Building Question: Scale Compensation

[knockwood]

Poking around through William Cumpiano's online articles earlier today, I came across a segment asserting that for optimal intonation, the distance from the nut to the centerpoint of the saddle should actually be 0.15" over the scale length upon which the fret spacing is based. For example, on a guitar slotted for a 24.9" scale, the actual distance from nut to saddle centerpoint should be 25.05"

 

Anyone familiar with this? Applied it?

 

My first kit (12-fret hog 000) is sitting in a closet at work waiting for me to gather tools... and work space... and knowledge... For now, I'm just doing a lot of reading and forehead-crinkling and head-scratching.

 

...and a lot of wondering about why more builders don't use metric. WTF? Just seems so much easier...

[Sweb]

I have been considering joining the ranks of builders. But, no, I haven't done any research of the technical side of things. However, now will I be checking those dims against my gear? Yep.
Have you?

[knockwood]

Originally posted by Sweb I have been considering joining the ranks of builders. But, no, I haven't done any research of the technical side of things. However, now will I be checking those dims against my gear? Yep. Have you?

 

 

I have. What I get on my D-1 is 25-5/16". I know from previous window shopping on Stewmac that Martin's '25.4"' scale length is actually 25.34", so basically the actual distance is virtually dead on. BUT... the intonation on this git is far from perfect.

[Sweb]

Okay. Using the data you supply in the thread starter and my limited abilities with the laws of relationships:

24.9/25.05=12.450/X where 12.450 is half of the scale length of 24.9. This should tell me where the dead center of the 12th fret lies for the (any?) string's harmonic (octave) taking into consideration the added .15 as a constant. I come up with 12.525 as the 12th fret's dead center. Is this a valid method for establishing correct harmonic intonation positioning? Or, is the intonation position pecular to each string? String science - I'm clueless.

[knockwood]

Originally posted by Sweb Okay. Using the data you supply in the thread starter and my limited abilities with the laws of relationships: 24.9/25.05=12.450/X where 12.450 is half of the scale length of 24.9. This should tell me where the dead center of the 12th fret lies for the (any?) string's harmonic (octave) taking into consideration the added .15 as a constant. I come up with 12.525 as the 12th fret's dead center. Is this a valid method for establishing correct harmonic intonation positioning? Or, is the intonation position pecular to each string? String science - I'm clueless.

 

 

Disclaimer: I'm absolutely the wrong guy to be supplying info about correct harmonic intonation positioning.... BUT since I'm bored... From my understanding of the article, the distance from nut to dead center on the 12th fret is not to be adjusted according to the suggested 0.15" compensation. On a 24.9" scale-length git, the 12th fret's dead center should still be 12.450" from the nut. What he's saying - I think - is that the total distance from nut to saddle-center should be twice the 12th-fret center distance from the nut, plus 0.15".

 

Lest I should hideously misquote Mr. C, here's a link to the article. Neither here nor there, there's also a really cool quote from an early Epi warranty card in here...:

 

http://www.cumpiano.com/Home/Newsletters/Issues/newsletter2.html

 

Also, Sweb, if you've been bitten by the building bug, you may be interested to know that for a mere five grand, you can spend two weeks one on one with Mr. Cumpiano and build your own git in the process... I allude to the cost only semi-sarcastically. Actually it seems to me like a serious bargain... seriously... except that I do not have the money to do it (which is where the semi-sarcasm comes in).

[Sweb]

"Now that your are the proud possessor of this instrument, learn to love it. Remember it is one of your most intimate possessions--closer to you perhaps than anything else you may own. For it is the voice of the music within you, singing or sighing with your mood, and forever faithful to your innermost whims. So protect it from careless hands. Keep it clean and dry. It is well made and rightly designed to stand constant use. Have faith in it to respond to your skill and magnify your best efforts. Give to it the best you have and the best will come back to you."
Epi A. Stathopoulo


Thanks for that. This should be a credo for this forum and made a sticky.

[guitarcapo]

My own personal experience with acoustic building has led me to believe that the bridge should be about 1/8" farther than double the nut to 12th fret distance on the high E side...and 1/4" more on the bass E string side.

things like the string guage and actual scale length may make this vary a bit.

[Freeman Keller]

Knock and Guitarcapo are right on - what ever you choose for a scale length determines the location of the 12th fret (and all of the ones up to that point based on some magic number that is 17.xxxxx inch (I'm at work and don't have my books). The saddle would be exactly twice that distance if the strings didn't stretch when you pushed them down. Since they do and that causes them to sharpen (has to do with the diameter of the wire core and a bunch of other stuff that likewise is at home) - it is necessary to move the break point a little farther away - and as I recall it was about an 1/8 of an inch. Then, of course, you need to angle the whole thing because the wire in the strings are different diameters.

I was reading Kincaide's book on guitar making the other night and he describes "equal temperment" as "making all of the strings sound equally out of tune with each other" or something like that.

When I built mine I just followed StewMac's instructions on the bridge location (and LMI's on the classical), then tweaked the saddle to get the intonation right. When I get to this point on the 12 string there will be a lot of measuring before I cut anything

BTW - this is the big "bridge in the wrong place" issue with those 60's and 70's Martins - many have their saddles twice the 12 fret distance with no compensation. There are some folks who fill the slot and reroute it in the right place - but if you play in the first position it probably doesn't matter.

http://p082.ezboard.com/ftheunofficialmartinguitarforumfrm2.showMessage?topicID=11552.topic

BTW2 - for anyone considering building one, Steve Kovacik has kits in about any configuration you could want right now. I'm considering laying away a maple jumbo cutaway for when I finish the 12 string...

BTW3 - the classical I built was metric - it was a PIA because all my measuring sticks are English - I finally broke down and bought a metric mechinists rule.

BTW4 - one of the things I didn't want to do on any of my home builts was to lay our the fret spacing and try to cut the slots right. I bought pre-cut fretboards for all of them. I built a dulcimer long ago and got some of the frets slightly off - you can really hear it.

[knockwood]

Originally posted by Freeman Keller Knock and Guitarcapo are right on - what ever you choose for a scale length determines the location of the 12th fret (and all of the ones up to that point based on some magic number that is 17.xxxxx inch (I'm at work and don't have my books). The saddle would be exactly twice that distance if the strings didn't stretch when you pushed them down. Since they do and that causes them to sharpen (has to do with the diameter of the wire core and a bunch of other stuff that likewise is at home) - it is necessary to move the break point a little farther away - and as I recall it was about an 1/8 of an inch. Then, of course, you need to angle the whole thing because the wire in the strings are different diameters. I was reading Kincaide's book on guitar making the other night and he describes "equal temperment" as "making all of the strings sound equally out of tune with each other" or something like that. When I built mine I just followed StewMac's instructions on the bridge location (and LMI's on the classical), then tweaked the saddle to get the intonation right. When I get to this point on the 12 string there will be a lot of measuring before I cut anything BTW - this is the big "bridge in the wrong place" issue with those 60's and 70's Martins - many have their saddles twice the 12 fret distance with no compensation. There are some folks who fill the slot and reroute it in the right place - but if you play in the first position it probably doesn't matter. http://p082.ezboard.com/ftheunofficialmartinguitarforumfrm2.showMessage?topicID=11552.topic BTW2 - for anyone considering building one, Steve Kovacik has kits in about any configuration you could want right now. I'm considering laying away a maple jumbo cutaway for when I finish the 12 string... BTW3 - the classical I built was metric - it was a PIA because all my measuring sticks are English - I finally broke down and bought a metric mechinists rule. BTW4 - one of the things I didn't want to do on any of my home builts was to lay our the fret spacing and try to cut the slots right. I bought pre-cut fretboards for all of them. I built a dulcimer long ago and got some of the frets slightly off - you can really hear it.

 

 

The magic number is 17.817. I got bored and put together an Excel book for fret-spacing a number of different scale lengths. I just factored in the compensation bit (just as a note at the bottom of each page). I'm very glad I ran into Cumpiano's article before trying to put together the Kovacik kit. The more I read, the more I'm amazed by the number of factors involved in making a guitar sound good... and the equal - actually much greater - number of ways to screw one up.

 

For future projects, I'd been hopping around the LMI site (my favorite window-shopping spot, lately) and noticed they will pre-arch and slot fretboards [for certain scale lengths]... Seems like a pretty attractive offering.

 

I have a copy of Kinkead's (Kinkade?) book. Not as intricately detailed as Cumpiano's text, but I like it because the information is somehow more simply conveyed - doesn't tie my wee brain in as many knots...