own natural frequency characteristics. At different points in the tonal range of a guitar different modes might become more or less significant to the overall sound. So there's a theoretical possibility that different points might be more significant at different frequencies but the points themselves shouldn't shift around. In practice, with conventional guitars, certain key points (related to relatively simple modes) are the ones that tend to be significant.

Too much for me to read above so if this has been said already sorry.  You can leave the top undrilled and put the sound holes in the sides. Try it, it works. Bigger may be better here, not sure, more testing needed.

Mark,

 Excellent post.  And I'm speaking as a guy with a degree in engineering.  The problem with systems analysis is that any time you try to analyze a system, you change the original conditions.  It's often instructive to observe what others have done before you and try analogous solutions.

Mark said:

Actually there's no good reason why this stuff should fry your brain. It kind of pisses me off a little when these sorts of discussions drift off into implying people fall into two stereotypes - the brainy but tedious geek or the plain Joe Everyman who shouldn't go fuddling his mind with complicated stuff. Science is no more than repeated application of simple methods for separating fact from fiction - all it requires is a bit of dedication and not giving up. (But maybe I'm just a tedious geek?)

If you really have no enthusiasm for reading up on the science and you just want to get on with building a guitar then there are some simple logical things that might help improve your chances of success.

First is the idea that good functional design often kind of 'looks right' as well. I don't have a hard scientific proof for this but I do have some experience - from studying for an engineering degree many years ago and continuing through building all kinds of stuff. As an engineering student I was taught that the mathematics of structural design often throws up results which contain proportions favoured by ancient civilisations whose design methods relied more on aesthetics (eg. the so called "golden ratio"). 

Second, it's worth learning from traditional designs. Conventional guitars (and other stringed instruments) look the way they do because lots and lots of builders have done a vast amount of trial-and-error work over many decades. The result of that evolutionary process is acoustic guitars that are remarkably consistent in form. What I mean is that although there are various types of guitars (different sizes, round or f-shape soundholes, etc.) there are also quite a few features that are similar in some ways across many different guitars. For example, the bridge of an acoustic guitar is never placed very near the edge of the soundboard nor right in the middle. There might be various schools of thought about exactly where it should go in between those two extremes but that might not matter as much as you think. The important lesson is that when you stand back a bit and look at the general picture then you see there's a range of things between certain limits that seem likely to at least work to some extent.

So my principles for quick simple CBG design go like this:

(1) Look at lots and lots of guitars so that basic forms and proportions seep into your subconscious.

[and I guess point (1a) is do a similar sort of thing with materials - learn which types of shape or which types of join are strong and which are weak]

(2) Work with what you've got in terms of boxes and other components - learn to accept there will be limitations and learn to appreciate quirks that produce surprisingly good results.

(3) Begin work by laying stuff out in an approximate way. Do plenty of sketches. Let your subconscious tell you when it looks like you've got things well proportioned.

(4) Refine your design from stage (3) by checking basic practical stuff - eg. Will things fit where you've put them? Have you avoided needing to cut the box or neck in such a way that there will be narrow or weak points? Will the action be about right? Will the strings pass over bridge and nut at sensible angles?

(5) Try to design in such a way that you can make critical bits first and then adjust the proportions of subsequent sections once you've seen how the first bits work out. eg. Ideally I'd like to be able to do all the cutting work on the box and install as much of the hardware as possible then try a little tap testing. The tap testing might suggest the bridge should be in a slightly different position. If so then I can alter the measurements for the neck to accommodate the necessary change to the bridge.

(6) Small soundholes can be made bigger but it's not easy to do the reverse.

(7) Once you've built a guitar there will always be a period of "settling in" during which you might fix minor problems and make small improvements. Andinstruments often seem to just "play in".

 

Finally, something more specific about soundholes. They AREN'T the part of the guitar from which most sound is emitted. Good scientific research has shown most of the sound radiated towards the audience comes from the soundboard. Soundholes obviously do affect the sound of a guitar, but seemingly in more subtle ways than most people think. One important thing they do (as I mentioned before) is alter the way the soundboard flexes as it vibrates in response to the strings. The size of the hole also affects the Helmoltz resonance (the resonance of the air inside the guitar body), but the significance of this is more subtle and complicated than people often think - it ain't a simple matter of adjusting the resonance to a particular note. There's a theory that the most important thing about the air inside the guitar is how it couples the soundboard to other parts of the instrument. My feeling is don't worry about it too much.

So...choose from some classic examples - a simple round soundhole, a pair of f-holes or a small cluster of small holes (as per Ovation acoustics).  DON'T MAKE THE HOLES TOO BIG (hole area detracts from soundboard area). Put the holes where they look right to your eye.

If it works then you've got a good design you can use again.

If it doesn't sound great at first then don't give up. It might improve with time. Try different strings and tunings because one of the secrets of CBGs is finding the best tonal range for a given box.

Keep going and try different designs - that's the only real way to learn. If you don't mind risking a box and some wasted time then throw all these principles out the window and build something totally different - you never know, you might just chance upon something that sounds fantastic.

 

 

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