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People have mentioned raising the string height and changing the break angle, but I'd be curious to hear opinions on changing the direction of force on the saddle. I tilt my saddle slots back to split the angle the strings make. The intent being to direct the force entirely down the height of the saddle and not against the front of the saddle slot. Anyone else try this?

Mike

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Montreal, Quebec
indianhillguitars.com

Mike:
I picked up on the back-tilted saddle from Rick Turner (steal ideas from the best). I use 9 degrees, as he does. It's not a new idea, though: violin bridges are set up so that they very nearly bisect the break angle over the top. They need to be that way; otherwise the force vector bends the bridge and you lose a lot of sound(especially when the bridge tips over!).

The backward tilt should not effect the way the strings drive the top. What it does do is reduce or eliminate the force trying to split out the front of the bridge, and increase the force on a UST by a little bit. With piezos every little bit helps.

Hi all,
I thought before this thread dies I'd thank everyone for their responses. I've been following them intently, studying and pondering. I see the issue is a lot more involved then I bargained for, but the discussion has, if not provided a definitive answer, made me much more informed of the factors involved. Right or wrong, it has helped me develop a mental model as to how I think the bridge and saddle function, that I will use going forward. As my small contribution, I'll share a somewhat crude experiment I did to demonstrate to myself the principles being discussed.

I mounted a 6" long board on a pivot above my work bench , sort of like a see-saw, then added a 1 1/2" block at one end of it. This was my surrogate bridge and saddle ( colored grey in my diagram). Strung a line with just under 30 lbs of weight over an improvised roller, and measured the downward force on the front of my "bridge" with a dowel and bathroom scale. I took measurements with a steep break angle of about 55 deg. and a shallow break angle of about 20 deg (measured off my 6" board). Both ways , my bathroom scale read 18 lbs. I repeated it all a few times with the same results.
Attachment:
Bridge test.jpg
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I think I'll let everyone draw their own conclusion as to the results, merit and faults of this. I think what it most proves is that I need to get a life!
Gerard

Wonderful experiment Gerry. My opinion: point of rotation is irrelevant if held constant. (Engineering is one of many fields that I don't have a degree in.)
Andy: I'm sorry we haven't heard from you. I think you had it nailed.
I think saddle position relative to front edge of bridge has some effect. I think bridge pin position is irrelevant. I think steel string bridges are "rigid" compared to the soundboards they interact with. I think the "rigidity" of classical bridges is debatable. I think data is fundamentally important, and physics is a prerequisite to interpreting data.

It's not the amount of torque or rotational force that's affected by the location of the bridge pins in
relation to the top of the saddle, but the direction of the forces. Having the pins in the rear block
creates a completely different set of forces than what are applied to a bridge when the anchor and fulcrum
are both located in the same foundation.

Down force is certainly an important one when it comes to creating tone, but the rotational forces
that are presented when the strings are trying to roll the bridge off of the top to relieve the tension that
is applied to them by tuning them to pitch are of paramount importance. As the strings cycle when activated
by the player striking them, their length changes in their respective cycle intervals and their tension, in turn,
decreases and returns to its maximum for that gauge and pitch. This creates the typical "rocking" of the
bridge and cyclic relieving and returning of the top's tension, thus servicing the desired pump like action
of the top that generates a lot of the volume and tone of the guitar.

Regards,
Kevin Gallagher/Omega Guitars

Kevin Gallagher wrote:
"As the strings cycle when activated by the player striking them, their length changes in their respective cycle intervals and their tension, in turn,
decreases and returns to its maximum for that gauge and pitch. This creates the typical "rocking" of the bridge and cyclic relieving and returning of the top's tension, thus servicing the desired pump like action of the top that generates a lot of the volume and tone of the guitar."

Nope.

That is, the tension does change twice per cycle, and that does cause the bridge to rock, but it's not the _major_ producer of sound. I've measured this one every which way and the answer always comes up the same: most of the sound is produced by the vertical component of the transverse string force. If you want the gory details, go to my web site and download:
http://www.alcarruthluthier.com/Downloa ... Theory.pdf
That's the update of my 'strings' article.

As a brief bit of food for thought:
Everyone agrees that archtop guitars don't 'see' the twice per cycle tension change that flat tops do: they're driven primarily by the transverse force. So, how come archtops don't sound an octave lower than flat tops?

Al,
I thought it obvious that there are two tension effects with the cycling of the strings in their
vibrational patterns so didn't feel the need to indicate it. I guess I should have. Also, I wasn't
implying that this rocking of the bridge, which occurs very obviously as well, is the primary or
chief creator or contributor to the tone or volume of a guitar when it's played, but one of many.

The cycle intervals are the same for the respective notes on a guitar whether and archtop or
a flat top. The "sensing" of the single lobe of the cycle by and archtop doesn't change the interval
at which a particular note cycles. I know you know this, but wanted to offer it for those who may
not have been exposed to these findings.

I've tested these things in every way that I could imagine and have relied on the imaginings of
as many builders as I've been able to test them in other ways, too. Always fascinating, always
interesting, and always enlightening.

Thanks,
Kevin Gallagher/Omega Guitars

Al,
After reading your post again, it actually occurred to me that it was pretty dismissive and arrogant.
The rocking of the bridge is in fact what is caused by the location of the pins as the anchor point and
the saddle as the lever being in the same foundation which is the bridge.

I know that you've done your share of testing and I'd never dismiss your findings whether they were
based in fact, theory or your own ideas with such shortness or lack of consideration for your time in
the business an number of guitars that you've built. I really would expect the same courtesy from you
since i've been at this thing a long time and have a lot of guitars under my belt.

It surprised me especially since you consider yourself and authority on this kind of subject matter.
The things that I stated in my post above are obvious and true and fall in the fundamental leverage
and tension physics realms for the most part. Do I consider myself such an expert that I'd be so quick
to dismiss your findings and ideas? Never happen and i've always enjoyed your input, put I've done
easily as many tests and experiments to arrive at my conclusions and my guitars have reflected the
value of those conclusions for the past 20 years and more.

Thanks,
Kevin Gallagher/Omega Guitars

First, my apologies.

As you may know, one lutherie author has been arguing that the tension change signal is the main driver of the top, through the bridge rocking mode. I've just been through a couple of weeks of discussion of this very point on another list, made up of folks who really should know better. Another member and I spent quite a lot of time, not just posting, but putting forth the mathematical reasoning (him) and running demonstation experiments (me) and putting out the results. So, when I saw your post I leapt into 'here we go again' mode. It was well past my bed time, and I'm afraid you just pushed the wrong button. I should not have reacted so strongly.

Al,
No problem. It just took me by surprise since you've always been a level headed and very patient poster who
also always has very practical and easy to understand reasons for your informative posts. I should have guessed
that there may have been some contributing circumstances.

Thanks for taking the time to clarify and explain, though. I enjoy your input on any of the forums and respect
you and your opinions, findings and ideas.

Best,
Kevin Gallagher/Omega Guitars

here's a simple static geometry addressing the original question, haven't had time to check it very close.

Simple Bridge

Hmm...the answer looks familiar

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Marc,

I didn't check your math, but I would argue the pivot point for the rocking motion of the bridge is at "B" rather than "P". What is holding P stationary? The termination of the string tension would tend to keep B stationary.

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Formerly known as Adaboy.......

In my musings I would argue that the pivot point is somewhere between p and b and is dependent on the characteristics of the top, bridge plate and bracing. Ignoring friction, the downward force vector at p, in the simple case, should be equal to the upward force vector at b which will cause a rotation but the actual pivot point would be between these.

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Steve Smith
"Music is what feelings sound like"