Intonation...moving the bridge...

[levin4now]

Hey.

Recently, I noticed my bridge was starting to lean towards the fretboard, sometime after I had replace strings on my mandolin. I tried to tip it back, but instead the foot of the bridge moved forward (towards the fretboard). I knew that spelled trouble for intonation. I moved it slightly back by hand, w/o out loosening strings. It seems that my mando doesn't quite 'stay' in tune like it used to. Or at least, as I tune from G to E string, the G is out by the time the E is in. (Presently it seems to be fine...).

My question is, if the 12th fret should be the exact halfway point b/w the bridge and the nut, how do you determine that on a bridge where (you might call this compensated?) the G and A strings rest on a point slightly towards the back of the bridge (towards the tailpiece), and the D and E strings are forwards, towards the fretboard? IOW, the measurements would be different, and the measurement (to me) would have to be taken somewhere in teh middle.

How do i do it? (check it?)

(i'm getting it setup professionally in a few weeks - never been done - so my problem will be solved soon, but if any of you have time...thanks!)

Alan

[grsnovi]

Alan,

The distance to your bridge is NOT exactly 2x the distance to the 12th fret - but that generally gets you in the general location. Depending on the string guage you use it is usually 12th 2x plus a little bit. It is also possible that your bridge will be skewed on an angle possibly closer to the nut on the treble side than on the bass side.

If you are in "perfect" tune open, play the note at the 12th fret and ping the harmonic there. If the harmonic and fretted note aren't the same note your intonation is off. If the fretted note is flat, the bridge needs to move towards the nut.

Like I said, the bridge can end up on an angle.

G

[labraid]

Hi Alan,
The tuning problem you're having is probably just that you are noticing something you didn't notice before. When you start tuning your G, then you move on to tune the D higher, the new string pressure puts enough compression on the neck to throw out the G tuning you just finished, making it flat. Move on to the next one, same thing happens. But as you get each string closer and closer to actual tuning, then go through one more ritual on each, they should stay right there in tune... neck compression stabilized.
Next issue, is have you ever taken your bridge off and played with it? Does the upper half move very loosely on the screws sticking out of the lower half? If so, there is too much play and this is probably why it is leaning. You'd need a new bridge, or at least someone experienced in repair to make things better.
The bridge is not exactly twice the distance from nut to the 12th. That is, as you said, the compensation. There is more compensation for thicker strings than thinner ones because your finger pressure in fretting them pulls them more sharp, therefore the compensation helps to flatten the sharp. Flat + sharp= right on. You place your bridge exactly where, fretting with normal, playing finger pressure, the twelfth fret fretted rings exactly one octave higher than the open string. You need a professional electronic tuner to accomplish this, or a professional opera singer. There is no measure that will tell you where to place the bridge, in other words. It depends on too many variables, the sound produced by those variables is "the proof which is the pudding"... Geez, I don't know if that parable was in context, but you get me here I hope... Get that bridge in the right place, be patient tuning and retuning 5 times when you put on new strings, and life will be full of joy, or at least as much joy as can be had when your wife leaves you for a new man, the pickup done broke down, and the old faithful hound done up and died on ye.. Ah yes, country music. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

[labraid]

By the way Alan, are you from Virginia? "Pungo Picker"? Anyway, Pungo's the name of a place near my old home in case I'm way off base here, not to confuse ye, hehe..

[Chris Baird]

It is generally best for most intermediate to advanced players to set the compensation off the 12th freted fret. Compensation, however, is always a compromise of various factors. The lower your action the less compromise. At a mid to high action the string strech varies quite abit up and down the fretboard. If you set your compensation off the 12th fret then the rest of the frets slowly go out of intonation as you move away from the 12th fret. If you never play down by the 12th fret is may be better to go off the 7th fret and make sure the note is a perfect fith above the open note. A very low action gives the best results and you can generally compensate off any fret between 3 and 15 with good results.

[Yonkle]

Try going here, this is a good site//
http://www.frets.com/FRETSPa....g3.html (http://www.frets.com/FRETSPages/Musician/Mandolin/MandoString/mandostring3.html)

[levin4now]

Thanks for all the responses everyone. I appreciate it.

This mandolin needs a full setup anyway - it is a year old and never been done. I want to replace the nut with something other than plastic (?) - it's an MK.

OldTymer, no I live in eastern North Carolina, 2 hours south of VaBeach. We live near the Pungo River, and an area known as "Pungo". There is the Pungo Lakes Nat'l Wildlife Refuge nearby as well.

ADM

[Chris "Bucket" Thomas]

OldTymer,

Do you live in Va. Beach?

I am waiting for the pickin' to start at the "Farmers Market".

Chris