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Alembic Club » Alembic Basses & Guitars » Archive: 2007 » Archive through January 09, 2007 » Intonation on basses with unadjustable bridges « Previous Next »

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Username: lysosome

Post Number: 99
Registered: 1-2006
Posted on Tuesday, December 26, 2006 - 7:48 pm:   Edit Post

Hey everyone. I've been out of the scene for a while, but it's good to be back. Unfortunately, due to financial problems, I had to sell my Alembic a few months ago. I don't have the cash for another right now, so I'm going to try the next best thing I can think of; building my own custom instrument. I gave it a shot about a year and a half ago, but messed up a couple of things, lost motivation, and it never got finished. I'm hoping with this try, that everything goes smoothly. I'm a little older and a little wiser, so maybe that'll work as an advantage. Who knows. Anyway, to the point!

I was looking through the galleries for some ideas on what kind of woods I might want to use when I remembered seeing a bass that Slawie had posted photos of. The bass had/has a bridge that is not adjustable for intonation - the slots are just fixed to the base of the piece of metal. Here's a link of you don't know what I mean:

I remember Dela saying that the Smithsonian bass was originally fitted with one of these bridges. For simplicity's sake, I'm hoping to make something similar for my bass, as I don't want to use a premanufactured bridge. I'm concearned about the bass staying in tune though. Can anyone fill me in on the secret to using one of these bridges successfully?

Thanks for any and all help!

Advanced Member
Username: 88persuader

Post Number: 246
Registered: 5-2004
Posted on Tuesday, December 26, 2006 - 9:18 pm:   Edit Post

Jim ... If you don't want to buy a premanufactured bridge (they're fairly cheap you know) one way to have SOME intonation control is to leave the bridge free floating and have the pressure of the strings hold it in place. You can pull it forward or back or slightly angle it for intonation sake. Of course every adjustment you make will in some ways effect the other strings and also it could move on it's own during play. I'd also recommend measuring a pre existing non-adjustable bridge before building one of your own. Most I've seen have some type of different intonation sloting for each string. Personally I'd recommend buying a premanufactured adjustable bridge. It would save you a lot of headaches and as I said they aren't that expensive if you go for a "fender type" bridge. In any event ... good luck with the build and please post photos when it's complete!
Intermediate Member
Username: jorge_s

Post Number: 111
Registered: 8-2002
Posted on Wednesday, December 27, 2006 - 9:11 am:   Edit Post

Yes I second what Raymond said. I've done this on a bass I built and with trial and error you can get pretty close. There is a detailed explanation on intonation in the guitar repair book by Dan Erlewine. Also Bob Benedetto explains how to make one from scratch in his archtop guitar building book.
Username: lysosome

Post Number: 100
Registered: 1-2006
Posted on Thursday, December 28, 2006 - 3:22 am:   Edit Post

Yeah, I know a premanufactured bridge would be a lot easier and cheaper, but what fun is that?!
Actually, I'll probably end up getting my own custom bridge made. I've been talking to Frank Difeo, who is a world renowned yoyo maker, and a great guy, about machining me a custom bridge and tailpiece for my future axe, so hopefully it'll work out.
I'll probably end up going with something adjustable when the time comes. The idea of such a simple bridge (that actually worked) is just something I'm playing around with in my head. I was just wondering if and how it worked.

thanks for the insight guys.

Jimmy (very, very tired)
Advanced Member
Username: dfung60

Post Number: 220
Registered: 5-2002
Posted on Thursday, December 28, 2006 - 7:31 am:   Edit Post

In a perfect world, you wouldn't need an adjustable bridge. Strings would vibrate perfectly, regardless of their gauge or construction. One end of the string would be fixed at the nut and the bridge would be a straight line parallel to the nut one scale length away.

Of course, real strings aren't perfect. They need quite a bit of mass to be tuned down this low and there are infinite combinations of core wire diameter, wrap wire diameter, number of wraps, and materials that all need to come together to make this happen. What you end up with is a string that has stiffness, generally more stiffness as you get to the bigger strings. The stiff end of the string won't vibrate as easily as the middle of the string, so it acts as if it were shorter than it really is. Unfortunately, each harmonic "sees" the stiffness differently, so a fundamental and it's harmonics will tend to be slightly out of tune with each other.

The intonation adjustments you do at the bridge try to compensate for the string's characteristics. On most basses, you'll see that you need to pull the bridge saddle back for the lower strings. The extra length compensates for the stiffness and hopefully will bring the note and harmonics back into tune with each other.

The proper intonation point is different for each string, but (assuming the manfacturer holds tight tolerances) you'll probably find that that point doesn't move over the life of the string or when you put on a new set of the same gauge. Change material, gauge, manufacturer or even your playing action and the proper setup will probably be different.

If you settle on one string setup, then you don't need adjustability on your bridge - you just need the saddles to be at those points that you determined to be the right ones. The problem is that people do change, and even if you don't, there's no guarantee that the strings that you like will place the saddles in a straight line.

Acoustic instrument don't have individually adjustable bridges like an electric guitar. That's because the bridge is primarily responsible for carrying the sound of the instrument to the soundboard. For an acoustic guitar or even an upright bass, you want that bridge to be light and totally solid. There, you trade off perfect intonation for better sound. On an electric, with magnetic pickups, the adjustable bridge gives you better control of intonation and playing action.

If you look at an Ovation roundback acoustic, you'll see that they shape the saddle to try to help the intonation a bit. There are similar steps on the old pre-Tuno-o-Matic bridges on Gibson electrics in the early 60's. Older Martins had split bridges too. Because you're more likely to be playing chords on a guitar, I think intonation problems are more noticeable on guitars than basses, but the problem with basses are that there needs to be a lot of bridge adjustment to fix the problem, so you're much more likely to have huge intonation errors.

The bridge on an upright bass is held down to the soundboard by string pressure alone (there is a post underneath the bridge to counteract the downforce), so it can be adjusted for particular strings, similar to what 88persuader mentions. I think you'll have a hard time generating enough downforce across the bridge for this to work well on an electric bass though. On an upright, the string end past the bridge is inches long and the anchor point is inches lower than the bridge, so there's a lot of force to hold the bridge in place. On an electric, the body is a lot smaller, so you'll have to do something to find an anchor point that will give you downforce. This is what that "tail" on Les Claypool's Carl Thompson bass is doing (it also has a non-adjustable bridge).

Of course, you'll have to machine your bridge to give you the action heights that you want as well, and those too change with strings. On one hand it's a pain in the ass to do all this stuff, on the other, this is sort of what acoustic guitar players have to deal with all the time. They have no choice, however!

If you're building one bass, then I think the non-adjustable bridge is going to be a lot of work. For a luthier who can incrementally try a lot of strings and locations, there's a much better chance that they can get good results with intonation and action adjustments.

One thing that you might think about trying if you want things to be different is something like the bridge used on Spectors and Steinbergers (on the headless Steinberger, the knob tuners are in the bridge too, but this is separate). The main body of the bridge is a big tray. Each string saddle is on a beefy rectangular block. Each block has set screws perpendicular to the bass body that adjust for the height and angle of this bridge piece. You string it up and scoot the blocks back and forth until the intonation is right, then you tigthen a setscrew at the side of the bridge which squeezes all the bridge pieces together, side to side. Once you've done that, the entire assembly is locked together as one and doesn't depend on screws or springs to hold it's position, so you get the benefits of solid construction without losing any adjustability. Way cool.

David Fung
Intermediate Member
Username: lysosome

Post Number: 101
Registered: 1-2006
Posted on Thursday, December 28, 2006 - 12:35 pm:   Edit Post


Thanks very much for taking the time to write that. That's probably about as close to a perfect explanation as we're going to get =)
I guess it's hats off to the luithers at Alembic yet again for making a bass with a bridge that probably wouldn't have worked for anyone else that tried to build it, hah.
So I guess that set-style bridge idea is out the window.

Thanks again to everyone.


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