Double Bass Bass Bridge Adjusters

[AGCurry]

That seems weird, if you want to have uneven strings one adjuster would take care of that.

Just to play devil's advocate: What if the one adjuster was in the middle?

If the curvature of the bridge is matched to that of the fingerboard, don't you want that relationship to remain constant through any changes you want to make to height of the strings? And wouldn't that be "why there are two adjusters", so any level changes would be equally spread across the bridge?

I really do understand what you're saying. I'm simply repeating what I was told by someone I respect. My inference is that, unless the balance is way off between the two adjusters, it's not a big enough difference to matter.

 

[N. Kentucky Bass]

I can see a reason for adjusting just one side, if you wanted to see how the strings feel and play slightly lower or higher. Moving one adjuster would mainly affect string height on that side's respective pair of strings, and to a lesser degree the neighboring third string. I'm going through this process now in preparation to tell my luthier how I want the setup to go.

 

[Wasnex]

That seems weird, if you want to have uneven strings one adjuster would take care of that. If the curvature of the bridge is matched to that of the fingerboard, don't you want that relationship to remain constant through any changes you want to make to height of the strings? And wouldn't that be "why there are two adjusters", so any level changes would be equally spread across the bridge?

As the bridge is adjusted the face of the instrument will compress. One side is supported by the sound post and will compress very little. The other side will move a bit more. Although I suspect the difference would be pretty minimal, I would expect that it would be necessary for adjustments to be asymmetrical to some degree. I believe this would be affected by seasonal changes.

Also in reading about how to cut a bridge, there appears to be different approaches. (My understanding is) One approach has the bridge radius follow the neck profile perfectly.

There are other approaches that have the radius expand from the G to the E side. I believe the idea is the strings should be setup progressively higher above the finger board from G to E...this makes sense to me, I.E. build at least part of the rise into the bridge.

In the event the radius of the bridge has the same profile as the finger board, the E side adjuster will have to be moved out a bit if you want the strings to rise progressively from G to E. I can't personally imagine why anyone would want all of the strings at the same height.

I would think that the angle of rise from G to E would vary a bit depending upon how high you want the action. In other words, both seasonal change and the height you run the strings would have some affect on how asymmetrical the adjustment is.

I am by no means an expert and I do not have any lutherie background, so maybe I am just confused...but I don't worry about asymmetry in bridge adjustments unless they are extreme enough to cause the the feet to start rocking up off the face of the instrument.

 

[Ed Fuqua]

Also in reading about how to cut a bridge, there appears to be different approaches. (My understanding is) One approach has the bridge radius follow the neck profile perfectly. There are other approaches that have the radius expand from the G to the E side. I believe the idea is the strings should be setup progressively higher above the finger board from G to E...this makes sense to me, I.E. build at least part of the rise into the bridge.

If the strings don't follow a curved radius, bowing the lower strings without running a bow into the upper strings becomes a problem, right? I mean some folks do have a setup that gives them a fairly flat plane over the strings because they NEVER play with a bow.

In the event the radius of the bridge has the same profile as the finger board, the E side adjuster will have to be moved out a bit if you want the strings to rise progressively from G to E. I can't personally imagine why anyone would want all of the strings at the same height.

You know, I haven't really thought about it and I have to get ready for a gig (I know, right!?!) but there does seem to be some allowance luthiers make so that there is a uniformity in the top of the string so that they all feel as if they are on the same - I hesitate to say 'plane' because it's not a straight line, so I'll stick with the radial curve; if the top of the string describes a uniform curve with the strings, given the difference in string diameter, the underside of the string will follow a different curve.

I would think that the angle of rise from G to E would vary a bit depending upon how high you want the action. In other words, both seasonal change and the height you run the strings would have some affect on how asymmetrical the adjustment is.

Given that I have a one piece bridge (and the Kriegel neck off mechanism makes changing the string height a function of the neck, not the bridge), I haven't noticed any disadvantage to a symmetrical affect. And given that adjustable bridges are a more modern solution to the mercurial changes wrought on string height by weather changes, does it make sense that asymmetry is why they are there?

I am by no means an expert and I do not have any lutherie background,...

Well, there's your recommendation right there. I've never worked on automobiles, but feel free to drop off your Ferrari, I've got some thoughts about what should work out OK.

 

[Wasnex]

If the strings don't follow a curved radius, bowing the lower strings without running a bow into the upper strings becomes a problem, right? I mean some folks do have a setup that gives them a fairly flat plane over the strings because they NEVER play with a bow.

You know, I haven't really thought about it and I have to get ready for a gig (I know, right!?!) but there does seem to be some allowance luthiers make so that there is a uniformity in the top of the string so that they all feel as if they are on the same - I hesitate to say 'plane' because it's not a straight line, so I'll stick with the radial curve; if the top of the string describes a uniform curve with the strings, given the difference in string diameter, the underside of the string will follow a different curve.

Given that I have a one piece bridge (and the Kriegel neck off mechanism makes changing the string height a function of the neck, not the bridge), I haven't noticed any disadvantage to a symmetrical affect. And given that adjustable bridges are a more modern solution to the mercurial changes wrought on string height by weather changes, does it make sense that asymmetry is why they are there?



Well, there's your recommendation right there. I've never worked on automobiles, but feel free to drop off your Ferrari, I've got some thoughts about what should work out OK.

Let's be clear, I am not telling anyone how to do the work or offering to do the work myself, but if I thought my Ferrari mechanic or upright bass luthier was doing something stupid, you can be sure we would have a conversation.

And it's not like I am totally ignorant on how an upright bass should be setup. A few months ago I went to a shop to try out some used carved Christopher basses. After a few minutes on one of the basses I asked the shop owner if any sort of setup was included. He asked why and I told him the fingerboard was not properly dressed. He did a quick inspection and agreed. By the way...he's an upright player and had played the bass and did not even notice the problem until I pointed it out.

While I totally respect your superior expertise in this area, you seem to be disregarding some basic physics and treating the face of the bass as a stable, unmoving surface. This is not an accurate assessment of how the panel behaves...a point which I am respectfully trying to draw to your attention. The instability of the face of the instrument must be taken into account during these discussions. Because the face of the instrument is not stable, bridge adjustments will be asymmetrical.

My comments are not related in the least to a bass that is setup with a flat fingerboard, so let's not go off onto an unrelated tangent.

I pulled an image from this thread: Fingerboard relationship to bridge

In the top image, the bridge is not cut properly.

In the middle image, string height is even from G to E. I believe this is the traditional shape.

In the bottom image, when the bridge has the same parabolic contour as the fingerboard, string height is even from G to E.

Notice the French cut variation on the bottom image. This is one source that seems to support the idea that the bridge may be cut so that the strings will rise slightly from G to E.

Here's another article that seems to be inferring the strings rise from G to E: Fingerboard Geometry | Looking at the radius - Joey Naeger Basses

In searching for comments on the string height of other upright bassists, my perception is it is common for strings to get progressively higher from G to E, but perhaps this is a jazz thing.

Here is a TB thread that discusses advantages and disadvantages of the parabolic shape.
Fingerboard and Bridge relationships

In the first post: The image of the parabolic shape clearly shows the height of the strings increasing from G to E.

IMHO what is done today is probably more relevant than what has been done historically. I wouldn't be surprised if seasonal adjustments were once addressed by switching out two or more bridges. Now most of us just adjust a few thumbwheels.

Hope you had a great gig!

 

[neilG]

You have a metal screw in wooden threads. I'd want to keep that setup as perpendicular as possible.

 

[Wasnex]

You have a metal screw in wooden threads. I'd want to keep that setup as perpendicular as possible.

I don't disagree, but take a look at this image and consider everything that is going on as you adjust the bridge.

The left side of the bass's front panel is very rigid due to the sound post. So as you adjust the bridge to raise the strings, the face of the bass (left side) will hardly compress; almost all of the adjustment goes towards raising the strings.

This is not the case for the right side. As you turn the adjuster, the face of the bass (right side) will compress. So part of the adjustment pushes the face of the instrument down and part of it pushes the bridge up. Because the adjustments is causing motion in two directions, more turns will be required to raise this side of the bridge to match the other side.

Of course, ideally you would shape the bridge so the feet are perfectly shaped to the face of the bass when the strings are at the optimum height and the bass is tuned to pitch...but if you make an adjustment at some later time, the setup will be pushed out of symmetry to some degree.

 

[neilG]

This is not the case for the right side. As you turn the adjuster, the face of the bass (right side) will compress. So part of the adjustment pushes the face of the instrument down and part of it pushes the bridge up. Because the adjustments is causing motion in two directions, more turns will be required to raise this side of the bridge to match the other side.

It's an interesting theory, and not one I've observed on my instruments, but I've never made measurements. Have you?

 

[BarfanyShart]

I think its okay for them to be uneven, they're never really going to be much more than a half turn off of each other, anyway. You should mark them, though, so you can always bring them back even should you desire to do so.

 

[Wasnex]

It's an interesting theory, and not one I've observed on my instruments, but I've never made measurements. Have you?

I was taught to put a hash mark on the adjuster and make symmetrical adjustments, but in my experience this rarely provides the desired results. Does that count?

 

[Fran Diaz]

I don't disagree, but take a look at this image and consider everything that is going on as you adjust the bridge.
View attachment 4044209

The left side of the bass's front panel is very rigid due to the sound post. So as you adjust the bridge to raise the strings, the face of the bass (left side) will hardly compress; almost all of the adjustment goes towards raising the strings.

This is not the case for the right side. As you turn the adjuster, the face of the bass (right side) will compress. So part of the adjustment pushes the face of the instrument down and part of it pushes the bridge up. Because the adjustments is causing motion in two directions, more turns will be required to raise this side of the bridge to match the other side.

Of course, ideally you would shape the bridge so the feet are perfectly shaped to the face of the bass when the strings are at the optimum height and the bass is tuned to pitch...but if you make an adjustment at some later time, the setup will be pushed out of symmetry to some degree.

I don't agree with this. I don't think that the top plate will go down on the bass side enough to be considered just because you rise the bridge adjuster.

 

[Wasnex]

I don't agree with this. I don't think that the top plate will go down on the bass side enough to be considered just because you rise the bridge adjuster.

In my experience it definitely becomes noticeable if you want to make a fairly large adjustment.

Here's why: As you raise the action, the break angle of the strings increases. This increases the downward force on the face of the instrument.

I am sure some of you will want to argue this point, so here's a little online calculator that claims to do the math for you if you know the string tension and break angle: Liutaio Mottola Lutherie Information Website

Now, consider how a screw works. The adjusters I found at Gollihur have 1/4" 20 threads. So a full rotation of the adjuster moves the bridge a fraction of an inch (assuming the face of the bass does not compress).

The mechanical advantage of the adjuster should reveal any asymmetrical movement in the face of the instrument. The idea with mechanical advantage is you trade a lot of motion for increased force. So you rotate the adjuster one turn, which is considerable rotational travel, but there is only a small displacement along the axis of the adjuster.

If there is even a slight asymmetry in the way the front panel moves, the difference will by magnified by the mechanical advantage of the adjusters. In other words, a small movement along the axis of the adjuster will require a noticeable amount of extra rotational travel to compensate. So you may not see the asymmetrical compression of the bass's face, but it's presence will be revealed through differences in the rotational travel of the adjusters. This is consistent with my experience on multiple basses.

I am not saying this is a huge factor, but I do think it's significant enough that your bridge feet may dig into the face of the bass a bit more if you make a big enough adjustment. So if you find you need or want to make a big adjustment, you may want to involve a luthier instead of just wanking on the adjusters.

 

[adarvas]

In my experience it definitely becomes noticeable if you want to make a fairly large adjustment.

Here's why: As you raise the action, the break angle of the strings increases. This increases the downward force on the face of the instrument.

I am sure some of you will want to argue this point, so here's a little online calculator that claims to do the math for you if you know the string tension and break angle: Liutaio Mottola Lutherie Information Website

Now, consider how a screw works. The adjusters I found at Gollihur have 1/4" 20 threads. So a full rotation of the adjuster moves the bridge a fraction of an inch (assuming the face of the bass does not compress).

The mechanical advantage of the adjuster should reveal any asymmetrical movement in the face of the instrument. The idea with mechanical advantage is you trade a lot of motion for increased force. So you rotate the adjuster one turn, which is considerable rotational travel, but there is only a small displacement along the axis of the adjuster.

If there is even a slight asymmetry in the way the front panel moves, the difference will by magnified by the mechanical advantage of the adjusters. In other words, a small movement along the axis of the adjuster will require a noticeable amount of extra rotational travel to compensate. So you may not see the asymmetrical compression of the bass's face, but it's presence will be revealed through differences in the rotational travel of the adjusters. This is consistent with my experience on multiple basses.

I am not saying this is a huge factor, but I do think it's significant enough that your bridge feet may dig into the face of the bass a bit more if you make a big enough adjustment. So if you find you need or want to make a big adjustment, you may want to involve a luthier instead of just wanking on the adjusters.

I agree with the previous comment. I always mark my adjusters and try to make even adjustments. First, of course, the bridge has to be shaped perfectly. I think the shaft compresses the bridge if the pressure goes sideways within the bridge. I've A/B-ed this and an uneven bridge changed how the string feels and sounds under the bow. It's a small but definite change. Having said all of that, I think once you know that your bass fluctuates between summer and winter roughly the same year after year, it's better to have two solid bridges. I'm in Toronto where the humidity in the summer can be tropical and the in-door humidity can dip under 20% during the winter. I have to adjust my electric basses every year but I don't think I ever had to adjust my double bass in 10 years.

 

[RBPCRC]

I asked a luthier about uneven bridge adjusters and he said that the only risk is that the bridge leg might crack. Then a couple weeks later asked a world renown bow maker whose bass (and other bowed instruments) luthier skills I hold in very high regard and he said uneven height is ok. I had my G adjuster 2 or 2.5 mm higher for a long period of time with no bad effects but it makes sense to me that it puts pressure on the inside of the bridge legs.