I've been searching through the articles on this site for information on selecting the position where the bridge should be. Obviously on an unfretted instrument you can move the bridge and experiment, but on a fretted guitar, once the frets are on and the neck is fixed that's it. You have committed yourself.

 

So is there any way to know on a box for box basis (not using formulas because I'm pretty sure that they are worthless unless you always use identical boxes) where the bridge should be to get the best results?

 

Now I've already done some test, but I don't know if they are the work of a visionary (don't laugh) or a pointless waste of time (odds on the latter). I was thinking that as far as the box is concerned it gets most of the string vibration through the bridge. If you want to simulate vibrations coming from the bridge can you use something else that will transmit vibrations and see (or rather hear) how they sound and make a choice based on that. I found a tuning fork and tried it at various places on three boxes that I intend to use soon.

The results from the three were quite different. Not surprisingly all gave the warmest and clearest sound in the centre of the box. The top one gave quite progressive results getting better quite gradually towards the centre. The left hand one was very even across it's width until right near the edge. The right hand one was a surprise as it sounded best right in the middle, tone falling off and getting soft of nasal even an inch away from the motif. Shame as I don't really want to put a bridge right on the motif but my tuning fork test suggests that it may be the best place.

 

So, finally, to the question. Has anyone done any tests - similar or otherwise - that give a good indication of where to put a bridge and that do not rely on ratios or formulas, but take into account the different characteristics of each box?

 

 

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John wrote:
> It takes 30 seconds or less to test. For a cost of half a minute of my time and no money
> (and with the chance of improved sound) why wouldn't I?

No argument here, sounds perfect to me.

But in asking about additional testing - I can imagine improvements. For example, back in the 80s I used a pink noise generator to test the frequency response of a room at different locations as an aid to the human ear (you mentioned hi fi). My hearing is over responsive to some high frequencies and under responsive to some low, and I'm hardly unusual in that regard. So, using something more objective than your ear is a possible improvement. Would the accuracy of something like this be affected after you add a neck, etc? Sure - but perhaps not substantially (at least with a bolt-on). Is it ultimately worthwhile or beyond the point of diminishing returns? I'd say that depends on how much effort it takes, how good your ears are, how you mount your necks, etc, etc.

Well said, Ken. Using cigar boxes I have never been able to duplicate the sound from one guitar to another, even with seemingly same boxes, too many variables. A great sounding box does not guarantee results in the finished guitar. Some sound great, and some are give-aways, most are good. I can with mandolins, but that is another story. 

ken farmer said:

John wrote:
> It takes 30 seconds or less to test. For a cost of half a minute of my time and no money
> (and with the chance of improved sound) why wouldn't I?

No argument here, sounds perfect to me.

But in asking about additional testing - I can imagine improvements. For example, back in the 80s I used a pink noise generator to test the frequency response of a room at different locations as an aid to the human ear (you mentioned hi fi). My hearing is over responsive to some high frequencies and under responsive to some low, and I'm hardly unusual in that regard. So, using something more objective than your ear is a possible improvement. Would the accuracy of something like this be affected after you add a neck, etc? Sure - but perhaps not substantially (at least with a bolt-on). Is it ultimately worthwhile or beyond the point of diminishing returns? I'd say that depends on how much effort it takes, how good your ears are, how you mount your necks, etc, etc.

Hi Herb.

 

I think to get the best results from the test you would need to use two unmodified boxes that had very similar characteristics under the tuning fork. If in the making the bridge position was significantly different, one placed as the test indicated and the other placed in what sounded like the wrong place and all other factors similar then that might be an indication.

 

Ideally you would also need boxes where there seemed to be a very noticable difference between the best and worst places. My original use of the fork test showed some boxes to be very tolerant of bridge position. Pretty much put it where you want and where it looks best. With one box though there was a big difference in the sound from place to place.

 

One refinement that occurred to me is to put the tuning fork on something about the same shape and material as the bridge you intend to use and place that on the box, so that the vibrations are spread in the way that they would be by the final bridge. Who knows. It may make a difference.

 

Anyway, it will be very interesting to know how you get on and if you think that there was any benefit in doing this. Best of luck.

herb berwald said:

I will be trying the tuning fork idea on my next build...At some time I should be making a duplicate of existing guitars and can then compare the differences..I do have some favorite boxes and tend to use these for multiple builds..

The point about mounting the neck is a good one. A point that was made earlier related to adding reinforcement and cutting sound holes. I will certainly be trying to leave my neck design flexible until I have added stiffeners to the box and cut sound holes. I will then retest and place the neck accordingly.

ken farmer said:

Is it ultimately worthwhile or beyond the point of diminishing returns? I'd say that depends on how much effort it takes, how good your ears are, how you mount your necks, etc, etc.

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

Can't hurt to try it. Pull out your drafting tools (and a tuning fork) and go at it.

The biggest problem that arises with this method is that the folks who decorate the boxes often key off of these same dimensions and you often engage key graphic elements of the box cover as a result of finding this sweet spot. 

Next approach is to extend the bridge base or bracing to engage (activate/vibrate) the "diagonals" or some proportional segment of the line length (space) between them. 

Good fodder for experimentation.

 

 

 

 

 

Hoov, Interesting and cool info! Thanks, Richard

Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

Can't hurt to try it. Pull out your drafting tools (and a tuning fork) and go at it.

The biggest problem that arises with this method is that the folks who decorate the boxes often key off of these same dimensions and you often engage key graphic elements of the box cover as a result of finding this sweet spot. 

Next approach is to extend the bridge base or bracing to engage (activate/vibrate) the "diagonals" or some proportional segment of the line length (space) between them. 

Good fodder for experimentation.

 

 

 

 

 



Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

 

OK, WHICH line again? (see illustration)

 

 

I used that ratio while building a kalimba. What do you do if the box is NOT in a golden ration?

 

 

 

 

 

 

Alan,

I will go to cad and draw the construction I described.

It works for any rectangle.

The wiki drawing you invoked is for a GM rectangle

Alan Roberts said:



Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

 

OK, WHICH line again? (see illustration)

 

 

I used that ratio while building a kalimba. What do you do if the box is NOT in a golden ration?

 

 

 

 

 

 

Ok here it is.

 



Hoov said:

Alan,

I will go to cad and draw the construction I described.

It works for any rectangle.

The wiki drawing you invoked is for a GM rectangle

Alan Roberts said:



Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

 

OK, WHICH line again? (see illustration)

 

 

I used that ratio while building a kalimba. What do you do if the box is NOT in a golden ration?

 

 

 

 

 

 

Ah HAH! OK, gotcha. The comment about the golden mean lead me astray.

By the way,

this construction applies to all sides and all intersections therefore multiple sweet spots are created. The major sweet spot is naturally dead center but the second is the one I described.There are many others falling on conjunctions of other diagonals and squares ad infinitum. (This is all proportional stuff Halves Quarters Eighths Pents and etc)

Here is another drawing showing the bridgepoints falling on the major sweet spot lines of intersection.

 

 



Hoov said:

Ok here it is.

 



Hoov said:

Alan,

I will go to cad and draw the construction I described.

It works for any rectangle.

The wiki drawing you invoked is for a GM rectangle

Alan Roberts said:



Hoov said:

Interesting discussion!

I am a newbie coming from the visual arts and from that realm the Greeks came up with the "Golden Mean" as a way to find dimensional "harmony" in a rectangle.  It works for the rectangular top of a CBG too.  First determine the (inside...unglued) corners of the rectangle.  Use a straightedge to determine the diagonals. Then use a square or compass to strike a line which squares one diagonal and intersects the opposite corner.  (You may want to duplicate your box on a piece of paper to do this rather than poke holes into your box.) The intersection of that line and the diagonal it squares will be a potential sweet spot for your bridge.  Run a line square to the centerline of your box through this point and this line will be the dynamic centerline of your bridge.  Then determine neck length and position it from this sweet spot based on your fretboard (nut to bridge) dimension.

 

OK, WHICH line again? (see illustration)

 

 

I used that ratio while building a kalimba. What do you do if the box is NOT in a golden ration?

 

 

 

 

 

 

Sorry ALAN,

All of this tripe was fed to me in Art and Culture Classes from WAY BACK in the conundrum.

 And from that I learned a few things about harmonies.

The fun part is that it is simple math.

 And better yet

The geometry is easy.

So if we keep it simple and don't mess with the basic design of the box the outcome can be simple too.

It is powerful

as it should be!

Hoov

Alan Roberts said:

Ah HAH! OK, gotcha. The comment about the golden mean lead me astray.

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