Replies to This Discussion

Permalink Reply by Mark on December 14, 2010 at 12:13pm

Not a stupid question at all. I'm assuming from what you've said that you understand you need to adjust the length of strings to compensate for the slight rise in pitch that's caused by them being pressed down onto the fretboard. Well, the change in pitch for a given string is affected by the material and gauge of the string, its length, the note to which it is tuned and the distance it is stretched as it is pushed down onto the fretboard. This latter factor is determined by the distance the string has to be pushed down when fretted (ie. the action).

If you want optimum compensation then you need a bridge with saddles that allow the length of each string to be adjusted independently - in which case you generally end up with the saddles in a wiggly line. If you have a one-piece bridge then the best you can do is to set it in a postion that approximates where the wiggly line would run, which tends to be at a slight angle. Generally the way to find that angle is to adjust the ends of the bridge to suit the outermost strings and assume things will be close enough for those in between.

So it isn't even a case of there being a single correct angle for a particular guitar, because the distance you need to move the bridge for optimum compensation will change if you change your tuning or string gauges or if you adjust the action. In practice, small variations in tuning or string gauges will often not make a huge difference and a lot of people manage to live with the result without adjusting the intonation.

A final reason why any two guitars are likely to have their bridges set differently is that no arrangement is perfect (not even when you've got individually adjustable saddles). For a start, the amount of string stretch due to fretting is slightly different at each fret position. Then there's the big problem that the positioning of frets on a guitar is a compromise (look up equal temperament and just intonation if you want technical detail). So all bridge positioning is a matter of compromise and approximation. Thus the final thing to say here is don't get too finicky about these things - once you've found a bridge position that sounds something like OK  then stick with it.

 

 

 

Permalink Reply by Mark Bliss on December 15, 2010 at 1:32am

Good answer, and well put!

I would only add that you might notice that nylon stringed instruments often have no compensation at the bridge, the string guage just doesnt vary as much and the string tension/guage simply doesnt require it.

Also, the "comprimise" can become more complicated with more strings. 3 shouldnt be to much of a problem, 4 or more it may become more noticeable. But as  Mark pointed out in his response, you can generally get it close enough and dont "fret" over it. These generally need not be precise instruments to get the desired results.

Permalink Reply by Roadkill a.k.a. John Maw on December 15, 2010 at 8:35am

Thanks to both of you. Much clearer now. Appreciate the help. I have seen a guitar with staggered frets so presumably the reason for that is connected to what has been discussed above. I haven't done a fretted instrument yet (next ones will be) and normal fretting sounds difficult enough without making it much harder.

Permalink Reply by carverman on December 20, 2010 at 4:52am

Very good information. The only thing that I can add is that if you are making a 6 string

with a movable bridge such as the one, I'm making, I first position the bridge at approximately at  1/2 the scale length.

ie: the bridge should be the same distance from the 12th fret as the nut is to the 12 fret.

 

Then test the harmonic at the 12th fret  on the high E against the fundamental note at the 12th,

to see if the pitch is sharp or flat and adjust that end of the bridge to try and match the

harmonic against the pitch of the  fundamental note. 

 I think it's a bit more critical for the treble strings over the bass to be in good intonation as

that helps with the tuning, but that again is just my opinion.

Permalink Reply by MichaelS Country Boy Guitars on December 22, 2010 at 3:10am

If your frettless you can overcome the compromise by moving your finger or slide a little this way or that if it sounds bad. Unfortunatly, or fortunatly, my ear is not that sensitive so it all sounds good to me, unless its way off. 

John H. Maw said:

Thanks to both of you. Much clearer now. Appreciate the help. I have seen a guitar with staggered frets so presumably the reason for that is connected to what has been discussed above. I haven't done a fretted instrument yet (next ones will be) and normal fretting sounds difficult enough without making it much harder.

Permalink Reply by Roadkill a.k.a. John Maw on December 22, 2010 at 4:19am

Hi Michael.

 

My first one was fretless (really so that I would have something to play as soon as possible), but I intend the next few to be fretted, which is why I am concerned to get it right and to understand more about issues of intonation.

 

The other thing that I find helps with an unfretted instrument is using a big wobbly vibrato. Hides a multitude of sins. Oh, no! I shouldn't have admitted to that.

 

As always, thanks for your help.

 

MichaelS said:

If your frettless you can overcome the compromise by moving your finger or slide a little this way or that if it sounds bad. Unfortunatly, or fortunatly, my ear is not that sensitive so it all sounds good to me, unless its way off. 

Permalink Reply by Mark Bliss on February 6, 2011 at 5:14pm

If you are a calculation type builder, heres something to consider:

Calculating compensation

Permalink Reply by Slowpaw Steve T on March 4, 2011 at 5:38am

Thought about this myself so may keep the bridge as a "floating" bridge to try out and estimate the best sounding angle...

Permalink Reply by Michael Glenn on May 24, 2011 at 9:17am

Hi guys,

 

So I've read over this thread, and I've read some articles from pro luthiers about intonation.  (Don't remember where I found the articles, someone on the Nation had posted a link.) 

 

I'm getting ready to do my first fretted instrument this week, and I'm thinking that it's next-to-impossible for anyone to get "perfect" intonation, and that even guys like Martin and Gibson and Fender guitars only ever get "close enough."  Is this correct?

 

The only instrument I have to compare to right now is a tenor Kala ukulele which was in the $2-300 price range and I can't get "perfect" intonation out of it - but then I can't get "perfect" tuning either so I just live with "close!"  :)  I'd like to sell fretted instruments though - have sold one fretless already - so I'm just curious as to how "close" the intonation really needs to be.

 

I'm training to be a piano tuner, btw, and my mentor tells me that when it comes to tuning a piano, if you tune each individual string to its "proper" pitch, then the strings played together won't sound right.  Is it the same with 3 and 4 string instruments?

 

Thanks,

Michael

Permalink Reply by Craig Cox on May 24, 2011 at 10:43am

here's the smidge I've learned building 4 fretted 3-stringers:

1. Fretting isn't that hard. You just have to be careful positioning. I've simply copied the fret positions of my good-quality six string acoustic. works fine. there are a number of useful threads hereabouts on fretting.

2. I've used a floating bridge, because I've noticed the intonation needs tweaking occasionally (new strings, different gauge, different tuning, etc.) Just makes it easy to quickly shift to compensate. String pressure is all you need to hold the bridge (and the nut) in place.

3. It's a cigar box guitar. Don't sweat it. Each of my builds has been an improvement on the previous, but none are what you might call professional luthiery! Still, like most other pursuits, one can get as nuts about "perfecting" cbgs as you like and have the temperament for.