Why ?

[KevWind]

Originally Posted by John Arnold

Force is a vector. It has amplitude and direction. The force on the bridge assembly where the strings exit is downward. Just like my example of the force on the saddles, the force at that location is at an angle bisecting the angle the string makes.
If you were to attach the strings to the back of the bridge, then you have a different situation. You would have a force pulling up on the bridge, causing it to lift from the back edge. Right now, the upward force is borne by the thick plywood.
Like so many of these situations, a simple diagram of the forces would surely help.

So in this case we could say " The Force May Be With You" :

[Otterhound]

Originally Posted by John Arnold

Force is a vector. It has amplitude and direction. The force on the bridge assembly where the strings exit is downward. Just like my example of the force on the saddles, the force at that location is at an angle bisecting the angle the string makes.
If you were to attach the strings to the back of the bridge, then you have a different situation. You would have a force pulling up on the bridge, causing it to lift from the back edge. Right now, the upward force is borne by the thick plywood.
Like so many of these situations, a simple diagram of the forces would surely help.

I like real examples . Although diagrams are typically useful , I thought that I would test this with a real world , tangible example .
Unlike some here , I have no horse in this race . I am simply testing a theory and observing the results .
So , with that said , it is now time to assemble an acoustic test mule with a slight variation on the typical setup .
This should be fun .

[Rudy4]

Originally Posted by Otterhound

Am I permitted to add bracing to the plywood ?

You could do anything you want, I don't understand the point, or the question. Perhaps you could re-phrase the theory that you are attempting to test?

What you show is basically no different than any other bridge that you normally see in an acoustic flat top guitar.

These sort of rhetorical questions are probably best answered by drawing a simple side profile of all the related points and then evaluating what you see for yourself.

It seems like simple physics to my mind.

[John Arnold]

Correct me if I am wrong, but I think Otterhound is trying to eliminate the torque on the bridge to keep it from rotating. But as long as the strings are anchored at the bridge, there will be a torque vector that is the result of the strings being about 1/2" above the top. For the purpose of this analysis, it does not matter where or how the strings are anchored, other than to change the location of the forces on the bridge itself. If you have a total string tension of 180 pounds, and the strings are 1/2" high, the torque will always be 90 inch pounds, regardless of how the strings are anchored.
BUT, the path of the strings will determine how much lifting force is applied to the bridge to top joint. Anchoring the strings underneath the top has a structural advantage, since a loose bridge will not fly off; the strings will hold it on the upper side of the bridge pins. Placing the pins on the lower edge of the bridge (like the electric bridge in the experiment) reduces the tendency for the bridge to lift, since the strings are pressing down on the bridge above the pins.

[Otterhound]

Originally Posted by Rudy4

You could do anything you want, I don't understand the point, or the question. Perhaps you could re-phrase the theory that you are attempting to test?

What you show is basically no different than any other bridge that you normally see in an acoustic flat top guitar.

These sort of rhetorical questions are probably best answered by drawing a simple side profile of all the related points and then evaluating what you see for yourself.

It seems like simple physics to my mind.

There is one very large difference . If you look , you will see that there are no screws to hold the bridge down or adhesive/s to do the same thing .
Obviously , no one can truly see that there are no adhesives so you will need to trust me when I tell that there are none .

[Otterhound]

Originally Posted by John Arnold

Correct me if I am wrong, but I think Otterhound is trying to eliminate the torque on the bridge to keep it from rotating. But as long as the strings are anchored at the bridge, there will be a torque vector that is the result of the strings being about 1/2" above the top. For the purpose of this analysis, it does not matter where or how the strings are anchored, other than to change the location of the forces on the bridge itself. If you have a total string tension of 180 pounds, and the strings are 1/2" high, the torque will always be 90 inch pounds, regardless of how the strings are anchored.
BUT, the path of the strings will determine how much lifting force is applied to the bridge to top joint. Anchoring the strings underneath the top has a structural advantage, since a loose bridge will not fly off; the strings will hold it on the upper side of the bridge pins. Placing the pins on the lower edge of the bridge (like the electric bridge in the experiment) reduces the tendency for the bridge to lift, since the strings are pressing down on the bridge above the pins.

You are close . You need to think less in the terms of absolutes . In fact , you are adding something that I have eliminated . The pins .

[RP]

The strings don't appear to be exactly perpendicular to the bridge plate nor probably the nut either...

[John Arnold]

no one can truly see that there are no adhesives so you will need to trust me when I tell that there are none .

I assumed there was no adhesive, since there is no need. The bridges on archtop guitars or violins are not glued, either.

Like other responders, I fail to see the point in this experiment, since there is no useful information that could not be gleaned through logic. The strings are pressing down on that bridge, so there is no other possible outcome.

In fact , you are adding something that I have eliminated . The pins .

The pins are irrelevant. If you drill smaller holes and thread the strings through from underneath, the results are the same. The smaller holes do add strength to the bridge, but the torque and tendency for the bridge to rotate are exactly the same.

[Rudy4]

Originally Posted by Otterhound

There is one very large difference . If you look , you will see that there are no screws to hold the bridge down or adhesive/s to do the same thing .
Obviously , no one can truly see that there are no adhesives so you will need to trust me when I tell that there are none .

I know you aren't using adhesive or screws.

I've built ukuleles using a variant of the same thing you show; the string is retained by a a knot that locks against the bottom of the soundboard. I do glue the bridge to the soundboard, but that's to keep the bridge from shifting forward over time due to the pull of the strings over the saddle.

There's nothing particularly wrong with your idea; it's been used in the past by builders. The bridge still needs something to keep it from shifting forward, and that's usually glue in the case of the modern steel string guitar. Note that bridges don't fly off if the glue fails, the bridge stays in place because the string balls lodge against the bridge plate. The "lifting" of the bridge from the surface of the soundboard is the result of the rotational forces imposed on the bridge by the previously mentioned vector forces.

The modern bridge pin system has nothing to do with holding the bridge and is there to make changing the strings easier. On a string-through ukulele you have to pss the string through from the top side, grab the free end, tie a secure stopper knot (Ashley's Stopper is best) and then pull the string back in place to lodge the knot against the bottom of the soundboard.

How were you anticipating a string change?

[Otterhound]

How were you anticipating a string change?[/QUOTE]
Via the first real usage of the sound port that I have known .
At the Harrisburg show , I was talking to a luthier that utilizes a pinless design very different from what I have come up with . He told me that he is beginning to use a removable panel/door in order to gain access to the inside of the body of an acoustic guitar .
I remain very grateful to him for being willing to discuss this so freely with a no name like myself . I keep asking and learning .
The strings feed upwards through the top .
I am using a 1/8" piece of Lexan beneath the bridge plate to anchor the strings .
I will be using a considerably smaller bridge both in footprint and thicknesses than what is typical . The loss in mass from the smaller bridge will be compensated for by adding mass under the top and/or using a thicker bridgeplate .
Fun things to mess around with .
Would it make sense to add mass to the bass side , treble side or would it make no difference ?
I may even try a split bridge or even go to the point of individual bridges for each string .
Just did a bit of research and it was Steve Klein that I was discussing this with at the Harrisburg Artisan Guitar Show .

[charles Tauber]

I don't understand what you are trying to do or for what purpose.

Originally Posted by Otterhound

I may even try a split bridge or even go to the point of individual bridges for each string.

I've done the split bridge thing on classical guitars in my "Kasha" days. Aside from "marketing", I don't see any advantage to doing it. In pre-CNC days, it was a lot of work to make.

Back in 1978, when I attended Charles Fox's school, he had a guitar there that he had made that had 6 individual bridges. His conclusion was that the isolation of strings made for a "dry" or "thin" sounding instrument, reducing the sympathetic resonance between strings.

[redir]

My guess is that Otter is wondering why this happens when his experiment clearly shows that it should not?

[John Arnold]

Because the strings go through the top at a different location.
Alvarez has been using a split bridge for a long time. It is certainly advisable to beef up the bridgeplate, since a typical one will not be strong enough. The bridge provides a lot of strength to that area of the top. Witness what happens when a bridge lifts. The top pulls up at the pin holes. It can break the top and bridgeplate, since there is force equal to the string tension, and the top is weakened by drilling six holes in it.

[charles Tauber]

Originally Posted by redir

My guess is that Otter is wondering why this happens when his experiment clearly shows that it should not?

As others have already noted, the OP has changed essential variables from the real-world situation, at least for acoustic guitars. In other words, the model he has created doesn't adequately represent the real-world situation sufficiently that conclusions drawn from the model apply to the real-world situation. That's one of the pitfalls to avoid when creating models, physical ones or mathematical ones. As stress analysts often say, "Things don't fail in the ways in which you've analyzed them, but in the ways that weren't included in your analysis."

To the OP, try the same experiment but with 1/8" thick plywood. You'll get a different result, one closer to the real-world situation of thin guitar tops with stiff bridges attached.

[Otterhound]

Originally Posted by charles Tauber

As others have already noted, the OP has changed essential variables from the real-world situation, at least for acoustic guitars. In other words, the model he has created doesn't adequately represent the real-world situation sufficiently that conclusions drawn from the model apply to the real-world situation. That's one of the pitfalls to avoid when creating models, physical ones or mathematical ones. As stress analysts often say, "Things don't fail in the ways in which you've analyzed them, but in the ways that weren't included in your analysis."

To the OP, try the same experiment but with 1/8" thick plywood. You'll get a different result, one closer to the real-world situation of thin guitar tops with stiff bridges attached.

Since I have failed to see a response from the party that you are quoting , I will ask again . Am I permitted to utilize bracing on the 1/8" plywood ?
I have changed nothing from the real world . I am questioning them .
Casting dispersions on a line of thinking without knowing the goal is far from fair dinkum .