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snowbird99
10-21-2014, 01:58 PM
I am an amateur builder working on a concert sized uke. I am using a standard 15" concert scale.

I have looked at several ukuleles online and I have seen that many of the bridges are positioned well in front of the sweet spot in the middle of the lower bout. I know that it is the trend to have a longer neck these days, but I am assuming that the longer neck is responsible for moving the bridge closer to the soundhole.

As I am building my uke, I want my bridge to land right in the middle of the lower bout. I have modified my design slightly to ensure that it does so. I am connecting to the body at the 12th fret (7.5 inches), then there will be an equal distance to the center of the lower bout.

I guess my question is: am I missing something here? I would assume that centering the bridge in the middle of the lower bout will optimize sound, but most of the ukes and guitars I have seen have a bridge that is moved closer to the soundhole.

Any thoughts or suggestions on the subject would be greatly appreciated.

Thanks.

IamNoMan
10-21-2014, 03:56 PM
I am an amateur luthier as well. I make no claims to great experience or expertise. And I suspect we will both learn something here. By bouts I presume you mean the two bell shaped cavities of the traditional ukulele sound box. Since the purpose of the bridge is to transmit vibration to the sound board and thence to the sound cavity It would make sense to place the bridge over the centerpoint of the radius of curvature of the larger bout (sweetspot). I suspect the sweet spot for the uke sound box as a whole is located halfway (1/2) between the centerpoints of the radii of curvature of both bouts. (it could easily by a different harmonic order, 1/3, 1/5, 1/7 etc but I don't think so). This distance could also be modified to compensate for the complex geometry of the sound box.

If this is totally confusing get a hold of a fretless banjo. Move the bridge to the center of the head. Play. Move the bridge off the sweetspot. Play. repeat until you have the desired sound qualities. For whatever reason the centerpoint of the banjo head is seldom where the bridge is located

Connecting the body to the neck at the 12 fret will make it more difficult for the musician to play in the second octave. The sound box/neck assembly restricting the hand and fingering.

Remember: Measure twice. Cut once. Still too short.

snowbird99
10-21-2014, 04:19 PM
I appreciate your input. That is interesting to think of a banjo and the fact that dead-center is rarely the sweet spot. I guess the exact sweet spot would be a factor of the dimensions of ukulele and the positioning and size of the sound hole. Is there an app for that? :)

I wish I had the time and resources to experiment with it. It would be fun to build my model that I have designed to connect at the 12th fret, then the same body, but connecting to the body at the 13th fret, which would move the bridge a little toward the soundhole, then build one to connect at the 14th fret with the bridge even closer to the soundhole. I would be curious to see if there as an noticeable difference in sound. If not, connecting at the 14th would be best to lengthen the playable area of the neck. Maybe that will become my 2 year project :)

Any other input or ideas would be appreciated. Thanks.

IamNoMan
10-21-2014, 04:27 PM
Here is something to consider. build a fretless uke. optimize the bridge location. Then go back and determine the proper scale length and intall the frets. You should be able to come up with an app or program for fret positions/scale length with little difficulty.

snowbird99
10-21-2014, 04:43 PM
That's sounds like an interesting idea. I am kind of new at this... how would I optimize the bridge location? Is there a way to try it in several locations without fully installing it?

BlackBearUkes
10-21-2014, 08:14 PM
The sweet spot may differ for each luthier. There is no one best sound, it's just what we prefer. I personally like a 12 fret neck and the bridge in the center of the lower bout, but the same sound result can be obtained by moving, reducing or enlarging the sound hole, modifying the bracing, wood selection, plus many other factors. I would suggest that you build with an open mind, read many of the great published books and articles, and learn by doing. What's the worse that can happen if you get it wrong?

rudy
10-22-2014, 01:59 AM
I am an amateur builder working on a concert sized uke. I am using a standard 15" concert scale.

I have looked at several ukuleles online and I have seen that many of the bridges are positioned well in front of the sweet spot in the middle of the lower bout. I know that it is the trend to have a longer neck these days, but I am assuming that the longer neck is responsible for moving the bridge closer to the soundhole.

As I am building my uke, I want my bridge to land right in the middle of the lower bout.

I have modified my design slightly to ensure that it does so. I am connecting to the body at the 12th fret (7.5 inches), then there will be an equal distance to the center of the lower bout.

I guess my question is: am I missing something here? I would assume that centering the bridge in the middle of the lower bout will optimize sound, but most of the ukes and guitars I have seen have a bridge that is moved closer to the soundhole.

Any thoughts or suggestions on the subject would be greatly appreciated.

Thanks.

Evaluate your reasoning based on the physics of how the bridge converts string energy to soundboard movement. The front of the bridge acts more as a fulcrum point with the rear of the bridge converting string energy to the "up and down" motion that creates audible sound. It becomes easier to understand the forces and movements coupled from string energy if you imagine a length-wise cross section of the entire instrument so you can rationalize the way the soundboard will move as the bridge acts upon it.

In your example you would be limiting the movement of the lower bout by (1) adding the bridge mass in the area where you would otherwise want to respond freely, and (2) coupling the bridge's natural rotational force to the bottom quarter of the lower bout, an area that won't generate a lot of movement to enable the production of sound energy.

If a bridge just moved up and down in response to string energy it would certainly make life a lot simpler to figure out how string energy couples to the instrument, but we're just not that lucky.:)

Beau Hannam Ukuleles
10-22-2014, 04:11 AM
DOnt worry about all this for your first builds-

On 12 and 14 fret instruments

Along the grain stiffness is greater then cross grain stiffness (across the lower bout). So (in theory) to get an even vibrating circle pattern, the bridge should actually be a bit forward to give the stiffer long grain more area to vibrate.

I thin my tops along the grain at the lower bout slightly more then on cross grain (at the 2 widest parts of the lower bout) to bring about and more even response and vibration pattern.

Of course, it's all splitting hairs though.

snowbird99
10-22-2014, 06:56 AM
The sweet spot may differ for each luthier. There is no one best sound, it's just what we prefer. I personally like a 12 fret neck and the bridge in the center of the lower bout, but the same sound result can be obtained by moving, reducing or enlarging the sound hole, modifying the bracing, wood selection, plus many other factors. I would suggest that you build with an open mind, read many of the great published books and articles, and learn by doing. What's the worse that can happen if you get it wrong?

Great feedback. Maybe I am overthinking it. I think I am going to start with a neck that connects at the 12th fret, a 14 fret fretboard to free up the soundboard a little bit, a 2 1/4" soundhole, and a bridge that is centered in the lower bout. I am not an expert, but logically it should perform pretty well.

BTW, my top bracing is going to be placed 3/8" from the soundhole on each side, and will be 3/16 x 3/8", slightly scalloped on both sides. Bridge plate, but no other bracing on top. I am excited to see how it all comes together. I will definitely be sharing some pictures as things come along.

snowbird99
10-22-2014, 07:12 AM
In your example you would be limiting the movement of the lower bout by (1) adding the bridge mass in the area where you would otherwise want to respond freely, and (2) coupling the bridge's natural rotational force to the bottom quarter of the lower bout, an area that won't generate a lot of movement to enable the production of sound energy.)

Thanks for your input. I think my reasoning for wanting the bridge in the center of the lower bout is because I envisioned that the sound energy would be best distributed that way because it is the widest part. Also, I imagined that a large part of the sound is generated between the bridge and the soundhole, and that a little more space there might increase volume if the soundboard is free to move and do its thing. A risk with that is being too loose and losing clarity.

I think Beau Hannam might be right that for my level of experience I am thinking about issues beyond my experience, but part of the fun for me is to learn the theories and try to apply them. I would love to build 3 exact ukes, but connect one at the 12th fret, one at the 13th fret, and one at the 14th fret. It would be interesting to see how the three bridge positions effected sound on the exact same body shape and soundhole size and position. Maybe in time :)

Moore Bettah Ukuleles
10-22-2014, 07:22 AM
That would be an interesting test. But I think it would be impossible for a hand builder to build three instruments alike. Any differences might well be attributed to the differences in the build itself and the variation in materials rather than the bridge position and I would think those differences would be very subtle. Playability is every bit as important as the particular sound you are trying to achieve. Many playing find a 12th fret neck/body joint to be limiting. Everything is a compromise and you need to find the balance that suits you best.

snowbird99
10-22-2014, 07:50 AM
That would be an interesting test. But I think it would be impossible for a hand builder to build three instruments alike. Any differences might well be attributed to the differences in the build itself and the variation in materials rather than the bridge position and I would think those differences would be very subtle. Playability is every bit as important as the particular sound you are trying to achieve. Many playing find a 12th fret neck/body joint to be limiting. Everything is a compromise and you need to find the balance that suits you best.

Thanks for your feedback Chuck. Like you say, I would imagine that it would be hard for a hand bulider to keep every variable constant except for the bridge positioning. Do you build your standard concerts to connect at the 12th, 13th, or 14th fret? Tenors?

Moore Bettah Ukuleles
10-22-2014, 02:43 PM
Thanks for your feedback Chuck. Like you say, I would imagine that it would be hard for a hand bulider to keep every variable constant except for the bridge positioning. Do you build your standard concerts to connect at the 12th, 13th, or 14th fret? Tenors?

The vast majority of my ukes, of any size, are 14th fret connections.

sequoia
10-22-2014, 04:05 PM
What a great question! As I see it, when the length of the fret-board increases then the size of the body must proportionally also increase to maintain the so-called "sweet spot". This would be taken care of in the original overall design..... Eventually as the scale length increases you end up with a ....4 stringed guitar. I think it ends up as a question of proportion. Just my armatures two cents worth. Thanks snowbird99 for getting me thinking about design. Hmmmm...

IamNoMan
10-22-2014, 04:18 PM
...when the length of the fret-board increases then the size of the body must proportionally also increase to maintain the so-called "sweet spot". This would be taken care of in the original overall design..... Eventually as the scale length increases you end up with a ....4 stringed guitar. I think it ends up as a question of proportion.....Hmmmm...When your thinking about this remember that your fretboard length can extend into the upper bout of the soundboard, perhaps as far as the edge of the sound hole. The sweet spot is more a matter of the upper and lower bout geometry than it is fretboard length or scale length.

tangimango
10-22-2014, 04:38 PM
if you connect 12 13 or 14 it will all be fine, do you want to connect at 12th like pepe ukes or 13th like koaloha ukes or 14 etc etc. the benefit of connecting at 14th fret is you get access to the extra frets, especially if you like to play down or up the neck. unless you have a cutaway even better. I would make an out line of the body your making and see if the 14th fret connect makes the bridge too close to the soundhole which I think looks funny IMO, so you have the option to go 13th next then 12th. if your using a 15" scale then just measure from top of the fretboard to the bridge nut slot give or take couple mm compensation. I would go for 14th fret because playing harmonics is so much easier for me.

snowbird99
10-22-2014, 04:39 PM
Evaluate your reasoning based on the physics of how the bridge converts string energy to soundboard movement. The front of the bridge acts more as a fulcrum point with the rear of the bridge converting string energy to the "up and down" motion that creates audible sound. It becomes easier to understand the forces and movements coupled from string energy if you imagine a length-wise cross section of the entire instrument so you can rationalize the way the soundboard will move as the bridge acts upon it.

In your example you would be limiting the movement of the lower bout by (1) adding the bridge mass in the area where you would otherwise want to respond freely, and (2) coupling the bridge's natural rotational force to the bottom quarter of the lower bout, an area that won't generate a lot of movement to enable the production of sound energy.

If a bridge just moved up and down in response to string energy it would certainly make life a lot simpler to figure out how string energy couples to the instrument, but we're just not that lucky.:)

Good input. It took me a little bit to absorb it, but now I've got your point. I think that in the end the only way I am going to find the answer for my design is to try different fret to body connecting points and see if I notice a difference among the 3. It will be hard to keep the variables consistent, but at least I will have a project to keep me busy for a while. Thank you all for your input.

rudy
10-23-2014, 02:19 AM
Good input. It took me a little bit to absorb it, but now I've got your point. I think that in the end the only way I am going to find the answer for my design is to try different fret to body connecting points and see if I notice a difference among the 3. It will be hard to keep the variables consistent, but at least I will have a project to keep me busy for a while. Thank you all for your input.

You're on the right track, but you do have to take into consideration that where your bridge ends up being located (as a result of chosen scale length and the fret number at which you choose to connect the neck to the body) is only a single variable among many.

MUCH more important is how your bridge / soundboard interacts with the bracing, and even more importantly, your bracing design and layout.

As far as a "sweet spot" goes, that's a moving target on any type of stringed instrument with a fixed bridge on a braced soundboard. The "sweet spot" is going to be determined by several factors such as soundboard shape / thickness, bracing location / pattern / shaping, geometry and relationship of upper/lower bouts and sound hole, sound hole size / body internal air volume / resonance, etc. You get the point.