Curious about bridge height, break angle and string gauge

[podzim02]

Hi All,

I'm not a builder, but I've been reading a lot of old posts about bridge height, break angle and string gauge, and I'd really appreciate hearing some thoughts on a hypothetical situation...

I'm wondering what would happen if someone had a new mandolin which happened to be optimized for medium gauge strings, and intentionally reset the neck resulting in a higher bridge height than what the mandolin had originally, in order achieve the exact break angle that would make light gauge strings have the same downward force as what medium strings did before the reset.

So my questions:

1. Assuming a very average bridge angle to being with, would the new break angle likely be out of an acceptable range after the reset? (given the amount it would have to change from the switch of medium to light gauge strings while keeping the same downward force)

2. Assuming the bridge mass and base dimension somehow stayed the same, would you expect there to be a noticeable change in volume?

[Les Corley]

Why would you want to spend hundreds to have a neck reset when you could spend 9.00 for a new pair of strings & get the same results

[podzim02]

Why would you want to spend hundreds to have a neck reset when you could spend 9.00 for a new pair of strings & get the same results

I'm not sure what you're getting at. The idea would be to preserve the downward force even after switching to lighter gauge strings.

[Marty Jacobson]

Podzim02, here is an excellent article from Lawrence Smart where he discusses many of the variables which can affect tone in mandolin construction.
http://smart-instruments.com/amluth95.html

A mandolin with a higher break angle and lighter strings will not sound exactly the same as a mandolin with a lower break angle and heavier strings. There's a lot more going on than just the downforce on the bridge. Additionally, for the geometry to work out, if you want to change the neck angle and still have the instrument feel, play, and look "right", usually other factors have to change, as well. Things like arch height, bridge location, bridge height, etc. All of those changes may be subtle when taken alone, but it's impossible to really test them alone, so that's really just hypothetical.

You might find this interesting. Ken Parker's newest line of archtops feature adjustable neck angle (which does not change the action, IIRC, though maybe I'm wrong about that) and adjustable tailpiece angle (lateral). So you can change the key break angle, and then you can also change the break angle over the bass or over the treble side. Without the instrument going out of tune, apparently. Brilliant.

[sunburst]

...Ken Parker's newest line of archtops feature adjustable neck angle (which does not change the action, IIRC, though maybe I'm wrong about that) and adjustable tailpiece angle (lateral)...

Actually, it is the action height that is adjustable, but as the neck is adjusted up or down the string break angle changes a little too. His guitars have had that feature for several years.

[fscotte]

Doesn't Siminoff have something to calculate downward force dependent upon string gauge?

[podzim02]

Podzim02, here is an excellent article from Lawrence Smart where he discusses many of the variables which can affect tone in mandolin construction.
http://smart-instruments.com/amluth95.html

Just read it, thanks.

A mandolin with a higher break angle and lighter strings will not sound exactly the same as a mandolin with a lower break angle and heavier strings. There's a lot more going on than just the downforce on the bridge. Additionally, for the geometry to work out, if you want to change the neck angle and still have the instrument feel, play, and look "right", usually other factors have to change, as well. Things like arch height, bridge location, bridge height, etc. All of those changes may be subtle when taken alone, but it's impossible to really test them alone, so that's really just hypothetical.

OK points taken. Yeah I was imagining tone being affected in unpredictable ways, but I was wondering mainly about volume, whether in principle it should end up about the same.

You might find this interesting. Ken Parker's newest line of archtops feature adjustable neck angle (which does not change the action, IIRC, though maybe I'm wrong about that) and adjustable tailpiece angle (lateral). So you can change the key break angle, and then you can also change the break angle over the bass or over the treble side. Without the instrument going out of tune, apparently. Brilliant.

Nice indeed.

[Julian Morris]

Hello, I'm new to Mandolin Cafe and have just come across this thread. I have just spent part of this morning investigating the relationship between tailpiece height and force on the bridge. Before I found this thread, or else I might not have put the time in trying to figure it out.

Attached is my spreadsheet. Basically, using the figures provided by D'Adddario for 8 of its standard mandolin strings, I have produced the horizontal and vertical components of the string tension for normal tuning. The result is quite interesting to my eyes. Firstly the changing of the angle between the neck side of the strings and the tailpiece side of the strings (what I suppose is commonly known as the break angle) has only a very small effect on the horizontal component (the tension that will be felt when fretting at the fingerboard). Secondly, the vertical component, the amount of pressing down on the soundboard by the strings through the bridge) varies considerably with break angle. For small break angles (like on my mandolin, 10 degrees) the alteration of the break angle produces an approximately proportional alteration of the vertical component. So, halving the break angle halves the vertical component.

I started looking into this because I would like semi-permanently to raise the tailpiece on my mandolin to minimise unnecessary force on the soundboard and to increase if possible volume and overtones. I think this will work quite well, I'd go as far as to say I'm convinced. I'd probably only be aiming for a 1 degree reduction in break angle initially.

If anyone wants to see the maths I have used let me know and I will scan it in.

By the way, being from Scotland I have converted everything to SI units (metric), imperial measurements hurt my head.

[fscotte]

What makes you think raising the tailpiece would increase volume?

[Nevin]

You can change the break angle by changing the tail piece to a longer one. I would think that would be esier than doing a neck reset. if you wanted more of a break ange than you could get from a different tail piece I think you woul be entering neck angle territory that could be uncomfortable to play.

[Julian Morris]

What makes you think raising the tailpiece would increase volume?

I think that the soundboard has a finite range of amplitude for oscillating and that excessive bridge pressure on a heavy soundboard like mine may act as a compressor. Somewhat like how a distortion effect on an amplifier clips the excessive amplitude and turns a sine wave into a square wave. As you turn the gain up the output goes up until the amplifier is saturated and then as you keep turning up the gain the output doesn't get any louder it just becomes more and more distorted towards a perfect square wave, losing more and more of the timbre and harmonics of the input.

So if my mandolin should be operating within the natural oscillation range of the soundboard and isn't because excessive pressure is causing wave clipping, it will be wasting energy and losing tone quality.

If my bridge pressure is as I suspect it is already too high, relaxing the pressure by reducing the break angle will open up the range of amplitudes for natural oscillation, and sweetening the tone into the bargain.

But I don't actually know for sure, I just have a personal conviction that it's worth a try. It must improve tone, but it only might improve volume.

[sunburst]

I think that the soundboard has a finite range of amplitude for oscillating and that excessive bridge pressure on a heavy soundboard like mine may act as a compressor. Somewhat like how a distortion effect on an amplifier clips the excessive amplitude and turns a sine wave into a square wave.

The problem with that is you should have stopped before you got into the analogy of the compressor and the truncated sine waves.
I suspect there can be damping of top movement resulting from excessive bridge pressure, but not my means of truncating waves. To understand the situation better, I suggest you do a little research into what is known (and measured using laser interferometry) about how tops (and backs) move when they are making sounds. Also, look into the ideas of Steinberger and others who believe that the bridge needs only enough pressure to stabilize it's position and any more may be excessive. In other words, I think you'll enjoy and benefit from learning what others have already done, written about, and discussed concerning bridge pressure.

[fscotte]

From my understanding and experience is that you cannot gain "energy" or tone, without sacrificing something else. So you get more volume, then something else is less. So you get more tone, then something else is sacrificed.

So even if you do achieve more volume by some means, you may find the resultant tone is less preferable to your ears.

[Julian Morris]

The problem with that is you should have stopped before you got into the analogy of the compressor and the truncated sine waves.
I suspect there can be damping of top movement resulting from excessive bridge pressure, but not my means of truncating waves. To understand the situation better, I suggest you do a little research into what is known (and measured using laser interferometry) about how tops (and backs) move when they are making sounds. Also, look into the ideas of Steinberger and others who believe that the bridge needs only enough pressure to stabilize it's position and any more may be excessive. In other words, I think you'll enjoy and benefit from learning what others have already done, written about, and discussed concerning bridge pressure.

Thanks, grest reply. I am new-ish to this, and I will certainly do a bit of research. I have mucked about before with set-up of guitars and a cheaper mandolin to very good effect, but I will be careful with my latest mandolin as it is a bit more expensive. Previous owner replaced the taipiece and put the repleacement on squint, so I have to move it anyway, but I thought I could lift it a bit in the process without too much harm. I'm with this Steinberger guy in principle, I will track down his work and see where that gets me. If I don't do something I feel like my mandlin is going to implode from unnecessary/excessive bridge pressure.

[HoGo]

1. Assuming a very average bridge angle to being with, would the new break angle likely be out of an acceptable range after the reset? (given the amount it would have to change from the switch of medium to light gauge strings while keeping the same downward force)?

On arch top mandolin there is more than just neck angle involved in the neck set. You can have identical bodies with different neck angles but with the same standard bridge height. Ther is some room in how high is the heel or neck overstand. If you use lower overstand you have to increase the angle to get standard bridge height. If your overstand is high, you need lower angle.

2. Assuming the bridge mass and base dimension somehow stayed the same, would you expect there to be a noticeable change in volume?

I think that if you adjust the neck angle (and thus the break angle over bridge) so that light strings apply same downforce on bridge the sound will differ. The downforce just "pre-tensions" the body but the movement of strings after plucking excites the vibrations. In such movement, mass must be one of most important factors and at least sustain will decrease with lighter gauge of strings and I'd guess volume as well.

[JeffD]

OK points taken. Yeah I was imagining tone being affected in unpredictable ways, but I was wondering mainly about volume, whether in principle it should end up about the same.

If this is more than just an intellectual exercise, (not that there is anything wrong with that), I can't figure out why, if medium strings give you the volume you want, you would try to get the same volume with lighter strings.

For those of you who have done the math, am I right in my speculation that if one were to do as suggested, perfectly, and have light strings at the same volume as the previous medium, that they would be as difficult to push down as were the medium, i.e. nothing gained in playability. The loss, thinking out loud, is the strings would be more likely to break.

[bart mcneil]

Of course you can change the bridge height if you remove the fret board and shim it with a slightly ramp shaped shim (similar to a section of house shingle). When the fret board is replaced on the shimmed neck it will function exactly as an mando with a altered neck angle. I have done this on an old mando with a bent neck to avoid having to try to straighten the neck itself and it worked perfectly I also had to shim the non-adjustable bridge but everything worked perfectly and it has lasted with no problems for about 8 years now.

My shim height also required shimming the bridge maybe 1/8 of an inch.

[Julian Morris]

Doesn't Siminoff have something to calculate downward force dependent upon string gauge?

Well, amn't I the twit! Here's a link I just found to the Siminoff test results.

http://siminoff.net/string-break-angle-loads/

My efforts weren't entirely wasteful, though. The calculations produce the same result as the test, and back up the evidence of a near-proportionate relationship between break angle and bridge load at angle at between 10 and 20 degrees. It seems to be true right across Siminoff's test range of angles.

That got me wondering, but then I realised it's fairly simple. For any angle (call it A) less than 30 degrees, A/Sin A is always about 60. The relationship between bridge pressure (B) and break angle is B = T Sin A where T is the string tension and A is the break angle.

That makes the graph from the Siminoff test the same as the graph of a Sine wave for angles up to 22 degrees. It certainly has that look about it.

Anyway, decosntruction the mandolin doesn't make it any less fun to play. If anything, it makes it more fun. And if the intellectul exercise leads to a better sound, all the better. Yee-hah! I'm off to work on Yakety Axe, which I have just tabbed from a You Tube video. Getting that tune up to tempo is where I really appreciate every tiny gain in action I have squeezed out of my instrument.

[Julian Morris]

Well, I'll give it a shot. You could argue though that like oiling the hinge on a door you're not putting more energy in but it is definitely easier to open the door. It's just a way of eliminating friction. which is undesirable absorption of energy. Maybe it's the same wit an instrucment? Vibrational energy could be being absorbed by the soundboard (converting it to heat, albeit in tiny amounts) and that by re-engineering the same energy could be released instead as sound.

The same argument seems to be used by Ken Parker in the above-mentioned video where he says that by using an ultra-light (hollow) bridge he releases more energy, making the instrument louder and more responsive.

[Julian Morris]

If this is more than just an intellectual exercise, (not that there is anything wrong with that), I can't figure out why, if medium strings give you the volume you want, you would try to get the same volume with lighter strings.

For those of you who have done the math, am I right in my speculation that if one were to do as suggested, perfectly, and have light strings at the same volume as the previous medium, that they would be as difficult to push down as were the medium, i.e. nothing gained in playability. The loss, thinking out loud, is the strings would be more likely to break.

Good question. The new tension required for light gauge strings T2 would be T1 x (UWM/UWL) where T1 is the tension required for medium gauge strings, UWL is the unit weight for medium gauge strings and UWL is the unit weight for light strings.

So for D'Addario 0.010s the UW(L) is 0.00002215 lb/in and for 0.011s it (UW(M) is 0.00002680. The tenson required for the same note to be produced is 0.002680/0.00002215 = 1.20, meaning 20% harder to fret.

To produce the same volume from lighter strings, it is necessary only to pick them harder? I don't know. Gut feeling is that the energy transmitted to the soundboard is dependent on the energy put into the strings by picking. It shouldn't make any appreciable difference to volume what gauge of strings you use.

[Julian Morris]

Siminoff site is saying "At about a 16° string break angle (which is what most F5 and A5 mandolins have), the average set of mandolin strings pushes down on the soundboard with a load of about 40-44 pounds, and this is typically the sweet spot for most mandolins."

My spreadsheet gives the same result, for a set of D'Addario 10s the force is 39.6 lb and for 11s it's 44.2 lb.

[fscotte]

Some of the finest sounding mandolins have usually been a little on the "quiet" side, in my experience.

I can make a very loud mandolin, so loud it becomes obnoxious. But has no guts or growl. With mandolins you have to be careful since small changes can result in big tonal changes.

[Julian Morris]

Some of the finest sounding mandolins have usually been a little on the "quiet" side, in my experience.

I can make a very loud mandolin, so loud it becomes obnoxious. But has no guts or growl. With mandolins you have to be careful since small changes can result in big tonal changes.

Ahh, yes, I have just realised you make mandolins. robably not a lot I can tell you about the whole thing, then? I am just thinking this through in public, and appreciating all feedback. The cross I have to bear in life is that I analyse things to death. Fun for me but boring for everyone else.

I will tread carefully with my experiments, as you advise. I don't want to create a noisy monster. I jam with too many of them already . Since I have to realign my tailpiece, I will lift it about 1 degree in the process and see how that goes. I also will fit a lighter bridge, the one I have got is for several reasons very annoying and bulky. That's reversible, obviously. Can't go too far wrong there.

Thanks again.

[JeffD]

It shouldn't make any appreciable difference to volume what gauge of strings you use.

I haven't thought this through but I suspect it is more complicated than that. I know my personal experience is with light strings compared to medium strings without changing anything else. In that case the medium strings are louder and fuller tone, the light strings are easier to fret and play fast. Right hand picking feels about the same, but for sure less volume with the lighter strings.

When picking harder to get comparable volume from light strings I find the tone goes tinny and thin.

But that is not the comparison that you are talking about. You are talking about lighter strings with modifications in angle and what not; adjustments to make the volume the same. My thinking is that if you have made all the adjustments to get the volume the same you might in the process have made the left hand playability the same. But I have never done the experiment.

I love over thinking things, but I am handicapped in that this is not an arena that I have any special knowledge. I just tune 'em up and play 'em. I don't do my own set ups or adjustments. I leave that to the experts.

[Larry Simonson]

Here is an experiment to try. Measure how much the top deflects when brought up to pitch for the heavier strings and original break angle, then sample the tone, volume, sustain, harmonic content etc so you have a baseline reading(not easy, maybe not possible?) Now install the lighter strings and keep raising the bridge until you get the same deflection and then repeat the tone, volume etc. sampling and compare that to you baseline. Of course the action will get more manly but you may figure out if intrusive surgery would be worthwhile.