Bridge Location Question

[Alexander Higgins]

I think this has been partly answered in reply to some of my previous posts, so forgive my confusion:
My neck-through "Hossenfeffer" bass CAD drawings proceeding nicely, albeit slowly as I try to make good decisions about fret scale, neck construction, etc. The scale will be 33.25" with 20 frets. When locating the bridge, I have assumed that I'd want to set it so that a point 33.25" away from the inside face of the nut would be centered on the "range" of the adjustable bridge saddles to allow for the most intonation adjustment. I've read posts saying that you should locate at the inward extreme of the intonation travel adjustment on the saddles. What's the theory behind this approach? Other threads have recommended using the Stewmac fret calculator to locate the 12th fret, then doubling that number to locate the bridge. Advice?

[John Catto]

Double the nut to 12th fret distance. Locate the bridge so the saddle for the lightest string is as far forward as it will comfortably go. If you locate the saddle in the middle you may not have enough travel to intonate the bass strings. In practice you only ADD compensation as the core of the string gets heavier. This is why on a guitar a plain G requires the saddle quite far back while a wound G (very thin core) needs to sit forward.

[David King]

Intonation compensates for the stiffness of the string as John has explained. A stiffer string doesn't bend exactly at the witness point (front edge of the saddle or the nut) but somewhere in front of it. Therefore the witness point must be moved back a bit for the string to play in tune over the whole fretboard since the frets can't move.

[Alexander Higgins]

Thanks, I always thought the intonation adjustment was to
Commpensate for varying string thickness, never considered that it was related to stiffness. My 12th fret is located 16.625" from the inside face of nut by stewmac fret calculator. Is this to center of fret slot, or edge of fret? Doubling that would be 33.25". So I should run the G string saddle as far towards the nut as it will go its adjustment slot and locate the knife edge of the saddle 33.25" from inside face of nut?

[Peter Wilcox]

My 12th fret is located 16.625" from the inside face of nut by stewmac fret calculator. Is this to center of fret slot, or edge of fret?

To the center of the slot if you're that good at measuring, since the slot is only about 1/50" wide

Doubling that would be 33.25". So I should run the G string saddle as far towards the nut as it will go its adjustment slot and locate the knife edge of the saddle 33.25" from inside face of nut?

In theory, yes. I'm not that great at measuring, so I back the saddle off 1/16" or so to give me a little leeway. It would be sad if the intonation were flat with the saddle all the way forward.

[Jason Rodgers]

Double the nut to 12th fret distance. Locate the bridge so the saddle for the lightest string is as far forward as it will comfortably go. If you locate the saddle in the middle you may not have enough travel to intonate the bass strings. In practice you only ADD compensation as the core of the string gets heavier. This is why on a guitar a plain G requires the saddle quite far back while a wound G (very thin core) needs to sit forward.

So I might sound really dumb here: in the case of a wound G, even though it is a larger diameter (core plus windings), it is in this case lighter than the high E because it has a thinner core? And so, the range of adjustability of a bridge should be based on the status of the G string? Huh, that's something I've never stopped and thunk about before.

[Peter Wilcox]

Jason, I don't think he was comparing a wound G to a plain E - rather to a plain G. I don't know the core diameter of a wound G (I suppose they can differ by manufacturer), so don't know how its compensation would compare to the E, and I would guess the windings would also contribute to some degree. I don't have any wound G's on instruments with adjustable saddles so can't eyeball it.

However, the instrument of concern here is a bass, whose lightest string is the G and will sit the farthest forward.

[John Catto]

Double the nut to 12th fret distance. Locate the bridge so the saddle for the lightest string is as far forward as it will comfortably go. If you locate the saddle in the middle you may not have enough travel to intonate the bass strings. In practice you only ADD compensation as the core of the string gets heavier. This is why on a guitar a plain G requires the saddle quite far back while a wound G (very thin core) needs to sit forward.

So I might sound really dumb here: in the case of a wound G, even though it is a larger diameter (core plus windings), it is in this case lighter than the high E because it has a thinner core? And so, the range of adjustability of a bridge should be based on the status of the G string? Huh, that's something I've never stopped and thunk about before.

Well you wouldn't be basing things on the status of the G string that's just an incidental. As already stated the compensation is based on the stiffness of the string based on it's core. The core of a wound G IS very thin probably close to a very light high E so the saddle goes way forward (as referenced by things like 60s compensated wrap bridges or Bigsby bridges), which is also why those bridges won't compensate with a plain G.

On a 4 string bass you have an interesting example since there are no unwound strings and all the strings have a fairly large core. My guess is that only very light gauge bass strings will intonate with the G string anywhere near full forward, medium and heavies will have the saddles a bit back. Be worth taking a ruler to an assortment of properly setup basses to get an overview. With guitars with typical string gauges, you can practically intonate by eye with a ruler once you know the pattern and be close. The only reason there's any variance is that different string manufacturers have different "recipes" using different core weights, metallurgy and stiffness so exact settings vary some.